Revealing Charge Transfer at the Interface of Spinel Oxide and Ceria during CO Oxidation

The interface created between an active metal and an oxide support is known to affect the catalytic performance because of the charge transfer process. However, oxide-oxide interfaces produced by supported spinel oxide catalysts have been less studied owing to their complex interface structures and synthetic challenges. Herein, a synthetic strategy for Co3O4, Mn3O4, and Fe3O4 nanocubes (NCs) with a controlled CeO2 layer enables investigation of the role of the interface in catalytic oxidation. Notably, CeO2-deposited Co3O4 NCs exhibited a 12-times higher CO oxidation rate than the pristine Co3O4 NCs. In situ characterization demonstrates that the deposited CeO2 prevents the reduction of Co3O4 by supplying oxygen. The maximized interface resulting from Co3O4 NCs with three facets covered by CeO2 layers was found to exhibit the highest CO oxidation rate even under O-2-deficient conditions, which resulted from the versatile variation in the oxidation state. This study provides a comprehensive understanding of the Mars-van Krevelen mechanism occurring on the nanoscale at the Co3O4-CeO2 interfaces. The same activity trend and hot electron flow are observed for H-2 oxidation reactions using catalytic nanodiodes, thereby demonstrating that the origin of the activity enhancement is charge transfer at the interface.