Influence of alkaline metal on performance of supported silicotungstic acid catalysts in glycerol dehydration towards acrolein

Abstract

A series of supported silicotungstic acid (H 4SiW 12O 40· xH 2O) catalysts was prepared from selected silica and alumosilicate carriers. Alkaline metals lithium, potassium and caesium were added to modify catalyst Brønsted acidity. Physico-chemical characterisation of the catalysts was carried out with nitrogen adsorption (BET), X-ray diffraction (XRD), and infrared (IR) and Raman spectroscopy and revealed that the nature of the alkaline metal is significant for (i) specific surface area which rises with metal ion radii and (ii) dispersion of active compound formed from alkaline metal and silicotungstic acid on the support surface. Interestingly, acidic properties rather do not depend on nature of alkaline metal. The catalysts were catalytically evaluated at standardised reaction conditions in a continuous flow lab scale set-up (10 wt.% of glycerol in water, 225–300 °C, modified contact time 0.15 kg h mol −1). Among the tested supported catalysts, lithium exchanged H 4SiW 12O 40· xH 2O showed highest activity and maximum selectivity of 70% for acrolein at complete conversion. Main effect of alkaline metal addition can be seen in improved selectivity and activity, in particular with silica supported catalysts.