New rare earth oxide catalysts for the transesterification of triglycerides with methanol resulting in biodiesel and pure glycerol

The transesterification of different oils and fats with methanol in the presence of various rare earth oxide (REO) containing heterogeneous catalysts was investigated. Pure rare earth oxides, supported rare earth oxides, and stoichiometric rare earth mixed oxide catalysts were prepared. The catalysts were characterized by X-ray powder diffraction (XRD), nitrogen adsorption isotherm (BET), thermogravimetric analysis (TGA), and temperature-programmed desorption of CO2 (TPD). The correlation of the catalyst structure and activity in batch wise lab-scale autoclave experiments was studied. Among the pure rare earth oxides, an exceptionally high activity was found for lanthanum oxide. Rare earth oxides on oxidic carriers lead to the formation of surface mixed oxide phases, while activated carbon enables to enhance the dispersion of the lanthanum oxide phase. A series of rare earth aluminates, titanates, and zirconates were prepared by flash combustion synthesis and a comparison of the surface activity is given.