In recent years, the catalytic properties of finely dispersed gold particles on oxide support
materials have attracted much attention. Such catalysts are active for several types of
oxidation reactions, in particular low-temperature carbon monoxide oxidation. The watergas-
shift (WGS) reaction and the selective oxidation of CO in the presence of hydrogen
are possible applications of gold-based catalysts.
In this thesis we attempted to detail the key issues relevant to the deactivation of
supported gold catalysts. A new aspect of the CO oxidation deactivation mechanism was
comprehensively discussed. It was found that titanate nanotube supported gold catalyst
(Au/TN), prepared by deposition precipitation, deactivated due to the formation of
bicarbonate species on gold-sites. Moisture prevented the formation and accumulation of
these species and also promoted the reaction. The Au/TN catalyst was characterised by
HRTEM, in-situ DRIFTS-Mass spectrometry, BET, etc.
Titanium dioxide (TiO2) is widely used as support material for various important
industrial catalysts and its modification may suite specific catalytic requirements. In this
work we have confirmed that the incorporation of nitrogen (N) into TiO2 increases the
concentration of oxygen ion vacancies. When tested for CO oxidation, the nitrogendoped
titania supported gold catalyst, Au/TiO2-xNx, was found to be a poor and unstable
catalyst compared to the pure titania supported gold catalyst, Au/TiO2. Both catalysts
were characterised by XRD, Raman spectroscopy, DRS-UV visible spectroscopy, TPO,
BET, HRTEM etc.
New Cu-based methanol synthesis catalysts, prepared by co-precipitation and deposition
precipitation, were physically mixed with _-Al2O3 and tested for the direct single-step
DME synthesis from syngas. The catalysts exhibited good CO conversion and DME
selectivity. The loading of gold on the methanol synthesis components of the bifunctional
catalysts promoted CO conversion and the WGS reaction. In addition, Au suppressed
iv
methanation on the bifunctional catalysts. The catalysts were characterised by TPR,
XRD, BET and XRF spectroscopy.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/4989 |
| Date | 27 June 2008 |
| Creators | Ntho, Thabang Abraham |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 1892714 bytes, application/pdf, application/pdf |
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