Valence restrictive metal-support interaction for boosting catalytic activity of Rh/CeO₂ in CO₂ hydrogenation

Metal-support interactions (MSI) profoundly modulate the catalytic properties of supported nanometal catalysts. However, a comprehensive understanding of their underlying mechanisms largely remains elusive. In this work, we propose a novel valence restrictive metal-support interaction (VR-MSI) through systematic theoretical and experimental studies of the various Rh-modified CeO₂(111) surfaces. It reveals that small Rh clusters are oxidized by the CeO₂ support and constantly maintain the +2 valence state, thus establishing a clear correlation between their sizes and the electronic properties for each Rh atom. The VR-MSI effect can therefore favor the adsorptions of negatively charged species at small supported Rh clusters through local electrostatic interactions, and for CO₂ hydrogenation reactions, the occurrence of active hydride species (H^-) can be effectively promoted by the supported Rh nanocluster toward highly selective and active CO₂ hydrogenation to CH₄. This discovery broadens our understanding of the MSI effect and the mechanism of selective hydrogenation in heterogeneous catalysis, offering new insights into the rational design of advanced hydrogenation catalysts.