Raman Spectroscopic Study of V/O-A12O3 Catalysts: Quantification of Surface Vanadia Species and Their Structure Reduced by Hydrogen
- ORNL
- Northwestern University, Evanston
- University of Glasgow
Two interesting topics about supported vanadia catalysts were studied using in situ UV and visible Raman and UV-vis diffuse reflectance spectroscopy (DRS): The quantification of different surface vanadia species and the hydrogen reduction of these vanadia species. Using the diffuse reflectance value as an external standard, we could correct the Raman intensity measurements of V/{theta}-Al{sub 2}O{sub 3} for the self-absorption effect. On the basis of the ability to selectively detect monovanadate (UV-excited), polyvanadate (visible-excited), and V{sub 2}O{sub 5} (visible-excited) in the Raman measurements, the distribution of monovanadate, polyvanadate, and V{sub 2}O{sub 5} present on dehydrated V/{theta}-Al{sub 2}O{sub 3} samples was successfully quantified as a function of surface VO{sub x} density. It is shown that monovanadate species are present at all surface VO{sub x} densities studied but are the dominant species at low surface VO{sub x} density. Polyvanadate and V{sub 2}O{sub 5} are also present and predominate on the surface at intermediate and high surface VO{sub x} density. The UV- and visible-excited Raman studies of the V/{theta}-Al{sub 2}O{sub 3} samples reduced in hydrogen show that polyvanadate and V{sub 2}O{sub 5} are more easily reduced than monovanadate species. UV Raman is better able to obtain information on reduced vanadia species than visible Raman, mainly because of a decrease in self-absorption and resonance enhancement in the UV region. Comparison of the UV Raman spectra from reduced V/{theta}-Al{sub 2}O{sub 3} with bulk vanadium oxide compounds suggests that reduced VO{sub x} species can assume a V{sub 2}O{sub 3}-like form. The reduced VO{sub x} species redisperse on the support surface upon reoxidation.
- Research Organization:
- Oak Ridge National Laboratory (ORNL)
- Sponsoring Organization:
- SC USDOE - Office of Science (SC)
- DOE Contract Number:
- AC05-00OR22725
- OSTI ID:
- 1042723
- Journal Information:
- Journal of Physical Chemistry C, Journal Name: Journal of Physical Chemistry C Journal Issue: 44 Vol. 111; ISSN 1932-7447
- Country of Publication:
- United States
- Language:
- English
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