Understanding the active-site nature of vanadia-based catalysts for oxidative dehydrogenation of ethylbenzene with CO2 via atomic layer deposited VOx on γ-Al2O3
2019
Yang, Guo-Qing | Wang, Huan | Gong, Ting | Song, Yong-Hong | Feng, Hao | Ge, Han-Qing | Ge, Hui-bin | Liu, Zhao-Tie | Liu, Zhong-Wen
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.
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