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

• Highly dispersed VO x species showed high apparent TOF value but low C 3 H 6 selectivity. • VO x species in low-polyvanadate form are deemed to be more active and stable in PDH. • VO x -C 3 H 5 species was speculated to be the important intermedia during PDH. • H 2 formation is deemed as the rate-limiting step over as-prepared V-HMS. Vanadium was introduced to hexagonal mesoporous SiO 2 (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 15.08 V atom·nm -2 . VO x species with different structure were analyzed by UV-vis spectroscopy, NH 3 -TPD, H 2 -TPR and XPS. High propylene space time yield of 0.73 kg·h -1 ·kg cat -1 and excellent regeneration behavior were achieved. Corelating VO x polymerization degree with catalytic performance, VO x 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 VO x as well as V 2 O 5 . 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., VO x -C 3 H 5 , was proposed to be an intermediate of gas-phase propylene.