Structural characteristics and reactivity properties of highly dispersed Al{sub 2}O{sub 3}/Si{sub 2} and V{sub 2}O{sub 5}/Al{sub 2}O{sub 3}/SiO{sub 2} catalysts
Highly dispersed Al{sub 2}O{sub 3}/SiO{sub 2} and V{sub 2}O{sub 5}/Al{sub 2}O{sub 3}/SiO{sub 2} catalysts under various conditions (e.g., hydration, dehydration, and methanol chemisorption) were investigated by in situ Raman and UV-vis-NIR diffuse reflectance spectroscopies. Temperature-programmed reduction and methanol oxidation were employed as chemical probe reactions to examine the reducibility and reactivity properties of these catalysts. The spectroscopic results revealed that the surface vanadium oxide species on the Al{sub 2}O{sub 3}/SiO{sub 2} supports are predominantly isolated VO{sub 4} units [O = V(O-Support){sub 3}] in the dehydrated state. The surface vanadium oxide species preferentially interact with the aluminum oxide species on the silica surface. Consequently, the reduction behavior of the surface vanadium oxide species is closer to that of V{sub 2}O{sub 5}/Al{sub 2}O{sub 3} at higher alumina loading. Furthermore, the turnover frequency of the surface VO{sub 4} species on Al{sub 2}O{sub 3}/SiO{sub 2} for methanol oxidation to redox products (formaldehyde, methyl formate, and dimethoxy methane) increases by an order of magnitude relative to the V{sub 2}O{sub 5}/SiO{sub 2} catalysts and is comparable to that of the V{sub 2}O{sub 5}/Al{sub 2}O{sub 3} catalysts. It is concluded that the substitution of the Si(IV)-O{sup {minus}} by the less electronegative Al(III)-O{sup {minus}} ligands for the isolated VO{sub 4} units is responsible for the enhanced reactivity of the surface V cations.
- Research Organization:
- Lehigh Univ., Bethlehem, PA (US)
- Sponsoring Organization:
- National Science Foundation (NSF); USDOE
- DOE Contract Number:
- FG02-93ER14350
- OSTI ID:
- 20076091
- Journal Information:
- Journal of Catalysis, Vol. 192, Issue 1; Other Information: PBD: 15 May 2000; ISSN 0021-9517
- Country of Publication:
- United States
- Language:
- English
Similar Records
Structural characteristics and catalytic properties of highly dispersed ZrO{sub 2}/SiO{sub 2} and V{sub 2}O{sub 5}/ZrO{sub 2}/SiO{sub 2} catalysts
In situ spectroscopic investigation of molecular structures of highly dispersed vanadium oxide on silica under various conditions