The molecular structures and reactivity of V <Subscript>2 </Subscript>O <Subscript>5 </Subscript>/TiO <Subscript>2 </Subscript>/SiO <Subscript>2 </Subscript> catalysts
نویسندگان
چکیده
A series of V205/TiO 2/SiO 2 catalysts were structurally investigated by in situ Raman spectroscopy and chemically probed by methanol oxidation in order to determine the molecular structure-reactivity relationships of the V205/TiO 2/SiO 2 catalysts. Only surface TiO,. species are present on the 3% TiO 2 /S iO 2 catalysts, and the surface TiO x species as well as bulk TiO 2 (anatase) particles coexist on the 40% TiO 2 /S iO 2 catalyst. The deposition of 1-3% vanadium oxide onto 3% TiO 2 /S iO 2 and 4% vanadium oxide onto 40% TiO 2 /S iO 2 forms only a surface vanadium oxide phase. In sire Raman studies reveal that the surface vanadium oxide species preferentially exist on the titania sites of the TiO 2/SiO 2 system. The interaction between the surface vanadia and the surface titania overlayer on SiO 2 increases the methanol oxidation reactivity by two orders of magnitude relative to V2Os/SiO 2. In the presence of bulk TiO 2 (anatase) particles on the SiO 2 support, the reactivity of the surface vanadia further increases by an order magnitude relative to the catalysts containing only surface titania, and is close to that of surface vanadia on bulk TiO 2. This suggests that the surface VO<TiO 2 (bulk) interactions results in a more active site than the surface VO.,.-TiOx-SiO 2 interactions. In addition, the V2Os/Ti02/S iO 2 catalysts exhibit high selectivity towards HCHO because redox sites are predominant on the surface of these catalysts with essentially no acid site present.
منابع مشابه
Symmetries and Conservation Laws of the System: u<Subscript>x</Subscript>= vw<Subscript>x</Subscript>, v<Subscript>y</Subscript>= u w<Subscript>y</Subscript>, uv+w<Subscript>xx</Subscript>+w<Subscript>yy</Subscript>=0
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