Gold catalysts for the low-temperature water-gas shift reaction

Carter, James 2016. Gold catalysts for the low-temperature water-gas shift reaction. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

The stability of gold catalysts in the low-temperature water-gas shift reaction (WGS) was investigated. Using state-of-the-art electron microscopy and x-ray photoelectron spectroscopy, the deactivation mechanism of 2wt% Au/CeZrO4 was probed. After exposure to reaction conditions, particle agglomeration and morphological changes were observed. Two strategies were developed to improve the stability of an Au/CeZrO4 catalyst: Modification of the supported metal and modification of the support. The former strategy involved the addition of Pd the catalyst, while the latter consisted of the use of sub-surface Mo dopants and the substitution of Zr for Ti or Al. A series of 2wt% Au, AuPd and Pd supported on CeZrO4 catalysts were prepared by deposition precipitation (DP) and screened for their WGS activity and stability. It was shown that the addition of Pd resulted in a significant decrease in the catalytic activity. There was no change in catalyst stability. Several characterisation methods showed that there was a particle size effect that explained the catalytic activity. A series of Mo-doped CeZrO4 supports were prepared and characterised using several characterisation methods. After the addition of 2wt% Au, the catalysts were screened for their WGS activity. It was shown that Mo poisoned the catalysts and there was no improvement to the catalyst stability. The role of the support was examined by preparing Ce0.5Ti0.5Ox and Ce0.5Al0.5Ox by a sol-gel methodology. After the deposition of Au by DP the catalysts were tested for WGS activity and stability and compared with an equivalent 2wt %Au/CeZrO4 catalyst. The 2 wt% Au/Ce0.5Ti0.5Ox was the most stable catalyst and was as active as 2wt%Au/CeZrO4. Ce0.5Ti0.5Ox was the subject of further work to establish the effect of the Ce:Ti ratio. Gold catalysts prepared by DP on CeaTi1-aOx (where a = 0, 0.1, 0.2, 0.5, 0.8, 0.9 or 1) were screened for WGS activity and stability before being characterised. Au/Ce0.2Ti0.8Ox exhibited the same stability as Au/Ce0.5Ti0.5Ox but achieved an even higher conversion. Characterisation showed that Au/Ce0.2Ti0.8Ox had similar chemical properties to the Au/Ce0.5Ti0.5Ox and an even higher surface area. The combination of defect sites, a high surface area, and a small crystallite size were concluded to be the key properties for an active WGS catalyst support.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Chemistry
Subjects:	Q Science > QD Chemistry
Date of First Compliant Deposit:	7 September 2016
Last Modified:	23 Aug 2021 13:48
URI:	https://orca.cardiff.ac.uk/id/eprint/94306

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