The chemical and physical effects of potassium promotion on prepared nickel-alumina catalysts have been examined using "<I>in-situ</I>" Diffuse Reflectance Infrared Fourier Transform Spectroscopy (DRIFTS), Temperature Programmed studies and X-ray Powder Diffraction (XRPD). Various preparative methods were explored to obtain catalyst samples with a high metallic surface area. A sequential precipitation technique was employed, yielding a highly loaded nickel alumina catalyst (56 %wt Ni) with the hydrotalcite structure, typical of other industrial catalysts. Subsequent potassium promotion of this initial catalyst was achieved by impregnation. X.R.P.D. studies showed no observable changes in the bulk structure of the catalyst at room temperature or during calcination with low loadings of potassium (≤ 1 %wt). However, at higher loadings, potassium carbonate/oxide peaks became apparent but there was no indication of any other potassium derivatives. The presence of potassium both inhibited the reduction of the catalyst and brought about a reduction of the nickel surface area in the final reduced catalyst. Infrared studies showed definite changes in the surface chemistry of the catalyst with potassium promotion. Adsorption of carbon monoxide showed a downward shift in the wavenumber of the characteristic bands together with an apparent change in the relative proportions of the different carbon monoxide adsorbed species. Temperature dependent adsorption studies further indicated the formation of an activated species which was increasingly stable as a function of potassium promotion. The same species was observed in analogous carbon dioxide experiments. The effect of potassium on the infrared spectra from adsorbed ethene, propene and but-1-ene was more subtle.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:657349 |
| Date | January 1994 |
| Creators | Marshall, Peter R. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/12572 |
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