Efficient Glycerol Carbonylation over Multimetallic ZIF Catalysts: Synergy of Structure Regulation and Charge Optimization

Efficient Glycerol Carbonylation over Multimetallic ZIF Catalysts: Synergy of Structure Regulation and Charge Optimization | 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 Efficient Glycerol Carbonylation over Multimetallic ZIF Catalysts: Synergy of Structure Regulation and Charge Optimization Liyao Zhao, Zhihao Lv, Shuqi Qi, Pingbo Zhang, Jiawen Zhang, Mingming Fan This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7987190/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 9 You are reading this latest preprint version Abstract The valorization of glycerol is a key research objective, and its carbonylation to glycerol carbonate represents a promising route. A major hurdle in this process is the development of efficient catalysts.This study systematically investigates the catalytic performance of various transition metal-based zeolitic imidazolate frameworks (ZIFs), including ZIF-8, ZIF-67, Cu-ZIF, Cu-ZIF-8, Cu-ZIF-67, and Co-ZIF-8, in the carbonylation of glycerol to glycerol carbonate. The results reveal that bimetallic ZIFs significantly enhance catalytic activity, among them, the Co-doped Pd/Co-ZIF-8-N catalyst exhibited the best performance, achieving a high glycerol carbonate yield of 92.97% and 96.37% selectivity, with a Pd loading of only 1%. Through characterization techniques such as Fourier Transform Infrared Spectroscopy (FT-IR), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), X-Ray Photoelectron Spectroscopy (XPS), and CO₂-Temperature Programmed Desorption (CO₂-TPD), we demonstrate that Co doping promotes the formation of carbon nanotubes, improves Pd dispersion, and modulates the acid-base properties of the material. Computational simulations further indicate that the combination of Co and Zn optimizes the natural charge distribution in the reaction transition state, facilitating electron transfer and thereby enhancing catalytic performance. Additionally, calcination temperature markedly influences the valence state and coordination environment of copper species, where the formation of a Cu-N₄ structure at high temperatures strengthens the synergistic effect with Pd. This work provides new mechanistic insights and material design strategies for the application of multimetallic ZIFs in carbonylation reactions. Glycerol carbonylation Multimetallic ZIFs Electron redistribution Synergistic catalysis Pd/Co-ZIF-8-N Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 1. Introduction Glycerol carbonate (hydroxymethyl dioxolane), abbreviated as GC, is a small molecule with significant practical value. This molecule has garnered widespread interest over the past two decades due to two main reasons: its broad reactivity, which enables various synthetic applications, and its potential as a method to enhance glycerol valorization[ 1 , 2 ]. As a green chemical, glycerol carbonate exhibits promising prospects for widespread application. Its excellent biodegradability, low toxicity, and multifunctionality make it highly suitable for use in solvents, materials, pharmaceuticals, and other fields [ 3 , 4 ]. With the optimization of production processes and technological advancements, glycerol carbonate is expected to become an increasingly important industrial raw material and green energy source, contributing to sustainable development and environmental protection. Generally, there are four primary methods for synthesizing glycerol carbonate: glycerol carbonylation (which requires catalysts) [ 1 , 5 – 7 ], transesterification (typically using dimethyl carbonate, DMC) [ 8 – 10 ], phosgene-based methods [ 11 ], and urea alcoholysis [ 12 , 13 ]. Each of these methods has its own advantages and disadvantages; however, the carbonylation reaction has gained widespread attention due to its unique advantage of water as the only byproduct, which is easy to purify and separate. Hu et al. discovered that glycerol carbonate could be easily synthesized through the oxidative carbonylation of glycerol using PdCl₂(phen) (phen = 1,10-phenanthroline) under CuI catalysis, achieving high conversion (95%) and selectivity (98%) with a TOF of 455 h⁻¹. This catalyst was also shown to be reusable up to five times without significant loss of activity [ 6 ]. Michele first reported the systematic study of copper (II)-catalyzed oxidative carbonylation for the synthesis of glycerol carbonate. The study found that copper (II) chloride effectively promoted this process under homogeneous conditions, using CO: O₂ (P = 4 MPa; P(O₂) = 0.7 MPa) in the presence of pyridine at 130°C in DMA, achieving excellent conversion (> 92%) and selectivity (> 93%) within a relatively short reaction time (3–4 hours) [ 14 ]. However, in these studies, the catalysts have not been employed in a supported form to improve activity, stability, or reduce costs. The catalytic properties of ZIF-derived carbon materials are expected to address these challenges [ 15 – 18 ]. Guo et al. developed a template-assisted strategy, in which ZIF-8 was confined to grow in the three-dimensional ordered template voids and pyrolyzed to produce hierarchical pores in nitrogen-doped carbon materials derived from MOFs. The layered nanostructures significantly facilitated the mass transfer of large molecules and exposed active sites, thus achieving satisfactory CO₂ photoconversion under mild conditions [ 19 ]. Zhang et al. reported a type of nitrogenated, layered carbon framework obtained via controlled carbonization of Zn-imidazole salt frameworks. The N-HLCF-xs materials combined primary three-dimensional micropores, secondary two-dimensional lamellar microstructures, and high-density nitrogen basic sites, which promoted their interaction with acidic COS and H₂S [ 20 ]. In this study, we explored the effects of different transition metals (Cu, Co, Zn) and their combinations on the glycerol carbonylation reaction. We found that when cobalt was used as a dopant metal (rather than a framework metal), it significantly enhanced the dispersion of the palladium active sites. At just 0.2% palladium by mass on the support, we achieved catalytic activity comparable to that optimized by other supports, which typically require around 1% palladium. The reaction yielded exceptionally high product yield and selectivity. Moreover, the study of the calcination temperature of copper revealed its unique behavior during the reaction process. We explored the reasons behind the changes induced by copper at different calcination temperatures and performed Gaussian simulations to model the transition states and electrostatic potential variations in the presence of multiple metals, further enriching the catalytic research on glycerol carbonylation. 2. Experimental section 2.1 Catalyst preparation The preparation of the catalyst Pd/Co-ZIF-8-N is illustrated in Scheme 1. First, 3.20 g of Zn(NO₃)₂·6H₂O and 0.18 g of Cu(NO₃)₂·3H₂O were dissolved in 75 mL of methanol. Then, 3.3 g of 2-methylimidazole was dissolved in 75 mL of methanol. The two solutions were mixed and stirred at room temperature for 24 hours. The mixture was then filtered using a water pump, and after washing three times with methanol, the product was dried at 80°C for 12–24 hours. Next, the support and palladium methanol solution (1 g/L) were mixed in a ratio of 1:0.002 and stirred for 24 hours. The resulting mixture was calcined in a tube furnace at 600°C to obtain the final catalyst, Pd/Co-ZIF-8-N, which exhibited a carbon nanotube morphology (with the temperature suffix indicating the calcination temperature). The preparation methods for other catalysts are described in detail in the supplementary materials. Schem1 Flowchart of catalyst Pd/Co-ZIF-8-N preparation. 3. Results and discussion The infrared spectra of the catalysts and supports are shown in Fig. 1a. Even after loading, Pd/Co-ZIF-8 retains the characteristic peaks of ZIF, including those at 3450, 3123, 2908, 1615, 1401, and 622 cm⁻¹, which correspond to the O-H stretch (from water in the air or solvents introduced during synthesis), the N-H stretch vibration, C-H stretch vibration, C = C and C = N stretches (from the imidazole ring), C-N stretch vibration, and Co-N stretch vibration. After calcination, the final catalyst shows a weakening and disappearance of the C-H stretch and bending vibration peaks, indicating the successful carbonization of the catalyst. The catalyst still retains the Co-N stretch vibration peak, which suggests the preservation of the metal framework [21, 22]. The infrared spectra of the copper-doped catalyst (Pd/Cu-ZIF-67-N) and the non-copper-doped catalyst (Pd/ZIF-67-N) are shown in Fig. 1c (FT-IR spectra for four catalysts were prepared based on the calcination temperatures corresponding to the activity inflection points, as shown in Fig. 6d). From the figure, it is evident that there is no significant difference, which implies that the integrity of the framework remains unchanged. However, the decline in activity of Pd/ZIF-67-N at high temperatures (700–900°C) cannot be accurately attributed to framework degradation from the infrared spectra. The infrared spectra of the six catalysts composed of copper, cobalt, and zinc are shown in Fig. 1b. After calcination, all the catalysts exhibited distinct stretching vibrations of the organic ligand 2-methylimidazole, including the C = C and C = N stretches (1615 cm⁻¹) and the C-N stretch (1401 cm⁻¹). The Zn-N characteristic peak at 630 cm⁻¹ weakened in the catalyst with ZIF-8 as the support and no cobalt, suggesting that some zinc underwent ion exchange with bimetallic ions during calcination. This is particularly evident due to the relatively low boiling point of metallic zinc. The Cu-N infrared vibration peak was not observed, leading to this phenomenon. This exchange facilitates metal electron transfer, thereby improving catalytic activity [23, 24]. Figure 2a presents the X-ray powder diffraction (XRD) patterns of the synthesized ZIF-8 and ZIF-67, which are consistent with the results simulated using Materials Studio 2019 (Fig. 2b), confirming the successful synthesis of the metal-organic frameworks. Figure 2b also simulates the XRD pattern of Co-ZIF-8, the precursor support for the catalyst Pd/Co-ZIF-8-N, and the comparison in Fig. 1c further confirms the successful synthesis of the support. After loading with palladium acetate, Co-ZIF-8 did not exhibit additional diffraction peaks, likely due to the low and dispersed loading of divalent palladium or its doping in the framework as Pd²⁺ ions. Subsequent calcination and reduction revealed palladium diffraction peaks, supporting this hypothesis. The calcined catalyst showed the face-centered cubic structure characteristic of metallic cobalt, with diffraction peaks at 44.2° (111), 51.5° (200), and 75.9° (220). The prepared catalyst also exhibited two broad diffraction peaks at 40.23° and 46.80°, corresponding to the (111) and (200) reflections of metallic palladium, indicating the successful loading of palladium [25–27]. After calcination, the precursor catalyst showed clear diffraction peaks of carbon materials. The peak at 25° (the "dumpling peak") corresponds to C(100), and the peaks at 44.27° and 51.61° correspond to the (111) and (200) crystal planes of cobalt (PDF#15–0806). This suggests that cobalt undergoes reduction after doping and calcination. However, the palladium peak did not appear after calcination, possibly because the palladium nanoparticles are either embedded within the framework or highly dispersed. This phenomenon can be attributed to the unique structural characteristics of the framework after calcination, which promotes the dispersion and anchoring of palladium. Figure 3 Scanning electron microscopy figures of Pd/ZIF-67-N Pd/Cu-MOF-N Pd/ZIF-8-N Pd/Cu-ZIF-8-N Pd/Cu-ZIF-67-N Pd/Co-ZIF-8-N six catalysts. Figures 3a-c show the catalysts prepared by calcining Pd-loaded ZIF-8, ZIF-67, and Cu-MOF under nitrogen. The images of catalysts a and b reveal clear octahedral structures, indicating that calcination at 600°C did not affect the basic morphology of ZIF-8 and ZIF-67. The average diameters of ZIF-8 and ZIF-67 were 2 µm and 0.2 µm, respectively, which is consistent with the typical synthesis methods reported in the literature. However, after calcination, the originally distinct particle structure of Cu-MOF disappeared (Fig. S3), transforming into fragmented, layered structures. This morphological degradation led to the loss of the high surface area characteristic of metal-organic frameworks, which is the main reason for the reduced activity [21]. Figures 3e-f show scanning electron microscopy (SEM) images of the three bimetallic ZIF catalysts: Pd/Cu-ZIF-8-N, Pd/Cu-ZIF-67-N, and Pd/Co-ZIF-8-N, representing Cu-Zn doping, Cu-Co doping, and Co-Zn doping, respectively [29]. Interestingly, the first two catalysts did not undergo significant changes in their morphology after calcination, retaining their original polyhedral or cubic structures. In contrast, Pd/Co-ZIF-8-N, after calcination, formed carbon nanotubes. As shown in Figs. 4a and b, the precursor and support of the Pd/Co-ZIF-8-N catalyst exhibited a regular cubic structure. The formation of carbon nanotubes is attributed to the presence of metal catalytic sites (e.g., iron, cobalt, nickel). During calcination, these metal particles assist in the decomposition of carbon sources (such as hydrocarbons) and catalyze the rearrangement of carbon atoms. The carbon atoms accumulate at the metal catalytic sites, forming tubular structures that then grow into carbon nanotubes. While Pd-Cu-ZIF-67-N also contains cobalt, its divalent Co forms a stable framework material, which stabilizes the carbon within the framework, making it less prone to catalytic rearrangement. The hollow tubular structure offers natural nanoscale pores that facilitate the diffusion of glycerol molecules into the tubes, allowing for full contact with the active palladium sites. Moreover, possible byproducts in the glycerol carbonylation reaction, such as polyglycerols, are less likely to pass through the nanotube pores. This tubular morphology also effectively controls the entry and exit of glycerol carbonate, enhancing catalytic selectivity. Furthermore, during palladium nanoparticle loading, the carbon nanotubes can evenly distribute and anchor the nanoparticles due to their unique morphology and structure, preventing aggregation and maintaining higher dispersion. This high dispersion increases the effective active sites of the metal catalyst, thereby reducing the amount of palladium required and directly lowering the cost of catalyst preparation. According to data obtained from Inductively coupled plasma optical emission spectroscopy (ICP-OES), the palladium loading in the calcined material was significantly reduced to just 1.11%, much lower than that reported for other catalytic materials [30–32]. To further investigate the influence of acid-base sites on the catalytic performance for glycerol oxidative carbonylation, the catalysts derived from three different bimetallic ZIF precursors were characterized by CO 2 -TPD analysis (Fig. 5a). According to the previously proposed mechanism (Fig. 5b), glycerol initially interacts with iodide ions to lose a hydrogen atom, forming the intermediate C 3 H 7 O 3 *. Interestingly, a stronger acidity of the catalyst appears to be detrimental to this reaction step. This is because the protons dissociated from acidic sites tend to combine with hydroxyl groups, suppressing the formation of the intermediate in the first reaction step. Experimental results using catalysts modified with benzoic acid further validate this hypothesis, as a significant reduction in activity was observed. As shown in Fig. 5a, Pd/Cu-ZIF-8-N, Pd/Cu-ZIF-67-N, and Pd/Co-ZIF-8-N exhibited notable signal peaks in the temperature ranges of 100°C and 400–500°C. These peaks suggest the presence of strong basicity, likely due to the calcination of the catalysts under nitrogen conditions. The peaks above 300°C confirm the existence of strong basic sites. By correlating the acidic properties of Co, Cu, and Zn in different oxidation states with Lewis acid-base theory, the theoretical acidity follows the order Co³⁺ >Cu²⁺ >Zn²⁺ >Co²⁺ >Cu⁺. Accordingly, the stronger acidity observed for Pd/Cu-ZIF-8-N and Pd/Co-ZIF-8-N can be attributed to their ZIF-8-derived framework, which is reflected in their catalytic performance. The metal Lewis acids enhance the reaction activity by coordinating with oxygen, redistributing the electronic density of the oxidant, lowering the redox potential, and thereby accelerating the charge transfer process. Figure 5c compares the yields and selectivity of six catalysts for the carbonylation reaction. Catalysts prepared with pure ZIF-8 and Cu-ZIF-8 exhibited the lowest activity, likely due to the relatively strong acidity of Cu²⁺ and Zn²⁺. Interestingly, Co-ZIF-8, which also uses ZIF-8 as a support, showed the highest activity. Further optimization revealed that the Co and Zn loading significantly impacts the catalytic performance. This effect is hypothesized to stem from the critical role of cobalt loading in the carbonization process of ZIF-8. Excessively high or low cobalt content disrupts the formation of carbon nanotubes, affecting pore size and specific surface area, which in turn influences the catalytic properties. Additionally, while the catalytic activity of Pd/Cu-ZIF-8-N was lower than that of Pd/Co-ZIF-8-N, it exhibited stronger basicity, as indicated by its unique strong peak in the range of 600–700°C, which was absent in the other two catalysts. This observation may be attributed to the unique coordination environment of Cu or the high content of monovalent copper (Cu⁺) under the calcination conditions. To investigate this further, X-ray photoelectron spectroscopy (XPS) analysis was performed on catalysts doped and undoped with Cu at various calcination temperatures. The Co 2p valence state signal peaks for Pd/ZIF-67-700, Pd/ZIF-67-900, Pd/Cu-ZIF-67-700, and Pd/Cu-ZIF-67-900 were tested. The Co 2p₃/₂ and Co 2p₁/₂ peaks for all four catalysts exhibited a shift of 0.5-1 eV compared to those in Fig. 7b, which is attributed to the different states of Co. According to the SEM morphology shown in Fig. 3e, the structures of these catalysts retained the framework shape, rather than adopting the carbon nanotube morphology of the Pd/Co-ZIF-8-N catalyst. This is because, in this case, cobalt forms an M-N₄ structure, a feature confirmed by both XPS and SEM analysis [19, 33, 34]. This special structure induces the solidification of the host metal and promotes charge transfer, which is conducive to the improvement of catalytic activity. Interestingly, when copper is doped, both Pd/Cu-ZIF-67-700 and Pd/Cu-ZIF-67-900 showed no satellite signal at 796 eV and 800.4 eV, indicating that copper suppresses the formation of Co₃O₄. From the comparison of activity for the two catalysts at different calcination temperatures (Fig. 6d), it is evident that copper-containing catalysts exhibit better activity between 200°C and 600°C compared to those without copper. This is likely directly related to the state of cobalt discussed earlier, as excessive Co₃O₄ content hinders the carbonylation reaction. As the calcination temperature increases further, the activity of copper-doped catalysts begins to decline. This is supported by the comparison of the Cu 2p spectra (Fig. 6c), where the largest difference in the Cu 2p₃/₂ convolution peak is observed. At 935 eV, the integrated area at 900°C calcination is 15% smaller than that at 700°C, corresponding to the Cu 2p₃/₂ peak of copper oxide. This indicates that high-temperature calcination facilitates the rearrangement of carbon, making it easier to form the Cu-N₄ state, which plays a beneficial role in the catalytic process. This is consistent with the significant increase in activity of Pd/Cu-ZIF-67-N under calcination conditions at 900°C and 950°C (Fig. 6d), as described earlier in Fig. 2d, where the reduced formation of copper oxides correlates with improved activity. Figure 6b shows the narrow N 1s XPS spectra of the four catalysts. The copper-doped catalysts exhibit lower graphitization degrees at 700–900°C compared to those without copper, which explains why the non-copper-doped catalysts have better activity in this temperature range. Overall, suppressing the formation of Co₃O₄ (which prevents the generation of non-divalent metals), maintaining the stability of the doped metal framework to form M-N₄ structures, and improving the graphitization degree all contribute to excellent performance in the carbonylation reaction [35]. To investigate the metal valence states and conditions of different catalysts after calcination, X-ray photoelectron spectroscopy (XPS) was first performed on the final catalyst. The wide spectrum of the Pd/Co-ZIF-8-N catalyst (Fig. 7a) reveals clear elemental valence state peaks (Zn 2p₁, Zn 2p, Co 2p, O 1s, N 1s, C 1s, Zn 3p) which provide insights into the elemental states of the catalyst. As shown in Fig. 7b, the peaks at 781 eV, 785.4 eV, 796 eV, and 800.4 eV correspond to Co 2p₃/₂, Co 2p₃/₂ satellite, Co 2p₁/₂, and Co 2p₁/₂ satellite peaks, respectively. These peaks indicate that cobalt is primarily in its oxidized state, with CoO and Co₃O₄ being the main forms. This is due to cobalt being doped into ZIF-8 as a catalyst, and after calcination, it forms carbon nanotubes rather than maintaining the framework structure and forming M-N₄ structures. This structure helps to improve the dispersion of Pd loading, thus enhancing catalytic activity, which is consistent with the activity results shown in Fig. 5c. The deconvolution of the C 1s spectrum (Fig. 7c) shows that the carbon material after calcination is similar to a graphene-like structure, with the C = C structure accounting for 84%. The C-N structure is derived from the 2-methylimidazole and nitrogen during calcination, which is confirmed by the N 1s deconvolution (pyridinic-N, pyrrolic-N, graphene-N). Interestingly, palladium, which is the active component for the carbonylation reaction, does not exhibit a prominent satellite peak. This is likely due to the low Pd loading, and the carbon nanotube structure aids in Pd dispersion, resulting in the absence of distinct peaks. Another possibility is that XPS primarily detects surface states rather than bulk phases, further suggesting that Pd is confined within the defects of the carbon nanotubes. Table 1 Summary of natural charges of different metal-forming transition states TS in TS Atom Number 1 2 3 4 5 Cu TS in 0.717 0.495 -0.489 -0.517 -0.831 Co TS in 0.619 0.610 -0.557 -0.519 -0.786 Zn TS in 1.097 0.378 -0.520 -0.551 -0.989 Pd TS in 0.474 0.683 -0.524 -0.508 -0.763 Cu TS 0.453 0.692 -0.508 -0.523 -0.748 Co TS 0.414 0.744 -0.550 -0.530 -0.721 Zn TS 0.579 0.669 -0.494 -0.515 -0.866 Pd TS 0.331 0.799 -0.514 -0.526 -0.730 To further investigate the influence of different metals on the reaction transition state, a computational study was conducted on the metals involved in the research and their associated transition states. The two key processes in the carbonylation reaction are the formation of the carbonyl group and the cyclization process. Simulations revealed that only palladium (Pd) can form the carbonyl group, while other transition metals cannot participate in this step. However, for the cyclization process, all the transition metals used in the study could form transition states. After IRC (Intrinsic Reaction Coordinate) analysis, the potential energy profiles of Cu, Co, Zn, and Pd are shown in Fig. 8. Based on the transition state energies and the potential energy of intermediates and products, the difficulty of the cyclization process follows the order: Pd > Cu > Co > Zn. Therefore, Cu, Co, and Zn are considered high activation energy catalysts compared to Pd, exhibiting some inhibitory effects on the reaction. As seen in the comparison of catalyst activity, the order of catalytic activity is Co-Zn > Co > Cu-Zn > Cu-Co > Cu > Zn, which slightly deviates from the simulation results. To further understand the role of transition metals, the natural charges of TS-in and TS were summarized for different metals. It was found that the natural charge of cobalt (Co) is lower than that of all other metals, excluding palladium (Pd), indicating greater stability of the transition state. Additionally, the two atoms involved in the reaction (atoms 2 and 5) corresponding to Co and Zn showed larger charge values, suggesting that these metals facilitate atomic interactions and thus promote the reaction. Consequently, from the charge distribution, the Co-Zn combination demonstrated a greater advantage, which also explains the catalytic activity ranking of the metal combinations. Furthermore, the influence of different calcination temperatures with and without copper (Cu) doping was further explained. Copper, as expected, is a low activation energy catalyst compared to other metals, and the variation in activity at high temperatures is primarily attributed to changes in charge distribution. At higher temperatures, Cu transitions from free divalent copper to a Cu-N 4 structure, which enhances the performance of metal combination catalysts at elevated temperatures. In conclusion, for guest metals like Cu, Co, and Zn, their effect on the transition state is primarily manifested through electron transfer, as revealed by the charge comparison. Moreover, the structure and calcination temperature of the catalyst significantly affect the charge distribution, and a detailed examination of the charge changes between key reacting atoms is essential to better explain the catalytic performance changes under multi-metal conditions in carbonylation reactions. 4. Conclusion In this study, a series of different metals and metal combinations as carriers were prepared, including ZIF-8, ZIF-67, Cu-ZIF, Cu-ZIF-8, Cu-ZIF-67, and Co-ZIF-8. These carriers underwent activity optimization after loading, and the final comparison revealed that Pd/Co-ZIF-8-N exhibited the best catalytic performance, achieving a high yield (92.97%) and selectivity (96.37%) during the reaction. The metal loading was only 1% after calcination and 0.2% before calcination. This performance is attributed to the catalytic role of cobalt in transforming the carbon framework into carbon nanotubes. Additionally, the influence of calcination temperature was also studied, revealing the unique activity characteristics of copper (Cu). The suppression of copper oxide formation and the enhancement of Cu-N 4 formation were identified as key factors in improving activity. Both material characterization and computational simulations were employed to investigate these aspects. The results showed that transition metals like Cu, Co, and Zn influence the transition state primarily through electron transfer. The structure and calcination temperature of the catalyst significantly alter this value, thereby impacting catalytic activity. Co and Zn played a critical role in promoting the carbon-oxygen bond formation during cyclization. Therefore, the changes in charge distribution and the synergistic effect of the multi-metal system in the carbonylation reaction provide a deeper understanding than simply comparing activation energies. This study offers new insights into the catalytic process of carbonylation reactions and lays the foundation for future research in this field. Declarations Competing Interests The authors declare no competing interests. Ethical and Consent to Participate Not applicable. Consent for Publication The manuscript represents original research work, and it has not been previously published or submitted elsewhere, nor is it under consideration for publication elsewhere. All participants have given their consent for publication of their data/information. Funding The financial support from the Natural Science Foundation of China (NSFC) (No. 22378163) and MOE & SAFEA for the 111 Project (B13025) is gratefully acknowledged. Author Contribution Liyao Zhao: Formal analysis, Supervision, Resources, Writing-Review & Editing. Zhihao Lv: Methodology, Resources, Visualization. Shuqi Qi: Investigation, Validation, Formal Analysis. Pingbo Zhang: Formal analysis, Investigation, Methodology, Writing-Original Draft. Jiawen Zhang: Investigation, Methodology, Supervision. Mingming Fan: Supervision, Resources, Methodology. Acknowledgement The financial support from the Natural Science Foundation of China (NSFC) (No. 22378163) and MOE & SAFEA for the 111 Project (B13025) is gratefully acknowledged. Data Availability Data will be made available on request. References Schäffner B, Schäffner F, Verevkin SP, Börner A (2010) Organic Carbonates as Solvents in Synthesis and Catalysis. 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Appl Catal B 242:485–498. https://doi.org/10.1016/j.apcatb.2018.10.005 Yao Y, Yin H, Zhang Y et al (2021) Fe, Cu-coordinated ZIF-derived bimetal encapsulated N-doped carbon nanotube for efficient remediation of various aqueous pollutants. Chem Eng J 426:131801. https://doi.org/10.1016/j.cej.2021.131801 Scheme Scheme 1 is available in the Supplementary Files section. Additional Declarations No competing interests reported. Supplementary Files Highlights.docx SI.docx GraphicalAbstract.docx Scheme.jpg Schem1 Flowchart of catalyst Pd/Co-ZIF-8-N preparation. Cite Share Download PDF Status: Under Review Version 1 posted Editorial decision: Revision requested 20 Nov, 2025 Reviews received at journal 20 Nov, 2025 Reviews received at journal 16 Nov, 2025 Reviewers agreed at journal 02 Nov, 2025 Reviewers agreed at journal 31 Oct, 2025 Reviewers invited by journal 31 Oct, 2025 Editor assigned by journal 31 Oct, 2025 Submission checks completed at journal 31 Oct, 2025 First submitted to journal 30 Oct, 2025 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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Pd/Cu-ZIF-67-900.\u003c/p\u003e","description":"","filename":"1.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7987190/v1/effa4b53647141539111216c.jpg"},{"id":95731489,"identity":"a44ff494-0a1d-4eb7-8b87-e3300a3db8b8","added_by":"auto","created_at":"2025-11-12 11:49:25","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":196089,"visible":true,"origin":"","legend":"\u003cp\u003e(a) ZIF-8 ZIF-67 XRD test diagram. (b) ZIF-8 ZIF-67 Co/ZIF-8 simulated XRD test diagram. (c) Co-ZIF-8 Pd/Co-ZIF-8 Pd/Co-ZIF-8-N XRD test diagram. (d) Pd/ZIF-67-700 Pd/Cu-ZIF-67-700 Pd/ZIF-67-900 Pd/Cu-ZIF-67-900 XRD diagram.\u003c/p\u003e","description":"","filename":"2.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7987190/v1/c0535df72eb9b5a38110bfe5.jpg"},{"id":95731492,"identity":"32d568f9-faf3-477b-9629-5e202c293dd0","added_by":"auto","created_at":"2025-11-12 11:49:25","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":354737,"visible":true,"origin":"","legend":"\u003cp\u003eScanning electron microscopy figures of Pd/ZIF-67-N Pd/Cu-MOF-N Pd/ZIF-8-N Pd/Cu-ZIF-8-N Pd/Cu-ZIF-67-N Pd/Co-ZIF-8-N six catalysts.\u003c/p\u003e","description":"","filename":"3.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7987190/v1/383c7737cb3d05597d395bf9.jpg"},{"id":95801760,"identity":"73f9cb76-9b79-4d5b-909f-f4df7ceaeba0","added_by":"auto","created_at":"2025-11-13 08:26:07","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":178723,"visible":true,"origin":"","legend":"\u003cp\u003eScanning electron microscopy figure of Co-ZIF-8 Pd/Co-ZIF-8 Pd/Co-ZIF-8-N.\u003c/p\u003e","description":"","filename":"4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7987190/v1/bbc93d086ded2d95ced42eb0.jpg"},{"id":95731496,"identity":"0c52a599-1c14-4a12-aa6a-6fdccbfa5a39","added_by":"auto","created_at":"2025-11-12 11:49:25","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":226568,"visible":true,"origin":"","legend":"\u003cp\u003ea) CO\u003csub\u003e2\u003c/sub\u003e-TPD characterization of Pd/Cu-ZIF-8-N Pd/Cu-ZIF-67-N Pd/Co-ZIF-8-N. (b) Schematic diagram of the mechanism of the carbonylation reaction. (c) Schematic diagram of the carbonylation reaction of the Pd/Cu-ZIF-67-N Pd/Cu-MOF-N Pd/Cu-ZIF-8-N Pd/Cu-ZIF-8-N Pd/Cu-ZIF-8-N Pd/Cu-ZIF-67-N Pd/ Co-ZIF-8-N activity test plots for six catalysts.\u003c/p\u003e","description":"","filename":"5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7987190/v1/24aa941654d63ef4a90520b9.jpg"},{"id":95731517,"identity":"03e3b4f2-34ee-404e-a1dc-b365c06fa8f7","added_by":"auto","created_at":"2025-11-12 11:49:25","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":486832,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Pd/ZIF-67-700 Pd/Cu-ZIF-67-700 Pd/ZIF-67-900 Pd/Cu-ZIF-67-900 Co2p XPS plot. (b) Pd/ZIF-67-700 Pd/Cu-ZIF-67-700 Pd/ZIF-67-900 Pd/Cu-ZIF-67-900 N1s XPS plot. (c) Pd/Cu-ZIF-67-700 Pd/Cu-ZIF-67-900 Cu2p XPS plot. (d) Comparison of the activity of catalysts Pd/ZIF-67-N and Pd/Cu-ZIF-67-N at different calcination temperatures.\u003c/p\u003e","description":"","filename":"6.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7987190/v1/a1bd129bda27793b5a3c7915.jpg"},{"id":95731494,"identity":"644ef466-0bc1-46a9-9f7c-8bc4aecf19cc","added_by":"auto","created_at":"2025-11-12 11:49:25","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":145380,"visible":true,"origin":"","legend":"\u003cp\u003e\u0026nbsp;(a) Pd/Co-ZIF-8-N XPS broad spectrum. (b) Pd/Co-ZIF-8-N XPS Co 2p plot. (c) Pd/Co-ZIF-8-N XPS C 1s plot. (d) Pd/Co-ZIF-8-N XPS Zn 2p plot. (e) Pd/Co-ZIF-8-N XPS N1s plot. (f) Pd/Co-ZIF-8-N XPS Pd 3d plot.\u003c/p\u003e","description":"","filename":"7.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7987190/v1/c3bc2f670f32cdef042642a0.jpg"},{"id":95731515,"identity":"85d5d5d8-d96e-445a-8f84-4a7d14e6fd59","added_by":"auto","created_at":"2025-11-12 11:49:25","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":78906,"visible":true,"origin":"","legend":"\u003cp\u003ePotential energy diagram of Cu Co Zn Pd for the ring-forming transition state of the carbonylation reaction\u003c/p\u003e","description":"","filename":"8.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7987190/v1/66a8082584f017370873eaa9.jpg"},{"id":95805349,"identity":"2885318c-b119-4e56-929b-c80021a5e8f9","added_by":"auto","created_at":"2025-11-13 08:40:47","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":2353501,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7987190/v1/afe11861-e75e-4285-a7be-46486516a08f.pdf"},{"id":95799359,"identity":"7ee8c4d5-2a89-4bed-8f1f-bca0262e6e8f","added_by":"auto","created_at":"2025-11-13 08:19:43","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":16823,"visible":true,"origin":"","legend":"","description":"","filename":"Highlights.docx","url":"https://assets-eu.researchsquare.com/files/rs-7987190/v1/d1d9881579e1672ac1f8e0c9.docx"},{"id":95801151,"identity":"e96b946e-f098-4783-9196-29c72bf1801c","added_by":"auto","created_at":"2025-11-13 08:24:36","extension":"docx","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":3454052,"visible":true,"origin":"","legend":"","description":"","filename":"SI.docx","url":"https://assets-eu.researchsquare.com/files/rs-7987190/v1/3106672281f29065c22c8235.docx"},{"id":95731500,"identity":"b1d60867-1c99-400d-b0a9-dc1335418704","added_by":"auto","created_at":"2025-11-12 11:49:25","extension":"docx","order_by":3,"title":"","display":"","copyAsset":false,"role":"supplement","size":1110737,"visible":true,"origin":"","legend":"","description":"","filename":"GraphicalAbstract.docx","url":"https://assets-eu.researchsquare.com/files/rs-7987190/v1/19d9cd57ada1d38c7811110f.docx"},{"id":95801313,"identity":"f129dcfe-a12a-4491-a4d4-1d69ce7eb479","added_by":"auto","created_at":"2025-11-13 08:24:53","extension":"jpg","order_by":4,"title":"","display":"","copyAsset":false,"role":"supplement","size":14900,"visible":true,"origin":"","legend":"\u003cp\u003eSchem1 Flowchart of catalyst Pd/Co-ZIF-8-N preparation.\u003c/p\u003e","description":"","filename":"Scheme.jpg","url":"https://assets-eu.researchsquare.com/files/rs-7987190/v1/0365882b568df7ee589ca901.jpg"}],"financialInterests":"No competing interests reported.","formattedTitle":"Efficient Glycerol Carbonylation over Multimetallic ZIF Catalysts: Synergy of Structure Regulation and Charge Optimization","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eGlycerol carbonate (hydroxymethyl dioxolane), abbreviated as GC, is a small molecule with significant practical value. This molecule has garnered widespread interest over the past two decades due to two main reasons: its broad reactivity, which enables various synthetic applications, and its potential as a method to enhance glycerol valorization[\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e]. As a green chemical, glycerol carbonate exhibits promising prospects for widespread application. Its excellent biodegradability, low toxicity, and multifunctionality make it highly suitable for use in solvents, materials, pharmaceuticals, and other fields [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. With the optimization of production processes and technological advancements, glycerol carbonate is expected to become an increasingly important industrial raw material and green energy source, contributing to sustainable development and environmental protection.\u003c/p\u003e\u003cp\u003eGenerally, there are four primary methods for synthesizing glycerol carbonate: glycerol carbonylation (which requires catalysts) [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan additionalcitationids=\"CR6\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e], transesterification (typically using dimethyl carbonate, DMC) [\u003cspan additionalcitationids=\"CR9\" citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e], phosgene-based methods [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e], and urea alcoholysis [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Each of these methods has its own advantages and disadvantages; however, the carbonylation reaction has gained widespread attention due to its unique advantage of water as the only byproduct, which is easy to purify and separate. Hu et al. discovered that glycerol carbonate could be easily synthesized through the oxidative carbonylation of glycerol using PdCl₂(phen) (phen\u0026thinsp;=\u0026thinsp;1,10-phenanthroline) under CuI catalysis, achieving high conversion (95%) and selectivity (98%) with a TOF of 455 h⁻\u0026sup1;. This catalyst was also shown to be reusable up to five times without significant loss of activity [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. Michele first reported the systematic study of copper (II)-catalyzed oxidative carbonylation for the synthesis of glycerol carbonate. The study found that copper (II) chloride effectively promoted this process under homogeneous conditions, using CO: O₂ (P\u0026thinsp;=\u0026thinsp;4 MPa; P(O₂)\u0026thinsp;=\u0026thinsp;0.7 MPa) in the presence of pyridine at 130\u0026deg;C in DMA, achieving excellent conversion (\u0026gt;\u0026thinsp;92%) and selectivity (\u0026gt;\u0026thinsp;93%) within a relatively short reaction time (3\u0026ndash;4 hours) [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eHowever, in these studies, the catalysts have not been employed in a supported form to improve activity, stability, or reduce costs. The catalytic properties of ZIF-derived carbon materials are expected to address these challenges [\u003cspan additionalcitationids=\"CR16 CR17\" citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e]. Guo et al. developed a template-assisted strategy, in which ZIF-8 was confined to grow in the three-dimensional ordered template voids and pyrolyzed to produce hierarchical pores in nitrogen-doped carbon materials derived from MOFs. The layered nanostructures significantly facilitated the mass transfer of large molecules and exposed active sites, thus achieving satisfactory CO₂ photoconversion under mild conditions [\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e]. Zhang et al. reported a type of nitrogenated, layered carbon framework obtained via controlled carbonization of Zn-imidazole salt frameworks. The N-HLCF-xs materials combined primary three-dimensional micropores, secondary two-dimensional lamellar microstructures, and high-density nitrogen basic sites, which promoted their interaction with acidic COS and H₂S [\u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e].\u003c/p\u003e\u003cp\u003eIn this study, we explored the effects of different transition metals (Cu, Co, Zn) and their combinations on the glycerol carbonylation reaction. We found that when cobalt was used as a dopant metal (rather than a framework metal), it significantly enhanced the dispersion of the palladium active sites. At just 0.2% palladium by mass on the support, we achieved catalytic activity comparable to that optimized by other supports, which typically require around 1% palladium. The reaction yielded exceptionally high product yield and selectivity. Moreover, the study of the calcination temperature of copper revealed its unique behavior during the reaction process. We explored the reasons behind the changes induced by copper at different calcination temperatures and performed Gaussian simulations to model the transition states and electrostatic potential variations in the presence of multiple metals, further enriching the catalytic research on glycerol carbonylation.\u003c/p\u003e"},{"header":"2. Experimental section","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\u003ch2\u003e2.1 Catalyst preparation\u003c/h2\u003e\u003cp\u003eThe preparation of the catalyst Pd/Co-ZIF-8-N is illustrated in Scheme 1. First, 3.20 g of Zn(NO₃)₂\u0026middot;6H₂O and 0.18 g of Cu(NO₃)₂\u0026middot;3H₂O were dissolved in 75 mL of methanol. Then, 3.3 g of 2-methylimidazole was dissolved in 75 mL of methanol. The two solutions were mixed and stirred at room temperature for 24 hours. The mixture was then filtered using a water pump, and after washing three times with methanol, the product was dried at 80\u0026deg;C for 12\u0026ndash;24 hours. Next, the support and palladium methanol solution (1 g/L) were mixed in a ratio of 1:0.002 and stirred for 24 hours. The resulting mixture was calcined in a tube furnace at 600\u0026deg;C to obtain the final catalyst, Pd/Co-ZIF-8-N, which exhibited a carbon nanotube morphology (with the temperature suffix indicating the calcination temperature). The preparation methods for other catalysts are described in detail in the supplementary materials.\u003c/p\u003e\u003cp\u003e\u003c/p\u003e\u003cp\u003eSchem1 Flowchart of catalyst Pd/Co-ZIF-8-N preparation.\u003c/p\u003e\u003c/div\u003e"},{"header":"3. Results and discussion","content":"\u003cp\u003eThe infrared spectra of the catalysts and supports are shown in Fig.\u0026nbsp;1a. Even after loading, Pd/Co-ZIF-8 retains the characteristic peaks of ZIF, including those at 3450, 3123, 2908, 1615, 1401, and 622 cm⁻\u0026sup1;, which correspond to the O-H stretch (from water in the air or solvents introduced during synthesis), the N-H stretch vibration, C-H stretch vibration, C\u0026thinsp;=\u0026thinsp;C and C\u0026thinsp;=\u0026thinsp;N stretches (from the imidazole ring), C-N stretch vibration, and Co-N stretch vibration. After calcination, the final catalyst shows a weakening and disappearance of the C-H stretch and bending vibration peaks, indicating the successful carbonization of the catalyst. The catalyst still retains the Co-N stretch vibration peak, which suggests the preservation of the metal framework [21, 22].\u003c/p\u003e\n\u003cp\u003eThe infrared spectra of the copper-doped catalyst (Pd/Cu-ZIF-67-N) and the non-copper-doped catalyst (Pd/ZIF-67-N) are shown in Fig.\u0026nbsp;1c (FT-IR spectra for four catalysts were prepared based on the calcination temperatures corresponding to the activity inflection points, as shown in Fig.\u0026nbsp;6d). From the figure, it is evident that there is no significant difference, which implies that the integrity of the framework remains unchanged. However, the decline in activity of Pd/ZIF-67-N at high temperatures (700\u0026ndash;900\u0026deg;C) cannot be accurately attributed to framework degradation from the infrared spectra.\u003c/p\u003e\n\u003cp\u003eThe infrared spectra of the six catalysts composed of copper, cobalt, and zinc are shown in Fig.\u0026nbsp;1b. After calcination, all the catalysts exhibited distinct stretching vibrations of the organic ligand 2-methylimidazole, including the C\u0026thinsp;=\u0026thinsp;C and C\u0026thinsp;=\u0026thinsp;N stretches (1615 cm⁻\u0026sup1;) and the C-N stretch (1401 cm⁻\u0026sup1;). The Zn-N characteristic peak at 630 cm⁻\u0026sup1; weakened in the catalyst with ZIF-8 as the support and no cobalt, suggesting that some zinc underwent ion exchange with bimetallic ions during calcination. This is particularly evident due to the relatively low boiling point of metallic zinc. The Cu-N infrared vibration peak was not observed, leading to this phenomenon. This exchange facilitates metal electron transfer, thereby improving catalytic activity [23, 24].\u003c/p\u003e\n\u003cp\u003eFigure\u0026nbsp;2a presents the X-ray powder diffraction (XRD) patterns of the synthesized ZIF-8 and ZIF-67, which are consistent with the results simulated using Materials Studio 2019 (Fig.\u0026nbsp;2b), confirming the successful synthesis of the metal-organic frameworks. Figure\u0026nbsp;2b also simulates the XRD pattern of Co-ZIF-8, the precursor support for the catalyst Pd/Co-ZIF-8-N, and the comparison in Fig.\u0026nbsp;1c further confirms the successful synthesis of the support. After loading with palladium acetate, Co-ZIF-8 did not exhibit additional diffraction peaks, likely due to the low and dispersed loading of divalent palladium or its doping in the framework as Pd\u0026sup2;⁺ ions. Subsequent calcination and reduction revealed palladium diffraction peaks, supporting this hypothesis. The calcined catalyst showed the face-centered cubic structure characteristic of metallic cobalt, with diffraction peaks at 44.2\u0026deg; (111), 51.5\u0026deg; (200), and 75.9\u0026deg; (220). The prepared catalyst also exhibited two broad diffraction peaks at 40.23\u0026deg; and 46.80\u0026deg;, corresponding to the (111) and (200) reflections of metallic palladium, indicating the successful loading of palladium [25\u0026ndash;27].\u003c/p\u003e\n\u003cp\u003eAfter calcination, the precursor catalyst showed clear diffraction peaks of carbon materials. The peak at 25\u0026deg; (the \u0026quot;dumpling peak\u0026quot;) corresponds to C(100), and the peaks at 44.27\u0026deg; and 51.61\u0026deg; correspond to the (111) and (200) crystal planes of cobalt (PDF#15\u0026ndash;0806). This suggests that cobalt undergoes reduction after doping and calcination. However, the palladium peak did not appear after calcination, possibly because the palladium nanoparticles are either embedded within the framework or highly dispersed. This phenomenon can be attributed to the unique structural characteristics of the framework after calcination, which promotes the dispersion and anchoring of palladium.\u003c/p\u003e\n\u003cp\u003eFigure\u0026nbsp;3 Scanning electron microscopy figures of Pd/ZIF-67-N Pd/Cu-MOF-N Pd/ZIF-8-N Pd/Cu-ZIF-8-N Pd/Cu-ZIF-67-N Pd/Co-ZIF-8-N six catalysts.\u003c/p\u003e\n\u003cp\u003eFigures\u0026nbsp;3a-c show the catalysts prepared by calcining Pd-loaded ZIF-8, ZIF-67, and Cu-MOF under nitrogen. The images of catalysts a and b reveal clear octahedral structures, indicating that calcination at 600\u0026deg;C did not affect the basic morphology of ZIF-8 and ZIF-67. The average diameters of ZIF-8 and ZIF-67 were 2 \u0026micro;m and 0.2 \u0026micro;m, respectively, which is consistent with the typical synthesis methods reported in the literature. However, after calcination, the originally distinct particle structure of Cu-MOF disappeared (Fig. S3), transforming into fragmented, layered structures. This morphological degradation led to the loss of the high surface area characteristic of metal-organic frameworks, which is the main reason for the reduced activity [21].\u003c/p\u003e\n\u003cp\u003eFigures\u0026nbsp;3e-f show scanning electron microscopy (SEM) images of the three bimetallic ZIF catalysts: Pd/Cu-ZIF-8-N, Pd/Cu-ZIF-67-N, and Pd/Co-ZIF-8-N, representing Cu-Zn doping, Cu-Co doping, and Co-Zn doping, respectively [29]. Interestingly, the first two catalysts did not undergo significant changes in their morphology after calcination, retaining their original polyhedral or cubic structures. In contrast, Pd/Co-ZIF-8-N, after calcination, formed carbon nanotubes. As shown in Figs.\u0026nbsp;4a and b, the precursor and support of the Pd/Co-ZIF-8-N catalyst exhibited a regular cubic structure. The formation of carbon nanotubes is attributed to the presence of metal catalytic sites (e.g., iron, cobalt, nickel). During calcination, these metal particles assist in the decomposition of carbon sources (such as hydrocarbons) and catalyze the rearrangement of carbon atoms. The carbon atoms accumulate at the metal catalytic sites, forming tubular structures that then grow into carbon nanotubes.\u003c/p\u003e\n\u003cp\u003eWhile Pd-Cu-ZIF-67-N also contains cobalt, its divalent Co forms a stable framework material, which stabilizes the carbon within the framework, making it less prone to catalytic rearrangement. The hollow tubular structure offers natural nanoscale pores that facilitate the diffusion of glycerol molecules into the tubes, allowing for full contact with the active palladium sites. Moreover, possible byproducts in the glycerol carbonylation reaction, such as polyglycerols, are less likely to pass through the nanotube pores. This tubular morphology also effectively controls the entry and exit of glycerol carbonate, enhancing catalytic selectivity. Furthermore, during palladium nanoparticle loading, the carbon nanotubes can evenly distribute and anchor the nanoparticles due to their unique morphology and structure, preventing aggregation and maintaining higher dispersion. This high dispersion increases the effective active sites of the metal catalyst, thereby reducing the amount of palladium required and directly lowering the cost of catalyst preparation. According to data obtained from Inductively coupled plasma optical emission spectroscopy (ICP-OES), the palladium loading in the calcined material was significantly reduced to just 1.11%, much lower than that reported for other catalytic materials [30\u0026ndash;32].\u003c/p\u003e\n\u003cp\u003eTo further investigate the influence of acid-base sites on the catalytic performance for glycerol oxidative carbonylation, the catalysts derived from three different bimetallic ZIF precursors were characterized by CO\u003csub\u003e2\u003c/sub\u003e-TPD analysis (Fig.\u0026nbsp;5a). According to the previously proposed mechanism (Fig.\u0026nbsp;5b), glycerol initially interacts with iodide ions to lose a hydrogen atom, forming the intermediate C\u003csub\u003e3\u003c/sub\u003eH\u003csub\u003e7\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e*. Interestingly, a stronger acidity of the catalyst appears to be detrimental to this reaction step. This is because the protons dissociated from acidic sites tend to combine with hydroxyl groups, suppressing the formation of the intermediate in the first reaction step. Experimental results using catalysts modified with benzoic acid further validate this hypothesis, as a significant reduction in activity was observed. As shown in Fig.\u0026nbsp;5a, Pd/Cu-ZIF-8-N, Pd/Cu-ZIF-67-N, and Pd/Co-ZIF-8-N exhibited notable signal peaks in the temperature ranges of 100\u0026deg;C and 400\u0026ndash;500\u0026deg;C. These peaks suggest the presence of strong basicity, likely due to the calcination of the catalysts under nitrogen conditions. The peaks above 300\u0026deg;C confirm the existence of strong basic sites.\u003c/p\u003e\n\u003cp\u003eBy correlating the acidic properties of Co, Cu, and Zn in different oxidation states with Lewis acid-base theory, the theoretical acidity follows the order Co\u0026sup3;⁺ \u0026gt;Cu\u0026sup2;⁺ \u0026gt;Zn\u0026sup2;⁺ \u0026gt;Co\u0026sup2;⁺ \u0026gt;Cu⁺. Accordingly, the stronger acidity observed for Pd/Cu-ZIF-8-N and Pd/Co-ZIF-8-N can be attributed to their ZIF-8-derived framework, which is reflected in their catalytic performance. The metal Lewis acids enhance the reaction activity by coordinating with oxygen, redistributing the electronic density of the oxidant, lowering the redox potential, and thereby accelerating the charge transfer process.\u003c/p\u003e\n\u003cp\u003eFigure\u0026nbsp;5c compares the yields and selectivity of six catalysts for the carbonylation reaction. Catalysts prepared with pure ZIF-8 and Cu-ZIF-8 exhibited the lowest activity, likely due to the relatively strong acidity of Cu\u0026sup2;⁺ and Zn\u0026sup2;⁺. Interestingly, Co-ZIF-8, which also uses ZIF-8 as a support, showed the highest activity. Further optimization revealed that the Co and Zn loading significantly impacts the catalytic performance. This effect is hypothesized to stem from the critical role of cobalt loading in the carbonization process of ZIF-8. Excessively high or low cobalt content disrupts the formation of carbon nanotubes, affecting pore size and specific surface area, which in turn influences the catalytic properties.\u003c/p\u003e\n\u003cp\u003eAdditionally, while the catalytic activity of Pd/Cu-ZIF-8-N was lower than that of Pd/Co-ZIF-8-N, it exhibited stronger basicity, as indicated by its unique strong peak in the range of 600\u0026ndash;700\u0026deg;C, which was absent in the other two catalysts. This observation may be attributed to the unique coordination environment of Cu or the high content of monovalent copper (Cu⁺) under the calcination conditions. To investigate this further, X-ray photoelectron spectroscopy (XPS) analysis was performed on catalysts doped and undoped with Cu at various calcination temperatures.\u003c/p\u003e\n\u003cp\u003eThe Co 2p valence state signal peaks for Pd/ZIF-67-700, Pd/ZIF-67-900, Pd/Cu-ZIF-67-700, and Pd/Cu-ZIF-67-900 were tested. The Co 2p₃/₂ and Co 2p₁/₂ peaks for all four catalysts exhibited a shift of 0.5-1 eV compared to those in Fig.\u0026nbsp;7b, which is attributed to the different states of Co. According to the SEM morphology shown in Fig.\u0026nbsp;3e, the structures of these catalysts retained the framework shape, rather than adopting the carbon nanotube morphology of the Pd/Co-ZIF-8-N catalyst. This is because, in this case, cobalt forms an M-N₄ structure, a feature confirmed by both XPS and SEM analysis [19, 33, 34]. This special structure induces the solidification of the host metal and promotes charge transfer, which is conducive to the improvement of catalytic activity. Interestingly, when copper is doped, both Pd/Cu-ZIF-67-700 and Pd/Cu-ZIF-67-900 showed no satellite signal at 796 eV and 800.4 eV, indicating that copper suppresses the formation of Co₃O₄.\u003c/p\u003e\n\u003cp\u003eFrom the comparison of activity for the two catalysts at different calcination temperatures (Fig.\u0026nbsp;6d), it is evident that copper-containing catalysts exhibit better activity between 200\u0026deg;C and 600\u0026deg;C compared to those without copper. This is likely directly related to the state of cobalt discussed earlier, as excessive Co₃O₄ content hinders the carbonylation reaction. As the calcination temperature increases further, the activity of copper-doped catalysts begins to decline. This is supported by the comparison of the Cu 2p spectra (Fig.\u0026nbsp;6c), where the largest difference in the Cu 2p₃/₂ convolution peak is observed. At 935 eV, the integrated area at 900\u0026deg;C calcination is 15% smaller than that at 700\u0026deg;C, corresponding to the Cu 2p₃/₂ peak of copper oxide. This indicates that high-temperature calcination facilitates the rearrangement of carbon, making it easier to form the Cu-N₄ state, which plays a beneficial role in the catalytic process. This is consistent with the significant increase in activity of Pd/Cu-ZIF-67-N under calcination conditions at 900\u0026deg;C and 950\u0026deg;C (Fig.\u0026nbsp;6d), as described earlier in Fig.\u0026nbsp;2d, where the reduced formation of copper oxides correlates with improved activity.\u003c/p\u003e\n\u003cp\u003eFigure\u0026nbsp;6b shows the narrow N 1s XPS spectra of the four catalysts. The copper-doped catalysts exhibit lower graphitization degrees at 700\u0026ndash;900\u0026deg;C compared to those without copper, which explains why the non-copper-doped catalysts have better activity in this temperature range. Overall, suppressing the formation of Co₃O₄ (which prevents the generation of non-divalent metals), maintaining the stability of the doped metal framework to form M-N₄ structures, and improving the graphitization degree all contribute to excellent performance in the carbonylation reaction [35].\u003c/p\u003e\n\u003cp\u003eTo investigate the metal valence states and conditions of different catalysts after calcination, X-ray photoelectron spectroscopy (XPS) was first performed on the final catalyst. The wide spectrum of the Pd/Co-ZIF-8-N catalyst (Fig.\u0026nbsp;7a) reveals clear elemental valence state peaks (Zn 2p₁, Zn 2p, Co 2p, O 1s, N 1s, C 1s, Zn 3p) which provide insights into the elemental states of the catalyst. As shown in Fig.\u0026nbsp;7b, the peaks at 781 eV, 785.4 eV, 796 eV, and 800.4 eV correspond to Co 2p₃/₂, Co 2p₃/₂ satellite, Co 2p₁/₂, and Co 2p₁/₂ satellite peaks, respectively. These peaks indicate that cobalt is primarily in its oxidized state, with CoO and Co₃O₄ being the main forms. This is due to cobalt being doped into ZIF-8 as a catalyst, and after calcination, it forms carbon nanotubes rather than maintaining the framework structure and forming M-N₄ structures. This structure helps to improve the dispersion of Pd loading, thus enhancing catalytic activity, which is consistent with the activity results shown in Fig.\u0026nbsp;5c.\u003c/p\u003e\n\u003cp\u003eThe deconvolution of the C 1s spectrum (Fig. 7c) shows that the carbon material after calcination is similar to a graphene-like structure, with the C\u0026thinsp;=\u0026thinsp;C structure accounting for 84%. The C-N structure is derived from the 2-methylimidazole and nitrogen during calcination, which is confirmed by the N 1s deconvolution (pyridinic-N, pyrrolic-N, graphene-N). Interestingly, palladium, which is the active component for the carbonylation reaction, does not exhibit a prominent satellite peak. This is likely due to the low Pd loading, and the carbon nanotube structure aids in Pd dispersion, resulting in the absence of distinct peaks. Another possibility is that XPS primarily detects surface states rather than bulk phases, further suggesting that Pd is confined within the defects of the carbon nanotubes.\u003c/p\u003e\n\u003cp\u003eTable 1 Summary of natural charges of different metal-forming transition states\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"6\" valign=\"top\" style=\"width: 554px;\"\u003e\n \u003cp\u003e\u003cimg width=\"243\" height=\"74\" 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\" alt=\"image\"\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"6\" valign=\"top\" style=\"width: 554px;\"\u003e\n \u003cp\u003e\u003cstrong\u003e\u0026nbsp; TS in \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; \u0026nbsp; TS\u003c/strong\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 93px;\"\u003e\n \u003cp\u003eAtom Number\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 93px;\"\u003e\n \u003cp\u003e1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 93px;\"\u003e\n \u003cp\u003e2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e5\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 93px;\"\u003e\n \u003cp\u003eCu TS in\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 93px;\"\u003e\n \u003cp\u003e0.717\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 93px;\"\u003e\n \u003cp\u003e0.495\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e-0.489\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e-0.517\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e-0.831\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 93px;\"\u003e\n \u003cp\u003eCo TS in\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 93px;\"\u003e\n \u003cp\u003e0.619\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 93px;\"\u003e\n \u003cp\u003e0.610\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e-0.557\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e-0.519\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e-0.786\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 93px;\"\u003e\n \u003cp\u003eZn TS in\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 93px;\"\u003e\n \u003cp\u003e1.097\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 93px;\"\u003e\n \u003cp\u003e0.378\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e-0.520\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e-0.551\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e-0.989\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 93px;\"\u003e\n \u003cp\u003ePd TS in\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 93px;\"\u003e\n \u003cp\u003e0.474\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 93px;\"\u003e\n \u003cp\u003e0.683\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e-0.524\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e-0.508\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e-0.763\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 93px;\"\u003e\n \u003cp\u003eCu TS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 93px;\"\u003e\n \u003cp\u003e0.453\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 93px;\"\u003e\n \u003cp\u003e0.692\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e-0.508\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e-0.523\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e-0.748\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 93px;\"\u003e\n \u003cp\u003eCo TS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 93px;\"\u003e\n \u003cp\u003e0.414\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 93px;\"\u003e\n \u003cp\u003e0.744\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e-0.550\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e-0.530\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e-0.721\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 93px;\"\u003e\n \u003cp\u003eZn TS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 93px;\"\u003e\n \u003cp\u003e0.579\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 93px;\"\u003e\n \u003cp\u003e0.669\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e-0.494\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e-0.515\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e-0.866\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 93px;\"\u003e\n \u003cp\u003ePd TS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 93px;\"\u003e\n \u003cp\u003e0.331\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 93px;\"\u003e\n \u003cp\u003e0.799\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e-0.514\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e-0.526\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 92px;\"\u003e\n \u003cp\u003e-0.730\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003eTo further investigate the influence of different metals on the reaction transition state, a computational study was conducted on the metals involved in the research and their associated transition states. The two key processes in the carbonylation reaction are the formation of the carbonyl group and the cyclization process. Simulations revealed that only palladium (Pd) can form the carbonyl group, while other transition metals cannot participate in this step. However, for the cyclization process, all the transition metals used in the study could form transition states. After IRC (Intrinsic Reaction Coordinate) analysis, the potential energy profiles of Cu, Co, Zn, and Pd are shown in Fig.\u0026nbsp;8. Based on the transition state energies and the potential energy of intermediates and products, the difficulty of the cyclization process follows the order: Pd\u0026thinsp;\u0026gt;\u0026thinsp;Cu\u0026thinsp;\u0026gt;\u0026thinsp;Co\u0026thinsp;\u0026gt;\u0026thinsp;Zn. Therefore, Cu, Co, and Zn are considered high activation energy catalysts compared to Pd, exhibiting some inhibitory effects on the reaction. As seen in the comparison of catalyst activity, the order of catalytic activity is Co-Zn\u0026thinsp;\u0026gt;\u0026thinsp;Co\u0026thinsp;\u0026gt;\u0026thinsp;Cu-Zn\u0026thinsp;\u0026gt;\u0026thinsp;Cu-Co\u0026thinsp;\u0026gt;\u0026thinsp;Cu\u0026thinsp;\u0026gt;\u0026thinsp;Zn, which slightly deviates from the simulation results.\u003c/p\u003e\n\u003cp\u003eTo further understand the role of transition metals, the natural charges of TS-in and TS were summarized for different metals. It was found that the natural charge of cobalt (Co) is lower than that of all other metals, excluding palladium (Pd), indicating greater stability of the transition state. Additionally, the two atoms involved in the reaction (atoms 2 and 5) corresponding to Co and Zn showed larger charge values, suggesting that these metals facilitate atomic interactions and thus promote the reaction. Consequently, from the charge distribution, the Co-Zn combination demonstrated a greater advantage, which also explains the catalytic activity ranking of the metal combinations.\u003c/p\u003e\n\u003cp\u003eFurthermore, the influence of different calcination temperatures with and without copper (Cu) doping was further explained. Copper, as expected, is a low activation energy catalyst compared to other metals, and the variation in activity at high temperatures is primarily attributed to changes in charge distribution. At higher temperatures, Cu transitions from free divalent copper to a Cu-N\u003csub\u003e4\u003c/sub\u003e structure, which enhances the performance of metal combination catalysts at elevated temperatures.\u003c/p\u003e\n\u003cp\u003eIn conclusion, for guest metals like Cu, Co, and Zn, their effect on the transition state is primarily manifested through electron transfer, as revealed by the charge comparison. Moreover, the structure and calcination temperature of the catalyst significantly affect the charge distribution, and a detailed examination of the charge changes between key reacting atoms is essential to better explain the catalytic performance changes under multi-metal conditions in carbonylation reactions.\u003c/p\u003e"},{"header":"4. Conclusion","content":"\u003cp\u003eIn this study, a series of different metals and metal combinations as carriers were prepared, including ZIF-8, ZIF-67, Cu-ZIF, Cu-ZIF-8, Cu-ZIF-67, and Co-ZIF-8. These carriers underwent activity optimization after loading, and the final comparison revealed that Pd/Co-ZIF-8-N exhibited the best catalytic performance, achieving a high yield (92.97%) and selectivity (96.37%) during the reaction. The metal loading was only 1% after calcination and 0.2% before calcination. This performance is attributed to the catalytic role of cobalt in transforming the carbon framework into carbon nanotubes. Additionally, the influence of calcination temperature was also studied, revealing the unique activity characteristics of copper (Cu). The suppression of copper oxide formation and the enhancement of Cu-N\u003csub\u003e4\u003c/sub\u003e formation were identified as key factors in improving activity. Both material characterization and computational simulations were employed to investigate these aspects. The results showed that transition metals like Cu, Co, and Zn influence the transition state primarily through electron transfer. The structure and calcination temperature of the catalyst significantly alter this value, thereby impacting catalytic activity. Co and Zn played a critical role in promoting the carbon-oxygen bond formation during cyclization. Therefore, the changes in charge distribution and the synergistic effect of the multi-metal system in the carbonylation reaction provide a deeper understanding than simply comparing activation energies. This study offers new insights into the catalytic process of carbonylation reactions and lays the foundation for future research in this field.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eCompeting Interests\u003c/strong\u003e\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003ch2\u003eEthical and Consent to Participate\u003c/h2\u003e\u003cp\u003eNot applicable.\u003c/p\u003e\u003c/p\u003e\u003cp\u003e\u003ch2\u003eConsent for Publication\u003c/h2\u003e\u003cp\u003eThe manuscript represents original research work, and it has not been previously published or submitted elsewhere, nor is it under consideration for publication elsewhere. All participants have given their consent for publication of their data/information.\u003c/p\u003e\u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e\u003cp\u003eThe financial support from the Natural Science Foundation of China (NSFC) (No. 22378163) and MOE \u0026amp; SAFEA for the 111 Project (B13025) is gratefully acknowledged.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eLiyao Zhao: Formal analysis, Supervision, Resources, Writing-Review \u0026amp; Editing. Zhihao Lv: Methodology, Resources, Visualization. Shuqi Qi: Investigation, Validation, Formal Analysis. Pingbo Zhang: Formal analysis, Investigation, Methodology, Writing-Original Draft. Jiawen Zhang: Investigation, Methodology, Supervision. Mingming Fan: Supervision, Resources, Methodology.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe financial support from the Natural Science Foundation of China (NSFC) (No. 22378163) and MOE \u0026amp; SAFEA for the 111 Project (B13025) is gratefully acknowledged.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eData will be made available on request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eSch\u0026auml;ffner B, Sch\u0026auml;ffner F, Verevkin SP, B\u0026ouml;rner A (2010) Organic Carbonates as Solvents in Synthesis and Catalysis. 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Chem Eng J 426:131801. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1016/j.cej.2021.131801\u003c/span\u003e\u003cspan address=\"10.1016/j.cej.2021.131801\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"},{"header":"Scheme ","content":"\u003cp\u003eScheme 1 is available in the Supplementary Files section.\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":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"catalysis-letters","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Catalysis Letters](https://link.springer.com/journal/10562)","snPcode":"10562","submissionUrl":"https://submission.springernature.com/new-submission/10562/3","title":"Catalysis Letters","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Glycerol carbonylation, Multimetallic ZIFs, Electron redistribution, Synergistic catalysis, Pd/Co-ZIF-8-N","lastPublishedDoi":"10.21203/rs.3.rs-7987190/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7987190/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eThe valorization of glycerol is a key research objective, and its carbonylation to glycerol carbonate represents a promising route. A major hurdle in this process is the development of efficient catalysts.This study systematically investigates the catalytic performance of various transition metal-based zeolitic imidazolate frameworks (ZIFs), including ZIF-8, ZIF-67, Cu-ZIF, Cu-ZIF-8, Cu-ZIF-67, and Co-ZIF-8, in the carbonylation of glycerol to glycerol carbonate. The results reveal that bimetallic ZIFs significantly enhance catalytic activity, among them, the Co-doped Pd/Co-ZIF-8-N catalyst exhibited the best performance, achieving a high glycerol carbonate yield of 92.97% and 96.37% selectivity, with a Pd loading of only 1%. Through characterization techniques such as Fourier Transform Infrared Spectroscopy (FT-IR), X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), X-Ray Photoelectron Spectroscopy (XPS), and CO₂-Temperature Programmed Desorption (CO₂-TPD), we demonstrate that Co doping promotes the formation of carbon nanotubes, improves Pd dispersion, and modulates the acid-base properties of the material. Computational simulations further indicate that the combination of Co and Zn optimizes the natural charge distribution in the reaction transition state, facilitating electron transfer and thereby enhancing catalytic performance. Additionally, calcination temperature markedly influences the valence state and coordination environment of copper species, where the formation of a Cu-N₄ structure at high temperatures strengthens the synergistic effect with Pd. This work provides new mechanistic insights and material design strategies for the application of multimetallic ZIFs in carbonylation reactions.\u003c/p\u003e","manuscriptTitle":"Efficient Glycerol Carbonylation over Multimetallic ZIF Catalysts: Synergy of Structure Regulation and Charge Optimization","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-11-12 11:49:20","doi":"10.21203/rs.3.rs-7987190/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-11-20T13:46:30+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-11-20T13:06:56+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-11-16T13:58:18+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"298085819496570735422193320621318902178","date":"2025-11-02T07:55:16+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"186948891364678049128733193263946834067","date":"2025-11-01T00:38:59+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-10-31T14:08:34+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-10-31T09:16:27+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-10-31T09:15:16+00:00","index":"","fulltext":""},{"type":"submitted","content":"Catalysis Letters","date":"2025-10-30T08:42:14+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"catalysis-letters","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"","sideBox":"Learn more about [Catalysis Letters](https://link.springer.com/journal/10562)","snPcode":"10562","submissionUrl":"https://submission.springernature.com/new-submission/10562/3","title":"Catalysis Letters","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"4a48f45c-e250-407a-ac0c-1f756831f82b","owner":[],"postedDate":"November 12th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2025-12-01T12:23:11+00:00","versionOfRecord":[],"versionCreatedAt":"2025-11-12 11:49:20","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7987190","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7987190","identity":"rs-7987190","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}