Transesterification of rapeseed oil with ethanol over heterogeneous heteropolyacids

Abstract Heterogeneized heteropolyacids, H 3 PW 12 O 40 /SiO 2 and Cs 2 HPW 12 O 40 were shown to catalyze rapeseed oil transesterification with ethanol in mild conditions. The number and the strength of the acid sites were evaluated by calorimetry. Over anhydrous H 3 PW 12 O 40 and Cs 2 HPW 12 O 40 , acid sites of homogeneous strength with heat of ammonia adsorption near 200 kJ mol −1 were measured. By contrast, H 3 PW 12 O 40 /SiO 2 showed sites of lower strength with a heterogeneous distribution. The catalytic activity did not correlate the acid strength of solid catalysts. Indeed, equivalent TOF were determined on H 3 PW 12 O 40 and silica supported H 3 PW 12 O 40 while lower TOF were measured on microporous Cs 2 HPW 12 O 40 . The TOF values were interpreted in terms of leaching of the active phase in the case of H 3 PW 12 O 40 /SiO 2 while reduced acid sites accessibility might explain the lower TOF measured on Cs 2 HPW 12 O 40 .