The objective of this project is to determine the origin of the support effect for supported vanadium oxide catalysts. Deposition of a two-dimensional vanadium-oxide overlayer on various oxide supports dramatically affects the reducibility, catalytic activity, and selectivity of the resultant surface phases. The cause of this is not understood; possibilities include structural changes in the surface overlayer and electronic effects of the oxide support ligands. Molecular structures of the surface vanadium-oxide overlayers are determined with a combination of laser Raman spectroscopy and solid-state vanadium-51 nuclear magnetic resonance. Oxide supports chosen for this work are silica, niobia, zirconia, and magnesia; these display a wide range of acidity/basicity, electronegativity, and potential for ligand effects. The reactivity of the catalysts is probed by temperature- programmed reduction and the structure-sensitive methanol oxidation reaction. The improved understanding of this system should lead to better control and design of vanadia catalysts and of reactor systems employing such catalysts, or in which they may be formed inadvertently. Such systems are receiving great attention as the method of choice for removal of nitrogen oxides (precursors of acid rain) from stationary sources. Other relevant processes include production of monomers for condensation polymers (polyesters, polyamides, etc.) synthetic sugars, and cracking and hydrotreating of petroleum.
