Oxidative Dehydrogenation of Propane to Propylene in the Presence of HCI Catalyzed by CeO2 and NiO-Modified CeO2 Nanocrystals

The oxidative dehydrogenation of propane is an attractive reaction for propylene production, but the over oxidation leads to low propylene selectivity at considerable propane conversions. Here, we report the oxidative dehydrogenation of propane by oxygen in the presence of hydrogen chloride. CeO2 was found to be an efficient catalyst for the conversion of propane to propylene by (O-2 + HCl). The reaction was structure-sensitive, and the catalytic behavior depended on the exposed facet of CeO2 nanocrystals. The nanorod exposing {110} and {100} facets showed the highest activity, whereas the nanocube enclosed by {100} facets was the most selective for propylene formation. The modification of CeO2 nanorods by NiO increased both propane conversion and propylene selectivity. A propylene selectivity of 80% was achieved at propane conversion of 69% over an 8 wt % NiO-CeO2 catalyst at 773 K, offering a single-pass propylene yield of 55%. No significant catalyst deactivation was observed in 100 h of reaction. HCl played a pivotal role in the selective formation of propylene, and more than 95% of HCl could be recovered after the reaction. The structure-property correlation indicates that the surface oxygen vacancy and the surface chloride coverage are two crucial factors determining the activity and selectivity. The mechanistic studies suggest that the peroxide species (O-2(2-)) formed by adsorption of O-2 on surface oxygen vacancies may activate chloride, generating a radical-like active chlorine species. The active chlorine species accounts for the activation of C-H bond of propane, forming propylene as a major product.