Quantitative structural analysis of dispersed vanadia species in TiO[sub 2] (anatase)-supported V[sub 2]O[sub 5]
- Univ. of California, Berkeley (United States)
Titania-supported V[sub 2]O[sub 5] catalysts are used industrially for the partial oxidation of hydrocarbons and for the selective catalytic reduction (SCR) of NO and NH[sub 3]. V[sub 2]O[sub 5]-TiO[sub 2] (anatase) catalysts have been studied under oxidizing and reducing conditions using in situ laser Raman spectroscopy (LRS) and temperature-programmed reduction (TPR) and oxidation (TPO). Quantitative Raman and TPO analysis of the oxidized samples show that these materials are comprised of a distribution of monomeric vanadyls, polymeric vanadates, and crystallites of V[sub 2]O[sub 5]. At low loadings, the predominant species are monomeric vanadyls, with the remaining vanadia being present in the form of polymeric vanadates. As the surface concentration of V[sub 2]O[sub 5] increases, a maximum in the concentration of the polymeric vanadates is detected. Crystallites of V[sub 2]O[sub 5] form at the expense of the polymeric vanadates as the loading is raised above the dispersive capacity of the TiO[sub 2] (anatase) support. An equilibrium polymerization model is proposed to account for the observed concentration of vanadia species, which leads to an initial polymer size of [approximately] 2 at low loadings, consistent with the formation of dimeric species. Raman and TPR/TPO studies of the reduction process indicate that the terminal V = O groups of the monomeric and polymeric vanadia species are removed preferentially to the bridging oxygen atoms of the polymeric species. The maximum loss of oxygen upon reduction is one oxygen atom per vanadium atom.
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 6916550
- Journal Information:
- Journal of Catalysis; (United States), Journal Name: Journal of Catalysis; (United States) Vol. 134:2; ISSN 0021-9517; ISSN JCTLA5
- Country of Publication:
- United States
- Language:
- English
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AMMONIA
CATALYST SUPPORTS
CATALYSTS
CHALCOGENIDES
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
CONTROL
DENITRIFICATION
HYDRIDES
HYDROCARBONS
HYDROGEN COMPOUNDS
KINETICS
LASER SPECTROSCOPY
MATHEMATICAL MODELS
NITRIC OXIDE
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SELECTIVE CATALYTIC REDUCTION
SPECTROSCOPY
STRUCTURAL CHEMICAL ANALYSIS
SURFACE PROPERTIES
TEMPERATURE CONTROL
THERMOCHEMICAL PROCESSES
TITANIUM COMPOUNDS
TITANIUM OXIDES
TRANSITION ELEMENT COMPOUNDS
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VANADIUM OXIDES