Density functional theory study of CO-induced segregation in gold-based alloys

Abstract

This paper reports a systematic study of the effect of CO gas on the chemical composition at the surface of gold-based alloys. Using DFT periodic calculations in presence of adsorbed CO the segregation behavior of group 9-10-11 transition metals (Ag, Cu, Pt, Pd, Ni, Ir, Rh, Co) substituted in semi-infinite gold surfaces is investigated. Although, CO is found to be more strongly adsorbed on (100) than on the (111) surface, the segregation of M impurities is found to be more pronounced on the (111) surface. The results reveal two competitive effects: the effect of M on CO and the effect of CO on M. Thus, on one hand, if M exists on the (100) gold facet, CO would be strongly adsorbed on it. But if M is initially located in the bulk, it would segregate to the (111) facet instead of the (100) in order to bind to CO.

Carbon Monoxide Poisoning Resistance and Structural Stability of Single Atom Alloys

“…are still in excellent agreement with ours due to a cancellation of the over-binding when the difference is taken between CO bound on a host and SAA material [32].…”

“…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][28][29][30][31][32][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].…”

“…Moreover, several theoretical studies have demonstrated the phenomenon of adsorbate induced segregation [27][28][29][30][31][32][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]. This study by Sansa et al predicts over-bound CO adsorption energies due to the use of the traditional PBE exchange-correlation functional rather than RPBE used in this case; though their values of ΔE…”

“…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.…”

Effects of pressure, temperature and atomic exchanges on phase separation dynamics in Au/Ni(111) surface alloy: Kinetic Monte Carlo study

“…The CO adsorption is a driving force for Pd preferential surface segregation on Au/Pd(111) [4,5] and induces migration of Cu on top of Cu/ Pt(111) generating a stable CO/CuPt surface alloy [6]. The COinduced surface segregation energies for gold-based alloys with transition metals (Ag, Cu, Pt, Pd, Ni, Ir, Rh, Co) are calculated by the density functional theory (DFT) [7]. An efficient segregation of Cu is demonstrated in Ag/Cu(100) alloy due to adsorption of O 2 [8].…”