Interfacial Unit-Dependent Catalytic Activity for CO Oxidation over Cerium Oxysulfate Cluster Assemblies.

Atomically precise cerium oxo clusters offer a platform to investigate structure-property relationships that are much more complex in the ill-defined bulk material cerium dioxide. We investigated the activity of the MCe torus family (M = Cd, Ce, Co, Cu, Fe, Ni, and Zn), a family of discrete oxysulfate-based Ce rings linked by monomeric cation units, for CO oxidation. CuCe emerged as the best performing MCe catalyst among those tested, prompting our exploration of the role of the interfacial unit on catalytic activity. Temperature-programmed reduction (TPR) studies of the catalysts indicated a lower temperature reduction in CuCe as compared to CeCe. diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) indicated that CuCe exhibited a faster formation of Ce and contained CO bridging sites absent in CeCe. Isothermal CO adsorption measurements demonstrated a greater uptake of CO by CuCe as compared to CeCe. The calculated energies for the formation of a single oxygen defect in the structure significantly decreased with the presence of Cu at the linkage site as opposed to Ce. This study revealed that atomic-level changes in the interfacial unit can change the reducibility, CO binding/uptake, and oxygen vacancy defect formation energetics in the MCe family to thus tune their catalytic activity.