Physicochemical characteristics of Cu/Zn/γ-Al2O3 catalyst and its mechanistic study in transesterification for biodiesel production

A series of novel mixed metal oxide catalysts with the incorporation of copper as a dopant supported on zinc-alumina (Cu/Zn/γ-Al2O3) for biodiesel production have been synthesized and characterized. ZnO is a solid base catalyst, but its weak surface basic properties have limited the usage of ZnO in the transesterification reaction of refined used cooking oil to biodiesel. To further improve the catalytic activity, the copper dopant was loaded by the wetness impregnation method. Cu/Zn/γ-Al2O3 catalyst of 10:90 wt% dopant-to-based (ZnO) ratio with calcination at 800 °C exhibited the highest biodiesel yield (89.5%) at optimum reaction conditions (65 °C, 10 wt% catalyst loading, 1:20 oil-to-methanol mol ratio and 2 h reaction time). The N2 adsorption-desorption and CO2-temperature programmed desorption analyses indicated that the material possessed a high surface area (149 m2/g) and high basicity (3.7424 mmol/g). The mechanistic study confirmed the catalytic reaction followed the Langmuir-Hinshelwood (LH) model, which involves the initial adsorption of reactants molecules on active sites of the catalyst surface.