Atomic layer deposition of vanadium over mesoporous materials for liquid phase epoxidation.
Epoxides are industrially important chemicals and there is a need to optimize reaction conditions. The aim of this project is to study pore diffusion effects on epoxidation in liquid phase reactions, specifically the trans-stilbene and cis-cyclooctene epoxidation. Model catalysts of vanadium grafted...
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| Format: | Final Year Project |
| Language: | English |
| Published: |
2009
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| Online Access: | http://hdl.handle.net/10356/16526 |
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| Institution: | Nanyang Technological University |
| Language: | English |
| Summary: | Epoxides are industrially important chemicals and there is a need to optimize reaction conditions. The aim of this project is to study pore diffusion effects on epoxidation in liquid phase reactions, specifically the trans-stilbene and cis-cyclooctene epoxidation. Model catalysts of vanadium grafted on mesoporous material with various pore diameters and structures were prepared via the atomic layer deposition method to ensure uniform dispersion of vanadium on the pore wall surface. The catalysts were characterized by nitrogen physisorption, X-ray diffraction, UV-visible, UV-Raman, hydrogen temperature-programmed reduction, and X- ray absorption near edge structure. The results show that V-MCM-41, V-SBA-15 and V-TUD-1 share similar properties with isolated VO4 species highly dispersed on the support materials. Reaction results show that conversions increase with vanadium percentage in the case of trans-stilbene, with the following conversion result at each vanadium percentage: V-TUD-1>V-SBA-15>V-MCM-41. This reaction conversion order is the same throughout the 24 hours reaction time and at increasing temperatures when 3 percent vanadium was used. It is postulated that more oxidant, i.e. t-butyl hydroperoxide can enter larger pores resulting in higher conversion rate, which explains higher conversion of V-SBA-15 as compared to V-MCM-41. V-TUD-1 shows sponge-like, three-dimensional structure which gives rise to lower diffusion resistance and hence leading to higher conversion as compared to SBA-15 and MCM-41. In conclusion, it is observed in the experiments that diffusion effect is prevalent in this particular epoxidation reaction. |
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