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.