STRUCTURE AND REACTIVITY OF TIN OXIDE-SUPPORTED VANADIUM-OXIDE CATALYSTS

The surface structure and reactivity of vanadium oxide monolayer catalysts supported on tin oxide were investigated by various physico-chemical characterization techniques. In this study a series of tin oxide supported vanadium oxide catalysts with various vanadia loadings ranging from 0.5 to 6.4 wt.% have been prepared and were characterized by means of X-ray diffraction, oxygen chemisorption at -78-degrees-C, solid state V-51 and H-1 nuclear magnetic resonance and electron spin resonance techniques. Reactivities of these catalysts were also evaluated for partial oxidation of methanol to formaldehyde at atmospheric pressure. Oxygen uptake results suggest the formation of V-oxide 'monolayer' at about 3.2 wt.% vanadia loading; where a maximum activity for methanol oxidation was also observed. Solid-state V-51 NMR results show the presence of two types of vanadium oxide species, one due to a dispersed phase and the other due to the crystalline vanadia phase, supporting oxygen chemisorption results. ESR results also reveal V-oxide in highly dispersed state at the same 3.2 wt.% loading. A direct relationship was also noted between the oxygen uptake and MeOH oxidation activity of the catalysts.