Surface composition of AgPd single-atom alloy catalyst in an oxidative environment

Abstract

Single-atom alloys (SAAs) have recently gained considerable attention in the field of heterogeneous catalysis research due to their potential for novel catalytic properties. While SAAs are often examined in reactions of reductive atmospheres, such as hydrogenation reactions, in the present work, we change the focus to AgPd SAAs in oxidative environments since Pd has the highest catalytic activity of all metals for oxidative reactions. Here, we examine how the chemical reactivity of AgPd SAAs differs from its constituent Pd in an oxidative atmosphere. For this purpose, electronic structure changes in an Ag0.98Pd0.02 SAA foil in 1 mbar of O2 were studied by in situ x-ray photoemission spectroscopy and compared with the electronic structure of a Pd foil under the same conditions. When heated in an oxidative atmosphere, Pd in Ag0.98Pd0.02 partly oxidizes and forms a metastable PdOx surface oxide. By using a peak area modeling procedure, we conclude that PdOx on Ag0.98Pd0.02 is present as thin, possibly monolayer thick, PdOx islands on the surface. In comparison to the PdO formed on the Pd foil, the PdOx formed on AgPd is substantially less thermodynamically stable, decomposing at temperatures about 270 °C lower than the native oxide on Pd. Such behavior is an interesting property of oxides formed on dilute alloys, which could be potentially utilized in catalytic oxidative reactions such as methane oxidation.

Embedded Oxidized Ag–Pd–Cu Ultrathin Metal Alloy Film Prepared at Low Temperature with Excellent Electronic, Optical, and Mechanical Properties

“…According to the data presented in Table S1, the lower transparency in the visible region of the OMO coatings deposited at Γ > 3% can be attributed to a decreased mobility of the free electrons in the metallic layer, i.e., an increase of Ω τ|Metal . This may be attributed to scattering by impurities associated with the incipient formation of a disordered oxide phase . We note that despite the success of our optical model in reproducing the optical properties of the different OMO coatings, the conclusions drawn from the modeling should be regarded with some caution.…”

“…This may be attributed to scattering by impurities associated with the incipient formation of a disordered oxide phase. 43 We note that despite the success of our optical model in reproducing the optical properties of the different OMO coatings, the conclusions drawn from the modeling should be regarded with some caution. In particular, multipole interactions with the surrounding ITO, although not a metallic conductor, are disregarded.…”

Thermally Stable AgPd@ZnO Bimetallic Alloy Nanoparticles for Ethanol Sensors with Long-Term Stability

“…In addition, Ag x Pd 100– x bimetallic NPs also play a vital chemical sensitization role in redox reactions, on account of their unique spillover effect and catalytic effect. Ag x Pd 100– x bimetallic NPs are excellent oxygen dissociation catalysts in the ambient air and have great capability for catalyzing the molecular oxygen dissociation compared to pristine ZnO and Pd . The catalyzed molecular oxygen dissociates on the surface of Ag x Pd 100– x bimetallic NPs and moves to the surface of the ZnO shell by the spillover mechanism.…”

Dilute Alloys Based on Au, Ag, or Cu for Efficient Catalysis: From Synthesis to Active Sites

“…7,26 Samples for UHV studies can be prepared by melting a quantitative amount of the two metals (e.g., Au slugs together with Pd granules) above their alloying temperature, followed by coldrolling into a foil and annealing (e.g., ∼1100 K) for grain growth; the samples are then cycled between thermal treatments and Ar ion sputtering to remove impurities, with a final step of thermal treatment under UHV conditions for recrystallization. 32 A more ubiquitous strategy is to introduce the minority species by physical vapor or electron beam deposition onto the surface of a pristine metal substrate, which has a well-defined crystalline orientation and an exceptionally low defect and impurity density (often commercially obtained), e.g., Pd/Au (111), Pt/Ag(100), Pt/Cu (111), etc.…”

“…Fundamental surface science studies of single atoms deposited on well-defined single-crystal metal surfaces led to the discovery of single and dilute atom alloy catalysts, a rare instance of fundamental studies initiating the development of a class of heterogeneous catalysts, as opposed to the more traditional approach of testing various catalysts and then turning to fundamental studies to gain mechanistic understanding and further optimize the catalyst. , Samples for UHV studies can be prepared by melting a quantitative amount of the two metals (e.g., Au slugs together with Pd granules) above their alloying temperature, followed by cold-rolling into a foil and annealing (e.g., ∼1100 K) for grain growth; the samples are then cycled between thermal treatments and Ar ion sputtering to remove impurities, with a final step of thermal treatment under UHV conditions for recrystallization . A more ubiquitous strategy is to introduce the minority species by physical vapor or electron beam deposition onto the surface of a pristine metal substrate, which has a well-defined crystalline orientation and an exceptionally low defect and impurity density (often commercially obtained), e.g., Pd/Au(111), Pt/Ag(100), Pt/Cu(111), etc.…”