Performance of gold catalysts for low temperature water gas shift

Master Thesis


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University of Cape Town

The ultimate objective of the study was to investigate the performance of suitably prepared gold catalysts for low temperature water gas shift (LTS) - and more specifically to investigate the performance of these catalysts at temperatures below those traditionally utilised. As opposed to the research undertaken to-date on gold catalysed water gas shift, the reaction was performed, as far as possible, under conditions resembling those found industrially, viz. conditions of temperature, pressure, WHSV and dry feed gas composition typical of those applicable to industrial LTS units. Important to this study was therefore the generation of a comprehensive performance benchmark for the commercially available LTS catalyst, a copper-based material, against which to compare the performance of the gold deposited catalysts. The gold catalysts were prepared by deposition-precipitation, a preparation procedure found to yield nano-sized gold particles, suggested in literature as being crucial for activity, on the metal oxide support. Using this procedure, gold promoted low (copper) and high (iron oxide) temperature shift catalysts and commercial zinc oxide supports were prepared and tested. A wide spectrum of Au particle sizes were prepared on the supports, ranging from approximately 3-500 nm. The gold promoted LTS catalyst was found to exhibit slightly higher activity than the commercially available catalyst at temperatures below the conventional LTS range. It would appear as if gold promotion is advantageous to the industrial catalyst and could impact greatly on LTS catalyst life. Even though substantially less active than the commercial copper catalyst was found, the gold promoted commercial zinc oxide catalyst exhibited significantly higher activity than that previously quoted in literature and better performance than the iron oxide supported catalysts of this study. Consequently, the Au/ZnO system exhibits good potential for further developments in terms of water gas shift conversion.

Bibliography: leaves 77-81.