CO adsorption on transition metal clusters: Trends from density functional theory

This work reports for the first time the trends for carbon monoxide (CO) chemisorption on transition metal clusters present in supported metal catalysts. In particular, the energetic, structural and infrared adsorption characteristics of linearly (atop) CO adsorbed on transition metal nano-clusters of less than 10 A in size were explored. Spin-unrestricted density functional theory (DFT) calculations were employed to explore the trends of CO adsorption energy (A(M-CO)) and C-O vibrational frequency (v(CO)) for clusters composed of Ni, Cu, Ru, Rh, Pd, Ag, It, Pt and Au. The effects of the transition metal electronic structure onto the adsorption energy of CO and the vibrational stretching frequency of C-O, and how these chemical parameters can be correlated to the catalytic activity of transition supported metal catalysts that involve the adsorption, surface diffusion, and C-O bond dissociation elementary steps in heterogeneous catalytic surface reactions, are discussed. Our findings show that an increase of the electronic d-shell occupancy and the principal quantum number (n) in transition metals causes an increase in the vibrational stretching frequency of the C-O bond. This trend is inconsistent with the classical Blyholder model for the metal-carbonyl bond. (C) 2008 Elsevier B.V. All rights reserved.