Facet specificity of yttrium doping on CO₂ methanation over Ni/CeO₂ catalysts

Ni/CeO₂ is widely reported as an outstanding catalyst for CO₂ methanation. Additionally, the base Ni/CeO₂ catalyst is often modified by alloying with active metal Ni or substitutional doping to CeO₂ support to further enhance its methanation performance. The latter will bring complex changes to the structures of catalytic interfaces, which are inadequately understood. In this study, we systematically investigate the structural, electronic and catalytic consequences of substitutional Y-doping to Ni/CeO₂ by preparing Ni catalysts supported on Y³⁺-doped CeO₂ nanorods with predominately (110) facets and CeO₂ nanocubes with predominately (100) facets. A combination of experimental and theoretical studies revealed that Y-doping on both facets afforded substantial boost to CO₂ methanation activity, which is linked to the formation of oxygen vacancies, the moderate basicity and the metal-support interaction across the Ni-CeO₂ interface. In situ DRIFTS experiments suggest that the Ni/Y-doped CeO₂ (110) interface favors the formation of formate species, which is an important intermediate of CO₂ methanation. The critical role of hydrogen spillover in activating subsequent reaction intermediates is also clearly observed. This facet-specific study of the doping effect provides a clear understanding in regarding the modulation of metal-support interaction (MSI) on Ni/CeO₂, thereby providing a scientific rationale for the design of high-efficiency metal/oxide catalysts.