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Gold catalysts for oxidation and hydrogenation reactions

Hall, Matthew Scott 2004. Gold catalysts for oxidation and hydrogenation reactions. PhD Thesis, Cardiff University.

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Abstract

Iron oxide supported gold catalysts were tested for the room temperature oxidation of carbon monoxide. The effect of heat treatment on the activity of the catalysts was investigated the catalysts being heated to 75, 120, 200, 300 and 400°C. The most active catalysts were obtained by using a calcination temperature of 120°C. Gold catalysts supported on zinc oxide were also tested for activity in the oxidation of carbon monoxide at room temperature. These catalysts were found to be less active than the Au/FejCh catalysts. The effect of heat treatment was also investigated, and the uncalcined catalysts were found to be the most active. Characterisation of both types of catalyst by XPS revealed a clear difference between catalysts of high and low conversion. Further investigation of the catalysts by XANES, TEM, and the XPS of gold colloids revealed that this difference was due to a change in the ratio of metallic and ionic gold, with the former being more abundant in catalysts with lower activities. The XANES analysis revealed the ionic gold to be in the form of Au1. XPS analysis of the samples also revealed the presence of a surface hydroxyl species in the catalysts with high activity constant with the Bond-Thompson mechanistic model for CO oxidation The iron oxide supported gold catalysts were also used in the hydrogenation of crotonaldehyde. The catalysts were tested for selectivity towards crotyl alcohol and total conversion at a variety of different heat treatments and reaction temperatures, and the highest conversions were obtained at a reaction temperature of 150°C. The best overall conversions were obtained with catalysts that had been heated at 75°C. The highest selectivity towards crotyl alcohol was obtained with catalysts which were calcined at 300°C. The affect of reduction on the activity of the catalysts for crotonaldehyde hydrogenation was also explored. It was found that catalysts that were not reduced prior to reaction had a higher activity and were less prone to deactivation during the reaction. The correlation between the oxidation state of the gold and the activity of the catalyst for the hydrogenation reaction was very similar to that found in the carbon monoxide oxidation catalysts. "High pressure" XPS studies were carried out on polycrystalline gold foil, an iron oxide film, and a thick gold film to test the contributions that part makes to the activity iron oxide supported gold catalysts. Both the gold foil and the iron oxide and thick gold films proved to be unreacrive towards carbon monoxide and oxygen.

Item Type: Thesis (PhD)
Status: Unpublished
Schools: Chemistry
Subjects: Q Science > QD Chemistry
ISBN: 9781303200526
Date of First Compliant Deposit: 30 March 2016
Last Modified: 10 Oct 2017 15:29
URI: http://orca-mwe.cf.ac.uk/id/eprint/55942

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