Activity and product distribution in Ni-Co and Ni-Cu catalyst-mediated lignin depolymerization into phenolic substances with isopropanol H-donating solvent

Activity and product distribution in Ni-Co and Ni-Cu catalyst-mediated lignin depolymerization into phenolic substances with isopropanol H-donating solvent | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Activity and product distribution in Ni-Co and Ni-Cu catalyst-mediated lignin depolymerization into phenolic substances with isopropanol H-donating solvent Remigius Nnadozie Ewuzie, Jackson Robinson Genza, Ahmad Zuhairi Abdullah This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-4297106/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 30 Jul, 2024 Read the published version in Environmental Science and Pollution Research → Version 1 posted 6 You are reading this latest preprint version Abstract Lignin, a vital renewable biopolymer, serves as Earth's primary source of aromatics and carbon. Its depolymerization presents significant potential for producing phenolic fine chemicals. This study assesses promoted Ni-based bimetallic catalysts (Ni-Co/C and Ni-Cu/C) supported on activated carbon in isopropanol for lignin depolymerization, compared to monometallic counterparts. BET, SEM, EDX, and XPS analyses highlight their physicochemical properties and promotional effects, enhancing hydrogenolysis activity and hydrogen transformation. Reaction parameter exploration elucidates the influence on lignin depolymerization, with cobalt and copper as promoters notably increasing conversion and monomer yield. Ni-Co/C exhibits the highest lignin conversion (94.2 %) and maximum monomer yield (53.1 wt. %) under specified conditions, with lower activation energy (36.1 kJ/mol) and higher turnover frequency (31.6 h−1) compared to Ni/C. FT-IR, GPC, GC-FID, and GC-MS analyses confirm effective depolymerization, identifying 20 monomer products. Proposed reaction mechanisms underscore the potential of Ni-based bimetallic catalysts for lignin valorization, offering insights into developing efficient catalytic systems for lignin hydrogenolysis. This research enhances understanding and facilitates the development of selective catalytic processes for lignin valorization. Lignin depolymerization phenolic substances Ni-based bimetallic catalysts promotional effect isopropanol solvent product distribution Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Introduction A special type of carbon-rich renewable resource that can be found on Earth is lignocellulosic biomass. As a result, this widely dispersed and readily available biomass resource is considered to be the most promising replacement for fossil fuel resources to produce useful biofuels and fine chemicals for the development of a sustainable society (Abdullah et al., 2009). Typically, lignocellulosic biomass is divided into three fractions: lignin, cellulose, and hemicellulose. Compared to the established technologies for the utilization of cellulose and hemicellulose. Lignin utilization is extremely challenging, because of its intricate molecular structure and multiple chemical bonds (Zhang et al., 2017a). However, lignin as one of the three main constituents of lignocellulosic biomass makes up around 15–30 % of its weight and accounts for about 30 %–40 % of plants' energy (Xue et al., 2022 ; Li et al., 2015). Additionally, lignin is the earth’s most common source of aromatics and natural biopolymer, For instance, the pulping industry alone produces over 130 million tonnes of lignin waste each year (van den Bosch et al., 2018 ; Poveda-Giraldo et al., 2021). Furthermore, there are several valuable functional groups in this renewable resource, such as benzene rings, phenolic hydroxyl groups, and methoxyl groups (Vriamont et al., 2019 ; Zhou et al., 2017). The aforementioned evidence demonstrates that lignin has the potential to be a superb starting material in producing biofuels and phenolic fine chemicals. A wide range of chemical conversion methods, such as hydrolysis (Ren et al., 2018 ; Zhu et al., 2019a), oxidation (Liu et al., 2023), pyrolysis (Zhang et al., 2017b), hydrocracking (Li et al., 2015b), hydrothermal (Wang et al., 2018 ; Kang et al., 2016), and hydrogenolysis (Hu et al., 2019a ; Hu et al., 2019b ; Guan et al., 2020), were employed for depolymerization of lignin and its model compounds. Among these, catalytic hydrogenolysis was shown to be the most promising method for lignin conversion. Typically, a heterogeneous catalyst based on either precious or transition metals is employed in such conversion processes. Transition metal catalysts are mostly based on Co, Fe, Cu, and Ni in particular (Zhai et al., 2017 ; He et al., 2012 ; Guo et al., 2023). Ni catalysts demonstrate remarkable selectivity in the breaking of the aryl ether (C-O) bond (Yang et al., 2021 ; Ye et al., 2021 ; Jiang and Hu, 2016 ; Jafarian et al., 2019). However, due to the limited stability and activity of Ni as a mono-metallic catalyst for lignin depolymerization under moderate reaction conditions, further enhancement of Ni catalysts is, therefore, desirable (De et al., 2016 ; Zhu et al., 2019b). Under moderate reaction conditions, noble metals such as Ru, Pd, and Pt, demonstrate high catalytic performance for lignin depolymerization (Jin et al., 2019 ; Shu et al., 2020). Despite the great activity for hydrogenolysis reactions the noble metal catalysts demonstrate, their inherent metal characteristics make them very active in the hydrogenation of aromatic rings to produce undesirable products (Gyergyek et al., 2018 ; Okoye et al., 2016 ; Lee et al., 2012). Since a phenomenon generally known as "promotional effects" exists, bimetallic catalysts are emerging as an attractive option (Liu et al., 2019 ; Tymchyshyn et al., 2019). This may result in increased catalytic stability, altered desired product selectivity, and improved catalytic activity. Kim and co-workers (2015) reported that the selective scission of the carbon-oxygen bond in benzyl phenyl ether, the bimetallic Fe-Pd/OMC catalysts demonstrated more activity and selectivity than the comparable monometallic catalyst. This was attributed to altering Pd's electronic properties by transferring electrons from Fe to Pd with the addition (Fe) as a second metal into the Pd/OMC catalyst. According to Zhang et al . (2016), the Pd-Ni bimetallic catalysts inherited the benefits of both noble and transition metals, whereby the catalyst's activity for hydrogenolysis reaction was enhanced by the Pd metal catalyst, and its selectivity altered by the addition of Ni, this is favorable for cleaving the C-O bond. Additionally, Mauriello et al . (2018) revealed that under the condition of transfer hydrogenolysis, bimetallic Pd-Ni catalysts can efficiently break the C-O bonds of different lignin model compounds. The synergistic effects between the two metal species contribute to the enhancement of the catalytic activity of lignin and its model compounds. Transition metal catalysts were acknowledged as a viable replacement for noble metal catalysts in the catalytic depolymerization of lignin due to the expensive nature of noble metal catalysts, which have demonstrated remarkable hydrogenolysis activity (Kim etal., 2018 ; Kim et al., 2017 ; Santos et al., 2018 ; Shu et al., 2019). Due to the excellent physicochemical characteristics of activated carbon such as high porosity, large surface area, superior electron conductivity, and moderate chemical inertness. Activated carbon plays the role of support as well as a catalyst for the lignin depolymerization reaction. The fact that carbon materials are mostly constituted of carbon and can even be produced directly from renewable resources such as biomass makes them advantageous since they are "sustainable" support materials for metallic catalysts (Wu et al., 2017 ; Lam and Luong, 2014). Therefore, in this regard, the transition metals loaded on activated carbon support were synthesized by the incipient-wetness impregnation method, and their performance in the catalytic hydrogenolysis of lignin was tested. In this study, transition metal catalyst Ni was selected as a base metal for catalytic depolymerization of lignin because of its high catalytic activity, adaptability, synergistic effects with other transition metal catalysts, stability, selectivity enhancement, and economic viability. Secondly, it is commonly known that nickel catalyst serves as the hydrogenolysis center for lignin's C-O and C-C bond cleavage. Furthermore, cobalt and copper transition metal catalysts were selected as the nickel promoters because of their great potential to interact with the d orbital of Ni metal electronically which will result in its partial filling. Thereby affecting both the activity and stability of nickel-based bimetallic catalysts in catalytic depolymerization reactions. Copper and cobalt were chosen as nickel promoters due to their exceptional attributes, including strong hydrogenating capabilities and effective hydrogen atom transfer. Serving as electron donors, copper and cobalt augment the electronic characteristics of nickel, fostering the formation of a more evenly dispersed layer and enhancing the activity of Ni-based bimetallic catalysts. This synergy not only improves the selectivity of monomer products but also facilitates lignin hydrogenolysis and enhances lignin substrate adsorption. Additionally, their presence offers a promising chemical pathway for maximizing monomer yields. Based on this, the performance of the promoted Ni-based bimetallic catalysts on activated carbon support (Ni-Co/C and Ni-Cu/C) was evaluated for the depolymerization of lignin. And compared to their corresponding monometallic catalysts. Additionally, this study evaluated the promotional effect of Ni-based bimetallic catalysts on lignin depolymerization, monomer product yield, and product distribution. The effects of the reaction and kinetic parameters were evaluated, and a possible reaction mechanism was proposed. The results revealed that Ni-based bimetallic catalysts offer enhanced catalytic performance, product selectivity, and stability in the lignin depolymerization compared to the corresponding monometallic catalysts. This breakthrough holds promise for the development of more sustainable and economically viable methods for producing high-value phenolic fine chemicals from lignin. Materials And Methods Materials Ni(NO 3 ) 2 ⋅6H 2 O, Co(NO 3 ) 2 ⋅6H 2 O, activated carbon support, isopropanol solvent (99.93 %), and ethanol solvent (99.7 %) were purchased from Chemiz (M) Sdn. Bhd. Selangor, Malaysia. Tetrahydrofuran was purchased from HmbG Chemicals, Malaysia. Phenol (99 %) was purchased from R&M Chemicals, Malaysia. Alkali lignin, Cu(NO 3 ) 2 ⋅6H 2 O, n-decane, 2-methylbenzofuran (96 %), 2-methoxy-4-methylphenol (>98 %), and guaiacol were purchased from Sigma Aldrich, USA. Preparation of catalysts The incipient-wetness impregnation method was used to synthesize all the catalysts. Using Ni(NO 3 ) 2 ⋅6H 2 O, Cu(NO 3 ) 2 ⋅6H 2 O, and Co(NO 3 ) 2 ⋅6H 2 O as the percussor materials. Firstly, activated carbon support was purified by stirring vigorously with deionized water at 100 °C for 4 h, after filtration, it was dried at 80 °C in a vacuum oven for 12 h. Following that, metal loading was carried out by impregnation. The solutions of Ni(NO 3 ) 2 ⋅6H 2 O, Cu(NO 3 ) 2 ⋅6H 2 O, and Co(NO 3 ) 2 ⋅6H 2 O were incorporated into 5 g of activated carbon support and then stirred for 1 h at 500 r/min. To remove the water, the resultant mixture was slowly heated to 60 °C and then dried in an oven overnight at 80 ℃. After drying, the sample was then calcined at 500 °C for 3 h under air conditions. The prepared catalysts are Ni-Co/C, Ni-Cu/C, Ni/C, Cu/C, and Co/C. The theoretical loading of Ni, Cu, and Co in all catalysts was 10 wt. % each. After cooling, the prepared catalysts were then stored in a vacuum desiccator before use. Characterization of catalysts The textural properties of the synthesized catalysts were measured by the N 2 adsorption−desorption isotherms using the ASAP 2020 Micromeritics, USA model. The surface area of the catalysts was determined by the Brunauer, Emmett, and Teller (BET) method. Furthermore, average pore size and pore volume were evaluated with the Barrett, Joyner, and Halenda (BJH) method. To confirm the distribution of metallic active components on the activated carbon support. The catalysts' morphology was examined using a scanning electron microscope (SEM), FEI QUANTA FEG 450, equipped with energy-dispersive X-ray (EDX) to determine the elemental compositions. To explore the metal's elemental states, the X-ray photoelectron spectroscopy (XPS) spectra of the catalysts were measured by AXIS Ultra DLD, Kratos spectrometer equipped with an Al Kα X-ray source. Thermocatalytic conversion of lignin The thermocatalytic conversion of lignin was conducted in an 80 mL stainless steel reactor (batch system) equipped with a mechanical stirrer. In a typical run, the autoclave was charged with 0.5 g of lignin, 0.3 g of catalyst, 16 mL of isopropanol, and 0.5 mL of n-decane. The reactor was pressurized with 4.0 MPa N 2 at ambient temperature after purging N 2 five times to remove air and moisture. After that, the reactor was gradually heated to 250 °C and the temperature was kept constant for 4 h at 700 rpm. When the reaction was completed, the reactor was then quenched using an ice-water bath to ambient temperature. Then the pressurized gas was released. Each experiment was performed three times. After each run, the reaction product mixture was separated by centrifugation into solid (catalyst and lignin residue) and liquid (volatile and nonvolatile fractions) using a centrifuge tube. By employing a mass spectrometer and gas chromatography (GC-MS, Agilent 5975C) coupled with an HP-5MS capillary column (30 m × 0.25 mm × 0.25 μm) with the helium of 1.0 mL/min. The aromatic and phenolic monomers were detected and identified. The following were the GC-MS's operating conditions: The injector temperature remains constant at 280 °C. The temperature of the oven was set to increase at a rate of 5 °C/min from 40 °C to 180 °C (2 min) and then 10 °C/min from 280 °C to 180 °C (2 min). The mass spectra were operated in electron impact (EI) mode at 70 eV. In this analysis, the mass spectra between m/z 40 and 550 were collected. With the use of gas chromatography and flame ionization detector (GC-FID, Agilent 7890A), and HP-5 MS capillary column (30 m × 0.25 mm × 0.25 μm). The yields of the main aromatic and phenolic monomers were quantified using an external standard method. The GC-FID operated under the following conditions: The oven was set to heat at a rate of 5°C/min from 80°C in (3 min) to 270 °C in (5 min). Meanwhile, the FID temperature was 280°C. The following equations are used to evaluate the lignin conversion rate and the yield of monomer products: Lignin conversion (%) = (L I L F )L I 100 % (1) Yield of monomer products (wt. %) = M W L I 100 % (2) Where L I and L F are the initial and final weights of lignin and M W is the weight of the monomer product. To determine the molecular weight of nonvolatile liquid products, tetrahydrofuran was used as the mobile phase in a gel permeation chromatography (GPC) analysis with the Agilent Technologies 1260 Infinity (HR 4E THF) instruments. To characterize the nonvolatile fraction on Shimadzu (50 FT-IR), Fourier-transform infrared spectroscopy (FT-IR) was performed by the ATR method. Reaction kinetics An 80 mL stainless steel batch reactor was employed to perform the kinetic reaction. 16 mL of isopropanol and appropriate amounts of lignin and catalysts were loaded in the reactor. The autoclave was sealed and purged with N 2 five times to drive out moisture and air. Following that, the reactor was pressurized with 4.0 MPa N 2 and gradually heated to 200 ℃ at 700 rpm. At 40, 80, 120, 160, 200, and 240 min, kinetic data were taken. Turnover number (TON) and Turnover frequency (TOF) are calculated as follows: TON = N R /N C (3) TOF = TON/t (4) Where, N R and N C are the number of moles of reactant converted and the number of moles of catalyst, and t is time in hour (h). In 40, 80, 120, and 160 min, respectively, the kinetic reactions were conducted at four different temperatures i.e. 473, 483, 493, and 503 K. The apparent activation energy (E a ) is then calculated using the Arrhenius equation; k = Ae (-Ea/RT) (5) Where k is the rate constant, A is the pre-exponential factor, E a is the apparent activation energy, R is the universal gas constant (8.314 J/(mol-K)) and T is the temperature in Kelvin. Results And Discussion Physiochemical properties of catalysts To explore the effect of the catalyst's properties on the lignin catalytic hydrogenolysis reaction performance, a series of characterization measurements such as BET, SEM, EDX, and XPS were performed. First, the N 2 adsorption/desorption measurements were performed to evaluate the catalysts' textural properties after preparation. The BET surface area, pore volume, and pore size are presented in Table 1 . The Ni/C catalyst exhibited a BET surface area of 633.4 m 2 /g, a pore volume of 0.076 cm 3 /g, and a pore size of 5.30 nm, while the Co/C catalyst showcased a BET surface area of 584.1 m 2 /g, a pore volume of 0.109 cm 3 /g, and a pore size of 6.81 nm. The porous structure of activated carbon facilitates the dispersion of metal sites. In comparison, the Ni-Co/C catalyst demonstrated a slightly reduced BET surface area of 556.6 m 2 /g, akin to Ni/C and Co/C. A similar trend was observed in pore size (3.53 nm). However, upon loading both metals, pore blockage ensued, leading to a significant decrease in both BET surface area and pore size. In addition, the Ni-Cu/C catalyst has the lowest BET surface area and pore volume of 537.6 m 2 /g and 0.063 cm 3 /g, respectively. Furthermore, all catalysts exhibited isotherms of N 2 adsorption/desorption that were comparable ( Fig. S1 ). The type-IV isotherms demonstrated that all catalysts were mesoporous. Table 1 Surface properties of the prepared catalysts. Secondly, SEM and EDX measurements were conducted to reveal the distribution of the loaded metals (Co and Ni) in the Ni-Co/C catalyst ( Fig. 1) . The SEM and EDX elemental mapping images of Co and Ni revealed that both Co (white dots) and Ni (pink dots) are present on the surface of the activated carbon support and are uniformly dispersed within the tested region. Similarly, Fig. 2 indicated the even dispersion of Cu and Ni elements on the surface of the support. According to reported literature, the interactions between Ni and Co enhanced the metal dispersion and provided more active sites, which typically enhance activity (Zhu et al., 2019a). Fig. S2, Fig. S3, and Fig. S4 represent the SEM and EDX elemental mapping images of the Ni/C, Co/C, and Cu/C catalysts respectively. EDX elemental analysis indicated that the elemental compositions of nickel and cobalt on the surface of Ni-Co/C were 17.76 wt. % and 12.90 wt. %, respectively. Similarly, the elemental compositions of nickel and copper on the surface of Ni-Cu/C were 26.37 wt. % and 6.17 wt. %. The results of EDX elemental analysis revealed that the elements (Ni and Co) coexist on the support. Fig. 1 SEM images of Ni-Co/C catalyst at a magnification of (a) 3 kX and (b) 30 kX with corresponding EDX mapping of (c) Ni and (d) Co. Fig. 2 SEM images of Ni-Cu/C catalyst at a magnification of (a) 10 kX and (b) 30 kX with corresponding EDX mapping of (c) Ni and (d) Co. Furthermore, XPS measurement was performed to further explore the electronic interactions between Ni and Co and to reveal their chemical states. As shown in Fig. 3 . The XPS spectra and the associated deconvolutions of Ni 2p on Ni/C and Ni-Co/C catalysts. Fig. 3 (a) and (c), reveal that the distinctive peaks between 861.2 and 860.7 eV were assigned to Ni 2+ , whereas the distinctive peaks between 854.3 and 853.7 eV were assigned to metallic Ni 0 . Revealing the presence of two different forms of Ni species in the prepared Ni/C and Ni-Co/C catalysts (Zhou et al., 2017). This is due to the possibility of environmental oxygen oxidizing the active Ni metal surface (Li et al., 2020). Ni 0 and Ni 2+ binding energies exhibited a slight drop which reveals the change in the chemical state of the bimetallic catalysts and the transfer of electrons from Co to Ni species. Similarly, Fig. 3 (b and d), shows the Co 2p spectra of the Co/C and Ni-Co/C catalysts. The Co 3+ and Co 2+ are attributable to the peaks at 785.9 eV and 795.7 eV, respectively. Whereas the peak at 802.8 eV corresponded to the Co satellite. Both the Co/C and the Ni-Co/C catalysts exhibit mixed valence states of Co. Conversely, for the Ni-Co/C catalyst, peaks corresponding to Co 3+ , Co 2+ , and Co satellite were slightly shifted to higher binding energy positions at 786.4 eV, 796.9 eV, and 804.1 eV. This reveals that the intense interactions between nickel and cobalt result in the transfer of electrons from cobalt to nickel (Hu and Lu, 2007). Additionally, two distinctive peaks in the Co 2p spectra of Co/C and Ni-Co/C catalysts, which appeared at 780.2 eV and 781.7 eV can be attributable to metallic Co 0 . In summary, the shift observed in the Co 2p and Ni 2p spectrum reveals that the strong electron interactions between nickel and cobalt enhanced the transfer of electrons and the formation of multiple electron-rich Ni sites. Fig. 3 The deconvolutions of Ni 2p and Co 2p XPS spectra of the (a) Ni/C, (b) Co/C, (c) Ni-Co/C, and (d) Ni-Cu/C catalysts. Catalytic hydrogenolysis of lignin The real motives behind the selection of cobalt and copper species as nickel promoters was to improve catalytic activity, stability, and product selectivity. The performance of monometallic catalysts (Cu/C, Co/C, Ni/C) and Ni-based bimetallic catalysts (Ni-Cu/C, Ni-Co/C) on the catalytic hydrogenolysis of lignin was tested in isopropanol solvent at 250 ℃, 4 MPa and 700 rpm, in 4 h. The results of the finding, which includes the percentage of lignin conversion and product distributions, are presented in Table 2 and Fig. S5. Low activity on lignin hydrogenolysis was exhibited by the Cu/C catalyst. It afforded only 16.2 wt. % of the total monomer product at 72.9 % lignin conversion. Also, the introduction of a Co/C catalyst afforded 17.5 wt.% of the total monomer products at a lignin conversion of 78.1 %. Cu/C and Co/C catalysts were not as effective as Ni/C catalysts, with 18.2 wt. % of total monomer product yield and the lignin conversion reaching 78.6 %. Zhu et al . reported catalytic depolymerization of lignin over Pt-Re/TiO 2 catalyst under isopropanol/water solvent at 240 in 12 h. Their study achieved 18.7 wt. % of the total yield of monomeric products (Zhu et al., 2019b). The introduction of Ni-based bimetallic catalysts (Ni-Cu/C) significantly improved the lignin conversion rate and total monomer product yield to 84.7 % and 33.0 wt. % respectively. Because of their hydrogenation abilities, Ni-based catalysts have the potential to increase catalytic performance and the efficiency of reaction by suppressing the formation of char (Korányi et al., 2017). Interestingly, Ni-Co/C catalyst exhibited a superior catalytic performance achieving the highest yield of monomer product of 53.1 wt. % and excellent lignin conversion of 94.2 %. According to Tian et al . (2022), in catalytic hydrogenolysis reaction of lignin model compound, over Ni-Co/SiO 2 -ZrO 2 catalyst at 240 °C and 1 MPa, in 4 h, 48.1 wt. % of the total yield of monomer products and 100 % conversion of guaiacol were achieved. In terms of product distribution, the selectivity of all the products was increased over the Ni-Co/C catalyst. The phenol selectivity was 2.9 wt. %, guaiacol selectivity was 43.8 wt. % and other aromatic products had a selectivity of 5.3 wt. %. The results of this finding revealed that the promotional effect of cobalt and copper in the bimetallic catalysts enhanced catalytic activity, stability, and product selectivity more than their monometallic counterparts. Table 2. Hydrogenolysis performance of lignin with monometallic and bimetallic catalysts. Analysis of volatile products To identify and quantify the volatile products from the lignin hydrogenolysis reaction, GC-MS and GC-FID analyses were performed. The results of the investigation as presented in Table 3 revealed that the monomer products were classified into phenols, guaiacols, other aromatics, and hydrogenated products. Under optimized reaction conditions, phenols afforded 2.9 wt. %, guaiacols afforded 43.8 wt. %, other aromatics afforded 5.3 wt. % and hydrogenated products afforded 1.2 wt. %, respectively. The product distribution reveals that the hydrogenolysis reaction converted all the lignin's main building blocks (H, G, and S units). The results of the quantitative analysis indicated that the maximum yield of 43.8 wt. % was guaiacols, which typically make up the coniferyl (G) structural unit of lignin. Similarly, the yields from sinapyl (S) and p-coumaryl (H) units from the product distribution are relatively low. This revealed that the G-unit is more reactive than the corresponding S and H-units. Table S1 provides the summary of GC-MS analysis of the product distributions obtained from lignin hydrogenolysis reactions. A total of 20 monomer products were successfully identified by the GC-MS analysis. Their various retention time, chromatogram areas, and chemical structures were also identified. Table 3 The major components of monomeric product yields Analysis of nonvolatile products Raw lignin and the nonvolatile products resulting from lignin depolymerization over both monometallic and Ni-based bimetallic catalysts underwent analysis via FT-IR and GPC characterizations. Initially, the raw lignin exhibited an average molecular weight of 1,717 g/mol with a polydispersity of 2.3, indicating a relatively high molecular weight distribution. However, following depolymerization, GPC measurements demonstrated a substantial decrease in molecular weight to 610 g/mol for the nonvolatile products across various catalysts. This reduction highlights the efficacy of the catalysts in facilitating lignin depolymerization, leading to a significant decrease in molecular weight, thereby offering valuable insights into the catalytic mechanisms involved in the process ( Table 4 ). The results of this investigation revealed that the nonvolatile products of lignin hydrogenolysis in the presence of Cu/C had a relatively high molecular weight (Mw) of 1,693 g/mol and the highest polydispersity (PID) of 2.2. With Ni/C and Co/C catalysts the molecular weight and polydispersity of the obtained nonvolatile products decreased to 929 g/mol, 807 g/mol, and 2.0, 1.8, respectively. Interestingly, the introduction of Ni-based bimetallic catalysts, specifically Ni-Cu/C and Ni-Co/C significantly decreased the molecular weight of the nonvolatile products to 612 g/mol and 610 g/mol respectively. The results obtained revealed the promotional effect of copper and cobalt in the bimetallic catalyst system enhanced lignin depolymerization reaction. The results were in agreement with the yields of monomer products obtained over monometallic and Ni-based bimetallic catalysts ( Table 2 ). Ni-based bimetallic catalysts also exhibited significantly lower values of polydispersity (1.5), revealing that the nonvolatile products had a concentrated distribution and the excellent hydrogenolysis efficiency of Ni-based bimetallic catalysts. Table 4 GPC analysis results of Mn, Mw, and PID for raw lignin and nonvolatile products. In addition, the FT-IR measurements of the nonvolatile products were performed and compared with the FT-IR measurements of raw lignin. As shown in Fig. S6 and Fig. S7 , the FT-IR spectra of nonvolatile products obtained from the catalytic hydrogenolysis reaction over Ni-based bimetallic catalysts were comparable. The medium peaks at 3,331 cm -1 and 1,379 cm -1 corresponded to the O–H bending vibration of the phenolic compounds (hydroxyl groups). It was observed that during the hydrogenolysis process, the absorption peaks changed significantly, revealing a transformation of the lignin structure. The O–H peak, for example, increased from 3,285cm -1 to 3,331 cm -1 , revealing that the hydrogenolysis process did occur and resulted in an increase in phenolic compounds. The characteristic absorption peaks at 2,961 cm -1 , 2,897 cm -1 , and 1,445 cm -1 were attributed to C–H stretching and bending vibration in the alkane or methoxy functional groups. Furthermore, the yield of guaiacols was revealed by an increase in the methoxy functional groups from 2,945 cm -1 to 2,961 cm -1 . Similarly, the strong absorption peaks at 1,734 cm −1 and 1,643 cm −1 were attributable to the C=O double bond stretching and bending vibration in the carboxyl group and benzene rings (Shu et al., 2016). The medium and strong peaks at 1,306 cm -1 and 1,128.36 cm -1 were equally attributed to the aromatic rings. Similarly, the increase in the aromatic ring peak from 1,113 cm -1 to 1,306 cm -1 reveals that the hydrogenation of the aromatic ring did occur, resulting in the formation of hydroxylated intermediate products. The C=C double bond bending vibration in alkenes can be assigned to three strong and medium peaks at 947 cm −1 , 808 cm −1 , and 675 cm -1 , respectively. Also, the appearance of the C=C double bond bending vibration in alkenes after the lignin catalytic hydrogenolysis reaction confirmed that lignin depolymerization exposed functional groups. The Ni-based bimetallic catalysts exhibited better catalytic activity in the lignin hydrogenolysis process through the absorption peak intensities. Effects of reaction temperature on lignin conversion and yield of monomer products Reaction parameters such as temperature, pressure, stirring speed, and catalyst dosage have significant effects on the performance of the hydrogenolysis reaction (Shao et al., 2018). Based on this fact, their effects on both the monomer product yield and lignin conversion rate were investigated. The effect of reaction temperature on the yield of monomer products and the lignin conversion rate were investigated. Fig. 4 shows the effect of reaction temperatures between 220 ℃ to 250 ℃ on the yield of monomer products and lignin conversion rate over Ni-Co/C catalyst. At an initial temperature of 220 ℃, 66.8 % of lignin was converted affording 17.5 wt. % monomer products. The lignin conversion rate increased to 78.6 % while the monomer product yield reached 26.3 wt. % as the temperature was raised to 230 ℃. When the reaction temperature was further increased to 240 ℃, the lignin conversion rate also increased to 82.7 % affording 36.9 wt. % monomer products. At an elevated reaction temperature of 250 ℃, 94.2 % of lignin was converted with an impressive yield of 53.1 wt. % of monomer products. Ambursa et al. (2016) reported 96 % conversion of lignin model compound (dibenzofuran) and 45 wt. % of hydrocarbon selectivity at 250 °C and 10 MPa over Ni-Cu/TiO 2 bimetallic catalysts. They observed that excessively high temperatures could cause the repolymerization of the monomer product and the non-volatile liquid products in the reaction to form solid residues (Joffres et al., 2016). Moderate reaction temperature promotes the scission of carbon-oxygen and carbon-carbon bonds by overcoming the energy barrier in the lignin hydrogenolysis reaction (Zhao et al., 2019). Regarding the distribution of products, guaiacol was the highest afforded 43.8 %, and other aromatic products afforded 5.3 wt. %, phenol afforded 2.9 wt. % and the least was the hydrogenated products afforded just 1.1 wt. %. 250 °C was the optimal reaction temperature that achieved the highest monomer product yield of 53.1 wt. % over Ni-Co/C catalyst. Fig. 4 Effects of reaction temperature on the hydrogenolysis performance of Ni-Co/C catalyst. (Reaction conditions: Lignin = 0.5 g, catalyst = 0.3 g, isopropanol =16 mL, n-decane = 0.5 mL, 4 h, 4 MPa, 700 rpm). Effects of reaction pressure on lignin conversion and yield of monomer products Reaction pressure is another important parameter that has a significant effect on the performance of the hydrogenolysis reaction. Fig. 5 shows the results of the investigation conducted on lignin hydrogenolysis reactions over Ni-Co/C catalyst at varying reaction pressures between 2 MPa to 5 MPa. At an initial reaction pressure of 2 MPa, only 70.3 % of lignin was converted, affording 18.4 wt. % monomer products. When the reaction pressure reached 3 MPa, the rate of lignin conversion increased to 77.6 % affording 29.9 wt. % monomer products. Zhai and his group reported the yield of monomer products of 39.5 wt. % over Ni-Fe/C at a reaction pressure and temperature of 2 MPa and 225 ℃ in 6 h where propylsyringol and propylguaiacol were the major products (Zhai et al., 2017). Both the lignin conversion and the monomer product yield significantly increased to 94.2 % and 53.1 wt. % respectively when the reaction pressure was increased to 4 MPa. Conversely, as the reaction pressure increased further to 5 MPa, both the lignin conversion rate and the yield of monomer products significantly decreased to 86.1 % and 38.8 wt. %, respectively. The yield of guaiacol and phenol monomers decreased significantly at high reaction pressure, most likely as a result of the formation of more volatile and saturated products (Wanmolee et al., 2018). The results of this investigation revealed that the reaction pressure of 4 MPa is the optimal pressure. And the promotion of catalytic hydrogenolysis of lignin at high pressure of 5 MPa is negligible. Fig. 5 Effects of reaction pressure on the hydrogenolysis performance of Ni-Co/C catalyst. (Reaction conditions: Lignin = 0.5 g, catalyst = 0.3 g, isopropanol =16 mL, n-decane = 0.5 mL, 4 h, 250 ℃, 700 rpm). Effects of stirring speed on lignin conversion and yield of monomer products The rate of lignin conversion and yield of monomer products are greatly influenced by stirring speed in the lignin hydrogenolysis reaction. In our previous study, stirring speed promotes the transfer of mass and heat, selectivity of product, and hydrogenolysis reaction kinetics (Ewuzie et al., 2023). It enhances the catalyst-lignin interactions within the reactor and enables effective reactions and uniform product compositions. To maximize the rate of reaction, the gradient of reactant concentration can be maintained under an optimal stirring speed. To run the reactions under kinetic control, the stirring speed was carefully varied from 500 rpm to 800 rpm. Fig. 6 shows the effects of stirring speed on the lignin conversion and yield of monomer products. When the reaction was run at 500 rpm, a relatively low monomer product yield of 19.0 wt. % was achieved at a 71.3 % lignin conversion rate. This would suggest that the reaction was likely limited by mass transfer processes, probably as a result of insufficient mixing and dispersion of the reactants. However, when the stirring speed was increased to 600 rpm, there was a sharp increase in the yield of the monomer product reaching 32.2 wt. %, while the lignin conversion rate increased to 80.5 %. Interestingly, the lignin conversion rate significantly improved reaching 94.2 %, and affording 53.1 wt. % monomer products as the stirring speed was increased to 700 rpm. This significant improvement suggests that the increased stirring speed provided better contact between the active components and the lignin substrate, enabling the active components to perform more efficiently thereby increasing the lignin conversion rate and monomer product yield. Surprisingly, when the stirring speed was further increased to 800 rpm, both the lignin conversion rate and monomer product yield significantly dropped to 88.4 % and 44.6 wt. %, respectively. These findings revealed that beyond 700 rpm, further increase in stirring speed hurts lignin conversion rate and monomer product yield. Fig. 6 Effects of stirring speed on the hydrogenolysis performance of Ni-Co/C catalyst. (Reaction conditions: Lignin = 0.5 g, catalyst = 0.3 g, isopropanol =16 mL, n-decane = 0.5 mL, 4 h, 250 ℃, and 4 MPa). Effects of Ni-Co/C catalyst dosage on the lignin hydrogenolysis reaction Catalyst dosage can also influence the rate of reaction, lignin conversion rate, monomer product yield, and in commercial applications, the process's economics. An in-depth investigation on the influence of Ni-Co/C catalyst dosage was conducted, and results are displayed in Fig. 7 . It can be observed that the monomer product yield and lignin conversion rate exhibited an increasing trend with decreasing catalyst-to-lignin ratios. Under optimal reaction conditions, 0.05 g, 0.1 g, 0.2 g, and 0.3 g of catalyst were used, resulting in lignin-to-catalyst ratios of 10, 5, 2.5, and 1.7. When the hydrogenolysis experiment was conducted with 0.05 g of Ni-Co/C catalyst only 68.8 % of lignin was converted affording 16.5 wt. % monomer products. As for the 0.1 g experiment, the lignin conversion rate and monomer product yield gradually increased to 76.5 % and 27.9 %, respectively. As the catalyst dosage was further increased to 0.2 g, the lignin conversion rate and monomer product yield equally increased reaching 84.7 % and 45.1 wt. %. Moreover, the standard run with 0.3 g of Ni-Co/C catalyst achieved the highest lignin conversion of 94.2 % and the maximum monomer product yield of 53.1 wt. %. Because of the improved lignin depolymerization that occurs when there are more catalytic sites present, the conversion of lignin and monomer product yield increases progressively with higher catalyst dosage (Zhao et al., 2019). Fig. 7 Effects of Ni-Co/C catalyst dosage on the lignin hydrogenolysis reaction. (Reaction conditions: Lignin = 0.5 g, isopropanol = 16 mL, n-decane = 0.5 mL, 250 ℃, 4 h, 4 MPa and 700 rpm). Kinetic study results To further confirm the improved catalytic performance and promotional effects of Ni-based bimetallic catalysts on lignin hydrogenolysis. A kinetic study on the rate of conversion of lignin with time over Ni-based bimetallic and monometallic catalysts was conducted. Fig. 8 presents the summary of TOF and E a for the rate of conversion of lignin over Ni-Co/C and Ni/C catalysts. The rate of conversion of lignin exhibited a linear increase from 29.8 % to 94.2 % over the Ni-Co/C catalyst and from 5.3 % to 78.6 % over the Ni/C catalyst between 40 min to 240 min ( Fig. 8(a)) . Under the same reaction conditions, the TOF over Ni/C catalyst was determined to be 4.4 h −1 . This value was calculated from the starting point of the linear kinetic plot. And that of the Ni-Co/C catalyst was calculated to be 36.1 h -1 , which is about eight times higher than the value with catalyst Ni/C. In addition, the kinetic study on lignin catalytic hydrogenolysis over Ni/C and Ni-Co/C catalysts at different temperatures was also conducted. As seen in Fig. 8(b) (Arrhenius plot), apparent activation energy (E a ) was calculated from the slope of the fitted linear plot [In(K) vs 1/T] and the E a for lignin depolymerization over Ni/C was found to be 50.0 kJ/mol. Lui and co-workers reported that an E a value of 48.0 kJ/mol was calculated from the kinetic study on a lignin model compound over Pd/C at 240 °C and 3.4 MPa in 4 h (Liu et al., 2017). In this study, the calculated E a value over the Ni-Co/C catalyst was 36.1 kJ/mol. Which is much lower compared to the E a value of the Ni/C catalyst. The results of the kinetic study coupled with higher TOF and lower E a of Ni-based bimetallic catalysts have further revealed the promotional effect of Co and Ni catalysts. Therefore, the addition of Co as a nickel promoter significantly enhanced the catalytic performance in the lignin hydrogenolysis reaction process. Fig. 8 Kinetic study on catalytic hydrogenolysis of lignin over Ni/C and Ni-Co/C catalysts. (Reaction conditions: Lignin = 0.5 g, catalyst = 0.3 g, isopropanol, = 16 mL, n-decane = 0.5 mL, 240 o C, 40 min, 700 rpm, and 4 MPa N 2 ). Possible reaction mechanism for catalytic depolymerization of lignin Based on the excellent results achieved, the possible reaction mechanism for catalytic depolymerization of lignin over Ni-based bimetallic catalyst (Ni-Co/C) under optimum reaction conditions is shown in Fig. 9 . Initially, lignin was chemically adsorbed on the surface of the catalyst and interacted with catalytic active sites. As a result, the aromatic ring was hydrogenated and formed hydroxylated intermediate products (phenol, 2-methoxyphenol, and 4-vinylpyridine) under isopropanol solvent. The hydroxylated intermediate products serve as the main building blocks for the catalytic reactions involving the breaking of bonds and fragmentation to produce phenol, guaiacols, and aromatic monomers. The interaction between the hydroxylated intermediate products and the catalytic active components (Ni and Co) facilitated the cleavage of β-O-4, β-5, and C-C ether bond linkages in the lignin structure. According to the report, H-radicals can be transferred to catalytic active sites such as Ni, Fe, Co, and Cu (Zhu et al., 2019a). Isopropanol as a hydrogen donor solvent, supplied all the required hydrogen for the bond cleavages and hydrogenation processes. In our previous study, Smaller aromatic fragments were formed due to the depolymerization of C-C, β-O-4, and β-5 ether bond linkages in the aromatic rings (Ewuzie et al., 2023). Furthermore, benzene, phenyl alcohol, and guaiiacyl aldehyde (aromatic fragments) reacted with active H-radical (hydrogenolysis reaction) producing phenols, guaiacols, and aromatic monomers. Hydrogen is activated on cobalt sites to produce active H-radicals, due to cobalt's ability to activate hydrogen (Lin et al., 2021). The two main products are phenol and aromatic monomers; hence it has been proposed that the most crucial step in producing the targeted products is the scission of the aromatic ring in lignin. A detailed chemical reaction route that breaks the C-O and C-C bonds in lignin to produce 2.9 wt. % phenols, 43.8 wt. % guaiacols, and 5.3 wt. % aromatic monomers is shown in Table 2. Because of the strong chemical interactions between the metal's d-states and aromatic ring, lignin was chemisorbed onto nickel's active sites. Then, the active H-radicals spill onto Ni sites and attack the C-C and C-O bonds in lignin. After which, the C-C and C-O bonds in lignin were broken, resulting in a 94.2 % lignin conversion. Fig. 9 Possible reaction mechanism for the catalytic depolymerization of lignin. Conclusion This study represents a significant step forward in harnessing the great potential of lignin as a valuable renewable resource in the production of phenolic fine chemicals. It also sheds light on the great potential of Ni-based bimetallic catalysts. A rigorous investigation of the potential of Co/C, Cu/C, Ni/C, Ni-Cu/C, and Ni-Co/C catalysts on the catalytic depolymerization of lignin under isopropanol solvent was conducted. Ni-based bimetallic catalysts demonstrated superior catalytic performance, enhanced product selectivity, and improved stability compared to their corresponding monometallic catalysts. BET, SEM, EDX, and XPS measurements revealed the physicochemical properties and promotional effects of these catalysts. Furthermore, the effects of reaction temperature, pressure, stirring speed, and catalyst dosage on the depolymerization of lignin were elucidated. The results of the investigation revealed that the addition of cobalt and copper as promoters to nickel significantly enhanced lignin conversion and monomer product yield. The Ni-Co/C catalyst exhibited remarkable performance, achieving the highest lignin conversion of 94.2 % and a maximum monomer product yield of 53.1 wt. % under optimal reaction conditions. The E a value of 36.1 kJ/mol for catalytic lignin depolymerization over Ni-Co/C was considerably lower compared to the corresponding monometallic catalyst Ni/C (50.0 kJ/mol). Similarly, the turnover frequency (TOF) of Ni-Co/C was substantially higher (31.6 h −1 ) compared to Ni/C (4.4 h −1 ), revealing the superior catalytic activity of the Ni-based bimetallic catalyst. The volatile and nonvolatile products were analyzed by GC-MS, GC-FID, GPC, and FT-IR measurements. A total of 20 monomer products were successfully identified in GC-MS analysis. A possible reaction mechanism was proposed to elucidate the catalytic pathways involved. This breakthrough holds significant promise for the sustainable production of high-value phenolic fine chemicals from lignin. And contributing to a more environmentally friendly and economically robust chemical industry. Declarations Acknowledgment This research work is fully funded by the Ministry of Higher Education Malaysia under the Fundamental Research Grant Scheme (FRGS/1/2021/TK0/USM/01/2). Ethics approval and consent to participate Not applicable Consent for publication Not applicable Availability of data and materials Not applicable Competing interests Not applicable Funding The authors acknowledge the Fundamental Research Grant Scheme (LRGS) from the Ministry of Higher Education of Malaysia (FRGS/1/2021/TK0/USM/01/2). Authors' contributions Remigius Nnadozie Ewuzie planned, and carried out the experimental work conceptualized by Ahmad Zuhairi Abdullah who is also involved in securing the research funding and supervision. Jackson Robinson Genza contributed to the analysis and interpretation of results and drafting of the manuscript. 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J Energy Inst 92: 74–81. https://doi.org/10.1016/j.joei.2017.11.004. Zhu C, Cao JP, Zhao XY, Xie T, Zhao M, Wei XY (2019b). Bimetallic effects in the catalytic hydrogenolysis of lignin and its model compounds on nickel-ruthenium catalysts. Fuel Process Technol 194: 106126. https://doi.org/10.1016/j.fuproc.2019.106126. Tables Table 1 Surface properties of the prepared catalysts. Catalyst BET Surface area a (m 2 /g) Pore Volume b (cm 3 /g) Pore Size b () Ni/C 633.4 0.076 5.30 Co/C 584.1 0.109 6.81 Ni-Co/C 556.6 0.174 3.53 Ni-Cu/C 537.6 0.063 4.13 a Brunauer, Emmett, and Teller (BET) multipoint technique. b Method by Barrett, Joyner, and Halenda (BJH). Table 2 Hydrogenolysis performance of lignin with monometallic and bimetallic catalysts. Entry Catalyst Conversion (%) Monomer products yield (wt.%) Phenols Guaiacols Other aromatic products Hydrogenated products Total yield 1 Cu/C 72.9 2.4 10.2 3.5 0.1 16.2 2 Co/C 78.1 2.0 12.2 3.1 0.2 17.5 3 Ni/C 78.6 2.1 11.7 3.8 0.6 18.2 4 Ni-Cu/C 84.7 2.5 26.4 3.6 0.5 33.0 5 Ni-Co/C 94.2 2.9 43.8 5.3 1.1 53.1 Reaction condition: lignin = 0.5 g, catalysts = 0.3 g, isopropanol = 16 mL, n-decane = 0.5 mL, 4 MPa N 2 , 250, 4 h and 700 rpm. Ni/C, Cu/C and Co/C catalysts were theoretically loaded with 10wt. % each. Similarly, 10 wt. % of both Ni, Co and Cu for the Ni-Cu/C and Ni-Co/C catalysts were also loaded. Table 3 The major components of monomeric product yields. Phenols Yield (wt. %) Guaiacols Yield (wt. %) Other Aromatics Yield (wt. %) Hydrogenated Products Yield (wt. %) Phenol 0.7 Phenol, 2-methoxy- 14.0 Benzene, 1,2-dimethoxy 1.5 Ethanone, 1-(2-hydroxy-5-methylphenol 0.6 Phenol, 4-ethyl 0.7 Creosol 7.0 3,4-Dimethoxytoluene 1.1 Ethanone, 1-(3-hydroxy-4-methoxy 0.6 Phenol, 3-(1-methylethyl) 0.7 Phenol, 2-propyl- 0.2 Benzene, 4-ethyl-1,2-dimethoxy 0.5 - - Phenol, 2,5-bis(1,1-dimethylethyl) 0.8 Phenol, 4-ethyl-2-methoxy 17.3 Benzoic acid, 3-(methylthio) 0.3 - - 2-Methoxy-4-vinylphenol 0.1 Benzeneacetic acid, 4-hydroxy 0.9 - - Eugenol 0.6 Benzene, 1,4-dimethoxy-2-methyl 0.2 - - Phenol, 2-methoxy-4-propyl- 2.6 Benzaldehyde, 2,4-dihydroxy 0.8 - - Phenol, 3-(dimethylamino) 1.0 - - - - Phenol, 4-(ethoxymethyl)-2-methoxy 1.0 - - - - Total 2.9 Total 43.8 Total 5.3 Total 1.2 Reaction conditions: Lignin=0.5g, catalyst = 0.3g, isopropanol = 16mL, n-decane = 0.5 mL, 250℃, 4MpaN 2 , 4h, and 700 rpm Using GC-MS, where acetophenone was used as the internal standard chemical. The components listed were those with a GC-MS yield of more than 0.1%. Table 4 GPC analysis results of Mn, Mw, and PID for raw lignin and nonvolatile products. Raw lignin and catalyst Number Average Molecular Weight (Mn)-g/mol Weight Average Molecular Weight (Mw)-g/mol Average Molecular Weight (Mz)-g/mol Polydispersity (PID)= (Mw/Mn) Molecular mass of polymer (Mp)-g/mol Raw lignin 757 1717 3178 2.3 1530 Cu/C 712 1693 3211 2.2 1607 Ni/C 461 929 1872 2.0 186 Co/C 448 807 1488 1.8 187 Ni-Cu/C 392 612 1030 1.6 315 Ni-Co/C 382 610 1054 1.6 304 Reaction conditions: Lignin = 0.5 g, catalyst = 0.3 g, Isopropanol, =16 mL, n-decane= 0.5 mL, 250, 4 h, 700 rpm and 4 MPa N 2 . Supplementary Files Supplementarydata.docx.docx Cite Share Download PDF Status: Published Journal Publication published 30 Jul, 2024 Read the published version in Environmental Science and Pollution Research → Version 1 posted Editorial decision: Major Revision 20 Jun, 2024 Reviewers agreed at journal 17 May, 2024 Reviewers invited by journal 16 May, 2024 Editor invited by journal 16 May, 2024 Editor assigned by journal 23 Apr, 2024 First submitted to journal 20 Apr, 2024 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-4297106","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":303477244,"identity":"0bd05cb6-d3e9-48a7-b998-6f1492fabc67","order_by":0,"name":"Remigius Nnadozie Ewuzie","email":"","orcid":"","institution":"Universiti Sains Malaysia","correspondingAuthor":false,"prefix":"","firstName":"Remigius","middleName":"Nnadozie","lastName":"Ewuzie","suffix":""},{"id":303477245,"identity":"ae4b0ea8-9e2a-4ced-a04e-3d96dbab55e0","order_by":1,"name":"Jackson Robinson Genza","email":"","orcid":"","institution":"Universiti Sains Malaysia","correspondingAuthor":false,"prefix":"","firstName":"Jackson","middleName":"Robinson","lastName":"Genza","suffix":""},{"id":303477246,"identity":"084a8807-30bc-4c21-945e-4ca65d9c5ab3","order_by":2,"name":"Ahmad Zuhairi Abdullah","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAtElEQVRIiWNgGAWjYDACCQYGZhDJxt5AshaeA6RpATESiNTBP7v9mXRBjUU+n+Qb4083GLYlEnSfxJ0DadIzjklYtknnmEnnMNwmrMVAIuGYNA+bhAEbUAszkVoS26R5/gG1SJ4x/kyklmQ2ad42oBYJHgPiHCZxI43ZmrcPqIUnrUw6x+C2MUEt/DPSH97m+VZnIN9+ePPnnIrbsgS1oLuTwZFULQwM9iTrGAWjYBSMgmEPAAnuMtgKboWDAAAAAElFTkSuQmCC","orcid":"","institution":"Universiti Sains Malaysia","correspondingAuthor":true,"prefix":"","firstName":"Ahmad","middleName":"Zuhairi","lastName":"Abdullah","suffix":""}],"badges":[],"createdAt":"2024-04-20 10:42:45","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-4297106/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-4297106/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s11356-024-34504-2","type":"published","date":"2024-07-30T15:57:32+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":57337081,"identity":"d3d31127-d7c2-4ad3-9c07-eba68c353e3c","added_by":"auto","created_at":"2024-05-29 09:39:53","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1881331,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of Ni-Co/C catalyst at a magnification of (a) 3 kX and (b) 30 kX with corresponding EDX mapping of (c) Ni and (d) Co.\u003c/p\u003e","description":"","filename":"Fig1.png","url":"https://assets-eu.researchsquare.com/files/rs-4297106/v1/896a963a656e48c14c002743.png"},{"id":57337079,"identity":"f718fa67-198d-4722-9ca1-fc0cced7afb7","added_by":"auto","created_at":"2024-05-29 09:39:53","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":2517972,"visible":true,"origin":"","legend":"\u003cp\u003eSEM images of Ni-Cu/C catalyst at a magnification of (a) 10 kX and (b) 30 kX with corresponding EDX mapping of (c) Ni and (d) Co.\u003c/p\u003e","description":"","filename":"Fig2.png","url":"https://assets-eu.researchsquare.com/files/rs-4297106/v1/632639f27aed96032ef0476b.png"},{"id":57337084,"identity":"bc4512ff-840f-4ab0-9341-84fef127e63e","added_by":"auto","created_at":"2024-05-29 09:39:55","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":608346,"visible":true,"origin":"","legend":"\u003cp\u003eThe deconvolutions of Ni 2p and Co 2p XPS spectra of the (a) Ni/C, (b) Co/C, (c) Ni-Co/C, and (d) Ni-Cu/C catalysts.\u003c/p\u003e","description":"","filename":"Fig3.png","url":"https://assets-eu.researchsquare.com/files/rs-4297106/v1/537bfe6e5f1d9404fa4a8b44.png"},{"id":57337074,"identity":"0f21d7f0-20cf-4884-b465-096be70098ce","added_by":"auto","created_at":"2024-05-29 09:39:52","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":358845,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of reaction temperature on the hydrogenolysis performance of Ni-Co/C catalyst. (Reaction conditions: Lignin = 0.5 g, catalyst = 0.3 g, isopropanol =16 mL, n-decane = 0.5 mL, 4 h, 4 MPa, 700 rpm).\u003c/p\u003e","description":"","filename":"Fig4.png","url":"https://assets-eu.researchsquare.com/files/rs-4297106/v1/8286302ce6a0a6cfff6548da.png"},{"id":57337771,"identity":"830bfa2b-6a55-4a7c-ad20-aa37b41517f2","added_by":"auto","created_at":"2024-05-29 09:47:53","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":323597,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of reaction pressure on the hydrogenolysis performance of Ni-Co/C catalyst. (Reaction conditions: Lignin = 0.5 g, catalyst = 0.3 g, isopropanol =16 mL, n-decane = 0.5 mL, 4 h, 250 ℃, 700 rpm).\u003c/p\u003e","description":"","filename":"Fig5.png","url":"https://assets-eu.researchsquare.com/files/rs-4297106/v1/07c4d2edc4a9cdec5aecffdc.png"},{"id":57337085,"identity":"84500e73-8ff9-45d3-8f02-bddf3944b567","added_by":"auto","created_at":"2024-05-29 09:39:55","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":332146,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of stirring speed on the hydrogenolysis performance of Ni-Co/C catalyst. (Reaction conditions: Lignin = 0.5 g, catalyst = 0.3 g, isopropanol =16 mL, n-decane = 0.5 mL, 4 h, 250 ℃, and 4 MPa).\u003c/p\u003e","description":"","filename":"Fig6.png","url":"https://assets-eu.researchsquare.com/files/rs-4297106/v1/03f644b6cf8c54e5da4b2014.png"},{"id":57337075,"identity":"00ccd64e-50d8-41bd-97dd-6b0fb2687114","added_by":"auto","created_at":"2024-05-29 09:39:53","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":308556,"visible":true,"origin":"","legend":"\u003cp\u003eEffects of Ni-Co/C catalyst dosage on the lignin hydrogenolysis reaction. (Reaction conditions: Lignin = 0.5 g, isopropanol = 16 mL, n-decane = 0.5 mL, 250 ℃, 4 h, 4 MPa and 700 rpm).\u003c/p\u003e","description":"","filename":"Fig7.png","url":"https://assets-eu.researchsquare.com/files/rs-4297106/v1/4f4862565de0aeab4d74241f.png"},{"id":57337082,"identity":"a622f4c5-576d-486c-9527-37f939cc881a","added_by":"auto","created_at":"2024-05-29 09:39:54","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":192697,"visible":true,"origin":"","legend":"\u003cp\u003eKinetic study on catalytic hydrogenolysis of lignin over Ni/C and Ni-Co/C catalysts. (Reaction conditions: Lignin = 0.5 g, catalyst = 0.3 g, isopropanol, = 16 mL, n-decane = 0.5 mL, 240 \u003csup\u003eo\u003c/sup\u003eC, 40 min, 700 rpm, and 4 MPa N\u003csub\u003e2\u003c/sub\u003e).\u003c/p\u003e","description":"","filename":"Fig8.png","url":"https://assets-eu.researchsquare.com/files/rs-4297106/v1/ce43089e247bf5569119d7ea.png"},{"id":57337083,"identity":"643694c0-2a44-4bc7-ac71-19b2e12b7876","added_by":"auto","created_at":"2024-05-29 09:39:54","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":276782,"visible":true,"origin":"","legend":"\u003cp\u003ePossible reaction mechanism for the catalytic depolymerization of lignin.\u003c/p\u003e","description":"","filename":"Fig9.png","url":"https://assets-eu.researchsquare.com/files/rs-4297106/v1/9b0f64eaa0e89b5f0d20ba39.png"},{"id":61794431,"identity":"b353ca72-db15-4a7c-8ed4-67751ca27d3c","added_by":"auto","created_at":"2024-08-05 16:18:18","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":8704073,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-4297106/v1/869e54bf-3185-41da-98d6-ec6bec6e4c46.pdf"},{"id":57337076,"identity":"a9c1809c-da8f-470a-883d-541949a6eb2b","added_by":"auto","created_at":"2024-05-29 09:39:53","extension":"docx","order_by":15,"title":"","display":"","copyAsset":false,"role":"supplement","size":2434880,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementarydata.docx.docx","url":"https://assets-eu.researchsquare.com/files/rs-4297106/v1/c65ef6fc016ee2f80c5bf026.docx"}],"financialInterests":"","formattedTitle":"Activity and product distribution in Ni-Co and Ni-Cu catalyst-mediated lignin depolymerization into phenolic substances with isopropanol H-donating solvent","fulltext":[{"header":"Introduction","content":"\u003cp\u003eA special type of carbon-rich renewable resource that can be found on Earth is lignocellulosic biomass. As a result, this widely dispersed and readily available biomass resource is considered to be the most promising replacement for fossil fuel resources to produce useful biofuels and fine chemicals for the development of a sustainable society (Abdullah et al., 2009). Typically, lignocellulosic biomass is divided into three fractions: lignin, cellulose, and hemicellulose.\u0026nbsp;Compared to the established technologies for the utilization of cellulose and hemicellulose. Lignin utilization is extremely challenging, because of its intricate molecular structure and multiple chemical bonds (Zhang et al., 2017a). However, lignin as one of the three main constituents of lignocellulosic biomass makes up around 15\u0026ndash;30 % of its weight and accounts for about 30 %\u0026ndash;40 % of plants\u0026apos; energy (Xue et al., 2022 ; Li et al., 2015). Additionally, lignin is the earth\u0026rsquo;s most common source of aromatics and natural biopolymer, For instance, the pulping industry alone produces over 130 million tonnes of lignin waste each year (van den Bosch et al., 2018 ; Poveda-Giraldo et al., 2021). Furthermore, there are several valuable functional groups in this renewable resource, such as benzene rings, phenolic hydroxyl groups, and methoxyl groups (Vriamont et al., 2019 ; Zhou et al., 2017). The aforementioned evidence demonstrates that lignin has the potential to be a superb starting material in producing biofuels and phenolic fine chemicals.\u003c/p\u003e\n\u003cp\u003eA wide range of chemical conversion methods, such as hydrolysis (Ren et al., 2018 ; Zhu et al., 2019a), oxidation (Liu et al., 2023), pyrolysis (Zhang et al., 2017b), hydrocracking (Li et al., 2015b), hydrothermal (Wang et al., 2018 ; Kang et al., 2016), and hydrogenolysis (Hu et al., 2019a ; Hu et al., 2019b ; Guan et al., 2020), were employed for depolymerization of lignin and its model compounds. Among these, catalytic hydrogenolysis was shown to be the most promising method for lignin conversion. Typically, a heterogeneous catalyst based on either precious or transition metals is employed in such conversion processes. Transition metal catalysts are mostly based on Co, Fe, Cu, and Ni in particular (Zhai et al., 2017 ; He et al., 2012 ; Guo et al., 2023). Ni catalysts demonstrate remarkable selectivity in the breaking of the aryl ether (C-O) bond (Yang et al., 2021 ; Ye et al., 2021 ; Jiang and Hu, 2016 ; Jafarian et al., 2019). However, due to the limited stability and activity of Ni as a mono-metallic catalyst for lignin depolymerization under moderate reaction conditions, further enhancement of Ni catalysts is, therefore, desirable (De et al., 2016 ; Zhu et al., 2019b). Under moderate reaction conditions, noble metals such as Ru, Pd, and Pt, demonstrate high catalytic performance for lignin depolymerization (Jin et al., 2019 ; Shu et al., 2020). Despite the great activity for hydrogenolysis reactions the noble metal catalysts demonstrate, their inherent metal characteristics make them very active in the hydrogenation of aromatic rings to produce undesirable products (Gyergyek et al., 2018 ; Okoye et al., 2016 ; Lee et al., 2012).\u003c/p\u003e\n\u003cp\u003eSince a phenomenon generally known as \u0026quot;promotional effects\u0026quot; exists, bimetallic catalysts are emerging as an attractive option (Liu et al., 2019 ; Tymchyshyn et al., 2019). This may result in increased catalytic stability, altered desired product selectivity, and improved catalytic activity. Kim and co-workers (2015) reported that the selective scission of the carbon-oxygen bond in benzyl phenyl ether, the bimetallic Fe-Pd/OMC catalysts demonstrated more activity and selectivity than the comparable monometallic catalyst.\u0026nbsp;This was attributed to altering Pd\u0026apos;s electronic properties by transferring electrons from Fe to Pd with the addition (Fe) as a second metal into the Pd/OMC catalyst. According to Zhang \u003cem\u003eet al\u003c/em\u003e. (2016), the Pd-Ni bimetallic catalysts inherited the benefits of both noble and transition metals, whereby the catalyst\u0026apos;s activity for hydrogenolysis reaction was enhanced by the Pd metal catalyst, and its selectivity altered by the addition of Ni, this is favorable for cleaving the C-O bond. Additionally, Mauriello \u003cem\u003eet al\u003c/em\u003e. (2018) revealed that under the condition of transfer hydrogenolysis, bimetallic Pd-Ni catalysts can efficiently break the C-O bonds of different lignin model compounds. The synergistic effects between the two metal species contribute to the enhancement of the catalytic activity of lignin and its model compounds. Transition metal catalysts were acknowledged as a viable replacement for noble metal catalysts in the catalytic depolymerization of lignin due to the expensive nature of noble metal catalysts, which have demonstrated remarkable hydrogenolysis activity (Kim etal., 2018 ; Kim et al., 2017 ; Santos et al., 2018 ; Shu et al., 2019).\u003c/p\u003e\n\u003cp\u003eDue to the excellent physicochemical characteristics of activated carbon such as high porosity, large surface area, superior electron conductivity, and moderate chemical inertness. Activated carbon plays the role of support as well as a catalyst for the lignin depolymerization reaction. The fact that carbon materials are mostly constituted of carbon and can even be produced directly from renewable resources such as biomass makes them advantageous since they are \u0026quot;sustainable\u0026quot; support materials for metallic catalysts (Wu et al., 2017 ; Lam and Luong, 2014). Therefore, in this regard, the transition metals loaded on activated carbon support were synthesized by the incipient-wetness impregnation method, and their performance in the catalytic hydrogenolysis of lignin was tested.\u003c/p\u003e\n\u003cp\u003eIn this study, transition metal catalyst Ni was selected as a base metal for catalytic depolymerization of lignin because of its high catalytic activity, adaptability, synergistic effects with other transition metal catalysts, stability, selectivity enhancement, and economic viability. Secondly, it is commonly known that nickel catalyst serves as the hydrogenolysis center for lignin\u0026apos;s C-O and C-C bond cleavage.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eFurthermore, cobalt and copper transition metal catalysts were selected as the nickel promoters because of their great potential to interact with the d orbital of Ni metal electronically which will result in its partial filling. Thereby affecting both the activity and stability of nickel-based bimetallic catalysts in catalytic depolymerization reactions.\u0026nbsp;Copper and cobalt were chosen as nickel promoters due to their exceptional attributes, including strong hydrogenating capabilities and effective hydrogen atom transfer. Serving as electron donors, copper and cobalt augment the electronic characteristics of nickel, fostering the formation of a more evenly dispersed layer and enhancing the activity of Ni-based bimetallic catalysts. This synergy not only improves the selectivity of monomer products but also facilitates lignin hydrogenolysis and enhances lignin substrate adsorption. Additionally, their presence offers a promising chemical pathway for maximizing monomer yields.\u003c/p\u003e\n\u003cp\u003eBased on this, the performance of the promoted Ni-based bimetallic catalysts on activated carbon support (Ni-Co/C and Ni-Cu/C) was evaluated for the depolymerization of lignin. And compared to their corresponding monometallic catalysts. Additionally, this study evaluated the promotional effect of Ni-based bimetallic catalysts on lignin depolymerization, monomer product yield, and product distribution. The effects of the reaction and kinetic parameters were evaluated, and a possible reaction mechanism was proposed. The results revealed that Ni-based bimetallic catalysts offer enhanced catalytic performance, product selectivity, and stability in the lignin depolymerization compared to the corresponding monometallic catalysts. This breakthrough holds promise for the development of more sustainable and economically viable methods for producing high-value phenolic fine chemicals from lignin.\u003c/p\u003e"},{"header":"Materials And Methods","content":"\u003cp\u003e\u003cstrong\u003eMaterials\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eNi(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026sdot;6H\u003csub\u003e2\u003c/sub\u003eO, Co(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026sdot;6H\u003csub\u003e2\u003c/sub\u003eO, activated carbon support, isopropanol solvent (99.93 %), and ethanol solvent (99.7 %) were purchased from Chemiz (M) Sdn. Bhd. Selangor, Malaysia. Tetrahydrofuran was purchased from HmbG Chemicals, Malaysia. Phenol (99 %) was purchased from R\u0026amp;M Chemicals, Malaysia. Alkali lignin, Cu(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026sdot;6H\u003csub\u003e2\u003c/sub\u003eO, n-decane, 2-methylbenzofuran (96 %), 2-methoxy-4-methylphenol (\u0026gt;98 %), and guaiacol were purchased from Sigma Aldrich, USA.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePreparation of catalysts\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe incipient-wetness impregnation method was used to synthesize all the catalysts. Using Ni(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026sdot;6H\u003csub\u003e2\u003c/sub\u003eO, Cu(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026sdot;6H\u003csub\u003e2\u003c/sub\u003eO, and Co(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026sdot;6H\u003csub\u003e2\u003c/sub\u003eO as the percussor materials. Firstly, activated carbon support was purified by stirring vigorously with deionized water at 100 \u0026deg;C for 4 h, after filtration, it was dried at 80 \u0026deg;C in a vacuum oven for 12 h. Following that, metal loading was carried out by impregnation. The solutions of Ni(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026sdot;6H\u003csub\u003e2\u003c/sub\u003eO, Cu(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026sdot;6H\u003csub\u003e2\u003c/sub\u003eO, and \u0026nbsp;Co(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e\u0026sdot;6H\u003csub\u003e2\u003c/sub\u003eO were incorporated into 5 g of activated carbon support and then stirred for 1 h at 500 r/min. To remove the water, the resultant mixture was slowly heated to 60 \u0026deg;C and then dried in an oven overnight at 80 ℃. After drying, the sample was then calcined at 500 \u0026deg;C for 3 h under air conditions. The prepared catalysts are Ni-Co/C, Ni-Cu/C, Ni/C, Cu/C, and Co/C. The theoretical loading of Ni, Cu, and Co in all catalysts was 10 wt. % each. After cooling, the prepared catalysts were then stored in a vacuum desiccator before use.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCharacterization of catalysts\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe textural properties of the synthesized catalysts were measured by the N\u003csub\u003e2\u003c/sub\u003e adsorption\u0026minus;desorption isotherms using the ASAP 2020 Micromeritics, USA model. The surface area of the catalysts was determined by the Brunauer, Emmett, and Teller (BET) method. Furthermore, average pore size and pore volume were evaluated with the Barrett, Joyner, and Halenda (BJH) method. To confirm the distribution of metallic active components on the activated carbon support. The catalysts\u0026apos; morphology was examined using a scanning electron microscope (SEM), FEI QUANTA FEG 450, equipped with energy-dispersive X-ray (EDX) to determine the elemental compositions. To explore the metal\u0026apos;s elemental states, the X-ray photoelectron spectroscopy (XPS) spectra of the catalysts were measured by AXIS Ultra DLD, Kratos spectrometer equipped with an Al K\u0026alpha; X-ray source.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eThermocatalytic conversion of lignin\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe thermocatalytic conversion of lignin was conducted in an 80 mL stainless steel reactor (batch system) equipped with a mechanical stirrer. In a typical run, the autoclave was charged with 0.5 g of lignin, 0.3 g of catalyst, 16 mL of isopropanol, and 0.5 mL of n-decane. The reactor was pressurized with 4.0 MPa N\u003csub\u003e2\u003c/sub\u003e at ambient temperature after purging N\u003csub\u003e2\u003c/sub\u003e five times to remove air and moisture. After that, the reactor was gradually heated to 250 \u0026deg;C and the temperature was kept constant for 4 h at 700 rpm. When the reaction was completed, the reactor was then quenched using an ice-water bath to ambient temperature. \u0026nbsp;Then the pressurized gas was released. Each experiment was performed three times.\u003c/p\u003e\n\u003cp\u003eAfter each run, the reaction product mixture was separated by centrifugation into solid (catalyst and lignin residue) and liquid (volatile and nonvolatile fractions) using a centrifuge tube. By employing a mass spectrometer and gas chromatography (GC-MS, Agilent 5975C) coupled with an HP-5MS capillary column (30 m \u0026times; 0.25 mm \u0026times; 0.25 \u0026mu;m) with the helium of 1.0 mL/min. The aromatic and phenolic monomers were detected and identified. The following were the GC-MS\u0026apos;s operating conditions: \u0026nbsp;The injector temperature remains constant at 280 \u0026deg;C. The temperature of the oven was set to increase at a rate of 5 \u0026deg;C/min from 40 \u0026deg;C to 180 \u0026deg;C (2 min) and then 10 \u0026deg;C/min from 280 \u0026deg;C to 180 \u0026deg;C (2 min). The mass spectra were operated in electron impact (EI) mode at 70 eV. In this analysis, the mass spectra between m/z 40 and 550 were collected.\u003c/p\u003e\n\u003cp\u003eWith the use of gas chromatography and flame ionization detector (GC-FID, Agilent 7890A), and HP-5 MS capillary column (30 m \u0026times; 0.25 mm \u0026times; 0.25 \u0026mu;m). The yields of the main aromatic and phenolic monomers were quantified using an external standard method. The GC-FID operated under the following conditions: The oven was set to heat at a rate of 5\u0026deg;C/min from 80\u0026deg;C in (3 min) to 270 \u0026deg;C in (5 min). Meanwhile, the FID temperature was 280\u0026deg;C. The following equations are used to evaluate the lignin conversion rate and the yield of monomer products:\u003c/p\u003e\n\u003cp\u003eLignin conversion (%)\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;=\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;(L\u003csub\u003eI\u003c/sub\u003eL\u003csub\u003eF\u003c/sub\u003e)L\u003csub\u003eI\u003c/sub\u003e \u0026nbsp;100 %\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;(1)\u003c/p\u003e\n\u003cp\u003eYield of monomer products (wt. %)\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;=\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;M\u003csub\u003eW\u003c/sub\u003eL\u003csub\u003eI\u003c/sub\u003e \u0026nbsp;100 %\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;(2)\u003c/p\u003e\n\u003cp\u003eWhere L\u003csub\u003eI\u003c/sub\u003e and L\u003csub\u003eF\u003c/sub\u003e are the initial and final weights of lignin and M\u003csub\u003eW\u003c/sub\u003e is the weight of the monomer product.\u003c/p\u003e\n\u003cp\u003eTo determine the molecular weight of nonvolatile liquid products, tetrahydrofuran was used as the mobile phase in a gel permeation chromatography (GPC) analysis with the Agilent Technologies 1260 Infinity (HR 4E THF) instruments. To characterize the nonvolatile fraction on Shimadzu (50 FT-IR), Fourier-transform infrared spectroscopy (FT-IR) was performed by the ATR method.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eReaction kinetics\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAn 80 mL stainless steel batch reactor was employed to perform the kinetic reaction. 16 mL of isopropanol and appropriate amounts of lignin and catalysts were loaded in the reactor. The autoclave was sealed and purged with N\u003csub\u003e2\u003c/sub\u003e five times to drive out moisture and air. Following that, the reactor was pressurized with 4.0 MPa N\u003csub\u003e2\u003c/sub\u003e and gradually heated to 200 ℃ at 700 rpm. At 40, 80, 120, 160, 200, and 240 min, kinetic data were taken. Turnover number (TON) and Turnover frequency (TOF) are calculated as follows:\u003c/p\u003e\n\u003cp\u003eTON = N\u003csub\u003eR\u003c/sub\u003e/N\u003csub\u003eC\u003c/sub\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;(3)\u003c/p\u003e\n\u003cp\u003eTOF = TON/t \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;(4)\u003c/p\u003e\n\u003cp\u003eWhere, N\u003csub\u003eR\u003c/sub\u003e and N\u003csub\u003eC\u003c/sub\u003e are the number of moles of reactant converted and the number of moles of catalyst, and t is time in hour (h).\u003c/p\u003e\n\u003cp\u003eIn 40, 80, 120, and 160 min, respectively, the kinetic reactions were conducted at four different temperatures i.e. 473, 483, 493, and 503 K. The apparent activation energy (E\u003csub\u003ea\u003c/sub\u003e) is then calculated using the Arrhenius equation;\u003c/p\u003e\n\u003cp\u003ek = Ae\u003csup\u003e(-Ea/RT)\u003c/sup\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;(5)\u003c/p\u003e\n\u003cp\u003eWhere k is the rate constant, A is the pre-exponential factor, E\u003csub\u003ea\u003c/sub\u003e is the apparent activation energy, R is the universal gas constant (8.314 J/(mol-K)) and T is the temperature in Kelvin.\u003c/p\u003e"},{"header":"Results And Discussion","content":"\u003cp\u003e\u003cstrong\u003ePhysiochemical properties of catalysts\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eTo explore the effect of the catalyst\u0026apos;s properties on the lignin catalytic hydrogenolysis reaction performance, a series of characterization measurements such as BET, SEM, EDX, and XPS were performed. First, the N\u003csub\u003e2\u003c/sub\u003e adsorption/desorption measurements were performed to evaluate the catalysts\u0026apos; textural properties after preparation. The BET surface area, pore volume, and pore size are presented in \u003cstrong\u003eTable 1\u003c/strong\u003e. The Ni/C catalyst exhibited a BET surface area of 633.4 m\u003csup\u003e2\u003c/sup\u003e/g, a pore volume of 0.076 cm\u003csup\u003e3\u003c/sup\u003e/g, and a pore size of 5.30 nm, while the Co/C catalyst showcased a BET surface area of 584.1 m\u003csup\u003e2\u003c/sup\u003e/g, a pore volume of 0.109 cm\u003csup\u003e3\u003c/sup\u003e/g, and a pore size of 6.81 nm. The porous structure of activated carbon facilitates the dispersion of metal sites. In comparison, the Ni-Co/C catalyst demonstrated a slightly reduced BET surface area of 556.6 m\u003csup\u003e2\u003c/sup\u003e/g, akin to Ni/C and Co/C. A similar trend was observed in pore size (3.53 nm). However, upon loading both metals, pore blockage ensued, leading to a significant decrease in both BET surface area and pore size. In addition, the Ni-Cu/C catalyst has the lowest BET surface area and pore volume of 537.6 m\u003csup\u003e2\u003c/sup\u003e/g and 0.063 cm\u003csup\u003e3\u003c/sup\u003e/g, respectively. Furthermore, all catalysts exhibited isotherms of N\u003csub\u003e2\u003c/sub\u003e adsorption/desorption that were comparable (\u003cstrong\u003eFig. S1\u003c/strong\u003e). The type-IV isotherms demonstrated that all catalysts were mesoporous.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1\u003c/strong\u003e Surface properties of the prepared catalysts.\u003c/p\u003e\n\u003cp\u003eSecondly, SEM and EDX measurements were conducted to reveal the distribution of the loaded metals (Co and Ni) in the Ni-Co/C catalyst (\u003cstrong\u003eFig. 1)\u003c/strong\u003e. The SEM and EDX elemental mapping images of Co and Ni revealed that both Co (white dots) and Ni (pink dots) are present on the surface of the activated carbon support and are uniformly dispersed within the tested region. Similarly, \u003cstrong\u003eFig. 2\u003c/strong\u003e indicated the even dispersion of Cu and Ni elements on the surface of the support.\u0026nbsp;According to reported literature, the interactions between Ni and Co enhanced the metal dispersion and provided more active sites, which typically enhance activity (Zhu et al., 2019a). \u003cstrong\u003eFig. S2, Fig. S3,\u003c/strong\u003e and \u003cstrong\u003eFig. S4\u003c/strong\u003e represent the SEM and EDX elemental mapping images of the Ni/C, Co/C, and Cu/C catalysts respectively. EDX elemental analysis indicated that the elemental compositions of nickel and cobalt on the surface of Ni-Co/C were 17.76 wt. % and 12.90 wt. %, respectively. Similarly, the elemental compositions of nickel and copper on the surface of Ni-Cu/C were 26.37 wt. % and 6.17 wt. %. The results of EDX elemental analysis revealed that the elements (Ni and Co) coexist on the support.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFig. 1\u003c/strong\u003e SEM images of Ni-Co/C catalyst at a magnification of (a) 3 kX and (b) 30 kX with corresponding EDX mapping of (c) Ni and (d) Co.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFig. 2\u0026nbsp;\u003c/strong\u003eSEM images of Ni-Cu/C catalyst at a magnification of (a) 10 kX and (b) 30 kX with corresponding EDX mapping of (c) Ni and (d) Co.\u003c/p\u003e\n\u003cp\u003eFurthermore, XPS measurement was performed to further explore the electronic interactions between Ni and Co and to reveal their chemical states. As shown in \u003cstrong\u003eFig. 3\u003c/strong\u003e. The XPS spectra and the associated deconvolutions of Ni 2p on Ni/C and Ni-Co/C catalysts. \u003cstrong\u003eFig. 3\u003c/strong\u003e(a) and (c), reveal that the distinctive peaks between 861.2 and 860.7 eV were assigned to Ni\u003csup\u003e2+\u003c/sup\u003e, whereas the distinctive peaks between 854.3 and 853.7 eV were assigned to metallic Ni\u003csup\u003e0\u003c/sup\u003e. Revealing the presence of two different forms of Ni species in the prepared \u0026nbsp;Ni/C and \u0026nbsp;Ni-Co/C catalysts (Zhou et al., 2017). This is due to the possibility of environmental oxygen oxidizing the active Ni metal surface (Li et al., 2020). Ni\u003csup\u003e0\u003c/sup\u003e and Ni\u003csup\u003e2+\u003c/sup\u003e binding energies exhibited a slight drop which reveals the change in the chemical state of the bimetallic catalysts and the transfer of electrons from Co to Ni species.\u003c/p\u003e\n\u003cp\u003eSimilarly, \u003cstrong\u003eFig. 3\u003c/strong\u003e (b and d), shows the Co 2p spectra of the Co/C and Ni-Co/C catalysts. The Co\u003csup\u003e3+\u003c/sup\u003e and Co\u003csup\u003e2+\u003c/sup\u003e are attributable to the peaks at 785.9 eV and 795.7 eV, respectively. Whereas the peak at 802.8 eV corresponded to the Co satellite. Both the Co/C and the Ni-Co/C catalysts exhibit mixed valence states of Co. Conversely, for the Ni-Co/C catalyst, peaks corresponding to Co\u003csup\u003e3+\u003c/sup\u003e, Co\u003csup\u003e2+\u003c/sup\u003e, and Co satellite were slightly shifted to higher binding energy positions at 786.4 eV, 796.9 eV, and 804.1 eV. This reveals that the intense interactions between nickel and cobalt result in the transfer of electrons from cobalt to nickel (Hu and Lu, 2007). Additionally, two distinctive peaks in the Co 2p spectra of Co/C and Ni-Co/C catalysts, which appeared at 780.2 eV and 781.7 eV can be attributable to metallic Co\u003csup\u003e0\u003c/sup\u003e. In summary, the shift observed in the Co 2p and Ni 2p spectrum reveals that the strong electron interactions between nickel and cobalt enhanced the transfer of electrons and the formation of multiple electron-rich Ni sites.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFig. 3\u003c/strong\u003e The deconvolutions of Ni 2p and Co 2p XPS spectra of the (a) Ni/C, (b) Co/C, (c) Ni-Co/C, and (d) Ni-Cu/C catalysts.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCatalytic hydrogenolysis of lignin\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe real motives behind the selection of cobalt and copper species as nickel promoters was to improve catalytic activity, stability, and product selectivity.\u0026nbsp;The performance of monometallic catalysts (Cu/C, Co/C, Ni/C) and Ni-based bimetallic catalysts (Ni-Cu/C, Ni-Co/C) on the catalytic hydrogenolysis of lignin was tested in isopropanol solvent at 250 ℃, 4 MPa and 700 rpm, in 4 h.\u0026nbsp;The results of the finding, which includes the percentage of lignin conversion and product distributions, are presented in \u003cstrong\u003eTable 2\u0026nbsp;\u003c/strong\u003eand\u003cstrong\u003e\u0026nbsp;Fig. S5.\u0026nbsp;\u003c/strong\u003eLow activity on lignin hydrogenolysis was exhibited by the Cu/C catalyst. It afforded only 16.2 wt. % of the total monomer product at 72.9 % lignin conversion. Also, the introduction of a Co/C catalyst afforded 17.5 wt.% of the total monomer products at a lignin conversion of 78.1 %. Cu/C and Co/C catalysts were not as effective as Ni/C catalysts, with 18.2 wt. % of total monomer product yield and the lignin conversion reaching 78.6 %. Zhu \u003cem\u003eet al\u003c/em\u003e. reported catalytic depolymerization of lignin over Pt-Re/TiO\u003csub\u003e2\u003c/sub\u003e catalyst under isopropanol/water solvent at 240 in 12 h. Their study achieved 18.7 wt. % of the total yield of monomeric products (Zhu et al., 2019b).\u003c/p\u003e\n\u003cp\u003eThe introduction of Ni-based bimetallic catalysts (Ni-Cu/C) significantly improved the lignin conversion rate and total monomer product yield to 84.7 % and 33.0 wt. % respectively. Because of their hydrogenation abilities, \u0026nbsp;Ni-based catalysts have the potential to increase catalytic performance and the efficiency of reaction by suppressing the formation of char (Kor\u0026aacute;nyi et al., 2017). Interestingly, Ni-Co/C catalyst exhibited a superior catalytic performance achieving the highest yield of monomer product of 53.1 wt. % and excellent lignin conversion of 94.2 %. According to Tian \u003cem\u003eet al\u003c/em\u003e. (2022), in catalytic hydrogenolysis reaction of lignin model compound, over Ni-Co/SiO\u003csub\u003e2\u003c/sub\u003e-ZrO\u003csub\u003e2\u003c/sub\u003e catalyst at 240\u0026thinsp; \u0026deg;C and 1\u0026thinsp;MPa, in 4 h, \u0026nbsp;48.1\u0026thinsp;wt. % of the total yield of monomer products and 100 % conversion of guaiacol were achieved. In terms of product distribution, the selectivity of all the products was increased over the Ni-Co/C catalyst. The phenol selectivity was 2.9 wt. %, guaiacol selectivity was 43.8 wt. % and other aromatic products had a selectivity of 5.3 wt. %. The results of this finding revealed that the promotional effect of cobalt and copper in the bimetallic catalysts enhanced catalytic activity, stability, and product selectivity more than their monometallic counterparts.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2.\u003c/strong\u003e Hydrogenolysis performance of lignin with monometallic and bimetallic catalysts.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eAnalysis of volatile products\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eTo identify and quantify the volatile products from the lignin hydrogenolysis reaction, GC-MS and GC-FID analyses were performed. The results of the investigation as presented in \u003cstrong\u003eTable 3\u003c/strong\u003e revealed that the monomer products were classified into phenols, guaiacols, other aromatics, and hydrogenated products.\u0026nbsp;Under optimized reaction conditions, phenols afforded 2.9 wt. %, guaiacols afforded 43.8 wt. %, other aromatics afforded 5.3 wt. % and hydrogenated products afforded 1.2 wt. %, respectively. The product distribution reveals that the hydrogenolysis reaction converted all the lignin\u0026apos;s main building blocks (H, G, and S units). The results of the quantitative analysis indicated that the maximum yield of 43.8 wt. % was guaiacols, which typically make up the coniferyl (G) structural unit of lignin. Similarly, the yields from sinapyl (S) and p-coumaryl (H) units from the product distribution are relatively low. This revealed that the G-unit is more reactive than the corresponding S and H-units.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable S1\u003c/strong\u003e provides the summary of GC-MS analysis of the product distributions obtained from lignin hydrogenolysis reactions.\u0026nbsp;A total of 20 monomer products were successfully identified by the GC-MS analysis. Their various retention time, chromatogram areas, and chemical structures were also identified.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 3\u003c/strong\u003e The major components of monomeric product yields\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eAnalysis of nonvolatile products\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eRaw lignin and the nonvolatile products resulting from lignin depolymerization over both monometallic and Ni-based bimetallic catalysts underwent analysis via FT-IR and GPC characterizations. Initially, the raw lignin exhibited an average molecular weight of 1,717 g/mol with a polydispersity of 2.3, indicating a relatively high molecular weight distribution. However, following depolymerization, GPC measurements demonstrated a substantial decrease in molecular weight to 610 g/mol for the nonvolatile products across various catalysts. This reduction highlights the efficacy of the catalysts in facilitating lignin depolymerization, leading to a significant decrease in molecular weight, thereby offering valuable insights into the catalytic mechanisms involved in the process (\u003cstrong\u003eTable 4\u003c/strong\u003e). The results of this investigation revealed that the nonvolatile products of lignin hydrogenolysis in the presence of Cu/C had a relatively high molecular weight (Mw) of 1,693 g/mol and the highest polydispersity (PID) of 2.2. With Ni/C and Co/C catalysts the molecular weight and polydispersity of the obtained nonvolatile products decreased to 929 g/mol, 807 g/mol, and 2.0, 1.8, respectively.\u0026nbsp;Interestingly, the introduction of Ni-based bimetallic catalysts, specifically Ni-Cu/C and Ni-Co/C significantly decreased the molecular weight of the nonvolatile products to 612 g/mol and 610 g/mol respectively.\u003c/p\u003e\n\u003cp\u003eThe results obtained revealed the promotional effect of copper and cobalt in the bimetallic catalyst system enhanced lignin depolymerization reaction. The results were in agreement with the yields of monomer products obtained over monometallic and Ni-based bimetallic catalysts (\u003cstrong\u003eTable 2\u003c/strong\u003e). Ni-based bimetallic catalysts also exhibited significantly lower values of polydispersity (1.5), revealing that the nonvolatile products had a concentrated distribution and the excellent hydrogenolysis efficiency of Ni-based bimetallic catalysts.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 4\u0026nbsp;\u003c/strong\u003eGPC analysis results of Mn, Mw, and PID for raw lignin and nonvolatile products.\u003c/p\u003e\n\u003cp\u003eIn addition, the FT-IR measurements of the nonvolatile products were performed and compared with the FT-IR measurements of raw lignin. As shown in \u003cstrong\u003eFig. S6\u0026nbsp;\u003c/strong\u003eand\u003cstrong\u003e\u0026nbsp;Fig. S7\u003c/strong\u003e, the FT-IR spectra of nonvolatile products obtained from the catalytic hydrogenolysis reaction over Ni-based bimetallic catalysts were comparable. The medium peaks at 3,331 cm\u003csup\u003e-1\u003c/sup\u003e and 1,379 cm\u003csup\u003e-1\u003c/sup\u003e corresponded to the O\u0026ndash;H bending vibration of the phenolic compounds (hydroxyl groups). It was observed that during the hydrogenolysis process, the absorption peaks changed significantly, revealing a transformation of the lignin structure. The O\u0026ndash;H peak, for example, increased from 3,285cm\u003csup\u003e-1\u003c/sup\u003e to 3,331 cm\u003csup\u003e-1\u003c/sup\u003e, revealing that the hydrogenolysis process did occur and resulted in an increase in phenolic compounds.\u003c/p\u003e\n\u003cp\u003eThe characteristic absorption peaks at 2,961 cm\u003csup\u003e-1\u003c/sup\u003e,\u0026nbsp;2,897 cm\u003csup\u003e-1\u003c/sup\u003e, and 1,445 cm\u003csup\u003e-1\u003c/sup\u003e were attributed to C\u0026ndash;H stretching and bending vibration in the alkane or methoxy functional groups. Furthermore, the yield of guaiacols was revealed by an increase in the methoxy functional groups from 2,945 cm\u003csup\u003e-1\u003c/sup\u003e to 2,961 cm\u003csup\u003e-1\u003c/sup\u003e. Similarly, the strong absorption peaks at 1,734 cm\u003csup\u003e\u0026minus;1\u003c/sup\u003e and 1,643 cm\u003csup\u003e\u0026minus;1\u003c/sup\u003e were attributable to the C=O double bond stretching and bending vibration in the carboxyl group and benzene rings (Shu et al., 2016). The medium and strong peaks at 1,306 cm\u003csup\u003e-1\u003c/sup\u003e and 1,128.36 cm\u003csup\u003e-1\u003c/sup\u003e were equally attributed to the aromatic rings.\u003c/p\u003e\n\u003cp\u003eSimilarly, the increase in the aromatic ring peak from 1,113 cm\u003csup\u003e-1\u003c/sup\u003e to 1,306 cm\u003csup\u003e-1\u003c/sup\u003e reveals that the hydrogenation of the aromatic ring did occur, resulting in the formation of hydroxylated intermediate products. The C=C double bond bending vibration in alkenes can be assigned to three strong and medium peaks at 947 cm\u003csup\u003e\u0026minus;1\u003c/sup\u003e, 808 cm\u003csup\u003e\u0026minus;1\u003c/sup\u003e, and 675 cm\u003csup\u003e-1\u003c/sup\u003e, respectively. Also, the appearance of the C=C double bond bending vibration in alkenes after the lignin catalytic hydrogenolysis reaction confirmed that lignin depolymerization exposed functional groups. The Ni-based bimetallic catalysts exhibited better catalytic activity in the lignin hydrogenolysis process through the absorption peak intensities.\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eEffects of reaction temperature on lignin conversion and yield of monomer products\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eReaction parameters such as temperature, pressure, stirring speed, and catalyst dosage have significant effects on the performance of the hydrogenolysis reaction (Shao et al., 2018). Based on this fact, their effects on both the monomer product yield and lignin conversion rate were investigated. The effect of reaction temperature on the yield of monomer products and the lignin conversion rate were investigated. \u003cstrong\u003eFig. 4\u003c/strong\u003e shows the effect of reaction temperatures between 220 ℃ to 250 ℃ on the yield of monomer products and lignin conversion rate over Ni-Co/C catalyst. At an initial temperature of 220 ℃, 66.8 % of lignin was converted affording 17.5 wt. % monomer products. The lignin conversion rate increased to 78.6 % while the monomer product yield reached 26.3 wt. % as the temperature was raised to 230 ℃. When the reaction temperature was further increased to 240 ℃, the lignin conversion rate also increased to 82.7 % affording 36.9 wt. % monomer products. At an elevated reaction temperature of 250 ℃, 94.2 % of lignin was converted with an impressive yield of 53.1 wt. % of monomer products.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp;\u0026nbsp;Ambursa et al.\u0026nbsp;(2016) reported 96 % conversion of lignin model compound (dibenzofuran) and 45 wt. % of hydrocarbon selectivity at 250 \u0026deg;C and 10 MPa over Ni-Cu/TiO\u003csub\u003e2\u003c/sub\u003e bimetallic catalysts. They observed that excessively high temperatures could cause the repolymerization of the monomer product and the non-volatile liquid products in the reaction to form solid residues\u0026nbsp;(Joffres et al., 2016). Moderate reaction temperature promotes the scission of carbon-oxygen and carbon-carbon bonds by overcoming the energy barrier in the lignin hydrogenolysis reaction (Zhao et al., 2019). Regarding the distribution of products, guaiacol was the highest afforded 43.8 %, and other aromatic products afforded 5.3 wt. %, phenol afforded 2.9 wt. % and the least was the hydrogenated products afforded just 1.1 wt. %. 250 \u0026deg;C was the optimal reaction temperature that achieved the highest monomer product yield of 53.1 wt. % over Ni-Co/C catalyst.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFig. 4\u003c/strong\u003e Effects of reaction temperature on the hydrogenolysis performance of Ni-Co/C catalyst. (Reaction conditions: Lignin = 0.5 g, catalyst = 0.3 g, isopropanol =16 mL, n-decane = 0.5 mL, 4 h, 4 MPa, 700 rpm).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eEffects of reaction pressure on lignin conversion and yield of monomer products\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eReaction pressure is another important parameter that has a significant effect on the performance of the hydrogenolysis reaction. \u003cstrong\u003eFig. 5\u003c/strong\u003e shows the results of the investigation conducted on lignin hydrogenolysis reactions over Ni-Co/C catalyst at varying reaction pressures between 2 MPa to 5 MPa. At an initial reaction pressure of 2 MPa, only 70.3 % of lignin was converted, affording 18.4 wt. % monomer products. When the reaction pressure reached 3 MPa, the rate of lignin conversion increased to 77.6 % affording 29.9 wt. % monomer products. Zhai and his group reported the yield of monomer products of 39.5 wt. % over Ni-Fe/C at a reaction pressure and temperature of 2 MPa and 225 ℃ in 6 h where propylsyringol and propylguaiacol were the major products (Zhai et al., 2017).\u003c/p\u003e\n\u003cp\u003eBoth the lignin conversion and the monomer product yield significantly increased to 94.2 % and 53.1 wt. % respectively when the reaction pressure was increased to 4 MPa. Conversely, as the reaction pressure increased further to 5 MPa, both the lignin conversion rate and the yield of monomer products significantly decreased to 86.1 % and 38.8 wt. %, respectively. The yield of guaiacol and phenol monomers decreased significantly at high reaction pressure, most likely as a result of the formation of more volatile and saturated products (Wanmolee et al., 2018). The results of this investigation revealed that the reaction pressure of 4 MPa is the optimal pressure. And the promotion of catalytic hydrogenolysis of lignin at high pressure of 5 MPa is negligible.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFig. 5\u003c/strong\u003e Effects of reaction pressure on the hydrogenolysis performance of Ni-Co/C catalyst. (Reaction conditions: Lignin = 0.5 g, catalyst = 0.3 g, isopropanol =16 mL, n-decane = 0.5 mL, 4 h, 250 ℃, 700 rpm).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eEffects of stirring speed on lignin conversion and yield of monomer products\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eThe rate of lignin conversion and yield of monomer products are greatly influenced by stirring speed in the lignin hydrogenolysis reaction. In our previous study, stirring speed promotes the transfer of mass and heat, selectivity of product, and hydrogenolysis reaction kinetics (Ewuzie et al., 2023). It enhances the catalyst-lignin interactions within the reactor and enables effective reactions and uniform product compositions.\u0026nbsp;To maximize the rate of reaction, the gradient of reactant concentration can be maintained under an optimal stirring speed. To run the reactions under kinetic control, the stirring speed was carefully varied from 500 rpm to 800 rpm.\u0026nbsp;\u003cstrong\u003eFig. 6\u003c/strong\u003e shows the effects of stirring speed on the lignin conversion and yield of monomer products. When the reaction was run at 500 rpm, a relatively low monomer product yield of 19.0 wt. % was achieved at a 71.3 % lignin conversion rate. This would suggest that the reaction was likely limited by mass transfer processes, probably as a result of insufficient mixing and dispersion of the reactants.\u003c/p\u003e\n\u003cp\u003eHowever, when the stirring speed was increased to 600 rpm, there was a sharp increase in the yield of the monomer product reaching 32.2 wt. %, while the lignin conversion rate increased to 80.5 %. Interestingly, the lignin conversion rate significantly improved reaching 94.2 %, and affording 53.1 wt. % monomer products as the stirring speed was increased to 700 rpm. This significant improvement suggests that the increased stirring speed provided better contact between the active components and the lignin substrate, enabling the active components to perform more efficiently thereby increasing the lignin conversion rate and monomer product yield. Surprisingly, when the stirring speed was further increased to 800 rpm, both the lignin conversion rate and monomer product yield significantly dropped to 88.4 % and 44.6 wt. %, respectively. These findings revealed that beyond 700 rpm, further increase in stirring speed hurts lignin conversion rate and monomer product yield.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFig. 6\u003c/strong\u003e Effects of stirring speed on the hydrogenolysis performance of Ni-Co/C catalyst. (Reaction conditions: Lignin = 0.5 g, catalyst = 0.3 g, isopropanol =16 mL, n-decane = 0.5 mL, 4 h, 250 ℃, and 4 MPa).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eEffects of Ni-Co/C catalyst dosage on the lignin hydrogenolysis reaction\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eCatalyst dosage can also influence the rate of reaction, lignin conversion rate, monomer product yield, and in commercial applications, the process\u0026apos;s economics. An in-depth investigation on the influence of Ni-Co/C catalyst dosage was conducted, and results are displayed in \u003cstrong\u003eFig. 7\u003c/strong\u003e. It can be observed that the monomer product yield and lignin conversion rate exhibited an increasing trend with decreasing catalyst-to-lignin ratios. Under optimal reaction conditions, 0.05 g, 0.1 g, 0.2 g, and 0.3 g of catalyst were used, resulting in lignin-to-catalyst ratios of 10, 5, 2.5, and 1.7. When the hydrogenolysis experiment was conducted with 0.05 g of Ni-Co/C catalyst only 68.8 % of lignin was converted affording 16.5 wt. % monomer products. As for the 0.1 g experiment, the lignin conversion rate and monomer product yield gradually increased to 76.5 % and 27.9 %, respectively.\u003c/p\u003e\n\u003cp\u003eAs the catalyst dosage was further increased to 0.2 g, the lignin conversion rate and monomer product yield equally increased reaching 84.7 % and 45.1 wt. %. Moreover, the standard run with 0.3 g of Ni-Co/C catalyst achieved the highest lignin conversion of 94.2 % and the maximum monomer product yield of 53.1 wt. %. Because of the improved lignin depolymerization that occurs when there are more catalytic sites present, the conversion of lignin and monomer product yield increases progressively with higher catalyst dosage (Zhao et al., 2019).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFig. 7\u003c/strong\u003e Effects of Ni-Co/C catalyst dosage on the lignin hydrogenolysis reaction. (Reaction conditions: Lignin = 0.5 g, isopropanol = 16 mL, n-decane = 0.5 mL, 250 ℃, 4 h, 4 MPa and 700 rpm).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003eKinetic study results\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eTo further confirm the improved catalytic performance and promotional effects of Ni-based bimetallic catalysts on lignin hydrogenolysis. A kinetic study on the rate of conversion of lignin with time over Ni-based bimetallic and monometallic catalysts was conducted. \u003cstrong\u003eFig. 8\u003c/strong\u003e presents the summary of TOF and E\u003csub\u003ea\u003c/sub\u003e for the rate of conversion of lignin over Ni-Co/C and Ni/C catalysts. The rate of conversion of lignin exhibited a linear increase from 29.8 % to 94.2 % over the Ni-Co/C catalyst and from 5.3 % to 78.6 % over the Ni/C catalyst between 40 min to 240 min (\u003cstrong\u003eFig. 8(a))\u003c/strong\u003e. Under the same reaction conditions, the TOF over Ni/C catalyst was determined to be 4.4 h\u003csup\u003e\u0026minus;1\u003c/sup\u003e. This value was calculated from the starting point of the linear kinetic plot. And that of the Ni-Co/C catalyst was calculated to be 36.1 h\u003csup\u003e-1\u003c/sup\u003e, which is about eight times higher than the value with catalyst Ni/C.\u003c/p\u003e\n\u003cp\u003eIn addition, the kinetic study on lignin catalytic hydrogenolysis over Ni/C and Ni-Co/C catalysts at different temperatures was also conducted. As seen in \u003cstrong\u003eFig. 8(b)\u003c/strong\u003e (Arrhenius plot), apparent activation energy (E\u003csub\u003ea\u003c/sub\u003e) was calculated from the slope of the fitted linear plot [In(K) vs 1/T] and the E\u003csub\u003ea\u003c/sub\u003e for lignin depolymerization over Ni/C was found to be 50.0 kJ/mol.\u0026nbsp;Lui and co-workers reported that an E\u003csub\u003ea\u003c/sub\u003e value of 48.0 kJ/mol was calculated from the kinetic study on a lignin model compound over Pd/C at 240 \u0026deg;C and 3.4 MPa in 4 h (Liu et al., 2017). In this study, the calculated E\u003csub\u003ea\u003c/sub\u003e value over the Ni-Co/C catalyst was 36.1 kJ/mol. Which is much lower compared to the E\u003csub\u003ea\u003c/sub\u003e value of the Ni/C catalyst. The results of the kinetic study coupled with higher TOF and lower E\u003csub\u003ea\u003c/sub\u003e of Ni-based bimetallic catalysts have further revealed the promotional effect of Co and Ni catalysts. Therefore, the addition of Co as a nickel promoter significantly enhanced the catalytic performance in the lignin hydrogenolysis reaction process.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFig. 8\u003c/strong\u003e Kinetic study on catalytic hydrogenolysis of lignin over Ni/C and Ni-Co/C catalysts. (Reaction conditions: Lignin = 0.5 g, catalyst = 0.3 g, isopropanol, = 16 mL, n-decane = 0.5 mL, 240 \u003csup\u003eo\u003c/sup\u003eC, 40 min, 700 rpm, and 4 MPa N\u003csub\u003e2\u003c/sub\u003e).\u003c/p\u003e\n\u003cp\u003e\u003cem\u003ePossible reaction mechanism for catalytic depolymerization of lignin\u003c/em\u003e\u003c/p\u003e\n\u003cp\u003eBased on the excellent results achieved, the possible reaction mechanism for catalytic depolymerization of lignin over Ni-based bimetallic catalyst (Ni-Co/C) under optimum reaction conditions is shown in \u003cstrong\u003eFig. 9\u003c/strong\u003e. Initially, lignin was chemically adsorbed on the surface of the catalyst and interacted with catalytic active sites. As a result, the aromatic ring was hydrogenated and formed hydroxylated intermediate products (phenol, 2-methoxyphenol, and 4-vinylpyridine) under isopropanol solvent.\u0026nbsp;The hydroxylated intermediate products serve as the main building blocks for the catalytic reactions involving the breaking of bonds and fragmentation to produce phenol, guaiacols, and aromatic monomers. The interaction between the hydroxylated intermediate products and the catalytic active components (Ni and Co) facilitated the cleavage of \u0026beta;-O-4, \u0026beta;-5, and C-C ether bond linkages in the lignin structure.\u0026nbsp;According to the report, H-radicals can be transferred to catalytic active sites such as Ni, Fe, Co, and Cu (Zhu et al., 2019a).\u003c/p\u003e\n\u003cp\u003eIsopropanol as a hydrogen donor solvent, supplied all the required hydrogen for the bond cleavages and hydrogenation processes. In our previous study, Smaller aromatic fragments were formed due to the depolymerization of \u0026nbsp;C-C, \u0026beta;-O-4, and \u0026beta;-5 ether bond linkages in the aromatic rings (Ewuzie et al., 2023). Furthermore, benzene, phenyl alcohol, and guaiiacyl aldehyde (aromatic fragments) reacted with active H-radical (hydrogenolysis reaction) producing phenols, guaiacols, and aromatic monomers. Hydrogen is activated on cobalt sites to produce active H-radicals, due to cobalt\u0026apos;s ability to activate hydrogen (Lin et al., 2021). The two main products are phenol and aromatic monomers; hence it has been proposed that the most crucial step in producing the targeted products is the scission of the aromatic ring in lignin.\u0026nbsp;A detailed chemical reaction route that breaks the C-O and C-C bonds in lignin to produce 2.9 wt. % phenols, 43.8 wt. % guaiacols, and 5.3 wt. % aromatic monomers is shown in \u003cstrong\u003eTable 2.\u0026nbsp;\u003c/strong\u003eBecause of the strong chemical interactions between the metal\u0026apos;s d-states and aromatic ring, lignin was chemisorbed onto nickel\u0026apos;s active sites. Then, the active H-radicals spill onto Ni sites and attack the C-C and C-O bonds in lignin. After which, the C-C and C-O bonds in lignin were broken, resulting in a 94.2 % lignin conversion.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFig. 9\u003c/strong\u003e Possible reaction mechanism for the catalytic depolymerization of lignin.\u003c/p\u003e"},{"header":"Conclusion","content":"\u003cp\u003eThis study represents a significant step forward in harnessing the great potential of lignin as a valuable renewable resource in the production of phenolic fine chemicals. It also sheds light on the great potential of Ni-based bimetallic catalysts. A rigorous investigation of the potential of Co/C, Cu/C, Ni/C, Ni-Cu/C, and Ni-Co/C catalysts on the catalytic depolymerization of lignin under isopropanol solvent was conducted. Ni-based bimetallic catalysts demonstrated superior catalytic performance, enhanced product selectivity, and improved stability compared to their corresponding monometallic catalysts. BET, SEM, EDX, and XPS measurements revealed the physicochemical properties and promotional effects of these catalysts. Furthermore, the effects of reaction temperature, pressure, stirring speed, and catalyst dosage on the depolymerization of lignin were elucidated. The results of the investigation revealed that the addition of cobalt and copper as promoters to nickel significantly enhanced lignin conversion and monomer product yield. The Ni-Co/C catalyst exhibited remarkable performance, achieving the highest lignin conversion of 94.2 % and a maximum monomer product yield of 53.1 wt. % under optimal reaction conditions.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe E\u003csub\u003ea\u003c/sub\u003e value of 36.1 kJ/mol for catalytic lignin depolymerization over Ni-Co/C was considerably lower compared to the corresponding monometallic catalyst Ni/C (50.0 kJ/mol). Similarly, the turnover frequency (TOF) of Ni-Co/C was substantially higher (31.6 h\u003csup\u003e\u0026minus;1\u003c/sup\u003e) compared to Ni/C (4.4 h\u003csup\u003e\u0026minus;1\u003c/sup\u003e), revealing the superior catalytic activity of the Ni-based bimetallic catalyst. The volatile and nonvolatile products were analyzed by GC-MS, GC-FID, GPC, and FT-IR measurements. A total of 20 monomer products were successfully identified in GC-MS analysis. A possible reaction mechanism was proposed to elucidate the catalytic pathways involved. This breakthrough holds significant promise for the sustainable production of high-value phenolic fine chemicals from lignin. And contributing to a more environmentally friendly and economically robust chemical industry.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgment\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research work is fully funded by the Ministry of Higher Education Malaysia under the Fundamental Research Grant Scheme (FRGS/1/2021/TK0/USM/01/2).\u003c/p\u003e\n\u003cp\u003eEthics approval and consent to participate\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003eConsent for publication\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003eAvailability of data and materials\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003eCompeting interests\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e\n\u003cp\u003eFunding\u003c/p\u003e\n\u003cp\u003eThe authors acknowledge the Fundamental Research Grant Scheme (LRGS) from the Ministry of Higher Education of Malaysia (FRGS/1/2021/TK0/USM/01/2).\u003c/p\u003e\n\u003cp\u003eAuthors\u0026apos; contributions\u003c/p\u003e\n\u003cp\u003eRemigius Nnadozie Ewuzie planned, and carried out the experimental work conceptualized by Ahmad Zuhairi Abdullah who is also involved in securing the research funding and supervision. Jackson Robinson Genza contributed to the analysis and interpretation of results and drafting of the manuscript. Ahmad Fawad contributed by providing some critical resources needed for the study while at the same time being involved in data interpretation.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eAuthors\u0026apos; information (optional)\u003c/p\u003e\n\u003cp\u003eNot applicable\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eAbdullah AZ, Razali N, Lee KT. Optimization of K/SBA-15 catalyzed transesterification of palm oil using response surface methodology (2009). Fuel Process Technol 90:958-964. https://doi.org/10.1016/j.fuproc.2009.03.023.\u003c/li\u003e\n \u003cli\u003eAmbursa MM, Ali TH, Lee HV, Sudarsanam P, Bhargava SK, Hamid SBA (2016). Hydrodeoxygenation of dibenzofuran to bicyclic hydrocarbons using bimetallic Cu-Ni catalysts supported on metal oxides. 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Fuel 218: 33\u0026ndash;40. https://doi.org/10.1016/j.fuel.2018.01.017.\u003c/li\u003e\n \u003cli\u003eSantos JL, Alda-Onggar M, Fedorov V, Peurla M, Er\u0026auml;nen K, M\u0026auml;ki-Arvela P, Centeno M, Murzin DY (2018). Hydrodeoxygenation of vanillin over carbon supported metal catalysts. Appl Catal A Gen 561: 137\u0026ndash;149. https://doi.org/10.1016/j.apcata.2018.05.010.\u003c/li\u003e\n \u003cli\u003eShao L, Zhang Q, You T, Zhang X, Xu F (2018). Microwave-assisted efficient depolymerization of alkaline lignin in methanol/formic acid media. Bioresour Technol 264: 238\u0026ndash;243. https://doi.org/10.1016/j.biortech.2018.05.083.\u003c/li\u003e\n \u003cli\u003eShu R, Long J, Xu Y, Ma L, Zhang Q, Wang T, Wang C, Yuan Z, Wu Q (2016). Investigation on the structural effect of lignin during the hydrogenolysis process. Bioresour Technol 200: 14\u0026ndash;22. https://doi.org/10.1016/j.biortech.2015.09.112.\u003c/li\u003e\n \u003cli\u003eShu R, Lin B, Wang C, Zhang J, Cheng Z, Chen Y (2019). Upgrading phenolic compounds and bio-oil through hydrodeoxygenation using highly dispersed Pt/TiO\u003csub\u003e2\u003c/sub\u003e catalyst. Fuel 239: 1083\u0026ndash;1090. https://doi.org/10.1016/j.fuel.2018.11.107.\u003c/li\u003e\n \u003cli\u003eShu R, Li R, Lin B, Luo B, Tian Z (2020). High dispersed Ru/SiO\u003csub\u003e2\u003c/sub\u003e-ZrO\u003csub\u003e2\u003c/sub\u003e catalyst prepared by polyol reduction method and its catalytic applications in the hydrodeoxygenation of phenolic compounds and pyrolysis lignin-oil. Fuel 265: 116962. https://doi.org/10.1016/j.fuel.2019.116962.\u003c/li\u003e\n \u003cli\u003eTian Z, Liang X, Li R, Wang C, Liu J, Lei L, Shu R, Chen Y (2022). Hydrodeoxygenation of guaiacol as a model compound of pyrolysis lignin-oil over NiCo bimetallic catalyst: Reactivity and kinetic study. Fuel 308: 122034. https://doi.org/10.1016/j.fuel.2021.122034.\u003c/li\u003e\n \u003cli\u003eTymchyshyn M, Yuan Z, Zhang Y, Xu CC (2019). Catalytic hydrodeoxygenation of guaiacol for organosolv lignin depolymerization\u0026ndash;Catalyst screening and experimental validation. Fuel 254: 115664. https://doi.org/10.1016/j.fuel.2019.115664.\u003c/li\u003e\n \u003cli\u003evan den Bosch S, Koelewijn SF, Renders T, van den Bossche G, Vangeel T, Schutyser W, Sels BF (2018). Catalytic strategies towards lignin-derived chemicals. Top Curr Chem 376: 36. https://doi.org/10.1007/s41061-018-0214-3.\u003c/li\u003e\n \u003cli\u003eVriamont CEJJ, Chen T, Romain C, Corbett P, Manageracharath P, Peet J, Conifer CM, Hallett JP, Britovsek GJP (2019). From lignin to chemicals: Hydrogenation of lignin models and mechanistic insights into hydrodeoxygenation via low-temperature C-O bond cleavage. 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Preparation of porous carbons by hydrothermal carbonization and KOH activation of lignite and their performance for electric double layer capacitor. Electrochim Acta 252: 397\u0026ndash;407. https://doi.org/10.1016/j.electacta.2017.08.176.\u003c/li\u003e\n \u003cli\u003eXue S, Luo Z, Sun H, Zhu W (2022). Product regulation and catalyst deactivation during ex-situ catalytic fast pyrolysis of biomass over nickel-molybdenum bimetallic modified micro-mesoporous zeolites and clays, Bioresour Technol 364: 128081. https://doi.org/10.1016/j.biortech.2022.128081.\u003c/li\u003e\n \u003cli\u003eYang Z, Feng J, Cheng H, Liu Y, Jiang J (2021). Directional depolymerization of lignin into high added-value chemical with synergistic effect of binary solvents. Bioresour Technol 321: 124440. https://doi.org/10.1016/j.biortech.2020.124440.\u003c/li\u003e\n \u003cli\u003eYe K, Liu Y, Wu S, Zhuang J (2021). A review for lignin valorization: Challenges and perspectives in catalytic hydrogenolysis. Ind Crops Prod 172: 114008. https://doi.org/10.1016/j.indcrop.2021.114008.\u003c/li\u003e\n \u003cli\u003eZhai Y, Li C, Xu G, Ma Y, Liu X, Zhang Y (2017). Depolymerization of lignin: Via a non-precious Ni-Fe alloy catalyst supported on activated carbon. Green Chem 19: 1895\u0026ndash;1903. https://doi.org/10.1039/c7gc00149e.\u003c/li\u003e\n \u003cli\u003eZhang JW, Cai Y, Lu GP, Cai C (2016). Facile and selective hydrogenolysis of \u0026beta;-O-4 linkages in lignin catalyzed by Pd-Ni bimetallic nanoparticles supported on ZrO\u003csub\u003e2\u003c/sub\u003e. Green Chem 18: 6229\u0026ndash;6235. https://doi.org/10.1039/c6gc02265k.\u003c/li\u003e\n \u003cli\u003eZhang Z, Song J, Han B (2017a). Catalytic transformation of lignocellulose into chemicals and fuel products in ionic liquids. Chem Rev 117:6834\u0026ndash;6880. https://doi.org/10.1021/acs.chemrev.6b00457.\u003c/li\u003e\n \u003cli\u003eZhang YQ, Liang P, Yu J, Zhu JL, Qin XZ (2017b). Studies of granular bed filter for dust removal in the process of coal pyrolysis by solid heat carrier. RSC Adv 7: 20266\u0026ndash;20272. https://doi.org/10.1039/C7RA01467H.\u003c/li\u003e\n \u003cli\u003eZhou M, Ye J, Liu P, Xu J, Jiang J (2017). Water-assisted selective hydrodeoxygenation of guaiacol to cyclohexanol over supported Ni and Co bimetallic catalysts. ACS Sustain Chem Eng 5(10): 8824-8835. https://doi.org/https://doi.org/10.1021/acssuschemeng.7b01615.\u003c/li\u003e\n \u003cli\u003eZhao W, Li X, Li H, Zheng X, Ma H, Long J, Li X (2019). Selective hydrogenolysis of lignin catalyzed by the cost-effective Ni metal supported on alkaline MgO. ACS Sustain Chem Eng 7: 19750\u0026ndash;19760. https://doi.org/10.1021/acssuschemeng.9b05041.\u003c/li\u003e\n \u003cli\u003eZhu C, Cao JP, Zhao XY, Xie T, Ren J, Wei XY (2019a). Mechanism of Ni-catalyzed selective C\u0026ndash;O cleavage of lignin model compound benzyl phenyl ether under mild conditions. J Energy Inst 92: 74\u0026ndash;81. https://doi.org/10.1016/j.joei.2017.11.004.\u003c/li\u003e\n \u003cli\u003eZhu C, Cao JP, Zhao XY, Xie T, Zhao M, Wei XY (2019b). Bimetallic effects in the catalytic hydrogenolysis of lignin and its model compounds on nickel-ruthenium catalysts. Fuel Process Technol 194: 106126. https://doi.org/10.1016/j.fuproc.2019.106126.\u003c/li\u003e\n\u003c/ol\u003e"},{"header":"Tables","content":"\u003cp\u003e\u003cstrong\u003eTable\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003e1\u0026nbsp;\u003c/strong\u003eSurface properties of the prepared catalysts.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"482\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"25.518672199170126%\"\u003e\n \u003cp\u003eCatalyst\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"27.38589211618257%\"\u003e\n \u003cp\u003eBET Surface area\u003csup\u003ea\u003c/sup\u003e (m\u003csup\u003e2\u003c/sup\u003e/g)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"25.518672199170126%\"\u003e\n \u003cp\u003ePore Volume\u003csup\u003eb\u003c/sup\u003e (cm\u003csup\u003e3\u003c/sup\u003e/g)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.57676348547718%\"\u003e\n \u003cp\u003ePore Size\u003csup\u003eb\u003c/sup\u003e ()\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"25.518672199170126%\"\u003e\n \u003cp\u003eNi/C\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"27.38589211618257%\"\u003e\n \u003cp\u003e633.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"25.518672199170126%\"\u003e\n \u003cp\u003e0.076\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.57676348547718%\"\u003e\n \u003cp\u003e5.30\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"25.518672199170126%\"\u003e\n \u003cp\u003eCo/C\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"27.38589211618257%\"\u003e\n \u003cp\u003e584.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"25.518672199170126%\"\u003e\n \u003cp\u003e0.109\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.57676348547718%\"\u003e\n \u003cp\u003e6.81\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"25.518672199170126%\"\u003e\n \u003cp\u003eNi-Co/C\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"27.38589211618257%\"\u003e\n \u003cp\u003e556.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"25.518672199170126%\"\u003e\n \u003cp\u003e0.174\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.57676348547718%\"\u003e\n \u003cp\u003e3.53\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"25.518672199170126%\"\u003e\n \u003cp\u003eNi-Cu/C\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"27.38589211618257%\"\u003e\n \u003cp\u003e537.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"25.518672199170126%\"\u003e\n \u003cp\u003e0.063\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.57676348547718%\"\u003e\n \u003cp\u003e4.13\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003csup\u003ea\u003c/sup\u003eBrunauer, Emmett, and Teller (BET) multipoint technique.\u003c/p\u003e\n\u003cp\u003e\u003csup\u003eb\u003c/sup\u003eMethod by Barrett, Joyner, and Halenda (BJH).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 2\u0026nbsp;\u003c/strong\u003eHydrogenolysis performance of lignin with monometallic and bimetallic catalysts.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"860\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"6.627906976744186%\" rowspan=\"2\"\u003e\n \u003cp\u003eEntry\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.930232558139535%\" rowspan=\"2\"\u003e\n \u003cp\u003eCatalyst\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.232558139534884%\" rowspan=\"2\"\u003e\n \u003cp\u003eConversion (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"72.20930232558139%\" colspan=\"5\"\u003e\n \u003cp\u003eMonomer products yield (wt.%)\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"14.67741935483871%\"\u003e\n \u003cp\u003ePhenols\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.774193548387096%\"\u003e\n \u003cp\u003eGuaiacols\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.838709677419356%\"\u003e\n \u003cp\u003eOther aromatic products\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"21.29032258064516%\"\u003e\n \u003cp\u003eHydrogenated products\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"27.419354838709676%\"\u003e\n \u003cp\u003eTotal yield\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"6.635622817229336%\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.942956926658905%\"\u003e\n \u003cp\u003eCu/C\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.244470314318976%\"\u003e\n \u003cp\u003e72.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.593713620488941%\"\u003e\n \u003cp\u003e2.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.107101280558789%\"\u003e\n \u003cp\u003e10.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.318975552968569%\"\u003e\n \u003cp\u003e3.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.366705471478463%\"\u003e\n \u003cp\u003e0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.79045401629802%\"\u003e\n \u003cp\u003e16.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"6.635622817229336%\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.942956926658905%\"\u003e\n \u003cp\u003eCo/C\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.244470314318976%\"\u003e\n \u003cp\u003e78.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.593713620488941%\"\u003e\n \u003cp\u003e2.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.107101280558789%\"\u003e\n \u003cp\u003e12.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.318975552968569%\"\u003e\n \u003cp\u003e3.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.366705471478463%\"\u003e\n \u003cp\u003e0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.79045401629802%\"\u003e\n \u003cp\u003e17.5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"6.635622817229336%\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.942956926658905%\"\u003e\n \u003cp\u003eNi/C\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.244470314318976%\"\u003e\n \u003cp\u003e78.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.593713620488941%\"\u003e\n \u003cp\u003e2.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.107101280558789%\"\u003e\n \u003cp\u003e11.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.318975552968569%\"\u003e\n \u003cp\u003e3.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.366705471478463%\"\u003e\n \u003cp\u003e0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.79045401629802%\"\u003e\n \u003cp\u003e18.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"6.635622817229336%\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.942956926658905%\"\u003e\n \u003cp\u003eNi-Cu/C\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.244470314318976%\"\u003e\n \u003cp\u003e84.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.593713620488941%\"\u003e\n \u003cp\u003e2.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.107101280558789%\"\u003e\n \u003cp\u003e26.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.318975552968569%\"\u003e\n \u003cp\u003e3.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.366705471478463%\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.79045401629802%\"\u003e\n \u003cp\u003e33.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"6.635622817229336%\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.942956926658905%\"\u003e\n \u003cp\u003eNi-Co/C\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.244470314318976%\"\u003e\n \u003cp\u003e94.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"10.593713620488941%\"\u003e\n \u003cp\u003e2.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"12.107101280558789%\"\u003e\n \u003cp\u003e43.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.318975552968569%\"\u003e\n \u003cp\u003e5.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.366705471478463%\"\u003e\n \u003cp\u003e1.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.79045401629802%\"\u003e\n \u003cp\u003e53.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eReaction condition: lignin = 0.5 g, catalysts = 0.3 g, isopropanol = 16 mL, n-decane = 0.5 mL, 4 MPa N\u003csub\u003e2\u003c/sub\u003e, 250, 4 h and 700 rpm. Ni/C, Cu/C and Co/C catalysts were theoretically loaded with 10wt. % each. Similarly, 10 wt. % of both Ni, Co and Cu for the Ni-Cu/C and Ni-Co/C catalysts were also loaded.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cstrong\u003eTable 3\u0026nbsp;\u003c/strong\u003eThe major components of monomeric product yields.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"864\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"12.05098493626883%\"\u003e\n \u003cp\u003ePhenols\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.6477404403244496%\" colspan=\"3\"\u003e\n \u003cp\u003eYield (wt. %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.295480880648899%\"\u003e\n \u003cp\u003eGuaiacols\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"9.038238702201623%\" colspan=\"2\"\u003e\n \u003cp\u003eYield (wt. %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.093858632676708%\" colspan=\"3\"\u003e\n \u003cp\u003eOther Aromatics\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.6477404403244496%\" colspan=\"3\"\u003e\n \u003cp\u003eYield (wt. %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.063731170336037%\" colspan=\"3\" valign=\"top\"\u003e\n \u003cp\u003eHydrogenated\u003c/p\u003e\n \u003cp\u003eProducts\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.466975666280415%\" colspan=\"4\"\u003e\n \u003cp\u003eYield (wt. %)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"0.6952491309385863%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"12.05098493626883%\"\u003e\n \u003cp\u003ePhenol\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.6477404403244496%\" colspan=\"3\"\u003e\n \u003cp\u003e0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.149478563151796%\" colspan=\"2\"\u003e\n \u003cp\u003ePhenol, 2-methoxy-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.342989571263036%\" colspan=\"2\"\u003e\n \u003cp\u003e14.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.093858632676708%\" colspan=\"3\"\u003e\n \u003cp\u003eBenzene, 1,2-dimethoxy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.6477404403244496%\" colspan=\"3\"\u003e\n \u003cp\u003e1.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.235225955967554%\" colspan=\"4\"\u003e\n \u003cp\u003eEthanone, 1-(2-hydroxy-5-methylphenol\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.13673232908459%\" colspan=\"2\"\u003e\n \u003cp\u003e0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"0.6952491309385863%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"12.05098493626883%\"\u003e\n \u003cp\u003ePhenol, 4-ethyl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.6477404403244496%\" colspan=\"3\"\u003e\n \u003cp\u003e0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.149478563151796%\" colspan=\"2\"\u003e\n \u003cp\u003eCreosol\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.342989571263036%\" colspan=\"2\"\u003e\n \u003cp\u003e7.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.093858632676708%\" colspan=\"3\"\u003e\n \u003cp\u003e3,4-Dimethoxytoluene\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.6477404403244496%\" colspan=\"3\"\u003e\n \u003cp\u003e1.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.235225955967554%\" colspan=\"4\"\u003e\n \u003cp\u003eEthanone, 1-(3-hydroxy-4-methoxy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.13673232908459%\" colspan=\"2\"\u003e\n \u003cp\u003e0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"0.6952491309385863%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"12.05098493626883%\"\u003e\n \u003cp\u003ePhenol, 3-(1-methylethyl)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.6477404403244496%\" colspan=\"3\"\u003e\n \u003cp\u003e0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.149478563151796%\" colspan=\"2\"\u003e\n \u003cp\u003ePhenol, 2-propyl-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.342989571263036%\" colspan=\"2\"\u003e\n \u003cp\u003e0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.093858632676708%\" colspan=\"3\"\u003e\n \u003cp\u003eBenzene, 4-ethyl-1,2-dimethoxy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.6477404403244496%\" colspan=\"3\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"19.235225955967554%\" colspan=\"4\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.13673232908459%\" colspan=\"2\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"0.6952491309385863%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"12.05098493626883%\"\u003e\n \u003cp\u003ePhenol, 2,5-bis(1,1-dimethylethyl)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.6477404403244496%\" colspan=\"3\"\u003e\n \u003cp\u003e0.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.149478563151796%\" colspan=\"2\"\u003e\n \u003cp\u003ePhenol, 4-ethyl-2-methoxy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"8.342989571263036%\" colspan=\"2\"\u003e\n \u003cp\u003e17.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.093858632676708%\" colspan=\"3\"\u003e\n \u003cp\u003eBenzoic acid, 3-(methylthio)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"7.6477404403244496%\" colspan=\"3\"\u003e\n \u003cp\u003e0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"14.947856315179607%\" colspan=\"3\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"18.424101969872538%\" colspan=\"3\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"0.6952491309385863%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"14.23611111111111%\" colspan=\"2\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"5.208333333333333%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.36111111111111%\" colspan=\"3\"\u003e\n \u003cp\u003e2-Methoxy-4-vinylphenol\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"9.027777777777779%\" colspan=\"3\"\u003e\n \u003cp\u003e0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\" colspan=\"3\"\u003e\n \u003cp\u003eBenzeneacetic acid, 4-hydroxy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\" colspan=\"3\"\u003e\n \u003cp\u003e0.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.393518518518519%\" colspan=\"4\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.689814814814815%\" colspan=\"2\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"14.23611111111111%\" colspan=\"2\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"5.208333333333333%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.36111111111111%\" colspan=\"3\"\u003e\n \u003cp\u003eEugenol\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"9.027777777777779%\" colspan=\"3\"\u003e\n \u003cp\u003e0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\" colspan=\"3\"\u003e\n \u003cp\u003eBenzene, 1,4-dimethoxy-2-methyl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\" colspan=\"3\"\u003e\n \u003cp\u003e0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.393518518518519%\" colspan=\"4\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.689814814814815%\" colspan=\"2\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"14.23611111111111%\" colspan=\"2\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"5.208333333333333%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.36111111111111%\" colspan=\"3\"\u003e\n \u003cp\u003ePhenol, 2-methoxy-4-propyl-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"9.027777777777779%\" colspan=\"3\"\u003e\n \u003cp\u003e2.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\" colspan=\"3\"\u003e\n \u003cp\u003eBenzaldehyde, 2,4-dihydroxy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\" colspan=\"3\"\u003e\n \u003cp\u003e0.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.393518518518519%\" colspan=\"4\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.689814814814815%\" colspan=\"2\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"14.23611111111111%\" colspan=\"2\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"5.208333333333333%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.36111111111111%\" colspan=\"3\"\u003e\n \u003cp\u003ePhenol, 3-(dimethylamino)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"9.027777777777779%\" colspan=\"3\"\u003e\n \u003cp\u003e1.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\" colspan=\"3\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\" colspan=\"3\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.393518518518519%\" colspan=\"4\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.689814814814815%\" colspan=\"2\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"14.23611111111111%\" colspan=\"2\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"5.208333333333333%\"\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.36111111111111%\" colspan=\"3\"\u003e\n \u003cp\u003ePhenol, 4-(ethoxymethyl)-2-methoxy\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"9.027777777777779%\" colspan=\"3\"\u003e\n \u003cp\u003e1.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\" colspan=\"3\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\" colspan=\"3\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.393518518518519%\" colspan=\"4\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.689814814814815%\" colspan=\"2\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"14.23611111111111%\" colspan=\"2\"\u003e\n \u003cp\u003eTotal\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"5.208333333333333%\"\u003e\n \u003cp\u003e2.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"17.36111111111111%\" colspan=\"3\"\u003e\n \u003cp\u003eTotal\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"9.027777777777779%\" colspan=\"3\"\u003e\n \u003cp\u003e43.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\" colspan=\"3\"\u003e\n \u003cp\u003eTotal\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"13.541666666666666%\" colspan=\"3\"\u003e\n \u003cp\u003e5.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"15.393518518518519%\" colspan=\"4\"\u003e\n \u003cp\u003eTotal\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"11.689814814814815%\" colspan=\"2\"\u003e\n \u003cp\u003e1.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eReaction conditions: Lignin=0.5g, catalyst = 0.3g, isopropanol = 16mL, n-decane = 0.5 mL, 250℃, \u0026nbsp;4MpaN\u003csub\u003e2 ,\u0026nbsp;\u003c/sub\u003e4h, and 700 rpm\u003c/p\u003e\n\u003cp\u003eUsing GC-MS, where acetophenone was used as the internal standard chemical. The components listed were those with a GC-MS yield of more than 0.1%.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 4\u0026nbsp;\u003c/strong\u003eGPC analysis results of Mn, Mw, and PID for raw lignin and nonvolatile products.\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\" width=\"839\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003eRaw lignin and catalyst\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003eNumber Average Molecular Weight (Mn)-g/mol\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003eWeight Average Molecular Weight (Mw)-g/mol\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003eAverage Molecular\u003c/p\u003e\n \u003cp\u003eWeight (Mz)-g/mol\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003ePolydispersity (PID)=\u003c/p\u003e\n \u003cp\u003e(Mw/Mn)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\" valign=\"top\"\u003e\n \u003cp\u003eMolecular mass of polymer (Mp)-g/mol\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003eRaw lignin\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e757\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e1717\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e3178\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e2.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e1530\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003eCu/C\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e712\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e1693\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e3211\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e2.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e1607\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003eNi/C\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e461\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e929\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e1872\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e2.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e186\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003eCo/C\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e448\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e807\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e1488\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e1.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e187\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003eNi-Cu/C\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e392\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e612\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e1030\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e1.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e315\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003eNi-Co/C\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e382\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e610\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e1054\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e1.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd width=\"16.666666666666668%\"\u003e\n \u003cp\u003e304\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eReaction conditions: Lignin = 0.5 g, catalyst = 0.3 g, Isopropanol, =16 mL, n-decane= 0.5 mL, 250, 4 h, 700 rpm and 4 MPa N\u003csub\u003e2\u003c/sub\u003e.\u003c/p\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":true,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"environmental-science-and-pollution-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"espr","sideBox":"Learn more about [Environmental Science and Pollution Research](https://www.springer.com/journal/11356)","snPcode":"11356","submissionUrl":"https://submission.nature.com/new-submission/11356/3","title":"Environmental Science and Pollution Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Lignin depolymerization, phenolic substances, Ni-based bimetallic catalysts, promotional effect, isopropanol solvent, product distribution","lastPublishedDoi":"10.21203/rs.3.rs-4297106/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-4297106/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"Lignin, a vital renewable biopolymer, serves as Earth's primary source of aromatics and carbon. Its depolymerization presents significant potential for producing phenolic fine chemicals. This study assesses promoted Ni-based bimetallic catalysts (Ni-Co/C and Ni-Cu/C) supported on activated carbon in isopropanol for lignin depolymerization, compared to monometallic counterparts. BET, SEM, EDX, and XPS analyses highlight their physicochemical properties and promotional effects, enhancing hydrogenolysis activity and hydrogen transformation. Reaction parameter exploration elucidates the influence on lignin depolymerization, with cobalt and copper as promoters notably increasing conversion and monomer yield. Ni-Co/C exhibits the highest lignin conversion (94.2 %) and maximum monomer yield (53.1 wt. %) under specified conditions, with lower activation energy (36.1 kJ/mol) and higher turnover frequency (31.6 h−1) compared to Ni/C. FT-IR, GPC, GC-FID, and GC-MS analyses confirm effective depolymerization, identifying 20 monomer products. Proposed reaction mechanisms underscore the potential of Ni-based bimetallic catalysts for lignin valorization, offering insights into developing efficient catalytic systems for lignin hydrogenolysis. This research enhances understanding and facilitates the development of selective catalytic processes for lignin valorization.","manuscriptTitle":"Activity and product distribution in Ni-Co and Ni-Cu catalyst-mediated lignin depolymerization into phenolic substances with isopropanol H-donating solvent","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-05-29 09:39:46","doi":"10.21203/rs.3.rs-4297106/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Major Revision","date":"2024-06-20T04:44:50+00:00","index":"","fulltext":""},{"type":"reviewerAgreed","content":"","date":"2024-05-17T16:22:55+00:00","index":0,"fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-05-17T03:29:36+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"Environmental Science and Pollution Research","date":"2024-05-16T16:22:11+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-04-23T04:41:19+00:00","index":"","fulltext":""},{"type":"submitted","content":"Environmental Science and Pollution Research","date":"2024-04-20T06:42:33+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"environmental-science-and-pollution-research","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"espr","sideBox":"Learn more about [Environmental Science and Pollution Research](https://www.springer.com/journal/11356)","snPcode":"11356","submissionUrl":"https://submission.nature.com/new-submission/11356/3","title":"Environmental Science and Pollution Research","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"f4c7c87a-d8f9-4490-baed-ec442bfb9242","owner":[],"postedDate":"May 29th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2024-08-05T16:13:20+00:00","versionOfRecord":{"articleIdentity":"rs-4297106","link":"https://doi.org/10.1007/s11356-024-34504-2","journal":{"identity":"environmental-science-and-pollution-research","isVorOnly":false,"title":"Environmental Science and Pollution Research"},"publishedOn":"2024-07-30 15:57:32","publishedOnDateReadable":"July 30th, 2024"},"versionCreatedAt":"2024-05-29 09:39:46","video":"","vorDoi":"10.1007/s11356-024-34504-2","vorDoiUrl":"https://doi.org/10.1007/s11356-024-34504-2","workflowStages":[]},"version":"v1","identity":"rs-4297106","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-4297106","identity":"rs-4297106","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}