ADSORPTION OF CO AND NO ON (111) AND (100) SURFACES OF PD3MN COMPAREDWITH PD - A THEORETICAL APPROACH

By means of extended Huckel calculations, the electronic properties of the (111) and (100) surface Pd atoms of the Pd3Mn alloy are compared with those of pure Pd. An electron transfer occurs from Mn to Pd, resu lting in an increased electron density on the surface Pd atom whatever Mn is present in the first or the second layer. The study of CO and N O adsorption shows for both molecules a decrease in the binding energy on the alloy surfaces compared with the pure metal surfaces, The N-O overlap population is found to be much smaller on the alloy, which mea ns that the N-O bond is weaker and hence that NO dissociates more easi ly than on pure Pd. Moreover, the bent form of NO is found to be prefe rred in most cases on the alloy, which is even more favourable for NO dissociation. Therefore, these results explain why the alloying of Pd with Mn enhances the catalytic behaviour of Pd for the CO+NO reaction if NO dissociation is the determining step. (C) 1998 Elsevier Science B.V.