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In Situ UV–vis–NIR Diffuse Reflectance and Raman Spectroscopic Studies of Propane Oxidation over ZrO2-Supported Vanadium Oxide Catalysts
| Content Provider | Semantic Scholar |
|---|---|
| Author | Gao, Xingtao Jehng, Jih-Mirn Wachs, Israel E. |
| Copyright Year | 2002 |
| Abstract | Abstract The molecular structures and oxidation states of supported 1–5% V 2 O 5 /ZrO 2 catalysts during propane oxidative dehydrogenation (ODH), with varying propane/O 2 ratios, were examined by in situ UV–vis–NIR diffuse reflectance and in situ Raman spectroscopic studies. The results indicate that the reduction extent of surface V 5+ cations to V 3+ /V 4+ cations under steady-state reaction conditions increases with the propane/O 2 ratio. At the same propane/O 2 ratio, the relative extent of reduction of the supported V 2 O 5 /ZrO 2 catalysts generally increases with the surface vanadia loading, and the polymerized surface VO 4 species are more extensively reduced than the isolated surface VO 4 species during steady-state propane oxidation. The reactivity studies reveal that at the same reaction conditions, both polymerized and isolated surface V cations are active sites for propane oxidation and that the specific catalytic reactivity (as measured by turnover frequency; TOF) is independent of the surface density of the two-dimensional vanadia overlayer on the ZrO 2 support. Furthermore, the relatively constant TOF with surface vanadia coverage demonstrates that propane ODH to propylene requires only one surface VO 4 site. However, the propylene selectivity increases with increasing surface vanadia loading due to the removal of nonselective surface sites, possibly terminal Zr–OH groups, on the ZrO 2 surface by the deposition of surface vanadia species. The propane/O 2 ratio greatly affects the selectivity of these catalysts. Highly oxygen-rich environments (e.g., propane/O 2 ratio = 1/10) give rise to the highest propylene selectivity, revealing that propylene production is favored on highly oxidized surface vanadia (+5) sites. Small V 2 O 5 crystallites above monolayer surface vanadia coverage do not contribute to propane ODH because of their low dispersion and low number of active surface sites (spectator vanadia species). |
| Starting Page | 43 |
| Ending Page | 50 |
| Page Count | 8 |
| File Format | PDF HTM / HTML |
| DOI | 10.1006/jcat.2002.3635 |
| Volume Number | 209 |
| Alternate Webpage(s) | http://www.lehigh.edu/operando/Publications/2002%20C3%20ODH%20over%20VOx-ZrO2%20UV-vis.pdf |
| Alternate Webpage(s) | https://doi.org/10.1006/jcat.2002.3635 |
| Language | English |
| Access Restriction | Open |
| Content Type | Text |
| Resource Type | Article |
