Dynamical and geometrical aspects of NO chemisorption on transition metals: Rh, Pd, and Pt

The technical relevance of Rh, Pd. and Pt as catalysts used to reduce NOx pollutants has stimulated great interest in a detailed understanding of the chemisorption process of these systems. While experiment indicates Ph to be a better catalyst than the other transition metals, theory still does not give a satisfying explanation for this behavior. We have examined the c(2 x 2) atop chemisorption of NO on Rh. Pd, and Pt substrates with our full-potential linearized augmented-plane-wave method for thin films. Simultaneous relaxation of the NO bond length and the distance between the metal and N, as well as surface relaxation of the metal, was performed. Various vibration frequencies were determined from the dynamical matrix of the system, The analysis of the dynamical matrix shows stronger bonding of NO to Pd and Pt compared to the Ph surface. We find the metal surface to be strongly affected by NO chemisorption. including a buckling that is about 50% larger on Pd anti Pt than on the Rh surface. While the calculated electronic properties, such as density of states, give very similar results for the three systems the geometric and dynamical properties may explain the observed higher efficiency of Rh as a catalyst.