Assessment of CaTiO3, CaMnO3, CaZrO3 and Ca2Fe2O5 perovskites as heterogeneous base catalysts for biodiesel synthesis

• Synthesis of calcium-containing perovskites by milling and calcination
• Calcium-containing perovskites exhibit low or no methanolysis activity at 60 °C.
• Two-phase CaO/CaTiO3 or CaO/Ca2Fe2O5 catalysts exhibit catalytic activity.
• CaO with rock salt structure is an active phase in multiphase catalysts.

Calcium-containing perovskites CaTiO3, CaMnO3, CaZrO3 and Ca2Fe2O5 were synthesized by calcination of mechanochemically treated stoichiometric mixtures of CaCO3 and either TiO2, MnO2, ZrO2 or Fe2O3 powders. X-ray diffraction analysis revealed a pure single perovskite phase for all four samples after calcination. This study proved that the pure perovskite phase exhibited low or no catalytic activity at 60 °C for the methanolysis of sunflower oil. However, at 165 °C FAME yield of more than 90% was reached after 2 h using CaTiO3, CaMnO3 and CaZrO3 as catalyst. Contrary to inactive pure perovskites at 60 °C, the CaTiO3 and Ca2Fe2O5 samples containing a very small amount of “free” CaO also showed methanolysis activity at 60 °C. This fact can be used to explain some contradictory statements reported in literature related to the perovskites as catalyst for biodiesel synthesis at mild temperatures.