Effects of support composition and pretreatment conditions on the structure of vanadia dispersed on SiO{sub 2}, Al{sub 2}O{sub 3}, TiO{sub 2}, ZrO{sub 2}, and HfO{sub 2}
Spectroscopic techniques (X-ray absorption, Raman, and UV-visible) were utilized to monitor the effect of adsorbed water, calcination temperature, and reduction in H{sub 2} on the structure of dispersed VO{sub x} for vanadia supported on SiO{sub 2}, Al{sub 2}O{sub 3}, TiO{sub 2}, ZrO{sub 2}, and HfO{sub 2} prepared with VO{sub x} surface densities ranging from 0.46 VO{sub x}/nm{sup 2} to 11.1 VO{sub x}/nm{sup 2}. Supported vanadia was found to exist as monovanadate, polyvanadate, or V{sub 2}O{sub 5} species, the distribution among these species depending on the support for a given VO{sub x} surface density. Dehydration resulted in the appearance of monovanadate species on all supports, with the extent of these species decreasing in the order HfO{sub 2} > Al{sub 2}O{sub 3} > ZrO{sub 2} > TiO{sub 2} > SiO{sub 2}. Hydration of the samples caused a decrease in the monovanadate species and a slight increase in polyvanadate species. Oxidation at elevated temperature resulted in an increase in the crystallinity of V{sub 2}O{sub 5} present on SiO{sub 2}, a conversion of V{sub 2}O{sub 5} into polyvanadate species on Al{sub 2}O{sub 3}, and the appearance of mixed-metal oxide phases on TiO{sub 2}, SrO{sub 2} (ZrV{sub 2}O{sub 7}), and HfO{sub 2} (HfV{sub 2}O{sub 7}). The appearance of an interaction between vanadia and titania coincides with the transformation from anatase to futile TiO{sub 2}. ZrV{sub 2}O{sub 7} and HfV{sub 2}O{sub 7} are postulated to form via the interaction of surface VO{sub x} species with the support as the support begins to undergo a phase transition from tetragonal to monoclinic. H{sub 2} reduction produced limited changes in the structure of dispersed vanadia except on Al{sub 2}O{sub 3} where V{sub 2}O{sub 5} was transformed into polyvanadate species.
- Research Organization:
- Univ. of California, Berkeley, CA (US)
- Sponsoring Organization:
- USDOE
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 20017529
- Journal Information:
- Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical, Vol. 104, Issue 7; Other Information: PBD: 24 Feb 2000; ISSN 1089-5647
- Country of Publication:
- United States
- Language:
- English
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