A common concept accounting for selectivity in mild and total oxidation reactions: The optical basicity of catalysts

Correlations are settled between the “optical basicity”, Λ, which is defined as the electron donating (accepting) power of the lattice oxygen (cation) of the solid, and its equivalent for the gaseous phase: the ionization energy of the molecules. The optical basicity of any catalytic oxide is easily calculated and depends on the cation(s) valence and coordination. The difference between the ionization energies of reactant and of product, ΔI, accounts for the Selectivity which is driven by the catalyst. Linear relationships ΔI = a Λ + b are drawn by gathering reaction-to-product/selective catalyst couples. The a and b constants depend on the nature of the reactant (paraffin, olefin, alcohol) and on the type of selective reaction (mild oxidation/oxidative dehydrogenation, ammoxidation, total oxidation). Some theoretical considerations are proposed to justify the linearity of the correlations, which permit to select a priori a selective catalyst for a given reaction.