Synthesis, Characterization and Catalytic Dehydration of Glycerol to Acrolein Over Phosphotungstic Acid Supported Y-Zeolite Catalysts

Abstract

Vapour phase catalytic dehydration of glycerol to acrolein was studied over phosphotungstic acid (PTA) supported (with different loadings of PTA) on Y-zeolite catalysts. The active component PTA was varied between 10 and 40% w/w on the support Y-zeolite and was synthesized by the wet impregnation method. The physico-chemical characterization of the catalyst samples was investigated by X-ray diffraction (XRD), FT-IR, Raman and by the gas adsorption measurements. The XRD results showed that active component PTA is highly dispersed in an amorphous form at lower loadings of PTA and attained a crystalline state beyond 20 wt% of PTA. Both Raman and FT-IR spectra indicated that the Keggin ion structure of PTA was present in a highly dispersed state in the supported PTA/zeolite catalysts as compared to the bulk form of PTA. Temperature programmed desorption (TPD) of ammonia and FT-IR spectra of pyridine adsorption were used to determine the acidic properties of the PTA catalysts. The TPD of ammonia showed the presence of moderate acidity on the catalyst surface. The total acidity increased with raise in PTA loading up to 20 wt% and beyond this, it had decreased. The FT-IR results suggested the presence of Bronsted acidity. The Pore size increased with PTA loading until 20 wt%. Finally, the PTA/zeolite catalysts were tested for the gas phase dehydration of glycerol in a fixed-bed, micro-reactor in the temperature range between 250 and 300 °C. Among all the catalysts tested, PTA (20 wt%)/zeolite showed a total conversion of 100% glycerol and a selectivity of 79% for acrolein. These results are correlated with surface acidity, textural and structural properties of the PTA/zeolite catalysts. Glycerol dehydration products over Lewis and Bronsted acidic sites.