Investigation of a molybdenum-containing silica catalyst synthesized by the sol–gel process in heterogeneous catalytic esterification reactions using methanol and ethanol

Abstract

Molybdenum-containing silica easily synthesized by the sol–gel process was evaluated as catalyst for heterogeneous esterification reaction of fatty acids using methanol and ethanol. The molybdenum content depended on the conditions employed during the synthesis. The solids were characterized by X-ray powder diffraction, textural analysis, X-ray photoelectronic spectroscopy, and inductively coupled plasma optical emission spectroscopy. The strength and distribution of the acid sites were assessed by the adsorption–desorption of n-butylamine as monitored by Fourier transform infrared spectroscopy and thermogravimetric analysis. Kinetic studies revealed high fatty acid conversion for both alcohols and diminished activity upon decreasing concentration of acid sites. Monitoring of the acid sites during the recycling experiments indicated association of the catalytic activity with Mo oxide species on the surface and with the availability of molybdenum-active sites displaying Brønsted–Lowry acidity in the silica structure.