Proximity Effects in Electronic Metal–Support Interactions: O-Vacancy Formation and CO Adsorption on Ru/ZrO ₂ Model Catalysts

Continuing our investigation of electronic metal–support interactions (EMSIs) in heterogeneous catalysis, we have investigated the influence of the position and the number of O-vacancies on their stabilization by the Ru nanorod, on the charge transfer from the support to the metal, and on CO adsorption on the Ru nanorod. Employing density functional theory-based calculations and using a model system consisting of a ZrO2(111) support and a three-layer Ru nanorod, we find that O-vacancies are significantly stabilized only if they are in direct contact with the Ru nanorod, with the extent of stabilization depending on the distance between vacancy and the nearest Ru atom at the interface. Vacancy formation beside the Ru nanorod or in deeper layers of the support is not enhanced by the metal. The Ru-induced stabilization of the O-vacancies is closely coupled with the charge transfer from the support to the metal upon vacancy formation, which is true also in the presence of neighboring O-vacancies. The CO adsorption energy can be substantially modified by four characteristic effects, including charge transfer from the support to the metal, coordination effects, a combination of COad-induced deformation energies and changes in the interface energy and direct interactions between CO and partly reduced Zr surface ions directly neighboring to an O-vacancy, depending on the adsorption site and on the number and positions of the O-vacancies. Thus, it is not possible to completely describe the adsorption properties by using the d-band model, in particular, not for adsorption on the interface sites. The general relevance of these findings for adsorption and catalytic reactions is discussed.