Vanadium and molybdenum oxide catalysts have been prepared on different Ti02 supports by a variety of methods. Solutions of VOC13, VO(O'Bu)3 and MoOC14 were used to graft VOX and MoOX monolayers onto the supports in a single treatment. The other methods were intended to produce more than one monolayer (i. e. aqueous impregnation and multiple treatments of VOC13 and VO(O1Bu)3 ). TPR and Raman spectroscopy showed the formation above the monolayer of a phase denoted as disordered vanadium oxide, which has the same reducibility as the monolayer species but which has a band in the Raman spectrum at 995 cm-l. Raman spectroscopy also showed the formation of a disordered molybdenum oxide phase. With supports which contained phosphorus and potassium as impurities, TPR and Raman spectoscopy indicated a potassium-containing vanadium oxide, which was difficult to reduce and which showed no band at 995 cm-1. "Paracrystalline" V205 and MoO3 are formed when the oxide content exceeds four monolayers. XPS measurements confirm the dispersion of MOX species (M = V, Mo) on the surface of the support in the monolayer region; they also show that disordered and paracrystalline oxide phases occupy a limited area of the monolayer surface, but could not distinguish between them. ESR results showed 95% of the supported vanadium in the oxidation state +5. Phosphorus and potassium impurities in (or on) the TiO2 support influence the structure and catalytic properties of the VOX monolayer phase. In the case of catalysts made on supports with low impurities, activities in butadiene oxidation and isopropanol decomposition are principally due to the monolayer species and little contribution is made by the disordered or paracrystalli ne V205, while in the catalysts made on the supports with relatively high level of impurities, the activities in both reactions increase with V205 content in the region of one to four monolayers. MoOX catalysts showed low activities and selectivities in butadiene oxidation.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:377347 |
| Date | January 1987 |
| Creators | Tahir, Saad Flamerz |
| Contributors | Bond, G. C. |
| Publisher | Brunel University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://bura.brunel.ac.uk/handle/2438/7887 |
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