Hydrogen sulphide emission by catalytic converter-fitted automobiles is a problem, because the gas has an extremely unpleasant odour, which is detectable by the human nose at concentrations below 1 ppm. The problematic hydrogen sulphide emissions are produced by the "storage release" mechanism, in which the catalyst absorbs sulphur dioxide during net oxidising conditions and releases it very rapidly as hydrogen sulphide when the stoichiometry of the exhaust gas changes to net reducing. After a prolonged period of oxidative storage the peak emission of hydrogen sulphide by "storage release" can greatly exceed that possible by direct conversion of sulphur dioxide during net reduction conditions (termed the "steady state" mode of emission). Components of the formulation of typical TWCs (Three Way Converters), as well as iron, nickel and barium doped analogues, were prepared. Storage-release sequences were then simulated on the samples at a number of different temperatures on purpose-built 'catalyst test apparatus'. Temperature programmed reductions were performed in the same apparatus by dosing the samples with sulphur dioxide in oxidising conditions at 500°C (the temperature at which the emission of hydrogen sulphide is conventionally said to become a problem). The TPR spectra exhibited sulphur dioxide and hydrogen sulphide peaks, the hydrogen sulphide peak always occurring at the higher temperature. The addition of platinum to various oxides and oxide mixtures was shown to increase the proportion of stored sulphur emitted as hydrogen sulphide and to lower the temperature at which storage-release effects occur. These effects were evident in the lowered temperatures at which the TPR spectra peak maxima occurred and the increased size of hydrogen sulphide peaks relative to hose of sulphur dioxide.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:652196 |
| Date | January 1998 |
| Creators | Harvey, Adam |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/10941 |
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