Catalytic activity of PtCu intermetallic compound for CO oxidation: A theoretical insight

To understand the microscopic mechanism of the CO oxidation reaction at PtCu nanoparticles, which have unique geometric and electronic structures compared to their component metals, we present here a theoretical study, based on density functional theory calculations, of the main reaction steps of this reaction. We examine the O-2 dissociation, the CO adsorption and the CO + O-2 reaction at an atomic level and use the computed geometries, Bader charges, and vibrational frequencies to rationalize the role of the intermetallic nanoparticles surface structure on the experimentally observed much higher activity of these nanoparticles as catalysts of the preferential oxidation of CO. By comparing with clean Pt (111) surface and with different Cu-doped models of this same surface, our results show that, at the surface, the presence of Cu induces the segregation of CO molecules at Pt sites and of O-2 molecules at Cu sites. Contrarily to Pt surfaces, the unassisted O-2 dissociation has a high barrier at the intermetallic nanoparticle surface and proceeds through a CO-assisted mechanism in which the new CO bond is formed while the O-O bond is broken with a kinetic barrier much lower than on either Pt (111) or in Pt-doped surfaces. The particular structure of the intermetallic surface is shown to have a significant role in the low kinetic barrier for the reaction, allowing for an easy approach of the CO to the adsorbed O-2 molecule that permits an early transition state with a low energetic barrier.

Automated summary

This study utilizes density functional theory calculations to investigate the main reaction steps of CO oxidation at PtCu nanoparticles, revealing the significant role of the intermetallic surface structure in the high catalytic activity of these nanoparticles. By comparing with clean Pt (111) surface and different Cu-doped models, it is found that the presence of Cu induces segregation of CO and O-2 molecules at specific sites, leading to a unique CO-assisted mechanism for O-2 dissociation with a lower kinetic barrier compared to traditional Pt surfaces.