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Title: 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

Abstract

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 isolatedmore » VO{sub 4} units is responsible for the enhanced reactivity of the surface V cations.« less

Authors:
;
Publication Date:
Research Org.:
Lehigh Univ., Bethlehem, PA (US)
Sponsoring Org.:
National Science Foundation (NSF); USDOE
OSTI Identifier:
20076091
DOE Contract Number:  
FG02-93ER14350
Resource Type:
Journal Article
Journal Name:
Journal of Catalysis
Additional Journal Information:
Journal Volume: 192; Journal Issue: 1; Other Information: PBD: 15 May 2000; Journal ID: ISSN 0021-9517
Country of Publication:
United States
Language:
English
Subject:
32 ENERGY CONSERVATION, CONSUMPTION, AND UTILIZATION; 10 SYNTHETIC FUELS; ALUMINIUM OXIDES; SILICON OXIDES; VANADIUM OXIDES; CATALYSTS; MORPHOLOGY; CATALYTIC EFFECTS; METHANOL; OXIDATION

Citation Formats

Gao, X., and Wachs, I.E. 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. United States: N. p., 2000. Web. doi:10.1006/jcat.2000.2822.
Gao, X., & Wachs, I.E. 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. United States. doi:10.1006/jcat.2000.2822.
Gao, X., and Wachs, I.E. Mon . "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". United States. doi:10.1006/jcat.2000.2822.
@article{osti_20076091,
title = {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},
author = {Gao, X. and Wachs, I.E.},
abstractNote = {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.},
doi = {10.1006/jcat.2000.2822},
journal = {Journal of Catalysis},
issn = {0021-9517},
number = 1,
volume = 192,
place = {United States},
year = {2000},
month = {5}
}