As the recent environmental legislation highlights the risks associated with the use of gasoline additives such as octane enhancers, hydroisomerisation of n-alkanes in the gasoline feed to their corresponding isomers emerges as a key industrial alternative. Important catalysts have previously been tested and abandoned due to a number of problems including cost and poor resistance to catalyst poisons even in trace quantities. The current research evaluated the potentials of zirconia supported molybdenum carbide catalysts as replacements. The active carbided MoO3/ZrO2, MoO3/SO42- -ZrO2 and Rh/MoO3/ZrO2 have been prepared by in situ carburisation with CH4/H2 at 650oC and characterised by N2 adsorption, X-ray diffraction, X-ray photoelectron spectroscopy, Diffuse Reflectance Fourier Transformed Infrared spectroscopy, and temperature programmed reduction and oxidation. The characterisation data showed the carburisation process to proceed in a stepwise manner, involving the participation of hydrogen and methane as reducing and carbiding agents, respectively. Low (0.5 wt %) Rh loading and pre-treatment cycle via reduction and reoxidation significantly reduced the carburisation temperature, with the extent of the effect been dependent on the MoO3 loading. All of the catalysts produced showed stable activity and selectivity. Over the carbided MoO3/ZrO2, the activity was generally low at 450oC, producing mainly hydrogenolysis products. However, the activity of carbided MoO3/SO42- -ZrO2 at 350-450oC showed strong dependence on the nature of the n-alkane with reaction rates being lower for the higher alkanes. n-Nonane and n-octane produced mainly hydrocracking products whereas n-hexane and n-heptane were converted to the corresponding isomers with a very high selectivity. The catalyst forms a potential material for hydroisomerisation of gasoline range light paraffins. The 10 wt% Rh/MoO3/ZrO2 catalyst was more active to hydrogenolysis than with 25 wt% Rh/MoO3/ZrO2 under similar conditions due to higher activity of Rh species. However, the hydroisomerisation selectivity was highly favoured at lower temperatures, especially with n-hexane.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:560897 |
| Date | January 2012 |
| Creators | Galadima, Ahmad |
| Publisher | University of Aberdeen |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://digitool.abdn.ac.uk:80/webclient/DeliveryManager?pid=189408 |
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