Benny, S.; (2010) High temperature water gas shift catalysts: a computer modelling study. Doctoral thesis , UCL (University College London).

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Abstract

The high-temperature (HT) Water Gas Shift (WGS) reaction has considerable technological relevance for lowering CO content during the conversion of natural gas or liquid hydrocarbons to hydrogen. Conventional HT-WGS catalysts based on oxides of iron and chromium are well established industrially. However, it is crucial to remove any impurities present such as Cr6+, S or N during the catalytic process. In particular, Cr6+ is regarded as a Class I carcinogen and its presence is restricted by EU legislation. Even though Cr6+ is reduced during the catalytic process, caution must still be taken to eliminate any further impurities. Hence, it is desirable to identify alternative promoters and develop a Cr-free HT-WGS catalyst. This thesis presents results obtained using atomistic simulation techniques to investigate the effect of Cr3+ and possible alternative dopants in three important iron oxide materials, Hematite (α-Fe2O3), Maghemite (γ-Fe2O3) and Magnetite (Fe3O4). The starting point is to develop an understanding of the structural properties and distribution of Cr3+ on the bulk and surface material of hematite. The critical stage of understanding the role of Cr3+ provides the basis from which criteria for novel dopants can be assessed. Al3+ and Mn3+ are proposed as the promising candidates on the basis of this study. The research has been extended to other complex iron oxides, such as maghemite and magnetite. In summary, the role of chromium in the HT-WGS reaction has been investigated to establish criteria for effective, alternative promoter dopants. This investigation has provided a detailed insight into the atomic level behaviour of Cr3+, Mn3+, Al3+ impurities in three major iron oxide phases. The alternative dopants predicted in this study have been the subject of parallel experimental studies conducted by Johnson Matthey. The results of this study are already benefiting the design of more efficient iron-oxide catalysts for the HT-WGS reaction.

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