First-principles study of Au–Cu alloy surface changes induced by gas adsorption of CO, NO, or O2

Abstract

The surface composition of bimetallics can be strongly altered by adsorbing molecules where the metal with the strongest interaction with the adsorbate segregates into the surface. To investigate the effect of reactive gas on the surface composition of Au-Cu alloy, we examined by means of density functional theory to study the segregation behavior of copper in gold matrices. The adsorption mechanisms of CO, NO, and O2 gas molecules on gold, copper, and gold-copper low index (111), (100), and (110) surfaces were analyzed from energetic and electronic points of view. Our results show a strong segregation of Cu toward the (110) surface in the presence of all adsorbed molecules. Interestingly, the Cu segregation toward the (111) and (100) surface could occur only in the presence of CO and at a lower extent in the presence of NO. The analysis of the electronic structure highlights the different binding characters of adsorbates inducing the Cu segregation.

Carbon Monoxide Poisoning Resistance and Structural Stability of Single Atom Alloys

“…This has previously been noted experimentally for dilute Pd/Cu SAA nanoparticles whereby exposure to CO pulls Pd to the surface and consequently enhances the activity of these nanoparticles towards acetylene hydrogenation [26]. Moreover, several theoretical studies have demonstrated the phenomenon of adsorbate induced segregation [27–33]. For example a study by Sansa et al on the CO induced segregation of single transition metal dopant atoms in Au reveals that the adsorption energy of CO is sufficient to promote dopant atom segregation to both the Au(111) and Au(100) surfaces from the bulk [32].…”

“…Additionally, we recognize that the presence of adsorbates may induce structural changes in binary alloy materials, such as segregation of atoms from the bulk into the surface layer, as well as promoting aggregation and island formation [26][27][28][29][30][31][32][33][34]. Such changes are caused by differences in adsorption behaviour between an adsorbate on each metallic component of the alloy; these differences can offset or increase the energy change upon restructuring of the material.…”

CO-Induced Aggregation and Segregation of Highly Dilute Alloys: A Density Functional Theory Study

“…Bimetallic catalysts often exhibit superior catalytic performance as compared to their monometallic counterparts. 1 As a consequence these catalysts have been the subject of extensive research, [2][3][4][5][6] being at the same time the workhorse of important large-scale applications, such as naphtha cracking, hydrotreating of crude oil, acrylonitrile synthesis, ammonia oxidation and the reduction of pollutants produced by diesel engines. 7,8 A new class of bimetallic catalysts, that has recently drawn a lot of attention, is single atom alloys (SAAs).…”

“…CO, H2, NO and O2) in the aim of improving the catalytic properties of the material. 6,28,[31][32][33][34] CO is typically used as a probe molecule for specifying the properties of adsorption on solid materials 32,35 and it is known for inducing morphological changes to the catalytic surface when adsorbed thereon. For example, highly mobile carbonyl species on Pt-and Pd-doped Fe3O4(001) are observed with scanning tunnelling microscopy (STM) after exposure of the surfaces to CO gas at low PCO (e.g.…”

Gas-induced selective re-orientation of Au–Cu nanoparticles on TiO2 (110)

“…More recently, Dhifallah and co-workers have suggested using firstprinciples calculation that the Cu segregation may also depend on the surface orientation. 50 b) Thermal stability of the core/shell structure In each of the GIXD experiments presented in figure 4 and 5 the gas has been pumped down and the system maintained under UHV at room temperature to investigate a possible diffusion of the Cu atoms back into the Au enriched core of the NP. Indeed, it has been shown that Cu atoms deposited onto ≈ 2 nm Au NPs at room temperature diffuse into them to form an alloy.…”