Nature of active phase of VOx catalysts supported on SiBeta for direct dehydrogenation of propane to propylene

Abstract

The VOx catalysts supported on dealuminated Beta zeolite (SiBeta) with varying V loadings (from 0.5 to 10 wt%) are prepared and tested for their catalytic activities in the reaction of direct dehydrogenation of propane to propylene (PDH). It is characterized that the VSiBeta catalysts possess different kinds of vanadium species on the SiBeta support, including monomeric or isolated VOx species at a low V loading, and polynuclear VOx species in different polymerization degrees at higher V loadings. The 3VSiBeta catalyst (V loading is 3 wt%), containing isolated VOx species in monolayer, shows around 40% of propane conversion with 90% of propylene selectivity (reaction conditions: 600 °C, 4000 mL g-1h-1) which are comparable to VSiBeta catalysts with higher V loadings. The catalytic activity exhibits a good linear relationship with the amount of generated acidic sites, which are derived from the interaction sites between VOx species and SiBeta support, and keeps stable after several regeneration cycles. Thus, as the VOx species directly contact with SiBeta support via V-O-Si bonds, a reactivity enhancement can be achieved. While, the initial valence state of V does not seem to influence the catalytic performance. Moreover, the aggregation degree of VOx species determines the propylene selectivity and deactivation rate, both of which increase as raising the V loading amount.