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

Abstract

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 H2. 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 H2. 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 H2 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 H2 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.

Interface atom mobility and charge transfer effects on CuO and Cu2O formation on Cu3Pd(111) and Cu3Pt(111)

“…S.11 in supplementary information. Additionally, the presence of single Pt atoms at the Cu metal-oxide interface weakens Cu-O bond 24 , consistent with the preferential formation of CuO (Cu–O: 0.188 and 0.196 nm) than (Cu–O: 0.185 nm) on Pt interface 42 .…”

“…Cu–platinum (Pt) alloys, viz., , also showed superior methanol oxidation and oxygen reduction performance 23 . Moreover, single Pt atoms at the Cu metal-oxide interface promote the reduction of by exposure 24 . These results indicate that choosing the right alloy components strongly affect reactivity.…”

CO2 Hydrogenation on NixMg1−xAl2O4: A Comparative Study of MgAl2O4 and NiAl2O4

“…(100) was predicted to be exothermic (207.4 kJ/mol), but that on reduced NiAl 2 O 4 (100) was predicted to be endothermic (693.6 kJ/mol). Kinetic enhancement by adjacent oxygen vacancies has been reported for transition metal oxides [39,40,43]. In particular, on PdO(101), oxygen vacancies were found to impact CO oxidation and thermal reduction kinetics significantly.…”

Techniques for the characterization of single atom catalysts

“…29,93 Introducing appropriate reactants and providing suitable reaction temperatures to the XPS chamber, XPS could be upgraded into ambient pressure XPS (AP-XPS), which allows the characterization of catalysts under the reaction atmosphere. 42,94,95 Over SACs, the singly dispersed atoms are highly unsaturated and interact with support, which makes the structure and electronic state of the SAs different from their metal or metal oxide counterparts. AP-XPS is applicable to study the property of the singly dispersed sites on SACs, given the SAs exist on the surface of catalysts.…”