The role of structural chemistry of selective catalysts in heterogeneous mild oxidation of hydrocarbons

The role of the structural chemistry of catalytic oxides in selective heterogeneous catalytic oxidations of hydrocarbons as studied by our group is emphasized. The solid oxide catalyst is viewed as a catalytic reagent which is regenerated at each redox cycle. New reactors like transported bed and catalytic membrane reactors use explicitly this principle. The nucleophilic nature of selective oxygen species is accounted for by a new numerical scale of Lewis-type acidity/basicity based on the optical basicity A, which is the electron donor power of the O(2-) oxygens linked to cation(s). Linear correlations, which can be used as predictive: trends, are drawn between the variation DeltaI of ionization potentials of reactant and product and the optical basicity of the selective catalyst (A). All selective oxidation reactions depending on the surface crystal field exerted by the solid crystal faces on the organic molecules. the spatial arrangement of metallic (Me) and oxygen atoms as well as the Me-O bond energies are shown to play a leading part. The specificity of the {100} cleavage face of (VO)(2)P(2)O(7) in the 14-electron oxidation of n-butane to maleic anhydride is demonstrated by considering the energy of Me-O bonds when facing the C-H, C-C, etc, bonds in the molecule of n-butane to be transformed. The three situations allowing invoking of site isolation are dealt with. Structural defects may be intrinsic to the active phase like in the case of mosaic crystals of (VO)(2)P(2)O(7) displaying nanodomains of {100} faces. Adding promotors to the active phase, or supporting the active phase as monolayers, are two other means which are discussed. (C) 2000 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.