Characterization and reactivity of 11-molybdo-1-vanadophosphoric acid catalyst supported on zirconia for dehydration of glycerol to acrolein

Abstract

A series of vanadium-substituted phosphomolybdic acid (HPA) catalysts supported on zirconia were prepared by impregnation method with varying the HPA active phase content from 10 to 50 wt% on the support. The calcined catalysts were characterized by X-ray diffraction, Raman spectroscopy, temperature-programmed desorption of NH3, FT-IR spectra of pyridine adsorption and surface area measurements. XRD results suggest that the active phase of heteropolyacid is present in a highly dispersed state at lower loadings and as a crystalline phase at higher HPA loadings and these findings are well-supported by the results of FT-IR and Raman spectra. Calcination of the samples did not affect the Keggin ion structure of HPA. The ammonia TPD results suggest that acidity of the catalysts was found to increase with increase of HPA loading up to 40 wt% and decreases at higher loadings. FT-IR spectra of pyridine adsorption show that the Brønsted acidic sites increase with increase of HPA loadings up to 40 wt% catalyst. However, Lewis acid sites decrease with increase of HPA loading. Catalytic properties were evaluated during vapour phase dehydration of glycerol to acrolein. The catalyst with 40 wt% HPA has exhibited excellent selectivity towards acrolein formation with complete conversion of glycerol at 225°C under atmospheric pressure. Catalytic performances during dehydration of glycerol are well-correlated with acidity of the catalysts. Zirconia-supported H4PMo11VO40 catalysts have been investigated in the vapour dehydration of glycerol to acrolein. The catalysts are highly active and selective during dehydration of glycerol under mild reaction conditions. The high selectivity of acrolein is attributed to the presence of Brønsted acidic sites in the catalysts.