Surface electronic structure and isomerization reactions of alkanes on some transition metal oxides

XP spectra of some reduced transition metal oxides are presented. Different number of free nd,(n + 1)s valence electrons in each case could be observed by the presence of a certain density of states (DOS) at the Fermi-level in the valence band (VB) energy region of the XP spectrum. Catalytic isomerization reactions of 2-methylpentane yielding 3-methylpentane and n-hexane at 350 degrees C have been observed on these reduced valence surface states. The bifunctional mechanism in terms of metallic and acidic sites required for such reactions is proposed by considering the metallic properties of the rutile deformed structure through the C-axis in the case of MoO2 and WO2, while the oxygen atom(s) in the lattice structure exhibit Bronsted acidic properties. On the other hand, highly reduced or clean surfaces of these transition metals yield hydrogenolysis catalytic reactions for the same reactant with methane as the major product. Ln all cases, the exposure of the lower valence oxidation states of bulk transition metal oxides to air results in the surface partial oxidation to the stable oxides such as MoO3, WO3, V2O5 and Nb2O5.