We studied the effect of Pd on the adsorption of CO on the tin oxide surface SnO2(1 1 0) by Density Functional Theory calculations. Molecular CO adsorbs more strongly in the presence of Pd pre-deposited on the surface. The most stable adsorption sites are those bonded to the Pd atom near a Pd top position on a tilted configuration. In this case the C-O distance increases, producing a weakening of the bond and the calculated stretching frequency decreases. Analysis of the atomic orbital interactions reveals that Pd CO bonding involves C s - O p and p orbitals from CO, with Pd d orbitals. For CO sites bonded to Pd, CO bonds to the surface producing a weakening of the surface Pd-O bond. The electronic configuration analysis shows that in all cases the CO molecule withdraws charge from the surface. (C) 2015 Elsevier B.V. All rights reserved.