CO Oxidation over AuPd(100) from Ultrahigh Vacuum to Near-Atmospheric Pressures: The Critical Role of Contiguous Pd Atoms

Abstract

It is demonstrated that gas-phase CO pressure higher than approximately 0.1 Torr is required to segregate a sufficient amount of Pd to the surface of a well-annealed AuPd(100) sample to form contiguous Pd sites. These contiguous sites are critical in dissociating O(2) for low-temperature CO oxidation, where CO chemisorbed on Au sites clearly participates in the reaction at temperatures below approximately 400 K. Measured reaction kinetics demonstrates that the higher reaction rate is achieved on a surface with higher coverages of contiguous Pd sites.

Understanding the synergistic effects of gold bimetallic catalysts

“…At Au/Pd < 1, the uptake of H 2 was equal to that of CO, while at Au/Pd P 1, the uptake of H 2 was only half that of CO. Evidently, the number of contiguous Pd atoms decreases while Pd single atoms isolated by gold atoms dominates the surface structure at Au/Pd ratios P1. Although contiguous Pd atoms are required in some oxidation reactions such as CO oxidation [108] and N 2 O decomposition [47], the configuration with single Pd atoms surrounded and isolated by Au atoms has found more applications in the selective hydrogenation reactions [109,110].…”

Near Ambient Pressure XPS Investigation of CO Oxidation Over Pd3Au(100)

“…Dissociation 210 of O2 on contiguous Pd sites on PdAu(100) has been reported by Gao et al [29,34]. It was conjectured 211 that dissociated O2 from these sites would spill over to Au and isolated Pd sites, allowing CO 212 oxidation to occur on these sites, as well as on contiguous Pd.…”

Theoretical insights on the effect of reactive gas on the chemical ordering of gold-based alloys

“…Bimetallic gold-palladium alloy Au-Pd catalyst is one of the bimetallic systems that have attracted the most significant interest due to its superior performance in various catalytic reactions [1,2,[5][6][7]10]. The interplay between gold and palladium components leads to its superior catalytic reactivity in terms of the so-called ligand and ensemble effects [39].…”

“…For instance, Piccolo et al have reported that the increase in the conversion rate of hydrogenation of butadiene into butenes observed on Au-Pd surfaces during time on stream could partly originate from a modification of the surface composition and precisely from Pd surface enrichment induced by reactant or product adsorption [40]. Recent studies of Goodman's group showed that CO adsorption induces Pd segregation on AuPd(100) surfaces [10,41]. The authors have reported that such segregation leads to the formation of contiguous Pd sites, at least Pd dimers able to dissociate O 2 , responsible for the observed enhancement of low-temperature CO oxidation reaction.…”

“…In the context of CO reforming, recent experiments on gold nanoparticles with different Ni contents show an improvement of the CO oxidation rate [9]. Palladium [10] and platinum [11] also emerge as good candidates for the enhancement of such reaction.…”