*4.4.3.3 Mixed metal oxides*

Mixed metal oxides have shown potential applicationsin terms of their catalytic activity in various reactions due to their increased active acidic or basic sites and large surface area. As a result of these characteristic, the mixed metal oxides can simultaneously catalyze the esterification and transesterification and increases the yield of reaction under mild reaction condition [32].

Many researchers have investigated the catalytic activity of mixed metal oxide for biodiesel production. Furata et al. [58] prepared the Al2O3/ZrO2/WO3 solid catalyst by co-precipitation method for biodiesel production from soybean oil. The catalyst was compatible for both esterification and transesterification at 250°C temperature and alcohol to oil molar ratio of 40:1, provided 90% methyl ester yield.
