DEHYDROGENATION OF ADSORBED METHOXY ON CLEAN AND OXIDIZED METALS - AN ELECTRONIC EFFECT AND ITS IMPLICATIONS

By means of an atom superposition and electron delocalization molecular orbital (ASED-MO) study it is shown that the reaction on Pt(111), CH3O(ads) --> CH2O(ads) + H(ads) (i), may be viewed as a hydride transfer and has a relatively low activation barrier. By contrast, the reaction CH3O(ads) + O(ads) --> CH2O(ads) + OH(ads) (ii) has a higher barrier because O(ads) is formally O2-, having formed two electron holes at the top of the filled Pt valence band, and in reaction ii there is a net promotion of two electrons from lower-lying O lone-pair orbitals to the hole orbitals. On the basis of the electron promotion concept, pathways for dehydrogenation of other hydrocarbon and oxygenate intermediates on oxidized metal surfaces are suggested.