Improvements in acidity for TiO2 and SnO2 via impregnation with MoO3 for the esterification of fatty acids

•Oxide matrixes (TiO2 and SnO2) were prepared using a chitosan-metal complex method.•MoO3 was impregnated on SnO2 and TiO2.•The acid strength of the active sites changed from weak or moderate to strong.•MoO3-impregnated SnO2 and TiO2 generates active catalysts for esterification.

The impregnation of TiO2 or SnO2 with MoO3 forms solid materials exhibiting high acidity (MoO3/TiO2 and MoO3/SnO2) that might be applied as catalysts for the esterification of fatty acids. TiO2 and SnO2 oxide matrixes were prepared using a metal-chitosan complex method, and the acidity of these materials was modified via impregnation with MoO3. These catalytic systems were characterized by FTIR, N2 adsorption/desorption isotherms, thermogravimetric analysis, and NH3 temperature programmed desorption (NH3-TPD) and tested in the esterification of fatty acids in the presence of methanol. The esterification reactions were carried out at three different temperatures (120 °C, 140 °C and 160 °C) with a 400:100 molar ratio of alcohol:fatty acid and 1% (mass) catalyst loading. Both TiO2 and SnO2 only exhibited catalytic activity after their acidity was improved via impregnation with MoO3, and yields of 80% and 90%, respectively, were achieved at 6 h and 160 ºC.