The work described in this thesis concerns the adsorption and decomposition of small hydrocarbon molecules on the surface of an alumina supported nickel catalysts. The catalyst was prepared using a co-precipitation method and contained 25% nickel by weight. Temperature programmed reduction revealed that reduction at over 550<SUP>o</SUP>C in hydrogen was necessary in order to fully reduce the catalyst. Nickel surface area measurements were performed using hydrogen chemisorption and nitrous oxide decomposition, revealing an area of 30→45m^2/g. X ray diffraction and transmission electron microscopy showed an average nickel particle diameter of 13nm. Total catalyst surface area was measured by nitrogen adsorption at -196°C, giving a value of 250m^2/g for the as prepared catalyst. Infrared studies were performed using a combination of Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), with a standard Spectratech cell, and transmission infrared spectroscopy, with a home made infrared cell. A passivation procedure was developed so that pre-reduced catalyst could be transferred to the infrared cells and re-reduced <i>in situ</i> at 300°C. The adsorption and reaction of the two simple alkenes, ethene and propene were investigated at temperatures between 25 and 300°C. The room temperature surface chemistry of both molecules was dominated by the initial formation of alkylidyne species, ethylidyne (CCH_3) from ethene and propylidyne (CCH_2CH_3) from propene. The ethylidyne formed from ethene decayed to surface methyl (CH_3) and C_4 containing species. These were hydrogenated to methane and butane respectively. Ethylidyne itself was stable to hydrogenation. Methane was the only product released during temperature programming of the sample up to 300°C in helium. Propylidyne formed from propene decayed to ethylidyne, methyl and other C_3 and C_6 containing carbonaceous deposits. Hydrogenation produced methane and propane, leaving propylidyne and ethylidyne. Temperature programming of these species in helium produced only methane, and heating in hydrogen produced a small quantity of hexane in addition. After ethene adsorption, only 77% of the carbon deposited could be removed during re-reduction. Temperature programmed oxidation removed all of the carbon but substantial re-oxidation of the nickel catalyst occurred.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:663766 |
| Date | January 1992 |
| Creators | Wilcock, Ian C. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/13231 |
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