The adsorption and reaction of various simple molecules (O<sub>2</sub>, NO, CO and NO<sub>2</sub>) commonly associated with gasoline engine exhaust catalysis were investigated on a model catalytic system under ultra-high vacuum conditions using a variety of surface science techniques including molecular beam scattering and temperature programmed desorption. The model catalytic surfaces studied were clean Pt(111), K/Pt(111) and BaO/Pt(111) surfaces. The alkaline and alkaline earth metal surfaces were prepared by metal vapour deposition (in an oxygen background in the case of BaO) and annealing. Also investigated was the ability of each of the catalytic surfaces to oxidise NO and CO and to store and reduce NO<sub>2</sub>. It was found that the clean Pt(111) surface was effective at oxidising CO provided the oxygen was in an adsorbed atomic form. Pt(111) was also found to be effective in the reduction of NO<sub>2 </sub>. NO and O<sub>2</sub> were found to react in a gas phase reaction that made mixed molecular beam studies problematic however it was found when beaming NO with a background pressure of O<sub>2</sub> that no Pt(111) catalysed surface reaction was observed. It was found that dosing K onto the Pt(111) surface increased the sticking coefficient of oxygen greatly and that more than a monolayer of K on the surface catalysed the reduction of NO to N<sub>2</sub>. Unlike the Pt(111) surface, K/Pt(111) was capable of storing NO<sub>2</sub> without it being immediately reduced. Potassium peroxide however was found to prevent NO<sub>2</sub> storage. In a similar fashion to K, NO<sub>2</sub> was stored on BaO, being released as NO and O<sub>2</sub> on heating. NO is partially reduced to N<sub>2</sub>O by the BaO surface at ambient temperature with increased temperature favouring complete reduction to N<sub>2</sub>.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:584323 |
| Date | January 2008 |
| Creators | Archard, Daniel |
| Publisher | Cardiff University |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://orca.cf.ac.uk/54721/ |
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