Characterization of γ-alumina-supported vanadium oxide monolayers

The structure and properties of vanadium oxide deposited on γ-alumina at submonolayer coverage have been investigated. Textural analysis, electron microscopy, and low energy ion scattering (LEIS) show that, for loadings up to at least 3.4 V/nm2, the vanadium oxide is present as a highly dispersed phase. LEIS experiments show that the development of the vanadium oxide monolayer proceeds in three steps. In the first step vanadium oxide is molecularly dispersed on γ-alumina as isolated monomeric and dimeric species. Above approximately 1.5 V/nm2 a second layer of vanadium oxide is formed on top of the dimeric species, resulting in the formation of oligomeric species. At coverages above 2.5 V/nm2 these small oligomeric species grow into polymeric vanadium oxide chains. TPR experiments show that reduction of these polymeric species proceeds at lower temperatures than reduction of the monomeric species, probably as a result of the weakening of the vanadium-oxygen bond.