The nature of VOx structures in HMS supported vanadium catalysts for non-oxidative propane dehydrogenation

Abstract

Vanadium was introduced to hexagonal mesoporous SiO2 (HMS) to prepare supported vanadium-based catalysts (V-HMS). Their catalytic performance in the non-oxidative propane dehydrogenation to propylene (PDH) was modulated with V surface density varying from 0.12 to 15.08V atom·nm−2. VOx species with different structure were analyzed by UV–vis spectroscopy, NH3-TPD, H2-TPR and XPS. High propylene space time yield of 0.73 kg·h−1·kgcat−1 and excellent regeneration behavior were achieved. Correlating VOx polymerization degree with catalytic performance, VOx aggregates, mainly in low-polyvanadate form, were established to reveal high intrinsic activity and stability in comparison with their counterparts, including isolated or/and highly polymerized VOx as well as V2O5. Temporal analysis of products (TAP) identified hydrogen formation as the rate-limiting step in the PDH reaction. In-situ DRIFTS was employed to investigate the reaction mechanism. V species containing C=C bond, i.e., VOx-C3H5, was proposed to be an intermediate of gas-phase propylene.