Perspectives on the effect of sulfur on the hydrocarbonaceous overlayer on iron Fischer-Tropsch catalysts
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Fischer-Tropsch synthesis (FTS) is commonly viewed as an alternative approach to the production of diesel fuels via sources independent of crude oil. The adaptability of the FTS process allows for the selective production of shorter chain C2 to C6 hydrocarbons and has the potential to be a legitimate source of useable chemical feedstocks with high value to the chemical manufacturing industry. Interestingly, although recognised as a poison in most catalytic systems, small amounts of sulfur in iron-based FTS catalysts has been demonstrated to promote catalyst reducibility and activity towards shorter chain hydrocarbons. However, it is not known what impact sulfur has on the formation of hydrocarbonaceous surface species that have been proposed to play a pivotal role in the mediation of reactants during iron FTS. Here we apply ambient pressure CO hydrogenation at 623 K on a selection of sulfur promoted iron FTS catalysts to investigate the effect of sulfur content on hydrocarbonaceous species formation. For the first time, we report the application of inelastic neutron scattering to quantify the presence of hydrocarbonaceous species under the presence of sulfur promotion. In combination with temperature programmed oxidation, X-ray diffraction, and Raman spectroscopy, we observe how low sulfur loadings (<700 ppm) perturb carbon and hydrogen retention levels. The results indicate that the presence and nature of the hydrocarbonaceous overlayer is sensitive to sulfur loading, with the reported loss in catalytic activity at high loadings correlating with the attenuation of hydrocarbonaceous surface species.
Warringham , R , Davidson , A L , Webb , P B , Tooze , R P , Parker , S F & Lennon , D 2019 , ' Perspectives on the effect of sulfur on the hydrocarbonaceous overlayer on iron Fischer-Tropsch catalysts ' , Catalysis Today , vol. In press . https://doi.org/10.1016/j.cattod.2019.02.035
Copyright © 2019 Elsevier B.V. All rights reserved. This work has been made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at https://doi.org/10.1016/j.cattod.2019.02.035
DescriptionSasol Ltd., the University of Glasgow and the EPSRC (grant numbers EP/P504937/1 and EP/P505534/1) are thanked for the provision of postgraduate studentships (RW and ALD). The STFC Rutherford Appleton Laboratory is thanked for access to neutron beam facilities. The Royal Society is thanked for the provision of an Industrial Fellowship (PBW).
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