Issue 15, 2002

Microstructural studies of the copper promoted iron oxide/chromia water-gas shift catalyst

Abstract

The microstructure of an iron oxide based high temperature water-gas shift (WGS) catalyst has been studied by X-ray diffraction (XRD), high resolution electron microscopy (HREM), high spatial resolution energy dispersive X-ray analysis (STEM-EDX) and X-ray photoelectron spectroscopy (XPS). The iron oxide contains a chromia additive that structurally stabilises the catalyst. Chemical microanalysis indicates that the chromia forms a solid solution within the magnetite Fe3O4 lattice and that no discrete chromia phases are formed. The level of Cr dissolution varies greatly at the intergranular level. XPS and STEM-EDX studies suggest that the activated catalyst is surface enriched in chromia. On the basis of these results a model for the stabilising effect is proposed in which the enriched surface ‘shell’ encapsulates each catalyst grain and, being more thermodynamically stable than the iron-rich core, reduces ion diffusion and sintering effects. A Cu dopant is often added to the Fe3O4/Cr2O3 catalyst to promote its activity. Chemical microanalysis shows that this dopant also exists in solid solution. Furthermore, STEM-EDX and XPS analyses indicate that the catalyst grains also exhibit a strong surface enrichment in the Cu species. Analysis of aged ex-reactor specimens suggest that deactivation occurs as a result of eventual sintering, with a substantial increase in grain-size relative to the fresh catalyst. The Cu dopant is also demonstrated to have a propensity to segregate as CuO on the surface of the catalyst grains in aged specimens.

Article information

Article type
Paper
Submitted
05 Mar 2002
Accepted
15 May 2002
First published
20 Jun 2002

Phys. Chem. Chem. Phys., 2002,4, 3902-3908

Microstructural studies of the copper promoted iron oxide/chromia water-gas shift catalyst

M. A. Edwards, D. M. Whittle, C. Rhodes, A. M. Ward, D. Rohan, M. D. Shannon, G. J. Hutchings and C. J. Kiely, Phys. Chem. Chem. Phys., 2002, 4, 3902 DOI: 10.1039/B202347B

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