Effects of Support and CO<sub>2</sub> on the Performances of Vanadium Oxide-Based Catalysts in Propane Dehydrogenation
Yuling Shan, Huai-Lu Sun, Shilei Zhao, Pei-Long Tang, Wenting Zhao, Junwei Ding, Wenlong Yu, Lina Li, Xiang Feng, De Chen
Abstract
Vanadium oxide-based catalysts are promising candidates for propane dehydrogenation (PDH) with and without CO2 introduction. In the present study, the effects of support and CO2 on the intrinsic activity of VOx-based catalysts were systematically investigated by a combination of experimental and theoretical calculations. The activity of VOx was found to vary significantly with oxide supports, among which the activity of ZrO2-supported VOx is 4 times higher than that of other samples, which can serve as highly active and stable catalysts at a H2/C3H8 ratio of 0.5. The experiments and established scaling relationships based on density functional theory calculations reveal that the chemical states of bridge oxygen in the V–O bond play critical roles in propane activation under the reductive condition, and the weaker VOx–support interactions result in lower electron density of bridge oxygen and thus contributing to higher C–H bond rupture capability as that of VOx/ZrO2. Relatively lower apparent activation energies of PDH in the CO2 atmosphere were observed for all samples. However, whether the activity promotional effect of CO2 could be observed experimentally depend largely on the coking behaviors of catalysts because the H2 lean conditions caused by CO2 would lead to faster deactivation of catalysts with a higher VOx polymerization degree and stronger support acidity. The basic principles established in the present study will help to further tune the micro-environment of the V–O active site for high-performance PDH and CO2-PDH reactions.