Reaction Sensitivity of Ceria Morphology Effect on Ni/CeO₂ Catalysis in Propane Oxidation Reactions

CeO₂ nanocubes (c-CeO₂), nanoparticles (p-CeO₂), and nanorods calcined at 500 °C (r-CeO₂-500) and 700 °C (r-CeO₂-700) were used as supports to synthesize a series of Ni/CeO₂ catalysts for the propane combustion and oxidative dehydrogenation of propane (ODHP) reactions. The Ni-CeO₂ interaction greatly promotes the reducibility of CeO₂, but CeO₂ morphology-dependent Ni-CeO₂ interaction was observed to form different speciation of Ni species (Ni²⁺ dissolved in CeO₂, highly dispersive NiO, NiO aggregate) and oxygen species (strongly activated oxygen species, medially activated oxygen species, weakly activated oxygen species) in various Ni/CeO₂ catalysts. Ni-CeO₂ interaction is stronger in Ni/c-CeO₂ catalysts than in other Ni/CeO₂ catalysts. Different morphology-dependences of Ni/CeO₂ catalysts in propane combustion and ODHP reactions were observed. The Ni/r-CeO₂-500 catalyst with the largest strongly activated oxygen species is most catalytic active in the propane combustion reaction while the Ni/c-CeO₂ catalyst with the largest amount of weakly activated oxygen species exhibits the best catalytic performance in the ODHP reaction. Thus, the CeO₂ morphology engineering strategy is effective in finely tuning the metal-CeO₂ interaction and the reactivity of oxygen species to meet the requirements of different types of catalytic oxidation reactions.