The role of redox, acid base and collective properties and of cristalline state of heterogeneous catalysts in the selective oxidation of hydrocarbons

The main aspects of heterogeneous selective oxidation on metal oxides are considered, in particular the importance of acid base and redox properties. Particular emphasis is placed on the dynamics of the surface under catalytic conditions which involves a redox process, dehydroxylation of the surface, reversible formation of point defects and shear plane transformations, changes in collective properties due to the adsorption of reactants/products and reduction of the solid ( electrical conductivity variations), amorphous state of a few surface top layers, etc. All these aspects affect the reaction mechanism and, subsequently, the activity and selectivity of the reactions and result in a very complex system, particularly difficult to characterise. However, despite this great complexity some general conclusions can be drawn.