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 heter ogeneous catalytic oxidations of hydrocarbons as studied by our group is em phasized. The solid oxide catalyst is viewed as a catalytic reagent which i s regenerated at each redox cycle. New reactors like transported bed and ca talytic membrane reactors use explicitly this principle. The nucleophilic n ature 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 t he electron donor power of the O2- oxygens linked to cation(s). Linear corr elations, which can be used as predictive: trends, are drawn between the va riation DeltaI of ionization potentials of reactant and product and the opt ical basicity of the selective catalyst (A). All selective oxidation reacti ons depending on the surface crystal field exerted by the solid crystal fac es on the organic molecules. the spatial arrangement of metallic (Me) and o xygen atoms as well as the Me-O bond energies are shown to play a leading p art. The specificity of the {100} cleavage face of (VO)(2)P2O7 in the 14-el ectron oxidation of n-butane to maleic anhydride is demonstrated by conside ring the energy of Me-O bonds when facing the C-H, C-C, etc, bonds in the m olecule of n-butane to be transformed. The three situations allowing invoki ng 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)P2O7 displa ying nanodomains of {100} faces. Adding promotors to the active phase, or s upporting the active phase as monolayers, are two other means which are dis cussed. (C) 2000 Academie des sciences / Editions scientifiques et medicale s Elsevier SAS.