Vapor Phase Dehydration of Glycerol to Acrolein Over Phosphotungstic Acid Catalyst Supported on Niobia

Abstract

The vapor phase dehydration of glycerol was carried out on niobia-supported phosphotungstic acid (PTA) catalysts. The catalysts were prepared by varying the active component PTA loadings ranging from 10 to 40 wt% on the support. The catalysts were characterized by powder X-ray diffraction, laser Raman spectroscopy, temperature programmed desorption of ammonia, ex-situ FT-IR spectra of adsorbed pyridine, BET surface area and pore size distribution. The XRD results suggest that the active phase of phosphotungstic acid was found to be highly dispersed at lower PTA loadings on the support. The findings of Raman spectra reveals that the catalyst with 30 PTA/Nb-400 clearly exhibit the primary structure of Keggin ion of hetropolyacid on the niobia support. NH3-TPD experiments confirm that the acidity of the catalyst increases with increase of PTA loading and decreases at higher loadings. The nature of acidic sites on the catalyst surface was investigated by the ex-situ pyridine adsorbed FT-IR spectroscopy and the results suggest that the catalyst with 30 PTA/Nb has shown stronger Bronsted acidic sites. Pore size distribution reveals that 30 PTA/Nb-400 exhibited lager average pore diameter than the other loadings. The Nb2O5-supported PTA catalysts have shown remarkable catalytic performance during the dehydration of glycerol to acrolein. The catalytic properties during glycerol dehydration are related to the surface acidic functionality of the catalyst.