The application of quasi-elastic neutron scattering to investigate hydrogen diffusion in an iron-based Fischer-Tropsch synthesis catalyst

Davidson, A. L., Webb, P. B., Silverwood, I. P. and Lennon, D. (2020) The application of quasi-elastic neutron scattering to investigate hydrogen diffusion in an iron-based Fischer-Tropsch synthesis catalyst. Topics in Catalysis, 63, pp. 378-385. (doi: 10.1007/s11244-020-01259-2)

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Iron-based Fischer–Tropsch synthesis (FTS) catalysts evolve in situ on exposure to synthesis gas (CO & H2) forming a mixture of iron oxides, iron carbides and carbonaceous deposits. Recently, the application of inelastic neutron scattering has shown the progressive formation of a hydrocarbonaceous overlayer during this catalyst conditioning period. The evolving nature of the catalyst alters the proportion of phases present within the catalyst, which may influence the transport of hydrogen within the reaction system. Preliminary quasi-elastic neutron scattering (QENS) measurements are used to investigate hydrogen diffusion within an un-promoted iron FTS catalyst that has experienced varying levels of time-on-stream (0, 12 and 24 h) of ambient pressure CO hydrogenation at 623 K. Measurements on the catalyst samples in the absence of hydrogen show the unreacted sample (t = 0 h) to exhibit little increase in motion over the temperature range studied, whereas the t = 12 and 24 h samples exhibit a pronounced change in motion with temperature. The contrast is attributed to the presence of the afore-mentioned hydrocarbonaceous overlayer. Measurements on the samples in the presence of liquid hydrogen show hydrogen diffusional characteristics to be modified as a function of the catalyst conditioning process but, due to the complexity of the evolving catalyst matrix, the hydrogen motion cannot be attributed to a particular phase or component of the catalyst. Problems in the use of hydrogen as a probe molecule in this instance are briefly considered. Coincident neutron diffraction studies undertaken alongside the QENS measurements confirm the transition from hematite pre-catalyst to that of Hägg carbide during the course of extended times-on-stream.

Item Type:Articles
Glasgow Author(s) Enlighten ID:Lennon, Professor David and Silverwood, Dr Ian and Davidson, Dr Alisha
Authors: Davidson, A. L., Webb, P. B., Silverwood, I. P., and Lennon, D.
College/School:College of Science and Engineering > School of Chemistry
Journal Name:Topics in Catalysis
ISSN (Online):1572-9028
Published Online:07 April 2020
Copyright Holders:Copyright © 2020 The Authors
First Published:First published in Topics in Catalysis 63:378–385
Publisher Policy:Reproduced under a Creative Commons licence

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Project CodeAward NoProject NamePrincipal InvestigatorFunder's NameFunder RefLead Dept
190262EPSRC Doctoral Training Grant 2010-14Mary Beth KneafseyEngineering and Physical Sciences Research Council (EPSRC)EP/P505534/1Research and Innovation Services