Vapour phase dehydration of glycerol to acrolein over vanadium phosphorous oxide (VPO) catalyst

Abstract

Vanadium phosphorus oxide (VPO) catalysts were synthesized with the different P/V ratios in the range of 0.6–2.0. These catalysts were characterized by EDX analysis, X-ray diffraction (XRD), scanning electron microscopy (SEM), UV-diffuse reflectance spectroscopy, laser Raman spectroscopy (LRS), temperature programmed desorption of ammonia, temperature programmed reduction and X-ray photoelectron spectroscopy. The XRD results of the VPO samples suggest that the sample with a P/V ratio less than unity possesses pure crystalline vanadia and β-VOPO₄ phases. However, the sample with a P/V ratio ≥1.0 contains various VOPO₄ and vanadyl pyrophosphate phases. The laser Raman spectroscopy and UV-DRS analysis of the samples also confirm the above findings. The ammonia TPD analysis suggests that the acidity of the catalyst increases up to a P/V ratio of ∼1.2 and furthermore no significant change in the acidity was noticed. The catalytic performances of these samples were investigated for gas phase glycerol dehydration reaction. The results reveal that the conversion and selectivity depend on the P/V ratio of the VPO catalyst. The XRD pattern of the spent samples suggests that the VPO phase undergoes phase change after the reaction. The XPS analysis result confirms the presence of a higher amount of V⁴⁺ species in the spent samples than the pure sample.