Structural characteristics and catalytic properties of highly dispersed ZrO2/SiO2 and V2O5/ZrO2/SiO2 catalysts

Highly dispersed ZrO2/SiO2 and V2O5/ZrO2/SiO2 catalysts were successfully s ynthesized by the incipient wetness impregnation method. The surface struct ures of these catalysts in hydrated and dehydrated states were characterize d by in situ Raman and UV-vis-near-infrared diffuse reflectance spectroscop ies. Temperature-programmed reduction and methanol oxidation were employed as chemical probe reactions to examine the reducibility and reactivity/sele ctivity properties of these catalysts. These characterization techniques de monstrate that both zirconium oxide and vanadium oxide species are highly d ispersed as two-dimensional metal oxide overlayers on the silica support. T he spectroscopic results revealed that the surface vanadium oxide species o n the highly dispersed ZrO2/SiO2 supports are predominantly isolated VO4 un its [O=V(O-support)(3)] in the dehydrated state and become polymerized vana dium oxide species upon hydration. The surface vanadium oxide species prefe rentially interact with the zirconium oxide species on the silica surface. The substitution of Si-IV-O- by Zr-IV-O- ligands significantly affects the chemical properties of the isolated VO4 units: the reducibility of the surf ace vanadium oxide species increases, and the methanol oxidation turnover f requency (TOF) increases by 1-2 orders of magnitude relative to V2O5/SiO2. The present study demonstrates that the support effect, variation in the re activity of supported metal oxide catalysts due to different oxide supports , essentially originates from the difference in oxygenated ligands around t he active metal cations.