REACTIVE INTERMEDIATES FORMED UPON ELECTRON-TRANSFER FROM THE SURFACEOF OXIDE CATALYSTS TO ADSORBED MOLECULES

The basic steps of catalytic oxidation processes at the surface of met al oxides consist in redox interactions involving the solid and one or more reactants (in particular molecular oxygen). The general redox pr operties 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 processe s. The principles of the EPR technique are briefly described in the fi rst part of this paper. In the second part routine methods to measure the electron donor and the electron acceptor ability of a surface (usi ng 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 ex amples of electron transfer are discussed in relation to the nature an d activation conditions of the solid. In conclusion the particular cas e of surface intermolecular electron transfer (SIET) is briefly illust rated. (C) 1998 Elsevier Science B.V. All rights reserved.