CexZr1–xO2-Supported CrOx Catalysts for CO2-Assisted Oxidative Dehydrogenation of Propane─Probing the Active Sites and Strategies for Enhanced Stability

CO₂-assisted oxidative dehydrogenation of propane (CO₂-ODH) represents an attractive approach for propylene production and CO₂ utilization. As a soft oxidant, CO₂ can minimize overoxidation of the hydrocarbons to enhance the propylene selectivity while increasing the equilibrium yield. However, a major challenge of CO₂-ODH is the rapid deactivation of the catalysts. The current study focuses on designing Ce_xZr_1–xO₂-mixed oxide-supported CrO_x catalysts for CO₂-ODH with enhanced product selectivity and catalyst stability. By doping 0–30% Ce in the Ce_xZr_1–xO₂ mixed oxide support, propane conversion of 53–79% was achieved at 600 °C, with propylene selectivity up to 82%. Compared to the pure ZrO₂-supported catalyst (i.e., 5 wt %Cr/ZrO₂), 20–30 %Ce doped catalysts (i.e., 5 wt %Cr/Ce_0.2Zr_0.8O₂ and 5 wt %Cr/Ce_0.3Zr_0.7O₂) inhibited the formation of CH₄ and ethylene and improved propylene selectivity from 57 to 77–82%. Detailed characterizations of the 5%Cr/Ce_0.2Zr_0.8O₂ catalyst and density functional theory (DFT) calculations indicated that Cr³⁺ is the active species during the CO₂-ODH reaction, and the reaction follows a non-redox dehydrogenation pathway. Coke formation was determined to be the primary reason for catalyst deactivation, and the addition of Ce to the ZrO₂ support greatly enhanced the coke resistance, leading to superior stability. Furthermore, coke removal by oxidizing the catalyst in air is effective in restoring its activity.