Investigation of V oxidation states in reduced V/Al{sub 2}O{sub 3} catalysts by XPS
- Univ. of Pittsburgh, PA (United States)
The distribution of vanadium oxidation states in a 5.9 wt% V/Al{sub 2}O{sub 3} catalyst reduced in H{sub 2} or CO was determined from XPS V 2p spectra. Principal component analysis (PCA) was used to statistically determine the number of components (oxidation states) that describe the V 2p{sub 3/2} envelope of the reduced V/Al{sub 2}O{sub 3} catalyst. The peak positions and FWHMs of the components were obtained from iterative target transformation factor analysis (ITTFA). The V 2p{sub 3/2} envelope is composed of two components (oxidation states), which are centered at 517.2 and 515.5 eV (FWHMs of 2.6 and 2.3 eV, respectively) when H{sub 2} is the reducing agent and at 517.3 and 515.8 eV (FWHMs 2.7-2.8 eV) when CO is the reducing agent. The components were assigned to V{sup 5+} and V{sup 3+} based on the difference in the binding energies and the results of a volumetric study of catalyst reduction in CO. The spectral information gained from PCA and ITTFA was used to curve fit the V 2p envelopes. The extent of reduction of the V phase was estimated from the relative abundances of V{sup 5+} and V{sup 3+} determined by curve fitting and corrected for the presumably lower dispersion of the V{sup 3+} species. The results indicated a decrease in the average oxidation state of V to 3.5 with increasing the reduction temperature in H{sub 2} up to 662{degrees}C. Reduction in the presence of CO was measured volumetrically and showed a decrease in the average oxidation state from 5 to 3.3 over the temperature range 155-510{degrees}C. Curve fitting the spectra of the CO-reduced samples using the two spectral components identified through factor analysis yielded an average oxidation state of ca.3.6 upon reduction at 510{degrees}C. 40 refs., 8 figs., 3 tabs.
- OSTI ID:
- 494290
- Journal Information:
- Journal of Catalysis, Vol. 162, Issue 2; Other Information: PBD: 1 Sep 1996
- Country of Publication:
- United States
- Language:
- English
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