This study concerns the development of a frequency response (FR) reactor capable of investigating heterogeneous catalytic systems under realistic operating conditions. Diffuse Reflectance Infrared Fourier Transform Spectrometry (DRIFTS) and mass spectrometry (MS) have been used together to follow the effects of modulation of the adsorbent/reactant gas composition as elevated temperatures and atmospheric pressure. Initial assessment of the performance of the reactor involved studies of the diffusion of propane though silicalite-1 using MS detection. A mathematical model has been developed to describe the diffusion of the propane, yielding diffusion and adsorption coefficients from the FR data. Investigations using the integrated DRIFTS/MS reactor have been made on the catalytic oxidation of CO over a 2% Rh/Al<sub>2</sub>O<sub>3</sub> catalyst supplied by Johnson Matthey. The catalyst was studied at different temperatures and in both a 'pre-reduced' and 'as received' state. Conventional studies involving CO uptake, temperature programming and desorption measurements showed that adsorbed species observed on the catalyst surface are in good agreement with the literature. Dicarbonyls, linear CO on both metallic and oxidised Rh sites, carbonates and bridging CO were all observed. Transient studies in the form of concentration modulation experiments were performed and showed the major active surface species to be linearly adsorbed CO on oxidised Rh sites (v<sub>CO </sub>= 2105 cm<sup>-1</sup>) on a catalyst surface otherwise dominated by unreactive CO adsorbed predominantly as the geminal dicarbonyl species. Full frequency response experiments were conducted over a narrower range of experimental conditions, but allowed calculation of surface residence times and activation energies for reaction of the surface Rh<sup>+</sup>CO species and desorption of CO<sub>2</sub>.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:642687 |
| Date | January 2000 |
| Creators | Cavers, Mark |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/12160 |
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