Eliminating Coordinatively Unsaturated Al 3 + Sites Increases the Activity of Al 2 O 3 -Supported Monomeric VO x in Nonoxidative Propane Dehydrogenation

A fundamental understanding of the interactions between the support and the supported species in heterogeneous catalysis is crucial, as the support can significantly influence the structural and chemical properties of the active supported species, thereby affecting their catalytic performance. In this study, the intrinsic effects of VOx-support interactions on the structure of VOx species and catalytic behavior of VOx–Al2O3 catalysts were investigated using nonoxidative propane dehydrogenation (PDH) as a model reaction. Complementary characterization studies of the catalysts revealed the presence of distinct monomeric VOx species (m-VOx), which are bonded to coordinatively unsaturated (Alcus) and saturated (Alcs) aluminum sites, respectively. Compared to m-VOx anchored on the Alcus sites, those bound to the Alcs sites exhibit a weaker strength of the V–O–Al bonds and accordingly higher reducibility. Remarkably, selectively eliminating Alcus sites but preserving Alcs sites by treating the catalyst with an NH3·H2O solution greatly enhanced the PDH activity, increasing the turnover frequency of VOx by more than 4-fold. Furthermore, kinetic analysis based on time-resolved in situ UV–vis spectroscopy demonstrated that the rate constant of the reduction of m-VOx species by H2 correlates positively with the Alcs content in the VOx–Al2O3 catalysts, establishing it as a reliable activity descriptor for the PDH reaction catalyzed by m-VOx. Thus, this work provides fundamental insights into how support identity matters, thereby contributing to the targeted development of active catalysts.