Reactive intermediates formed upon electron transfer from the surface of oxide catalysts to adsorbed molecules

The basic steps of catalytic oxidation processes at the surface of metal oxides consist in redox interactions involving the solid and one or more reactants (in particular molecular oxygen). The general redox properties of a metal oxide can be investigated by means of the electron paramagnetic resonance (EPR) technique which is capable of detecting the paramagnetic centers often formed upon one electron redox processes. The principles of the EPR technique are brie¯y described in the ®rst part of this paper. In the second part routine methods to measure the electron donor and the electron acceptor ability of a surface (using particular probe molecules) are described. Finally the paper deals with the interactions of molecular oxygen with the surfaces of oxides leading to electron transfer towards the adsorbed molecule. Various examples of electron transfer are discussed in relation to the nature and activation conditions of the solid. In conclusion the particular case of surface intermolecular electron transfer (SIET) is brie¯y illustrated