An ab-initio MO study on metal oxide catalytic surfaces

The activation of the Mo=O bond in mixed molybdenum oxide compounds has been studied by means of ab-initio MO methods on mono- and bi-nuclear metal oxide clusters. The clusters, containing Mo, Nb and V, have been chosen to represent the assumed catalytic sites of mixed molybdenum oxide compounds. The analysis of bond length and orbitals shows that the Mo=O bond can be activated by a neighboring metal oxide unit through the interaction of the molecular orbitals of the two sub-units. The present investigation thus shows that the juxtaposition of different metal oxide units in catalysts is not only important in providing a suitable geometry of the surface, but also in providing an indirect mechanism for activation and deactivation of catalytic sites via neighboring structural elements. (C) 1999 Published by Elsevier Science B.V. All rights reserved.