Role of HO Adsorption in CO Oxidation over Cerium-Oxide Cluster Anions (CeO)O ( = 1-4).

Water (HO) is ubiquitous in the environment and inevitably participates in many surface reactions, including CO oxidation. Acquiring a fundamental understanding of the roles of HO molecules in CO oxidation poses a challenging but pivotal task in real-life catalysis. Herein, benefiting from state-of-the-art mass-spectrometric experiments and quantum chemical calculations, we identified that the dissociation of a HO molecule on each of the cerium oxide cluster anions (CeO)O ( = 1-4) at room temperature can create a new atomic oxygen radical (O) that then oxidizes a CO molecule. The size-dependent reactivity of HO-mediated CO oxidation on (CeO)O clusters was rationalized by the orbital compositions (O) and energies of the lowest unoccupied molecular orbitals of active O radicals modified by HO dissociation. Our findings not only provide new insights into HO-mediated CO oxidation but also demonstrate the importance of HO in modulating the reactivity of the O radicals.