Synthesis Method Effect on the Catalytic Performance of Acid–Base Bifunctional Catalysts for Converting Low-Quality Waste Cooking Oil to Biodiesel

Abstract

Synthesis method effect on surface properties of doped V2O5 metal oxide into CaO-based catalysts as acid–base bifunctional catalysts have been studied. Various acid–base bifunctional catalysts were synthesized via co-precipitation, impregnation, and physical mixing methods. X-ray diffraction (XRD), Fourier Transform Infra-Red (FT-IR) and X-ray fluorescence (XRF) analyses of all prepared samples confirmed that V2O5 was well dispersed on the surface of CaO catalysts. V2O5-CaO catalyst synthesized via the co-precipitation method exhibited the highest FAME yield (78.48%) under mild reaction conditions with waste cooking oil among other synthesized catalysts. This superiority is attributed to its highest total acid–base sites per catalyst surface area and mesoporous structure. The simultaneous esterification-transesterification activity was greatly affected by catalyst surface properties (i.e., the strength of acidity and basicity), the total amount of acid–base sites, and surface area. These results were supported by the N2-adsorption, Temperature Programmed Desorption (TPD)-CO2, and TPD-NH3 data. Thus, our work showed that co-precipitation was the most promising preparation method for maximizing the total acid–base sites per catalyst surface area and acid–base strength of the catalyst. The remarkable strength of the acid–base and total amount of acid–base sites of the V2O5-CaO catalyst is caused by the synergistic effect of the dual acid sites (Brønsted and Lewis) and base sites on the catalysts. Graphical Abstract: (Figure presented.)