Advancing Biodiesel Production from Waste Cooking Oil: Optimization and Characterization of Manganese-Based Catalysts

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In recent years, the production of biodiesel has garnered significant attention from both industries and researchers globally. Waste cooking oil (WCO) has emerged as a promising feedstock for biodiesel production, drawing the interest of researchers. Utilizing WCO in biodiesel production is not only cost-effective but also addresses the disposal challenges associated with this waste cooking oil. The aim of the present study is to synthesis Ce/Mn(10:90)/γ-Al 2 O 3 using incipient wetness impregnation (IWI) methods, with the goal of facilitating the biodiesel production from WCO. Various preparation parameters, comprising calcination temperatures and based loadings as well as various reaction conditions for the transesterification reaction such as catalyst loading, methanol to oil molar ratio, reaction temperature and time were optimized. From the results, the maximum conversion of triglyceride achieved was 97% for Ce/Mn(10:90)/γ-Al 2 O 3 catalyst calcined at 800 o C. The optimum reaction conditions were 10 wt% of catalyst loading and 1:24 of methanol to oil ratio at 65°C of reaction temperature for 3 hrs. This outstanding performance can be attributed to the catalyst's high surface area of 143. m 2 /g, large pore size of 8.75 nm, and smaller particle size of 0.462 nm, collectively enhancing its catalytic efficiency. Biodiesel waste cooking oil manganese oxide catalyst transesterification reaction Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Introduction Petroleum, as known as crude oil, a non-renewable fossil fuel acts as the primary propellent contributing to the transportation sector predominantly. The elevated necessity and substantially reliance on the crude oil endangering the future as this natural resource is facing severe depletion and devitalization [ 1 ]. This issue prompted the evolution and emergence of the renewable energy supplies and ecologically friendly biomass-derived fuels, also called biodiesel or fatty acid methyl ester (FAME) as the alternative for the petroleum-based fuels, owing to the fact of its properties of being benign, biodegradability, technical viability, lower greenhouse gas (GHG) emissions, and carbon neutrality [ 2 ], [ 3 ]. Transesterification process is applied in the generation of biodiesel by reacting the fats and oils, commonly noted as triglycerides, which are normally found in the waste cooking oils, including the vegetable oils and animal fats with methanol to obtain more desired product of methyl esters [ 4 ] and with the purpose of reducing the kinematic viscosities of vegetable oils or animal fats from higher to lower viscosities range in petrol diesel [ 5 ]. The catalyst, no matter of its properties of being acidic, basic or enzymatic, therefore, plays an important role in speeding up the reaction and enhancing the biodiesel yield. Homogeneous catalysts, especially those in basic form, for example sodium hydroxide, NaOH and sodium ethoxide, C 2 H 5 ONa are widely utilized in industrial currently contributes to higher reaction rate with minimal temperature requirements [ 6 ]. The catalysts possess high catalytic activity as they are easily soluble in methanol and provide high efficiency in biodiesel conversion. The cost of producing biodiesel could be increased, nevertheless, due to homogeneous base catalyst restrictions, such as wastewater generation from the separation of excessive catalyst and glycerol and low biodiesel yield resulting from the saponification reaction [ 7 ]. Hence, more reusable and environmentally stable heterogeneous catalysts are introduced to reduce the environmental pollutants. The frequent employment of heterogeneous catalysts in the reaction of biodiesel production brings the advantages of high recyclability and reusability, ease of removal of the catalyst and minimal contamination of the finished product [ 8 ]. Due to their reusability and lack of need for water treatment or purification, solid base heterogeneous catalysts enable simultaneous transesterification and esterification processes and lower production costs. In recent years, a large number of heterogeneous catalysts such as metal oxides, alkaline earth metals, mixed metal oxides, lipase, zeolites and transition metals have been used in laboratory-scale biodiesel production [ 9 ], [ 10 ]. Manganese oxide is highly efficient catalyst for biodiesel synthesis and was effective for transesterification at high temperature and pressures, as it could facilitates the conversion of free fatty acids by providing acid and basic sites for the reaction. The catalyst could maintain high water content in the feedstock without losing efficiency [ 11 ]. It also had a lengthy catalyst life and a low rate of activity loss [ 12 ]. However, undoped MnO has a number of drawbacks in terms of application. The leaching of the undoped catalyst can have a detrimental impact on its catalytic activity, leading to interactions with free fatty acids and consequent soap production, ultimately causing catalyst deactivation. To address these challenges, the incorporation of rare metal elements such as La, Ce, Nd, and Sm through doping not only offers a solution to these drawbacks but also serves to enhance the catalyst's basicity, increase its surface area, and reduce particle size, as discussed in references [ 13 ], [ 14 ]. In this study, we aimed to develop a heterogeneous Ce/Mn(10:90)/γ-Al 2 O 3 catalyst for catalysing the transesterification of WCO. This research involved the optimization of catalyst preparation under varying calcination temperatures and loading conditions. Additionally, we explored different reaction parameters, including catalyst loading, methanol-to-oil molar ratio, reaction temperature, and reaction time. To comprehensively evaluate the physical and chemical properties of the prepared catalysts, various characterization techniques were employed. These included X-ray diffraction (XRD), CO 2 -temperature programmed desorption (CO 2 -TPD), N 2 adsorption-desorption, field emission scanning electron microscopy coupled with energy dispersive spectrometer (FESEM-EDX), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Our aim was to gain a thorough understanding of the catalytic activity with catalysts' structural and chemical attributes. Experimental 2.1 Chemicals and Reagents WCO was used as feedstock and obtained from domestic area in Johor Bahru, Johor, Malaysia. The obtained WCO was filtered to remove solid particles before heated at 100 o C for 1 h to remove moisture content. The TAN value for fresh WCO was measured at 1.65 mg KOH/g. The WCO was then treated with 0.8 mL 0.4% NH 3 -PEG diluted in 100 mL of isopropanol to reduce the amount of free fatty acid. The final TAN value for the treated WCO was 1.12 mg KOH/g. For catalyst preparation, manganese nitrate tetrahydrate Mn(NO 3 ) 2 .4H 2 O was used as the based catalyst, while cerium nitrate hexahydrate Ce(NO 3 ) 3 .6H 2 O was used as the dopant. All the chemicals were purchased from Sigma Aldrich. Gamma-aluminum oxide beads, γ-Al 2 O 3 obtained from Sigma Aldrich with 3.0 mm in diameter was used as catalyst support in this research. Methanol (CH 3 OH) from QReC were utilized as a reactant and solvent in the transesterification process, respectively. 2.2 Catalyst Preparation All the prepared catalysts were synthesized by incipient wetness impregnation method. 5 g of Mn(NO 3 ) 2 .4H 2 O and 0.376 g of Ce(NO 3 ) 3 .6H 2 O were dissolved in 5 mL of distilled water each in 100 mL of beaker. The solutions were then mixed together and stirred continuously for 30 min at room temperature. Later, 5 g of alumina beads was immersed into the mixed solution for 1 h. The supported catalyst was then dried in an oven at 80–90℃ for 24 h followed by calcination in the furnace at 700 o C for 5 hrs at a flow rate of 10℃/min. The catalyst was labelled as Ce/Mn(10:90)/γ-Al 2 O 3 . The procedures were repeated for catalyst with Ce loadings of 5–30 wt%, and calcination temperatures of 800-1000 o C. 2.3 Transesterification Reaction The catalytic activity of the prepared catalysts was evaluated via transesterification process of WCO. 6% w/w of catalyst loadings with 1:18 ratio of oil to methanol were prepared and placed in a biodiesel reactor well-equipped with a paraffin oil bath, a magnetic stirrer, a Liebig condenser with two tubings and a thermometer. The reaction of transesterification was carried out in three-necked round bottom flask and the mixture was refluxed at the constant temperature of 65°C in a duration of 3 hrs under continuous magnetic stirring. After 3 hours, the mixture was poured into a separatory funnel for extraction purposes. The desired product, biodiesel, which was placed on top of the layer was collected in a centrifuge tube, whereas the bottom layer, which contained the unwanted glycerol and catalysts, was discarded in a small beaker. Then, the centrifuge tube which filled with the biodiesel was centrifuged at 5000 rpm for 20 mins to remove and separate the unwanted products from the biodiesel. Finally, the biodiesel was transferred into the sample vial and its weight was recorded for calculation purpose. The procedures were repeated for different catalyst loading (3, 6, 10, 15 and 20% w/w), methanol to oil molar ratio (12, 18, 24, 30 and 36), reaction temperature (45, 55, 65 and 75℃) and time (1, 2, 3, 4 and 5 hrs). The obtained biodiesel was further analyzed using Gas Chromatography-Flame Ionization Detector (GC Agilent 6890N model) equipped with MET-Biodiesel capillary column (14 m × 0.53 mm × 16 µ m) with helium as the carrier gas. The oven temperature was set at 200ºC. The column temperature was set with ramp rate 20 ºC/min up to 350ºC for 15 minutes. The maximum temperature of injector and detector were programmed at 350ºC. The sample size injected was 1 µL on-column from 1:1000 µL dilution of sample to n-hexane. 2.4 Characterization Analysis The technique of X-ray diffraction was used to provide information about the crystal structure and particle size. Diffractometer D5000 Siemens Crystalloflex equipped with Cu-K𝛼 radiation over 2θ values between 20° to 80° was utilized to study and measure the pattern of X-ray diffraction. The data was analyzed by using Diffrac Plus software and a comparison between the peak intensity, position and width was made via Powder Diffraction File (PDF) database. Field emission scanning electron microscopy (FESEM) analysis was performed using a scanning electron microscope, a Hitachi SU8020 FESEM integrated with an EDX analyzer to establish the catalysts' morphology, particle size, and shape. To acquire the required magnification image, the sample was bombarded under 25 kV resolution using an electron gun and tungsten filament. Additionally, the catalysts' basicity was assessed by temperature-programmed utilizing a thermal conductivity detector-equipped Micromeritics Autochem 2920 for CO 2 desorption (CO 2 -TPD). Moreover, with the aid of Micromeritics ASAP 2010, the nitrogen sorption analysis (NA) was used to determine the average catalyst's pore size, diameter, volume, type, shape and surface area. Using the Brunauer-Emmett-Teller (BET) approach, the specific surface area was determined from the adsorption curve, whereas employing Barret-Joyner-Hallender (BJH) method aided in the calculation of the pore size distribution from the desorption curve. XPS was preformed and analyzed by Kratos Surface Analysis Spectrometer XSAM HS instrument using Mg-Kα (1253.6 eV) as the X-ray source, while transmission electron microscopy (TEM) was used to measure the particle size, shape and morphology structure of the potential catalysts. It was performed using JEOL-JEM 2100 operated at maximum 200 kV with a theoretical resolution of 0.9 nm. Results and Discussion 3.1 Optimization Parameters In this research, the optimization of catalyst preparation and transesterification reaction conditions were conducted and the studied parameters were the calcination temperatures (700–1000°C), catalyst ratios (70–95 wt%), methanol-oil ratios, reaction temperatures, catalyst dosage and reaction time. The feedstocks used was WCO and its free fatty acid (FFA) composition is tabulated in Table 1 with TAN value of 1.65 mg KOH/g (without treated). It has been demonstrated that the FFA content in WCO includes saturated fatty acids such as palmitic acid (C16:0) and stearic acid (C18:0) with 18 and 16 carbon chains, and the unsaturated fatty acids such as oleic acid (C18:1) and linoleic acid (C18:2). From the table, the major composition of FFA was 39% of palmitic acid and 44% of oleic acid. Table 1 Percent composition of free fatty acid in waste cooking oil Free fatty acid component Composition (%) Palmitic acid (C16:0) 39 Stearic acid (C18:0) 4 Oleic acid (C18:1) 44 Linoleic acid (C18:2) 13 3.1.1 Effect of Calcination Temperatures towards Ce/Mn (10:90)/γ-Al 2 O 3 catalyst The bimetallic oxide Ce/Mn/γ-Al 2 O 3 catalyst with 10:90 ratio was synthesized at different calcination temperatures (700–1000°C). Figure 1 illustrates a noticeable increase in the TG conversion of the Ce/Mn (10:90)/γ-Al 2 O 3 catalyst with rising calcination temperature. Specifically, the catalytic activity of Ce/Mn (10:90)/γ-Al 2 O 3 catalyst increased from 89.7–95.4% when the catalyst was calcined at 700°C to 800°C. However, beyond 800°C, there was a decline in TG conversion to 91.9%, attributed to significant active site deformation at higher temperatures. The calcination temperature, according to Roy et al. [ 15 ] is a crucial factor in regulating surface defects and the interaction between metal oxides. 3.1.2 Effect of Dopant Loadings in Ce/Mn/γ-Al 2 O 3 Catalyst The prepared catalysts of Ce/Mn/γ-Al 2 O 3 calcined at 800°C were optimized in different ratio to based loadings. The studied ratios are 5:95, 10:90, 20:80 and 30:70 wt%. The purpose of this study is to investigate the role of dopant loading on the performance of catalytic activity towards transesterification reaction of WCO. Figure 2 shows the trend of TG conversion over different ratio loadings. Overall, the similar trends of increasing and decreasing of catalytic activity were observed for the Ce/Mn/γ-Al 2 O 3 catalyst. According to Fig. 2 , the TG conversion demonstrated an increase from 93.0–95.4% as the Ce loading in Ce/Mn/γ-Al 2 O 3 catalyst increased from 5 to 10 wt%. This enhancement in the conversion could be attributed to the greater dispersion of active sites on the catalyst surface, as proposed by Nasreen et al.[ 16 ] The decreasing of TG conversion to about 88% was observed when the Ce loading beyond 10 wt % was used. The decline was likely due to an excess of Ce loading which could probably lead to the blocking the active sites presence on the catalyst surface as reported by Cannilla et al. [ 17 ]. Therefore, the best Ce/Mn (10:90)/γ-Al 2 O 3 catalyst 3.1.3 Effect of Reaction Temperatures The efficiency and performance of transesterification of WCO are influenced by the reaction temperature. To see how temperature affects the conversion of triglyceride, the reaction was studied at temperatures ranging from 45 to 85°C. Figure 3 demonstrates the trend of TG conversion on the different reaction temperatures. The boiling point of methanol is 68 o C. Generally, the conversion exhibited an increasing trend until reaching an optimal level. It can be observed that an increasing trend in conversion occurred as the temperature increased, reaching its optimum at 65°C with a remarkable 95.4% TG conversion, significantly affecting the conversion rate. The higher temperature allow for more active particle movement and more collisions between particles, thus accelerating the reaction. However, as expected, the conversion begins to decrease beyond 65 o C. The reaction temperature should be kept below the boiling point of methanol to prevent the evaporation of the alcohol. These findings align with prior research by Foroutan et. al. and Karthikeyan et al. [ 18 ], [ 19 ]. 3.1.4 Effect of Catalyst loading Optimal catalyst dosage not only enhances biodiesel production but also prevents the soaping reaction that can occur during the biodiesel production process, as reported by Seffati et al. [ 20 ]. Therefore, this research was investigated the effect of catalyst dosage on TG conversion efficacy, utilizing varying dosages of Ce/Mn(10:90)/γ-Al 2 O 3 catalyst in the range of 3 to 20 wt. %. Other conditions, including a reaction temperature of 65°C of and 18:1 methanol to oil ratio were kept constant at 1 h. The catalyst was calcined at 800 o C for 5 hrs. Figure 4 demonstrated that the transesterification reaction strictly depends upon the amount of catalyst applied. It can be seen that the conversion of TG increases with increasing catalyst dosage up to a certain point. This phenomenon may be attributed to a mixing problem involving the reaction product and solid catalyst. Utilizing 3 wt. % catalysts in the reaction, resulted in a conversion of up to 79.04%. Further increase in catalyst dosage to 10 wt. % yielded a conversion of up to 95.91%. This improvement could be attributed to the increasing number of active sites found on the catalyst surface which could then help boosting the transesterification reaction as stated by Eldiehy et al. [ 21 ]. However, a further increase in the catalyst dosage to 15 wt. % and 20 wt. %, reduced the conversion of TG (88%). This decrease may be attributed to the rising fluid viscosity of the reaction medium, hindering mass transfer between oil catalyst and methanol as suggested by Sahani et al. [ 22 ]. 3.1.5 Effect of Oil to Methanol Ratio The molar ratio is a significant parameter affecting the efficiency of biodiesel production. Generally, transesterification reaction is a reversible reaction; meaning that the excessive amount of alcohol favors the reaction. Methanol, in particular, enhances the efficiency of this process. The impact of the methanol to oil ratio on TG conversion from waste cooking oil is illustrated in Fig. 5 . The result indicates that an increase in methanol to oil ratio from 12:1 to 24:1 increased the TG conversion. The ratio of 24:1 yielded the highest conversion of 96.07%. However, further increases led to a decrease in TG conversion. This was due to the fact that when methanol level is increased, glycerol became extensively dissolved in the excess methanol, preventing methanol from interacting with the catalyst and thus lowering the catalyst activity as stated by Bai et al. [ 23 ]. 3.1.6 Effect of Reaction Time The reaction time holds significant economic importance and contributes to energy savings in biodiesel production. Its impact on biodiesel efficiency was investigated by conducting tests across varied reaction times ranging from 1 to 5 hrs, while other conditions were kept at constant as optimized (reaction temperature at 65°C, methanol to oil ratio was 24:1 and 10 wt. % catalyst dosage). As shown in Fig. 6 , at 1 h reaction time, about 96% of TG conversion was recorded and this remained relatively stable until 3 hrs reaction time. Similar observation was made by Roy et al. [ 15 ]. Prolonged the reaction time beyond 3 hrs led to a reduction in conversion percentage. This can be attributed to the reaction reaching equilibrium, and initiating the occurrence of reverse reaction [ 24 ]. Based on this observation, it can be concluded that a 1 h retention time is sufficient for the transesterification of WCO in this study. 3.2 Reusability Testing Reusability is one of the most vital parameters of the solid catalyst as their effectiveness rely on its stability. Indeed, a highly stable catalyst can significantly reduce the cost of biodiesel production. After the first reaction, the Ce/Mn (10:90)/γ-Al 2 O 3 catalyst was filtered and washed several times with methanol to eliminate the organic filths residue adsorbed on the catalyst surface before dried at 90°C in the oven for an overnight. The catalyst was then reused for another transesterification reaction with new WCO and methanol loaded in similar amount to the initial reaction. The results showed that the Ce/Mn (10:90)/γ-Al 2 O 3 catalyst can be recycled up to 4 cycles with TG conversion maintained above 94%. However, a slight decrease in conversion was observed in the 6th cycles (about 88%). This decline could be attributed to the deactivation of active catalytic sites caused by the leaching of active compounds into the oil medium. It can be summarized from the results obtained in Figs. 1 – 7 , the optimum conditions for producing biodiesel from WCO using Ce/Mn (10:90)/γ-Al 2 O 3 catalyst are with reaction temperature 65 o C for 1 h, the methanol to oil ratio of 24:1 and a catalyst dosage of 10 wt%. The catalyst was calcined at 800 o C for 5 hrs and can be reused up to 5 cycles without deterioration. 3.3 Characterization Analysis 3.3.1 Nitrogen Sorption Analysis The BET surface area, size and pore volume of the prepared Ce/Mn (10:90)/γ-Al 2 O 3 catalyst are recorded in Table 2 . Precisely, the elevation of the calcination temperatures over Ce/Mn (10:90)/γ-Al 2 O 3 catalyst showed significant effect on the surface area. As shown in Table 2 , the Ce/Mn (10:90)/γ-Al 2 O 3 catalyst calcined at 700ºC having surface area of 128 m 2 /g. After calcination of the catalyst at 800ºC, it displayed slight increase in the surface area to 143 m 2 /g. This result is in a harmony with the TG activity toward the calcination temperature whereby the conversion of TG increases as the calcination temperature rises from 700ºC (89.78%) to 800ºC (95.40%). It has been shown that the surface area is part of the important factors that led to higher catalytic activity in accordance with results obtained by Nasreen et al. [ 16 ]. Table 2 Textural properties prepared catalysts calcined at different temperatures and ratios Catalyst Calcination temperature (ºC) Surface area (SV) (m 2 / g) Average pore size (nm) Total pore volume (cm 2 /g) Total basicity (mmol/g) Ce/Mn(10:90)/γ-Al 2 O 3 700 128 10.9 0.44 0.839 Ce/Mn(10:90)/γ-Al 2 O 3 800 143 8.8 0.46 1.543 Ce/Mn(10:90)/γ-Al 2 O 3 900 97 15.0 0.43 0.641 Ce/Mn(20:80)/γ-Al 2 O 3 800 127 11.1 0.46 0.636 Ce/Mn(5:95)/γ-Al 2 O 3 800 128 10.8 0.43 - Nevertheless, the calcination temperature’s elevation to 900ºC led to a decreased surface area to 97 m 2 /g result from the sintering effect as demonstrated by Tan et al.[ 11 ]and Roy et al [ 15 ].This can be attributed to the closure of fine pores on the surface of catalyst. The surface area of Ce/Mn (5:95)/γ-Al 2 O 3 (128 m 2 /g) and Ce/Mn (20:80)/γ-Al 2 O 3 catalysts (127 m 2 /g) was lower compared to the surface area of Ce/Mn (10:90)/γ-Al 2 O 3 catalyst even when calcined at the same temperature of 800 o C. The lower surface area is the reason for the decreased activity of the catalyst as shown in Fig. 8. This may be due to the diffusion limitation between the reactants and the active sites located in the catalyst pores as reported by Eldiehy et al. [ 21 ]. The surface area is inversely proportional to the pore diameter of the catalyst. The higher surface area can be achieved by a smaller of the pore diameter. It can be seen in Table 2 that smaller pore diameter (8.8 nm) was observed for the catalyst with highest surface area, Ce/Mn (10:90)/γ-Al 2 O 3 (800 o C). When increasing calcination temperatures up to 900ºC, the pore diameters also increase to 15.0 nm. This observation is attributable to the decreased number of pores in the samples. However, from the pore size distribution plot in Fig. 8a, the pore size of the catalyst was mostly below 50 nm, presented a mesoporous structure of the catalyst. Furthermore, the total pore volume over Ce/Mn (10:90)/γ-Al 2 O 3 rise up from 0.438 cm 3 /g to 0.462 cm 3 /g as the calcination temperature increased from 700ºC to 800ºC and slightly decreased to 0.428 cm 3 /g (900ºC). The high surface area and pore volume of the Ce/Mn (10:90)/γ-Al 2 O 3 catalyst calcined at 800ºC are believed to be an important factor for solid catalysts which affects the catalytic activity by offering a number of reachable active species. The connection between the high surface area and the pore volume was proportionate to each other. The total pore volume for Ce/Mn (5:95)/γ-Al 2 O 3 and Ce/Mn (20:80)/γ-Al 2 O 3 catalysts were found to be approximately similar, which are about 0.43 cm 3 /g and 0.45 cm 3 /g, respectively. Based on Fig. 8, all the prepared Ce/Mn/γ-Al 2 O 3 catalysts exhibited a type IV isotherm with hysteresis type H4. This feature is typical of mesoporous material with slit-shaped pore that provided the optimal pore size to adsorb the reacting gas species on the catalyst surface as suggested by Ryu et al. [ 25 ]A stepwise multilayer adsorption process is represented by type IV, and it takes place on a solid which has slit-shaped pores of variable size and shape. Based on isotherm plot, the P/P o hysteresis closure point increases as the calcination raised from 700°C to 900°C. The closure hysteresis at high P/Po of Ce/Mn (10:90)/γ-Al 2 O 3 catalyst calcined at 800°C revealed the contraction and slow re-expansion of the pore adsorbent showed the pore adsorbent's contraction and ensuring gradual re-expansion. 3.3.2 X-Ray Diffraction The crystalline phases and structure of the prepared catalysts were investigated using X-ray powder diffraction (XRD) analysis. Figure 9 displays the XRD patterns of Ce/Mn/γ-Al 2 O 3 catalysts subjected to different calcination temperatures (700°C, 800°C, and 900°C) and dopant loadings (10–20 wt%). The XRD peak analysis of the Ce/Mn(10:90)/γ-Al 2 O 3 catalyst calcined at 700°C (Fig. 9a) revealed the diffraction pattern of Al 2 O 3 (JCPDS 35–0121). The five peaks at 2θ values of 32.7°, 37.80°, 39.55°, 45.99° and 67.07° corresponding to the oriented growth and can be perfectly indexed to the cubic crystal face of (022), (131), (222), (040) and (044), respectively Meanwhile, MnO 2 , identified by its tetragonal crystal structure (JCPDS 151–3978), displays four diffraction peaks at 2θ values of 37.59°, 42.04°, 56.42° and 67.71°, accurately aligned with lattice planes (121), (031), (060) and (710). Additional analysis identifies cubic Mn 2 O 3 (JCPDS 151–4239) exhibiting distinct peaks at 2θ values of 23.13°, 32.95°, 38.23°, 49.55°, and 55.18°, with (121), (222), (040), (143), and (044) lattice planes. Orthorhombic Mn 3 O 4 is observed with two diffraction peaks at 2θ values of 33.52° (023) and 45.00° (132). Meanwhile, hexagonal CeO 2 shows peaks at 2θ values of 32.0° (101) and 55.51° (444). The same pattern was observed for the Ce/Mn(10:90)/γ-Al 2 O 3 catalyst calcined at 800 o C. However, at a calcination temperature of 900 o C, the peaks corresponding to Mn 2 O 3 (c) and CeO 2 (h) were absent, which might be the reason of decreasing the catalytic activity (Fig. 1 ). Hence, it can be concluded that these two species significantly contribute to enhancing the biodiesel activity. Figure 9 . XRD diffractograms for Ce/Mn(10:90)/γ-Al 2 O 3 calcined at temperatures of (a) 700 °C, (b) 800°C, and (c) 900°C while, and d) Ce/Mn(20:80)/γ-Al 2 O 3 catalysts 3.3.3 X-Ray Photoelectron Spectroscopy Analysis Figure 10 depicts the narrow scan for each element of Al 2 p , O 1 s , Mn 2 p and Ce 3 d over Ce/Mn (10:90)/γ-Al 2 O 3 catalyst calcined at temperature of 700, 800 and 900ºC. The binding energy recorded from XPS was compared with the binding energy from National Institute of Standards and Technology (NIST). The XPS spectra of Ce/Mn (10:90)/γ-Al 2 O 3 catalyst calcined at 700ºC to 900ºC, display one peak of Al 2 p . The peak detected at binding energy around 74 eV was attributed to the Al 2 O 3 species when comparing to the binding energy obtained from NIST database and also demonstrated by Djebaili et al. [ 26 ]. This is in line with the result obtained from XRD in Fig. 9 whereby only one species of Al 2 O 3 was detected in the catalyst samples. For O 1 s exhibits three overlying deconvoluted peaks at binding energies of 529 to 532 eV corresponding to the various molecular oxygen species attached to the metal oxide on the surface of catalyst. As reported by Zhang et al. [ 27 ] and Deraz et al. [ 28 ], the binding energies for O 1 s at 529.8- 530.9 eV was allotted to lattice oxygen (O lat ), 531.12 to 531.16 eV for surface-adsorbed oxygen (O ads ) and 532.13 eV for surface-adsorbed molecular water (O surf ). The deconvolution of the Mn 2 p signal revealed three distinct peaks, correspond to a doublet splitting of 2 p 3/2 and 2 p 1/2 with binding energy difference of 12 eV. These peaks were identified as representing the Mn 2+ , Mn 3+ , and Mn 4+ oxidation states, consistent with findings from XRD analysis. Specifically, the binding energy peak at 644 eV is attributed to Mn 4+ , indicative of the MnO 2 species presence in Ce/Mn(10:90)/γ-Al 2 O 3 catalyst. The deconvoluted peaks at 641.6 and 639.8 eV correspond to Mn 3+ and Mn 2+ , respectively which are associated with the Mn 3 O 4 species, a mixture of MnO and Mn 2 O 3 . Notably, the Mn 3+ composition predominates in catalyst calcined at 700℃, while calcination at 900℃ results in the absence of Mn 2 O 3 (Fig. 9a), leading to a diminished presence of Mn 3+ . Meanwhile, the oxidation state of cerium is identified through Ce 3 d 5/2 and 3 d 3/2 spin-orbit states, with a splitting of 19.80 eV[ 27 ], as illustrated in Fig. 10 . All observed peaks correspond to the Ce 4+ oxidation state, confirming the presence of CeO 2 species, which is in line with the results from XRD analysis. Although CeO 4 did not exhibit crystalline peaks in the XRD pattern (Fig. 9) and appeared amorphous, its presence was still detected through XPS due to the technique's high sensitivity to chemical information. The first two peaks on the left, with binding energies of 902.1 and 907.2 eV, are attributed to Ce 3 d 5/2 of the (5 d 6 s )⁰ 4 f ² O 2 p ⁴ and (5 d 6 s )⁰ 4 f ¹ O 2 p ⁵ configurations, while the peak at 914.1 eV is associated with the Ce 4 f ²-O 2 p ⁵ configuration. 3.3.4 Field emission scanning electron microscopy The morphology of the Ce/Mn/γ-Al 2 O 3 catalyst at varying dopant ratios and calcination temperatures is depicted in Fig. 11 . The images show that the catalyst particles are agglomerated on the surface, giving the catalyst a rough morphology. The FESEM image of the Ce/Mn (10:90)/γ-Al 2 O 3 catalyst calcined at 700°C (Fig. 11 a) reveals a non-uniform structure with a variety of average particle diameters from 8 to 11 nm. As the calcination temperature rose to 800°C, a uniformly distributed surface morphology with smaller particles was observed. It could provide a greater specific surface area as reported by Deraz et al. and Ullaz et al.[ 29 ] [ 30 ] This result correlates with N 2 sorption analysis in Table 2 , which showed that the Ce/Mn (10:90)/γ-Al 2 O 3 catalyst calcined at 800°C had the highest surface area and displayed porous characteristics that contributed to its catalytic activity in transesterifying waste cooking oil. Therefore, the catalytic activity of the Ce/Mn (10:90)/γ-Al 2 O 3 catalyst was maximized at a calcination temperature of 800°C. In contrast, the surface morphology displayed in Fig. 11 c shows crystallites with a densely packed arrangement, indicating the formation of larger particles due to the sintering effect. This resulted in a reduction of surface area to 92 cm 2 /g for the catalyst calcined at 900°C. A similar surface morphology was observed for the Ce/Mn(5:95)/γ-Al 2 O 3 and Ce/Mn(20:80)/γ-Al 2 O 3 catalysts. 3.3.5 Transmission Electron Microscopy Transmission Electron Microscopy (TEM) images of Ce/Mn (10:90)/γ-Al 2 O 3 subjected to various calcination temperatures are presented in Figs. 12 – 14 . The TEM images reveal a range of morphologies, including nanorod-like particles across the catalysts. Specifically, the Ce/Mn (10:90)/γ-Al 2 O 3 particles calcined at 700°C (Fig. 12 ) and 800°C (Fig. 13 ) have sizes ranging from 2 to 4 nm. For the catalyst calcined at 900°C, TEM images display an agglomeration of irregularly shaped particles with sizes between 3 and 5 nm (Fig. 14 ). These observations are consistent with FESEM results, which indicate an increase in particle size with higher calcination temperatures. The High-Resolution Transmission Electron Microscopy (HRTEM) visualization of the Ce/Mn(10:90)/ Al 2 O 3 catalyst calcined at 800℃ is illustrated in Fig. 13 , revealing discernible lattice spacings of 0.156 nm, 0.168 nm, and 0.2 nm. These measurements consistently align with the respective values associated with (121) tetragonal MnO 2 , (044) cubic Mn 2 O 3 , and (023) orthorhombic Mn 3 O 4 . Additionally, a lattice fringe measured at 0.13 nm corresponds to the d -spacing of the Al 2 O 3 (044) plane, while a d -spacing of 0.27 nm is identified with the (101) planes of CeO 2 . This structural representation confirms the presence of cerium and manganese oxides on the surface of alumina support, corroborating the X-Ray Diffraction (XRD) data. The same species were observed in the catalyst calcined at 700°C. Conversely, the HRTEM image did not detect the lattice fringes of CeO 2 and Mn 2 O 3 on the catalyst calcined at 900°C (Fig. 14 ), reinforcing the findings from the XRD analysis. 3.3.6 CO 2 -Temperature Programmed Desorption (CO 2 -TPD) The CO 2 -TPD analysis was conducted to investigate the basicity of the synthesized Ce/Mn (10:90)/γ-Al 2 O 3 catalyst. Figure 15 illustrates the CO 2 -TPD profiles, while the total basicity is shown in Table 2 . Basicity is an essential property influencing the catalytic performance, particularly in transesterification reactions [ 27 ]. As shown in Fig. 15 , the CO 2 -TPD profile for the Ce/Mn (10:90)/γ-Al 2 O 3 catalyst reveals a variety of desorption peaks, indicating the presence of basic sites with different strengths. Each catalyst typically displayed three main CO 2 desorption peaks. The peak at below 180°C was associated with weak basic sites. These sites are crucial for initial adsorption and activation of reactants. Intermediate basic sites, with CO 2 desorption between 180°C and 630°C, offer moderate strength and play a significant role in facilitating various reaction steps. Desorption of CO 2 above 630°C was attributed to adsorption at strong basic sites, as reported by Ma et al. [ 31 ] are essential for breaking stronger bonds in the reactants, thus enhancing catalytic activity. Catalysts with a higher proportion of intermediate and strong basic sites are expected to exhibit better performance in transesterification due to their enhanced ability to activate and transform reactant molecules. All identified basic sites were linked to the contributions of the individual oxides of manganese and cerium on the surface of catalyst. From the Table 2 , the total basicity follows the order of Ce/Mn (10:90)/γ-Al 2 O 3 800 o C (1.543 mmol/g) > 700 o C (0.839 mmol/g) > 900 o C (0.641 mmol/g) ~ Ce/Mn (20:80)/γ-Al 2 O 3 (0.636 mmol/g). The data suggest that calcining the Ce/Mn (10:90)/γ-Al 2 O 3 catalyst at 800°C provides the highest total basicity. This temperature appears to be optimal for generating a high number of active basic sites without causing detrimental structural changes that reduce basicity. At 900°C, the significant drop in total basicity indicates that this temperature may be too high, potentially causing sintering or other structural effects that diminish the number of active sites. This statement can be supported with the data obtained from FESEM, XRD and XPS analysis. The absence of Mn 2 O 3 and CeO 2 species resulted in reduced basicity, leading to lower catalytic performance. In conclusion, the total basicity data highlight the importance of calcination temperature in optimizing the basic properties of Ce/Mn/γ-Al 2 O 3 catalysts. Calcining at 800°C is shown to be the most effective for maximizing total basicity and, consequently, catalytic activity. Conclusion In these studies, a Ce/Mn catalyst supported on alumina was effectively employed to transesterify waste cooking oil into biodiesel. The Ce/Mn/γ-Al₂O₃ catalyst, with a Ce-to-Mn molar ratio of 10:90 and calcined at 800°C, achieved over 96% triglyceride (TG) conversion under optimal conditions: a reaction temperature of 65°C, a methanol-to-oil ratio of 24:1, and a reaction time of 3 hours. This high efficiency is attributed to the catalyst's large surface area of 143 m 2 /g with small particle size 8.8 nm and high basicity about 1.543 mmol/g. Notably, the Ce/Mn(10:90)/γ-Al₂O₃ catalyst demonstrated excellent reusability, maintaining high triglyceride conversion rates across seven cycles, with only a slight decrease from 97–94%, likely due to a gradual reduction in basic sites. This makes Ce/Mn(10:90)/γ-Al₂O₃ a promising catalyst for the cost-effective conversion of waste cooking oil into biodiesel. Declarations Acknowledgements This work was supported by the Universiti Teknologi Malaysia for UTM-FR PY/2019/01760 (21H03). thanks, Jazan University for financial support and thanks the Saudi Arabian Cultural Mission (SACM). Author contributions Nashwa Alahmar: Conceptualization, Investigation, Resources, Writing – original draft Software. Nur Izyan Binti Wan Azelee :Funding acquisition . Susilawati Toemen : Project administration. Conflicts of Interest All authors declare that there is no conflict of interest Data Availability All data are represented in the manuscript there is no additional supported data References N. F. Sulaiman, W. A. W. Abu Bakar, and R. Ali, “Response surface methodology for the optimum production of biodiesel over Cr/Ca/gamma-Al2O3 catalyst: Catalytic performance and physicochemical studies,” Renew Energy , vol. 113, pp. 697–705, Dec. 2017, doi: 10.1016/j.renene.2017.06.007. O. Farobie and E. 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Additional Declarations No competing interests reported. Cite Share Download PDF Status: Published Journal Publication published 02 Jan, 2025 Read the published version in Scientific Reports → Version 1 posted Editorial decision: Revision requested 15 Oct, 2024 Reviews received at journal 14 Oct, 2024 Reviews received at journal 13 Oct, 2024 Reviewers agreed at journal 04 Oct, 2024 Reviewers agreed at journal 04 Oct, 2024 Reviewers invited by journal 04 Oct, 2024 Editor assigned by journal 04 Oct, 2024 Editor invited by journal 04 Oct, 2024 Submission checks completed at journal 02 Oct, 2024 First submitted to journal 26 Sep, 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. 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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-5158584","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":366315914,"identity":"6cc72ac2-fc65-4019-82eb-3414602e47d9","order_by":0,"name":"Nashwa Mohammed Alahmar","email":"","orcid":"","institution":"Universiti Teknologi Malaysia","correspondingAuthor":false,"prefix":"","firstName":"Nashwa","middleName":"Mohammed","lastName":"Alahmar","suffix":""},{"id":366315915,"identity":"f1a9d808-703d-4b8b-96c8-9e5d6767cb61","order_by":1,"name":"Nur Izyan Binti Wan Azelee","email":"","orcid":"","institution":"Universiti Teknologi 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11:47:34","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":66109,"visible":true,"origin":"","legend":"\u003cp\u003eThe effect of reaction temperature towards transesterification reaction over Ce/Mn (10:90)/γ-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst [Constant conditions: methanol to oil ratio of 18:1 for 1 h using 6 wt% catalyst dosage, the catalyst calcined at 800℃ for 5 hrs]\u0026nbsp;\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-5158584/v1/b9fb11640fda978b676ce5e3.png"},{"id":68824357,"identity":"18ccf93f-3440-42f6-ae4a-028017d62e6b","added_by":"auto","created_at":"2024-11-12 11:47:34","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":58972,"visible":true,"origin":"","legend":"\u003cp\u003eThe effect of Ce/Mn(10:90)/g-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3 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hrs]\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-5158584/v1/9c89421a9fbffea9126e21ab.png"},{"id":68825261,"identity":"6a92f603-6883-4d71-83da-576f9f28930e","added_by":"auto","created_at":"2024-11-12 11:55:34","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":58022,"visible":true,"origin":"","legend":"\u003cp\u003eThe effect of reaction time towards transesterification reaction [Constant conditions: methanol to oil ratio of 24:1 at 65\u003csup\u003eo\u003c/sup\u003eC 10 wt% loading of catalyst calcined at 800℃ for 5 hrs]\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-5158584/v1/742c0e44325de1c2783f50ba.png"},{"id":68825562,"identity":"6ba4d3ca-6e11-47f6-ab53-7de70a1322a8","added_by":"auto","created_at":"2024-11-12 12:03:34","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":61596,"visible":true,"origin":"","legend":"\u003cp\u003eThe reusability test over Ce/Mn(10:90)/γ-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u0026nbsp;catalyst calcined at 800°C for 5 hrs [Constant conditions: methanol to oil ratio of 24:1 at 65\u003csup\u003eo\u003c/sup\u003eC for 1 h using 10 wt% loading of catalyst calcined at 800℃ for 5 hrs]\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-5158584/v1/7cac84f88a844e2ea10b2323.png"},{"id":68825563,"identity":"b2dd5824-ee11-4593-a3cd-a134c5555523","added_by":"auto","created_at":"2024-11-12 12:03:34","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":264249,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Pore size distribution and (b) Isotherms over Ce/Mn/gAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-5158584/v1/bebab60414a895387f771bbe.png"},{"id":68825264,"identity":"6e0e9763-4ab3-4624-9a83-582f3dfae4c4","added_by":"auto","created_at":"2024-11-12 11:55:34","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":188053,"visible":true,"origin":"","legend":"\u003cp\u003eXRD diffractograms for Ce/Mn(10:90)/g-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e calcined at temperatures of (a) 700 °C, (b) 800°C, and (c) 900°C while, and d) Ce/Mn(20:80)/g-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalysts\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-5158584/v1/a5178afb7d62c599a8101704.png"},{"id":68827002,"identity":"fe8d62d9-790a-4193-ac31-eceda2621a05","added_by":"auto","created_at":"2024-11-12 12:11:34","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":494129,"visible":true,"origin":"","legend":"\u003cp\u003eThe narrow scan of Al 2\u003cem\u003ep\u003c/em\u003e, O 1\u003cem\u003es\u003c/em\u003e, Mn 2\u003cem\u003ep\u003c/em\u003e and Ce 3\u003cem\u003ed\u003c/em\u003e from XPS spectra for Ce/Mn (10:90)/γ-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst calcined at temperatures of (a) 700, (b) 800 and (c) 900ºC for 5 hours\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-5158584/v1/1ac9da30fcdbcd1506a9d79a.png"},{"id":68825267,"identity":"f0965a27-2287-4e79-bd94-8c981881183a","added_by":"auto","created_at":"2024-11-12 11:55:34","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":1971599,"visible":true,"origin":"","legend":"\u003cp\u003eFESEM image of Ce/Mn(10:90)/γ-Al2O3 at calcination temperatures of (a) 700℃, (b) 800℃ (c) 900℃ and (d) Ce/Mn(5:95)/γ-Al2O3 (e) Ce/Mn(20:80)/γ-Al2O3 catalysts.\u0026nbsp;\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-5158584/v1/38078dfdab48d21898269c9e.png"},{"id":68824362,"identity":"a829256f-495a-4d3e-ad2c-f2da230e64cb","added_by":"auto","created_at":"2024-11-12 11:47:34","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":1828249,"visible":true,"origin":"","legend":"\u003cp\u003eTEM image for Ce/Mn 10:90)/γ- Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u0026nbsp;catalyst calcined at 700 ℃ for 5 hours and HRTEM showing the lattice fringes of (a) Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u0026nbsp;(044), (b) MnO\u003csub\u003e2 \u003c/sub\u003e(121) (c) Mn\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3 \u003c/sub\u003e(044) (d)Mn\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (023) and (e) CeO\u003csub\u003e2\u003c/sub\u003e (101)\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-5158584/v1/9eccc64e26cb60d792a7bd51.png"},{"id":68824359,"identity":"ddb04050-baf9-41f9-89c4-d82f26c90af7","added_by":"auto","created_at":"2024-11-12 11:47:34","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":1827891,"visible":true,"origin":"","legend":"\u003cp\u003eTEM image for Ce/Mn (10:90)/γ-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u0026nbsp;catalyst calcined at 800 °C for 5 hours and HRTEM showing the lattice fringes of (a) Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u0026nbsp;(044), (b) MnO\u003csub\u003e2 \u003c/sub\u003e(121) (c) Mn\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3 \u003c/sub\u003e(044) (d) Mn\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (023) and (e) CeO\u003csub\u003e2\u003c/sub\u003e (101)\u003c/p\u003e","description":"","filename":"13.png","url":"https://assets-eu.researchsquare.com/files/rs-5158584/v1/bed6e67aaca89a27781562a6.png"},{"id":68825565,"identity":"a7187eaf-84c7-4531-8827-95720779a36b","added_by":"auto","created_at":"2024-11-12 12:03:34","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":2937629,"visible":true,"origin":"","legend":"\u003cp\u003eTEM image for Ce/Mn (10:90)/γ-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u0026nbsp;catalyst calcined at 900 C for 5 hours and HRTEM showing the lattice fringes of (a) Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u0026nbsp;(044), (b) MnO\u003csub\u003e2 \u003c/sub\u003e(121) and (c)Mn\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (023)\u003c/p\u003e","description":"","filename":"14.png","url":"https://assets-eu.researchsquare.com/files/rs-5158584/v1/7b1ad4d0f78ac375dfd75fc3.png"},{"id":68824364,"identity":"87dbe047-0269-48aa-9cee-aa4f9c69f894","added_by":"auto","created_at":"2024-11-12 11:47:34","extension":"png","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":176122,"visible":true,"origin":"","legend":"\u003cp\u003eThe CO\u003csub\u003e2\u003c/sub\u003e-TPD profile for Ce/Mn/γ-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u0026nbsp;catalysts with different calcination temperature and dopant ratio to based calcined for 5 hours.\u003c/p\u003e","description":"","filename":"15.png","url":"https://assets-eu.researchsquare.com/files/rs-5158584/v1/73487aa98f9e8d862cfbdaf2.png"},{"id":73093235,"identity":"da3ec35f-d2c4-4a7e-b7cd-2aeee1c0b4d1","added_by":"auto","created_at":"2025-01-06 16:11:33","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":13126307,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-5158584/v1/4de29e36-d202-4dec-80b9-2a6e1962027b.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Advancing Biodiesel Production from Waste Cooking Oil: Optimization and Characterization of Manganese-Based Catalysts","fulltext":[{"header":"Introduction","content":"\u003cp\u003ePetroleum, as known as crude oil, a non-renewable fossil fuel acts as the primary propellent contributing to the transportation sector predominantly. The elevated necessity and substantially reliance on the crude oil endangering the future as this natural resource is facing severe depletion and devitalization [\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e]. This issue prompted the evolution and emergence of the renewable energy supplies and ecologically friendly biomass-derived fuels, also called biodiesel or fatty acid methyl ester (FAME) as the alternative for the petroleum-based fuels, owing to the fact of its properties of being benign, biodegradability, technical viability, lower greenhouse gas (GHG) emissions, and carbon neutrality [\u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e], [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e]. Transesterification process is applied in the generation of biodiesel by reacting the fats and oils, commonly noted as triglycerides, which are normally found in the waste cooking oils, including the vegetable oils and animal fats with methanol to obtain more desired product of methyl esters [\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e] and with the purpose of reducing the kinematic viscosities of vegetable oils or animal fats from higher to lower viscosities range in petrol diesel [\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eThe catalyst, no matter of its properties of being acidic, basic or enzymatic, therefore, plays an important role in speeding up the reaction and enhancing the biodiesel yield. Homogeneous catalysts, especially those in basic form, for example sodium hydroxide, NaOH and sodium ethoxide, C\u003csub\u003e2\u003c/sub\u003eH\u003csub\u003e5\u003c/sub\u003eONa are widely utilized in industrial currently contributes to higher reaction rate with minimal temperature requirements [\u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e]. The catalysts possess high catalytic activity as they are easily soluble in methanol and provide high efficiency in biodiesel conversion. The cost of producing biodiesel could be increased, nevertheless, due to homogeneous base catalyst restrictions, such as wastewater generation from the separation of excessive catalyst and glycerol and low biodiesel yield resulting from the saponification reaction [\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e]. Hence, more reusable and environmentally stable heterogeneous catalysts are introduced to reduce the environmental pollutants.\u003c/p\u003e \u003cp\u003eThe frequent employment of heterogeneous catalysts in the reaction of biodiesel production brings the advantages of high recyclability and reusability, ease of removal of the catalyst and minimal contamination of the finished product [\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e]. Due to their reusability and lack of need for water treatment or purification, solid base heterogeneous catalysts enable simultaneous transesterification and esterification processes and lower production costs. In recent years, a large number of heterogeneous catalysts such as metal oxides, alkaline earth metals, mixed metal oxides, lipase, zeolites and transition metals have been used in laboratory-scale biodiesel production [\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e], [\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e]. Manganese oxide is highly efficient catalyst for biodiesel synthesis and was effective for transesterification at high temperature and pressures, as it could facilitates the conversion of free fatty acids by providing acid and basic sites for the reaction. The catalyst could maintain high water content in the feedstock without losing efficiency [\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e]. It also had a lengthy catalyst life and a low rate of activity loss [\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e].\u003c/p\u003e \u003cp\u003eHowever, undoped MnO has a number of drawbacks in terms of application. The leaching of the undoped catalyst can have a detrimental impact on its catalytic activity, leading to interactions with free fatty acids and consequent soap production, ultimately causing catalyst deactivation. To address these challenges, the incorporation of rare metal elements such as La, Ce, Nd, and Sm through doping not only offers a solution to these drawbacks but also serves to enhance the catalyst's basicity, increase its surface area, and reduce particle size, as discussed in references [\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e], [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e]. In this study, we aimed to develop a heterogeneous Ce/Mn(10:90)/γ-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst for catalysing the transesterification of WCO. This research involved the optimization of catalyst preparation under varying calcination temperatures and loading conditions. Additionally, we explored different reaction parameters, including catalyst loading, methanol-to-oil molar ratio, reaction temperature, and reaction time. To comprehensively evaluate the physical and chemical properties of the prepared catalysts, various characterization techniques were employed. These included X-ray diffraction (XRD), CO\u003csub\u003e2\u003c/sub\u003e-temperature programmed desorption (CO\u003csub\u003e2\u003c/sub\u003e-TPD), N\u003csub\u003e2\u003c/sub\u003e adsorption-desorption, field emission scanning electron microscopy coupled with energy dispersive spectrometer (FESEM-EDX), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS). Our aim was to gain a thorough understanding of the catalytic activity with catalysts' structural and chemical attributes.\u003c/p\u003e"},{"header":"Experimental","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Chemicals and Reagents\u003c/h2\u003e \u003cp\u003eWCO was used as feedstock and obtained from domestic area in Johor Bahru, Johor, Malaysia. The obtained WCO was filtered to remove solid particles before heated at 100\u003csup\u003eo\u003c/sup\u003eC for 1 h to remove moisture content. The TAN value for fresh WCO was measured at 1.65 mg KOH/g. The WCO was then treated with 0.8 mL 0.4% NH\u003csub\u003e3\u003c/sub\u003e-PEG diluted in 100 mL of isopropanol to reduce the amount of free fatty acid. The final TAN value for the treated WCO was 1.12 mg KOH/g. For catalyst preparation, manganese nitrate tetrahydrate Mn(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e.4H\u003csub\u003e2\u003c/sub\u003eO was used as the based catalyst, while cerium nitrate hexahydrate Ce(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e.6H\u003csub\u003e2\u003c/sub\u003eO was used as the dopant. All the chemicals were purchased from Sigma Aldrich. Gamma-aluminum oxide beads, γ-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e obtained from Sigma Aldrich with 3.0 mm in diameter was used as catalyst support in this research. Methanol (CH\u003csub\u003e3\u003c/sub\u003eOH) from QReC were utilized as a reactant and solvent in the transesterification process, respectively.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec4\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Catalyst Preparation\u003c/h2\u003e \u003cp\u003eAll the prepared catalysts were synthesized by incipient wetness impregnation method. 5 g of Mn(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e.4H\u003csub\u003e2\u003c/sub\u003eO and 0.376 g of Ce(NO\u003csub\u003e3\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e.6H\u003csub\u003e2\u003c/sub\u003eO were dissolved in 5 mL of distilled water each in 100 mL of beaker. The solutions were then mixed together and stirred continuously for 30 min at room temperature. Later, 5 g of alumina beads was immersed into the mixed solution for 1 h. The supported catalyst was then dried in an oven at 80\u0026ndash;90℃ for 24 h followed by calcination in the furnace at 700\u003csup\u003eo\u003c/sup\u003eC for 5 hrs at a flow rate of 10℃/min. The catalyst was labelled as Ce/Mn(10:90)/γ-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e. The procedures were repeated for catalyst with Ce loadings of 5\u0026ndash;30 wt%, and calcination temperatures of 800-1000\u003csup\u003eo\u003c/sup\u003eC.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section2\"\u003e \u003ch2\u003e2.3 Transesterification Reaction\u003c/h2\u003e \u003cp\u003eThe catalytic activity of the prepared catalysts was evaluated via transesterification process of WCO. 6% w/w of catalyst loadings with 1:18 ratio of oil to methanol were prepared and placed in a biodiesel reactor well-equipped with a paraffin oil bath, a magnetic stirrer, a Liebig condenser with two tubings and a thermometer. The reaction of transesterification was carried out in three-necked round bottom flask and the mixture was refluxed at the constant temperature of 65\u0026deg;C in a duration of 3 hrs under continuous magnetic stirring. After 3 hours, the mixture was poured into a separatory funnel for extraction purposes. The desired product, biodiesel, which was placed on top of the layer was collected in a centrifuge tube, whereas the bottom layer, which contained the unwanted glycerol and catalysts, was discarded in a small beaker. Then, the centrifuge tube which filled with the biodiesel was centrifuged at 5000 rpm for 20 mins to remove and separate the unwanted products from the biodiesel. Finally, the biodiesel was transferred into the sample vial and its weight was recorded for calculation purpose. The procedures were repeated for different catalyst loading (3, 6, 10, 15 and 20% w/w), methanol to oil molar ratio (12, 18, 24, 30 and 36), reaction temperature (45, 55, 65 and 75℃) and time (1, 2, 3, 4 and 5 hrs). The obtained biodiesel was further analyzed using Gas Chromatography-Flame Ionization Detector (GC Agilent 6890N model) equipped with MET-Biodiesel capillary column (14 m \u0026times; 0.53 mm \u0026times; 16 \u0026micro; m) with helium as the carrier gas. The oven temperature was set at 200\u0026ordm;C. The column temperature was set with ramp rate 20 \u0026ordm;C/min up to 350\u0026ordm;C for 15 minutes. The maximum temperature of injector and detector were programmed at 350\u0026ordm;C. The sample size injected was 1 \u0026micro;L on-column from 1:1000 \u0026micro;L dilution of sample to n-hexane.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section2\"\u003e \u003ch2\u003e2.4 Characterization Analysis\u003c/h2\u003e \u003cp\u003eThe technique of X-ray diffraction was used to provide information about the crystal structure and particle size. Diffractometer D5000 Siemens Crystalloflex equipped with Cu-K\u0026#120572; radiation over 2θ values between 20\u0026deg; to 80\u0026deg; was utilized to study and measure the pattern of X-ray diffraction. The data was analyzed by using Diffrac Plus software and a comparison between the peak intensity, position and width was made via Powder Diffraction File (PDF) database. Field emission scanning electron microscopy (FESEM) analysis was performed using a scanning electron microscope, a Hitachi SU8020 FESEM integrated with an EDX analyzer to establish the catalysts' morphology, particle size, and shape. To acquire the required magnification image, the sample was bombarded under 25 kV resolution using an electron gun and tungsten filament. Additionally, the catalysts' basicity was assessed by temperature-programmed utilizing a thermal conductivity detector-equipped Micromeritics Autochem 2920 for CO\u003csub\u003e2\u003c/sub\u003e desorption (CO\u003csub\u003e2\u003c/sub\u003e-TPD). Moreover, with the aid of Micromeritics ASAP 2010, the nitrogen sorption analysis (NA) was used to determine the average catalyst's pore size, diameter, volume, type, shape and surface area. Using the Brunauer-Emmett-Teller (BET) approach, the specific surface area was determined from the adsorption curve, whereas employing Barret-Joyner-Hallender (BJH) method aided in the calculation of the pore size distribution from the desorption curve. XPS was preformed and analyzed by Kratos Surface Analysis Spectrometer XSAM HS instrument using Mg-Kα (1253.6 eV) as the X-ray source, while transmission electron microscopy (TEM) was used to measure the particle size, shape and morphology structure of the potential catalysts. It was performed using JEOL-JEM 2100 operated at maximum 200 kV with a theoretical resolution of 0.9 nm.\u003c/p\u003e \u003c/div\u003e"},{"header":"Results and Discussion","content":"\u003cdiv id=\"Sec8\"\u003e\n \u003ch2\u003e3.1 Optimization Parameters\u003c/h2\u003e\n \u003cp\u003eIn this research, the optimization of catalyst preparation and transesterification reaction conditions were conducted and the studied parameters were the calcination temperatures (700\u0026ndash;1000\u0026deg;C), catalyst ratios (70\u0026ndash;95 wt%), methanol-oil ratios, reaction temperatures, catalyst dosage and reaction time. The feedstocks used was WCO and its free fatty acid (FFA) composition is tabulated in Table \u003cspan\u003e1\u003c/span\u003e with TAN value of 1.65 mg KOH/g (without treated). It has been demonstrated that the FFA content in WCO includes saturated fatty acids such as palmitic acid (C16:0) and stearic acid (C18:0) with 18 and 16 carbon chains, and the unsaturated fatty acids such as oleic acid (C18:1) and linoleic acid (C18:2). From the table, the major composition of FFA was 39% of palmitic acid and 44% of oleic acid.\u003c/p\u003e\n \u003cdiv\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 1\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003ePercent composition of free fatty acid in waste cooking oil\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"2\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFree fatty acid component\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eComposition (%)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePalmitic acid (C16:0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e39\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eStearic acid (C18:0)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e4\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eOleic acid (C18:1)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e44\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eLinoleic acid (C18:2)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e13\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec9\"\u003e\n \u003ch2\u003e3.1.1 Effect of Calcination Temperatures towards Ce/Mn (10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst\u003c/h2\u003e\n \u003cp\u003eThe bimetallic oxide Ce/Mn/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst with 10:90 ratio was synthesized at different calcination temperatures (700\u0026ndash;1000\u0026deg;C). Figure \u003cspan\u003e1\u003c/span\u003e illustrates a noticeable increase in the TG conversion of the Ce/Mn (10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst with rising calcination temperature. Specifically, the catalytic activity of Ce/Mn (10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst increased from 89.7\u0026ndash;95.4% when the catalyst was calcined at 700\u0026deg;C to 800\u0026deg;C. However, beyond 800\u0026deg;C, there was a decline in TG conversion to 91.9%, attributed to significant active site deformation at higher temperatures. The calcination temperature, according to Roy et al. [\u003cspan\u003e15\u003c/span\u003e] is a crucial factor in regulating surface defects and the interaction between metal oxides.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec10\"\u003e\n \u003ch2\u003e3.1.2 Effect of Dopant Loadings in Ce/Mn/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e Catalyst\u003c/h2\u003e\n \u003cp\u003eThe prepared catalysts of Ce/Mn/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e calcined at 800\u0026deg;C were optimized in different ratio to based loadings. The studied ratios are 5:95, 10:90, 20:80 and 30:70 wt%. The purpose of this study is to investigate the role of dopant loading on the performance of catalytic activity towards transesterification reaction of WCO. Figure \u003cspan\u003e2\u003c/span\u003e shows the trend of TG conversion over different ratio loadings. Overall, the similar trends of increasing and decreasing of catalytic activity were observed for the Ce/Mn/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst.\u003c/p\u003e\n \u003cp\u003eAccording to Fig. \u003cspan\u003e2\u003c/span\u003e, the TG conversion demonstrated an increase from 93.0\u0026ndash;95.4% as the Ce loading in Ce/Mn/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst increased from 5 to 10 wt%. This enhancement in the conversion could be attributed to the greater dispersion of active sites on the catalyst surface, as proposed by Nasreen et al.[\u003cspan\u003e16\u003c/span\u003e] The decreasing of TG conversion to about 88% was observed when the Ce loading beyond 10 wt % was used. The decline was likely due to an excess of Ce loading which could probably lead to the blocking the active sites presence on the catalyst surface as reported by Cannilla et al. [\u003cspan\u003e17\u003c/span\u003e]. Therefore, the best Ce/Mn (10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec11\"\u003e\n \u003ch2\u003e3.1.3 Effect of Reaction Temperatures\u003c/h2\u003e\n \u003cp\u003eThe efficiency and performance of transesterification of WCO are influenced by the reaction temperature. To see how temperature affects the conversion of triglyceride, the reaction was studied at temperatures ranging from 45 to 85\u0026deg;C. Figure \u003cspan\u003e3\u003c/span\u003e demonstrates the trend of TG conversion on the different reaction temperatures. The boiling point of methanol is 68\u003csup\u003eo\u003c/sup\u003eC. Generally, the conversion exhibited an increasing trend until reaching an optimal level.\u003c/p\u003e\n \u003cp\u003eIt can be observed that an increasing trend in conversion occurred as the temperature increased, reaching its optimum at 65\u0026deg;C with a remarkable 95.4% TG conversion, significantly affecting the conversion rate. The higher temperature allow for more active particle movement and more collisions between particles, thus accelerating the reaction. However, as expected, the conversion begins to decrease beyond 65\u003csup\u003eo\u003c/sup\u003eC. The reaction temperature should be kept below the boiling point of methanol to prevent the evaporation of the alcohol. These findings align with prior research by Foroutan et. al. and Karthikeyan et al. [\u003cspan\u003e18\u003c/span\u003e], [\u003cspan\u003e19\u003c/span\u003e].\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec12\"\u003e\n \u003ch2\u003e3.1.4 Effect of Catalyst loading\u003c/h2\u003e\n \u003cp\u003eOptimal catalyst dosage not only enhances biodiesel production but also prevents the soaping reaction that can occur during the biodiesel production process, as reported by Seffati et al. [\u003cspan\u003e20\u003c/span\u003e]. Therefore, this research was investigated the effect of catalyst dosage on TG conversion efficacy, utilizing varying dosages of Ce/Mn(10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst in the range of 3 to 20 wt. %. Other conditions, including a reaction temperature of 65\u0026deg;C of and 18:1 methanol to oil ratio were kept constant at 1 h. The catalyst was calcined at 800\u003csup\u003eo\u003c/sup\u003eC for 5 hrs.\u003c/p\u003e\n \u003cp\u003eFigure \u003cspan\u003e4\u003c/span\u003e demonstrated that the transesterification reaction strictly depends upon the amount of catalyst applied. It can be seen that the conversion of TG increases with increasing catalyst dosage up to a certain point. This phenomenon may be attributed to a mixing problem involving the reaction product and solid catalyst. Utilizing 3 wt. % catalysts in the reaction, resulted in a conversion of up to 79.04%. Further increase in catalyst dosage to 10 wt. % yielded a conversion of up to 95.91%. This improvement could be attributed to the increasing number of active sites found on the catalyst surface which could then help boosting the transesterification reaction as stated by Eldiehy et al. [\u003cspan\u003e21\u003c/span\u003e]. However, a further increase in the catalyst dosage to 15 wt. % and 20 wt. %, reduced the conversion of TG (88%). This decrease may be attributed to the rising fluid viscosity of the reaction medium, hindering mass transfer between oil catalyst and methanol as suggested by Sahani et al. [\u003cspan\u003e22\u003c/span\u003e].\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec13\"\u003e\n \u003ch2\u003e3.1.5 Effect of Oil to Methanol Ratio\u003c/h2\u003e\n \u003cp\u003eThe molar ratio is a significant parameter affecting the efficiency of biodiesel production. Generally, transesterification reaction is a reversible reaction; meaning that the excessive amount of alcohol favors the reaction. Methanol, in particular, enhances the efficiency of this process. The impact of the methanol to oil ratio on TG conversion from waste cooking oil is illustrated in Fig. \u003cspan\u003e5\u003c/span\u003e. The result indicates that an increase in methanol to oil ratio from 12:1 to 24:1 increased the TG conversion. The ratio of 24:1 yielded the highest conversion of 96.07%. However, further increases led to a decrease in TG conversion. This was due to the fact that when methanol level is increased, glycerol became extensively dissolved in the excess methanol, preventing methanol from interacting with the catalyst and thus lowering the catalyst activity as stated by Bai et al. [\u003cspan\u003e23\u003c/span\u003e].\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec14\"\u003e\n \u003ch2\u003e3.1.6 Effect of Reaction Time\u003c/h2\u003e\n \u003cp\u003eThe reaction time holds significant economic importance and contributes to energy savings in biodiesel production. Its impact on biodiesel efficiency was investigated by conducting tests across varied reaction times ranging from 1 to 5 hrs, while other conditions were kept at constant as optimized (reaction temperature at 65\u0026deg;C, methanol to oil ratio was 24:1 and 10 wt. % catalyst dosage). As shown in Fig. \u003cspan\u003e6\u003c/span\u003e, at 1 h reaction time, about 96% of TG conversion was recorded and this remained relatively stable until 3 hrs reaction time. Similar observation was made by Roy et al. [\u003cspan\u003e15\u003c/span\u003e]. Prolonged the reaction time beyond 3 hrs led to a reduction in conversion percentage. This can be attributed to the reaction reaching equilibrium, and initiating the occurrence of reverse reaction [\u003cspan\u003e24\u003c/span\u003e]. Based on this observation, it can be concluded that a 1 h retention time is sufficient for the transesterification of WCO in this study.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec15\"\u003e\n \u003ch2\u003e3.2 Reusability Testing\u003c/h2\u003e\n \u003cp\u003eReusability is one of the most vital parameters of the solid catalyst as their effectiveness rely on its stability. Indeed, a highly stable catalyst can significantly reduce the cost of biodiesel production. After the first reaction, the Ce/Mn (10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst was filtered and washed several times with methanol to eliminate the organic filths residue adsorbed on the catalyst surface before dried at 90\u0026deg;C in the oven for an overnight. The catalyst was then reused for another transesterification reaction with new WCO and methanol loaded in similar amount to the initial reaction.\u003c/p\u003e\n \u003cp\u003eThe results showed that the Ce/Mn (10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst can be recycled up to 4 cycles with TG conversion maintained above 94%. However, a slight decrease in conversion was observed in the 6th cycles (about 88%). This decline could be attributed to the deactivation of active catalytic sites caused by the leaching of active compounds into the oil medium.\u003c/p\u003e\n \u003cp\u003eIt can be summarized from the results obtained in Figs. \u003cspan\u003e1\u003c/span\u003e\u0026ndash;\u003cspan\u003e7\u003c/span\u003e, the optimum conditions for producing biodiesel from WCO using Ce/Mn (10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst are with reaction temperature 65\u003csup\u003eo\u003c/sup\u003eC for 1 h, the methanol to oil ratio of 24:1 and a catalyst dosage of 10 wt%. The catalyst was calcined at 800\u003csup\u003eo\u003c/sup\u003eC for 5 hrs and can be reused up to 5 cycles without deterioration.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec16\"\u003e\n \u003ch2\u003e3.3 Characterization Analysis\u003c/h2\u003e\n \u003cdiv id=\"Sec17\"\u003e\n \u003ch2\u003e3.3.1 Nitrogen Sorption Analysis\u003c/h2\u003e\n \u003cp\u003eThe BET surface area, size and pore volume of the prepared Ce/Mn (10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst are recorded in Table \u003cspan\u003e2\u003c/span\u003e. Precisely, the elevation of the calcination temperatures over Ce/Mn (10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst showed significant effect on the surface area. As shown in Table \u003cspan\u003e2\u003c/span\u003e, the Ce/Mn (10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst calcined at 700\u0026ordm;C having surface area of 128 m\u003csup\u003e2\u003c/sup\u003e/g. After calcination of the catalyst at 800\u0026ordm;C, it displayed slight increase in the surface area to 143 m\u003csup\u003e2\u003c/sup\u003e/g. This result is in a harmony with the TG activity toward the calcination temperature whereby the conversion of TG increases as the calcination temperature rises from 700\u0026ordm;C (89.78%) to 800\u0026ordm;C (95.40%). It has been shown that the surface area is part of the important factors that led to higher catalytic activity in accordance with results obtained by Nasreen et al. [\u003cspan\u003e16\u003c/span\u003e].\u003c/p\u003e\n \u003cdiv\u003e\n \u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption language=\"En\"\u003e\n \u003cdiv\u003eTable 2\u003c/div\u003e\n \u003cdiv\u003e\n \u003cp\u003eTextural properties prepared catalysts calcined at different temperatures and ratios\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ccolgroup cols=\"6\"\u003e\u003c/colgroup\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCatalyst\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCalcination temperature\u003c/p\u003e\n \u003cp\u003e(\u0026ordm;C)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSurface area (SV)\u003c/p\u003e\n \u003cp\u003e(m\u003csup\u003e2\u003c/sup\u003e/ g)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAverage pore size\u003c/p\u003e\n \u003cp\u003e(nm)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTotal pore volume\u003c/p\u003e\n \u003cp\u003e(cm\u003csup\u003e2\u003c/sup\u003e/g)\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTotal basicity\u003c/p\u003e\n \u003cp\u003e(mmol/g)\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCe/Mn(10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e700\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e128\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.44\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.839\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCe/Mn(10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e800\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e143\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.543\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCe/Mn(10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e900\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e97\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e15.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.641\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCe/Mn(20:80)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e800\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e127\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e11.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.636\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCe/Mn(5:95)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e800\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e128\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.43\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e-\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eNevertheless, the calcination temperature\u0026rsquo;s elevation to 900\u0026ordm;C led to a decreased surface area to 97 m\u003csup\u003e2\u003c/sup\u003e/g result from the sintering effect as demonstrated by Tan et al.[\u003cspan\u003e11\u003c/span\u003e]and Roy et al [\u003cspan\u003e15\u003c/span\u003e].This can be attributed to the closure of fine pores on the surface of catalyst. The surface area of Ce/Mn (5:95)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (128 m\u003csup\u003e2\u003c/sup\u003e/g) and Ce/Mn (20:80)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalysts (127 m\u003csup\u003e2\u003c/sup\u003e/g) was lower compared to the surface area of Ce/Mn (10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst even when calcined at the same temperature of 800\u003csup\u003eo\u003c/sup\u003eC. The lower surface area is the reason for the decreased activity of the catalyst as shown in Fig.\u0026nbsp;8. This may be due to the diffusion limitation between the reactants and the active sites located in the catalyst pores as reported by Eldiehy et al. [\u003cspan\u003e21\u003c/span\u003e]. The surface area is inversely proportional to the pore diameter of the catalyst. The higher surface area can be achieved by a smaller of the pore diameter. It can be seen in Table \u003cspan\u003e2\u003c/span\u003e that smaller pore diameter (8.8 nm) was observed for the catalyst with highest surface area, Ce/Mn (10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (800\u003csup\u003eo\u003c/sup\u003eC). When increasing calcination temperatures up to 900\u0026ordm;C, the pore diameters also increase to 15.0 nm. This observation is attributable to the decreased number of pores in the samples. However, from the pore size distribution plot in Fig.\u0026nbsp;8a, the pore size of the catalyst was mostly below 50 nm, presented a mesoporous structure of the catalyst.\u003c/p\u003e\n \u003cp\u003eFurthermore, the total pore volume over Ce/Mn (10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e rise up from 0.438 cm\u003csup\u003e3\u003c/sup\u003e/g to 0.462 cm\u003csup\u003e3\u003c/sup\u003e/g as the calcination temperature increased from 700\u0026ordm;C to 800\u0026ordm;C and slightly decreased to 0.428 cm\u003csup\u003e3\u003c/sup\u003e/g (900\u0026ordm;C). The high surface area and pore volume of the Ce/Mn (10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst calcined at 800\u0026ordm;C are believed to be an important factor for solid catalysts which affects the catalytic activity by offering a number of reachable active species. The connection between the high surface area and the pore volume was proportionate to each other. The total pore volume for Ce/Mn (5:95)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and Ce/Mn (20:80)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalysts were found to be approximately similar, which are about 0.43 cm\u003csup\u003e3\u003c/sup\u003e/g and 0.45 cm\u003csup\u003e3\u003c/sup\u003e/g, respectively.\u003c/p\u003e\n \u003cp\u003eBased on Fig.\u0026nbsp;8, all the prepared Ce/Mn/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalysts exhibited a type IV isotherm with hysteresis type H4. This feature is typical of mesoporous material with slit-shaped pore that provided the optimal pore size to adsorb the reacting gas species on the catalyst surface as suggested by Ryu et al. [\u003cspan\u003e25\u003c/span\u003e]A stepwise multilayer adsorption process is represented by type IV, and it takes place on a solid which has slit-shaped pores of variable size and shape. Based on isotherm plot, the P/P\u003csub\u003eo\u003c/sub\u003e hysteresis closure point increases as the calcination raised from 700\u0026deg;C to 900\u0026deg;C. The closure hysteresis at high P/Po of Ce/Mn (10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst calcined at 800\u0026deg;C revealed the contraction and slow re-expansion of the pore adsorbent showed the pore adsorbent\u0026apos;s contraction and ensuring gradual re-expansion.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec18\"\u003e\n \u003ch2\u003e3.3.2 X-Ray Diffraction\u003c/h2\u003e\n \u003cp\u003eThe crystalline phases and structure of the prepared catalysts were investigated using X-ray powder diffraction (XRD) analysis. Figure\u0026nbsp;9 displays the XRD patterns of Ce/Mn/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalysts subjected to different calcination temperatures (700\u0026deg;C, 800\u0026deg;C, and 900\u0026deg;C) and dopant loadings (10\u0026ndash;20 wt%). The XRD peak analysis of the Ce/Mn(10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst calcined at 700\u0026deg;C (Fig. 9a) revealed the diffraction pattern of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (JCPDS 35\u0026ndash;0121). The five peaks at 2\u0026theta; values of 32.7\u0026deg;, 37.80\u0026deg;, 39.55\u0026deg;, 45.99\u0026deg; and 67.07\u0026deg; corresponding to the oriented growth and can be perfectly indexed to the cubic crystal face of (022), (131), (222), (040) and (044), respectively\u003c/p\u003e\n \u003cp\u003eMeanwhile, MnO\u003csub\u003e2\u003c/sub\u003e, identified by its tetragonal crystal structure (JCPDS 151\u0026ndash;3978), displays four diffraction peaks at 2\u0026theta; values of 37.59\u0026deg;, 42.04\u0026deg;, 56.42\u0026deg; and 67.71\u0026deg;, accurately aligned with lattice planes (121), (031), (060) and (710). Additional analysis identifies cubic Mn\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (JCPDS 151\u0026ndash;4239) exhibiting distinct peaks at 2\u0026theta; values of 23.13\u0026deg;, 32.95\u0026deg;, 38.23\u0026deg;, 49.55\u0026deg;, and 55.18\u0026deg;, with (121), (222), (040), (143), and (044) lattice planes. Orthorhombic Mn\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e is observed with two diffraction peaks at 2\u0026theta; values of 33.52\u0026deg; (023) and 45.00\u0026deg; (132). Meanwhile, hexagonal CeO\u003csub\u003e2\u003c/sub\u003e shows peaks at 2\u0026theta; values of 32.0\u0026deg; (101) and 55.51\u0026deg; (444).\u003c/p\u003e\n \u003cp\u003eThe same pattern was observed for the Ce/Mn(10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst calcined at 800\u003csup\u003eo\u003c/sup\u003eC. However, at a calcination temperature of 900\u003csup\u003eo\u003c/sup\u003eC, the peaks corresponding to Mn\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (c) and CeO\u003csub\u003e2\u003c/sub\u003e (h) were absent, which might be the reason of decreasing the catalytic activity (Fig. \u003cspan\u003e1\u003c/span\u003e). Hence, it can be concluded that these two species significantly contribute to enhancing the biodiesel activity.\u003c/p\u003e\n \u003cp\u003e\u003cstrong\u003eFigure 9\u003c/strong\u003e. XRD diffractograms for Ce/Mn(10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e calcined at temperatures of (a) 700 \u0026deg;C, (b) 800\u0026deg;C, and (c) 900\u0026deg;C while, and d) Ce/Mn(20:80)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalysts\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec19\"\u003e\n \u003ch2\u003e3.3.3 X-Ray Photoelectron Spectroscopy Analysis\u003c/h2\u003e\n \u003cp\u003eFigure \u003cspan\u003e10\u003c/span\u003e depicts the narrow scan for each element of Al 2\u003cem\u003ep\u003c/em\u003e, O 1\u003cem\u003es\u003c/em\u003e, Mn 2\u003cem\u003ep\u003c/em\u003e and Ce 3\u003cem\u003ed\u003c/em\u003e over Ce/Mn (10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst calcined at temperature of 700, 800 and 900\u0026ordm;C. The binding energy recorded from XPS was compared with the binding energy from National Institute of Standards and Technology (NIST). The XPS spectra of Ce/Mn (10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst calcined at 700\u0026ordm;C to 900\u0026ordm;C, display one peak of Al 2\u003cem\u003ep\u003c/em\u003e. The peak detected at binding energy around 74 eV was attributed to the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e species when comparing to the binding energy obtained from NIST database and also demonstrated by Djebaili et al. [\u003cspan\u003e26\u003c/span\u003e]. This is in line with the result obtained from XRD in Fig.\u0026nbsp;9 whereby only one species of Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e was detected in the catalyst samples. For O 1\u003cem\u003es\u003c/em\u003e exhibits three overlying deconvoluted peaks at binding energies of 529 to 532 eV corresponding to the various molecular oxygen species attached to the metal oxide on the surface of catalyst. As reported by Zhang et al. [\u003cspan\u003e27\u003c/span\u003e] and Deraz et al. [\u003cspan\u003e28\u003c/span\u003e], the binding energies for O 1\u003cem\u003es\u003c/em\u003e at 529.8- 530.9 eV was allotted to lattice oxygen (O\u003csub\u003elat\u003c/sub\u003e), 531.12 to 531.16 eV for surface-adsorbed oxygen (O\u003csub\u003eads\u003c/sub\u003e) and 532.13 eV for surface-adsorbed molecular water (O\u003csub\u003esurf\u003c/sub\u003e).\u003c/p\u003e\n \u003cp\u003eThe deconvolution of the Mn 2\u003cem\u003ep\u003c/em\u003e signal revealed three distinct peaks, correspond to a doublet splitting of 2\u003cem\u003ep\u003c/em\u003e\u003csub\u003e3/2\u003c/sub\u003e and 2\u003cem\u003ep\u003c/em\u003e\u003csub\u003e1/2\u003c/sub\u003e with binding energy difference of 12 eV. These peaks were identified as representing the Mn\u003csup\u003e2+\u003c/sup\u003e, Mn\u003csup\u003e3+\u003c/sup\u003e, and Mn\u003csup\u003e4+\u003c/sup\u003e oxidation states, consistent with findings from XRD analysis. Specifically, the binding energy peak at 644 eV is attributed to Mn\u003csup\u003e4+\u003c/sup\u003e, indicative of the MnO\u003csub\u003e2\u003c/sub\u003e species presence in Ce/Mn(10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst. The deconvoluted peaks at 641.6 and 639.8 eV correspond to Mn\u003csup\u003e3+\u003c/sup\u003e and Mn\u003csup\u003e2+\u003c/sup\u003e, respectively which are associated with the Mn\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e species, a mixture of MnO and Mn\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e. Notably, the Mn\u003csup\u003e3+\u003c/sup\u003e composition predominates in catalyst calcined at 700℃, while calcination at 900℃ results in the absence of Mn\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (Fig. 9a), leading to a diminished presence of Mn\u003csup\u003e3+\u003c/sup\u003e.\u003c/p\u003e\n \u003cp\u003eMeanwhile, the oxidation state of cerium is identified through Ce 3\u003cem\u003ed\u003c/em\u003e\u003csub\u003e5/2\u003c/sub\u003e and 3\u003cem\u003ed\u003c/em\u003e\u003csub\u003e3/2\u003c/sub\u003e spin-orbit states, with a splitting of 19.80 eV[\u003cspan\u003e27\u003c/span\u003e], as illustrated in Fig. \u003cspan\u003e10\u003c/span\u003e. All observed peaks correspond to the Ce\u003csup\u003e4+\u003c/sup\u003e oxidation state, confirming the presence of CeO\u003csub\u003e2\u003c/sub\u003e species, which is in line with the results from XRD analysis. Although CeO\u003csub\u003e4\u003c/sub\u003e did not exhibit crystalline peaks in the XRD pattern (Fig. 9) and appeared amorphous, its presence was still detected through XPS due to the technique\u0026apos;s high sensitivity to chemical information. The first two peaks on the left, with binding energies of 902.1 and 907.2 eV, are attributed to Ce 3\u003cem\u003ed\u003c/em\u003e\u003csub\u003e5/2\u003c/sub\u003e of the (5\u003cem\u003ed\u003c/em\u003e 6\u003cem\u003es\u003c/em\u003e)⁰ 4\u003cem\u003ef\u003c/em\u003e\u0026sup2; O 2\u003cem\u003ep\u003c/em\u003e⁴ and (5\u003cem\u003ed\u003c/em\u003e 6\u003cem\u003es\u003c/em\u003e)⁰ 4\u003cem\u003ef\u003c/em\u003e\u0026sup1; O 2\u003cem\u003ep\u003c/em\u003e⁵ configurations, while the peak at 914.1 eV is associated with the Ce 4\u003cem\u003ef\u003c/em\u003e\u0026sup2;-O 2\u003cem\u003ep\u003c/em\u003e⁵ configuration.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec20\"\u003e\n \u003ch2\u003e\u003cem\u003e3.3.4\u003c/em\u003e Field emission scanning electron microscopy\u003c/h2\u003e\n \u003cp\u003eThe morphology of the Ce/Mn/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst at varying dopant ratios and calcination temperatures is depicted in Fig. \u003cspan\u003e11\u003c/span\u003e. The images show that the catalyst particles are agglomerated on the surface, giving the catalyst a rough morphology. The FESEM image of the Ce/Mn (10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst calcined at 700\u0026deg;C (Fig. \u003cspan\u003e11\u003c/span\u003ea) reveals a non-uniform structure with a variety of average particle diameters from 8 to 11 nm. As the calcination temperature rose to 800\u0026deg;C, a uniformly distributed surface morphology with smaller particles was observed. It could provide a greater specific surface area as reported by Deraz et al. and Ullaz et al.[\u003cspan\u003e29\u003c/span\u003e] [\u003cspan\u003e30\u003c/span\u003e] This result correlates with N\u003csub\u003e2\u003c/sub\u003e sorption analysis in Table \u003cspan\u003e2\u003c/span\u003e, which showed that the Ce/Mn (10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst calcined at 800\u0026deg;C had the highest surface area and displayed porous characteristics that contributed to its catalytic activity in transesterifying waste cooking oil. Therefore, the catalytic activity of the Ce/Mn (10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst was maximized at a calcination temperature of 800\u0026deg;C. In contrast, the surface morphology displayed in Fig. \u003cspan\u003e11\u003c/span\u003ec shows crystallites with a densely packed arrangement, indicating the formation of larger particles due to the sintering effect. This resulted in a reduction of surface area to 92 cm\u003csup\u003e2\u003c/sup\u003e/g for the catalyst calcined at 900\u0026deg;C. A similar surface morphology was observed for the Ce/Mn(5:95)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and Ce/Mn(20:80)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalysts.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec21\"\u003e\n \u003ch2\u003e\u003cem\u003e3.3.5\u003c/em\u003e Transmission Electron Microscopy\u003c/h2\u003e\n \u003cp\u003eTransmission Electron Microscopy (TEM) images of Ce/Mn (10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e subjected to various calcination temperatures are presented in Figs. \u003cspan\u003e12\u003c/span\u003e\u0026ndash;\u003cspan\u003e14\u003c/span\u003e. The TEM images reveal a range of morphologies, including nanorod-like particles across the catalysts. Specifically, the Ce/Mn (10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e particles calcined at 700\u0026deg;C (Fig. \u003cspan\u003e12\u003c/span\u003e) and 800\u0026deg;C (Fig. \u003cspan\u003e13\u003c/span\u003e) have sizes ranging from 2 to 4 nm. For the catalyst calcined at 900\u0026deg;C, TEM images display an agglomeration of irregularly shaped particles with sizes between 3 and 5 nm (Fig. \u003cspan\u003e14\u003c/span\u003e). These observations are consistent with FESEM results, which indicate an increase in particle size with higher calcination temperatures.\u003c/p\u003e\n \u003cp\u003eThe High-Resolution Transmission Electron Microscopy (HRTEM) visualization of the Ce/Mn(10:90)/ Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst calcined at 800℃ is illustrated in Fig. \u003cspan\u003e13\u003c/span\u003e, revealing discernible lattice spacings of 0.156 nm, 0.168 nm, and 0.2 nm. These measurements consistently align with the respective values associated with (121) tetragonal MnO\u003csub\u003e2\u003c/sub\u003e, (044) cubic Mn\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, and (023) orthorhombic Mn\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e. Additionally, a lattice fringe measured at 0.13 nm corresponds to the \u003cem\u003ed\u003c/em\u003e-spacing of the Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (044) plane, while a \u003cem\u003ed\u003c/em\u003e-spacing of 0.27 nm is identified with the (101) planes of CeO\u003csub\u003e2\u003c/sub\u003e. This structural representation confirms the presence of cerium and manganese oxides on the surface of alumina support, corroborating the X-Ray Diffraction (XRD) data. The same species were observed in the catalyst calcined at 700\u0026deg;C. Conversely, the HRTEM image did not detect the lattice fringes of CeO\u003csub\u003e2\u003c/sub\u003e and Mn\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e on the catalyst calcined at 900\u0026deg;C (Fig. \u003cspan\u003e14\u003c/span\u003e), reinforcing the findings from the XRD analysis.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec22\"\u003e\n \u003ch2\u003e\u003cem\u003e3.3.6\u003c/em\u003e CO\u003csub\u003e2\u003c/sub\u003e-Temperature Programmed Desorption (CO\u003csub\u003e2\u003c/sub\u003e-TPD)\u003c/h2\u003e\n \u003cp\u003eThe CO\u003csub\u003e2\u003c/sub\u003e-TPD analysis was conducted to investigate the basicity of the synthesized Ce/Mn (10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst. Figure \u003cspan\u003e15\u003c/span\u003e illustrates the CO\u003csub\u003e2\u003c/sub\u003e-TPD profiles, while the total basicity is shown in Table \u003cspan\u003e2\u003c/span\u003e. Basicity is an essential property influencing the catalytic performance, particularly in transesterification reactions [\u003cspan\u003e27\u003c/span\u003e]. As shown in Fig. \u003cspan\u003e15\u003c/span\u003e, the CO\u003csub\u003e2\u003c/sub\u003e-TPD profile for the Ce/Mn (10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst reveals a variety of desorption peaks, indicating the presence of basic sites with different strengths. Each catalyst typically displayed three main CO\u003csub\u003e2\u003c/sub\u003e desorption peaks. The peak at below 180\u0026deg;C was associated with weak basic sites. These sites are crucial for initial adsorption and activation of reactants. Intermediate basic sites, with CO\u003csub\u003e2\u003c/sub\u003e desorption between 180\u0026deg;C and 630\u0026deg;C, offer moderate strength and play a significant role in facilitating various reaction steps. Desorption of CO\u003csub\u003e2\u003c/sub\u003e above 630\u0026deg;C was attributed to adsorption at strong basic sites, as reported by Ma et al. [\u003cspan\u003e31\u003c/span\u003e] are essential for breaking stronger bonds in the reactants, thus enhancing catalytic activity. Catalysts with a higher proportion of intermediate and strong basic sites are expected to exhibit better performance in transesterification due to their enhanced ability to activate and transform reactant molecules. All identified basic sites were linked to the contributions of the individual oxides of manganese and cerium on the surface of catalyst.\u003c/p\u003e\n \u003cp\u003eFrom the Table \u003cspan\u003e2\u003c/span\u003e, the total basicity follows the order of Ce/Mn (10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e 800\u003csup\u003eo\u003c/sup\u003eC (1.543 mmol/g)\u0026thinsp;\u0026gt;\u0026thinsp;700\u003csup\u003eo\u003c/sup\u003eC (0.839 mmol/g)\u0026thinsp;\u0026gt;\u0026thinsp;900\u003csup\u003eo\u003c/sup\u003eC (0.641 mmol/g)\u0026thinsp;~\u0026thinsp;Ce/Mn (20:80)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e (0.636 mmol/g). The data suggest that calcining the Ce/Mn (10:90)/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst at 800\u0026deg;C provides the highest total basicity. This temperature appears to be optimal for generating a high number of active basic sites without causing detrimental structural changes that reduce basicity. At 900\u0026deg;C, the significant drop in total basicity indicates that this temperature may be too high, potentially causing sintering or other structural effects that diminish the number of active sites. This statement can be supported with the data obtained from FESEM, XRD and XPS analysis. The absence of Mn\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and CeO\u003csub\u003e2\u003c/sub\u003e species resulted in reduced basicity, leading to lower catalytic performance. In conclusion, the total basicity data highlight the importance of calcination temperature in optimizing the basic properties of Ce/Mn/\u0026gamma;-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalysts. Calcining at 800\u0026deg;C is shown to be the most effective for maximizing total basicity and, consequently, catalytic activity.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e"},{"header":"Conclusion","content":"\u003cp\u003eIn these studies, a Ce/Mn catalyst supported on alumina was effectively employed to transesterify waste cooking oil into biodiesel. The Ce/Mn/γ-Al₂O₃ catalyst, with a Ce-to-Mn molar ratio of 10:90 and calcined at 800\u0026deg;C, achieved over 96% triglyceride (TG) conversion under optimal conditions: a reaction temperature of 65\u0026deg;C, a methanol-to-oil ratio of 24:1, and a reaction time of 3 hours. This high efficiency is attributed to the catalyst's large surface area of 143 m\u003csup\u003e2\u003c/sup\u003e/g with small particle size 8.8 nm and high basicity about 1.543 mmol/g. Notably, the Ce/Mn(10:90)/γ-Al₂O₃ catalyst demonstrated excellent reusability, maintaining high triglyceride conversion rates across seven cycles, with only a slight decrease from 97\u0026ndash;94%, likely due to a gradual reduction in basic sites. This makes Ce/Mn(10:90)/γ-Al₂O₃ a promising catalyst for the cost-effective conversion of waste cooking oil into biodiesel.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003e\u0026nbsp;Acknowledgements\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;This work was supported by the Universiti Teknologi Malaysia for UTM-FR PY/2019/01760 (21H03). thanks, Jazan University for financial support and thanks the Saudi Arabian Cultural Mission (SACM).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;Author contributions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eNashwa Alahmar:\u003c/strong\u003eConceptualization, Investigation, Resources, Writing \u0026ndash; original draft Software. \u003cstrong\u003eNur Izyan Binti Wan Azelee\u003c/strong\u003e\u003csup\u003e\u0026nbsp;\u003c/sup\u003e:Funding acquisition . \u003cstrong\u003eSusilawati Toemen\u003c/strong\u003e:\u0026nbsp;Project administration.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eConflicts of Interest\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAll authors declare that there is no conflict of interest\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eData Availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp; \u0026nbsp;\u003c/strong\u003eAll data are represented in the manuscript there is no additional supported data \u0026nbsp;\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eN. 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Gao, \u0026ldquo;Kinetics studies of biodiesel production from waste cooking oil using FeCl3-modified resin as heterogeneous catalyst,\u0026rdquo; \u003cem\u003eRenew Energy\u003c/em\u003e, vol. 107, pp. 522\u0026ndash;530, 2017, doi: 10.1016/j.renene.2017.02.007.\u003c/li\u003e\n\u003c/ol\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":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Biodiesel, waste cooking oil, manganese oxide, catalyst, transesterification reaction","lastPublishedDoi":"10.21203/rs.3.rs-5158584/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-5158584/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eBiodiesel stands as a non-toxic, biodegradable, and environmentally friendly substitute for conventional petroleum-based fuels. In recent years, the production of biodiesel has garnered significant attention from both industries and researchers globally. Waste cooking oil (WCO) has emerged as a promising feedstock for biodiesel production, drawing the interest of researchers. Utilizing WCO in biodiesel production is not only cost-effective but also addresses the disposal challenges associated with this waste cooking oil. The aim of the present study is to synthesis Ce/Mn(10:90)/γ-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e using incipient wetness impregnation (IWI) methods, with the goal of facilitating the biodiesel production from WCO. Various preparation parameters, comprising calcination temperatures and based loadings as well as various reaction conditions for the transesterification reaction such as catalyst loading, methanol to oil molar ratio, reaction temperature and time were optimized. From the results, the maximum conversion of triglyceride achieved was 97% for Ce/Mn(10:90)/γ-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e catalyst calcined at 800\u003csup\u003eo\u003c/sup\u003eC. The optimum reaction conditions were 10 wt% of catalyst loading and 1:24 of methanol to oil ratio at 65\u0026deg;C of reaction temperature for 3 hrs. This outstanding performance can be attributed to the catalyst's high surface area of 143. m\u003csup\u003e2\u003c/sup\u003e/g, large pore size of 8.75 nm, and smaller particle size of 0.462 nm, collectively enhancing its catalytic efficiency.\u003c/p\u003e","manuscriptTitle":"Advancing Biodiesel Production from Waste Cooking Oil: Optimization and Characterization of Manganese-Based Catalysts","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2024-11-12 11:47:29","doi":"10.21203/rs.3.rs-5158584/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2024-10-15T13:00:12+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-10-14T09:49:47+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2024-10-14T03:31:33+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"273919289035238041297915249672294216970","date":"2024-10-04T15:14:33+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"337922852856888040898996075649605307945","date":"2024-10-04T13:43:43+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2024-10-04T12:55:38+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2024-10-04T12:45:02+00:00","index":"","fulltext":""},{"type":"editorInvited","content":"","date":"2024-10-04T10:56:14+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2024-10-02T09:43:30+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2024-09-26T12:05:35+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"418cb650-66c6-4199-b34c-1d27bba4bf9f","owner":[],"postedDate":"November 12th, 2024","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-01-06T16:00:39+00:00","versionOfRecord":{"articleIdentity":"rs-5158584","link":"https://doi.org/10.1038/s41598-024-82845-2","journal":{"identity":"scientific-reports","isVorOnly":false,"title":"Scientific Reports"},"publishedOn":"2025-01-02 15:57:16","publishedOnDateReadable":"January 2nd, 2025"},"versionCreatedAt":"2024-11-12 11:47:29","video":"","vorDoi":"10.1038/s41598-024-82845-2","vorDoiUrl":"https://doi.org/10.1038/s41598-024-82845-2","workflowStages":[]},"version":"v1","identity":"rs-5158584","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-5158584","identity":"rs-5158584","version":["v1"]},"buildId":"qtupq5eGEP_6zYnWcrvyt","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}