Partial oxidation reactions on phosphate-based catalysts

In this work emphasis has been placed on phosphate-based catalysts used for partial oxidation reactions, such as vanadyl pyrophosphate, iron phosphates and hydrogen/hydroxy-phosphates, zirconium hydrogen phosphates as layered compounds used to stabilise/entrap Cr and V oxyhydroxy-macrocations. It is shown that, in partial oxidation reactions, the catalyst surface behave in a rather dynamic and labile way, reconstructing under activation and/or catalytic reaction conditions and adapting itself to the stereochemistry of the reactants. The active sites are shown to have a molecular size, to be isolated and to present several catalytic functions, as hydrocarbon activation, H atom abstraction, lattice oxygen incorporation and electron transfer through the solid material to allow the redox process to occur. The metal cations are the active species and the role of the phosphate tetrahedra is not only to bind the MO6 octahedra together to constitute a dense or layered compound but also to bring some specific redox and acid-base properties.