Structural characteristics and reactivity/reducibility properties of dispersed and bilayered V{sub 2}O{sub 5}/TiO{sub 2}/SiO{sub 2} catalysts
- Lehigh Univ., Bethlehem, PA (United States)
- UOP Research, Des Plaines, IL (United States)
- CSIC, Madrid (Spain). Inst. de Catalisis y Petroleoquimica
Dispersed and bilayered V{sub 2}O{sub 5}/TiO{sub 2}/SiO{sub 2} catalysts were successfully synthesized by the incipient wetness impregnation method, and their surface structures under various conditions were extensively investigated by combined in situ Raman, UV-vis-NIR diffuse reflectance and X-ray absorption near-edge spectroscopies, as well as X-ray photoelectron spectroscopy. Temperature-programmed reduction and methanol oxidation were employed as chemical probe reactions to examine the reducibility and reactivity/selectivity of these catalysts. The spectroscopic results revealed that both vanadium oxide and titanium oxide on SiO{sub 2} are dispersed as two-dimensional metal oxide overlayers. The surface vanadium oxide species on the dispersed TiO{sub 2}/SiO{sub 2} are predominantly isolated VO{sub 4} units [O{double_bond}V(O-support){sub 3}] in the dehydrated state and become polymerized VO{sub 5}/VO{sub 6} units upon hydration. The surface vanadium oxide species preferentially interact with the surface titanium oxide species on silica, and the V(V) cations possess oxygenated ligands of Si(IV){single_bond}O{sup {minus}} and Ti(IV){single_bond}O{sup {minus}} in the O{double_bond}V(O-support){sub 3} unit with varying ratios from 3:0 to 0:3, which depends on the vanadia and titania loadings. The varying ratio of the Si(IV){single_bond}O{sup {minus}} and Ti(IV){single_bond}O{sup {minus}} oxygenated ligands significantly affects the chemical properties of the isolated VO{sub 4} units. Consequently, the reducibility of the surface vanadium oxide species is altered and the reduction occurs over a wider temperature range. In addition, the methanol oxidation turn-over frequency of the surface VO{sub 4} species on TiO{sub 2}/SiO{sub 2} increases an order of magnitude relative to V{sub 2}O{sub 5}/SiO{sub 2}. Thus, the oxygenated ligands around the V cations play a critical role in determining the reactivity of the surface vanadium oxide species on the oxide supports.
- Sponsoring Organization:
- National Science Foundation, Washington, DC (United States); USDOE, Washington, DC (United States)
- DOE Contract Number:
- FG02-93ER14350
- OSTI ID:
- 335240
- Journal Information:
- Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical, Vol. 103, Issue 4; Other Information: PBD: 28 Jan 1999
- Country of Publication:
- United States
- Language:
- English
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