Accelerated Cu2O Reduction by Single Pt Atoms at the Metal-Oxide Interface

The reducibility of metal oxides, when they serve as the catalyst support or are the active sites themselves, plays an important role in heterogeneous catalytic reactions. Here we present an integrated experimental and theoretical study that reveals how the addition of small amounts of atomically dispersed Pt at the metal/oxide interface dramatically enhances the reducibility of a Cu2O thin film by H-2. X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption (TPD) results reveal that, upon oxidation, a PtCu single-atom alloy (SAA) surface is covered by a thin Cu2O film and is, therefore, unable to dissociate H-2. Despite this, in situ studies using ambient-pressure (AP) XPS reveal that the presence of a small amount of Pt under the oxide layer can, at the single-atom limit, promote the reduction of Cu2O by H-2 at room temperature. We built two density functional theory based surface models to better understand these experimental findings: a Cu2O/Cu(111)-like surface oxide layer, known as the "29" oxide, in which Pt is alloyed into the Cu(111) surface, as well as a PtCu SAA. Our calculations suggest that the increased activity is due to the presence of atomically dispersed Pt under the surface oxide layer, which weakens the Cu-O bonds in its immediate vicinity, thus making the interface between subsurface Pt and the surface oxide a nucleation site for the formation of metallic Cu. This initial step in the reduction process results in the presence of surface Pt atoms surrounded by metallic Cu patches, and the Pt atoms become active in H-2 dissociation, which consequently accelerates the reduction of the oxide layer. This work demonstrates how isolated Pt atoms at the metal/oxide interface of a Cu-based catalyst accelerate the reduction of the oxide and, therefore, help maintain the active, reduced state of the catalyst under the reaction conditions.