A theoretical study of the adsorption of simple molecules on MgO surfaces: CO, HCO, HOC, H 2CO, HCOH, CH 2OH and CH 3O

Abstract

The adsorption of a series of molecules at the (001) surface of MgO and at an impurity Cu + ion therein has been studied by means of a combination of ab initio molecular orbital and lattice defect methods. The molecular species investigated include CO, HCO, HOC, H 2CO and HCOH, and CH 3O and CH 2OH, all of potential importance in CO/H 2 chemistry. Binding energies of each species adsorbing either through carbon or oxygen have been derived from SCF studies using split-valence basis sets throughout. Additional calculations involving more flexible basis sets, with incorporation of electron correlation have also been performed. Binding through oxygen leads to very similar relative stabilities of the minima on both [CH 2O] and [CH 3O] potential energy surfaces to those predicted for the “free” gas-phase species, and is in general the energetically preferred mode of interaction when binding with an Mg 2+ ion of the non-defective surface. Binding through carbon is the energetically preferred path in interactions with the Cu + dopant ion, however, leading to significant changes in the “free” species energetics. This enhanced binding is attributed to the contribution from π back-donation, an effect which is of importance only in interactions with the dopant ion and which is found to be sensitive to the incorporation of electron correlation.