Understanding the active-site nature of vanadia-based catalysts for oxidative dehydrogenation of ethylbenzene with CO2 via atomic layer deposited VOx on γ-Al2O3

Abstract

Supported vanadium oxides are widely used as active catalysts for a number of oxidation and oxidative dehydrogenation reactions, and the understanding the structure-function relationship is of great importance for developing more efficient vanadium oxide catalysts. In this work, atomic layer deposition (ALD) was utilized to disperse sub-monolayer VOx over a commercial γ-Al2O3 support. Characterization results indicate that highly dispersed VOx species with different structures were obtained by simply changing the number of ALD cycles. The vanadium oxides synthesized by performing 1 cycle of ALD were exclusively isolated monomeric VOx. With increasing the number of ALD cycles from 3 to 8, the polymeric VOx spices were formed, and the polymerization extent or domain size of VOx was increased. On the contrary, crystalline V2O5 besides polymeric VOx was found if the number of ALD cycles was extended to 12. Catalytic performances of ALD VOx/γ-Al2O3 were evaluated for the oxidative dehydrogenation of ethylbenzene with CO2 (CO2-ODEB), and the isolated monomeric VOx species were found to be more active and more stable than the polymeric VOx species and crystalline V2O5. By correlating the specific activity and the structural characteristics of ALD VOx/γ-Al2O3 catalysts, the VOAl bonds were concluded as the key active sites for CO2-ODEB.