(1)H and (13)C solution- and solid-state NMR investigation into wax products from the Fischer-Tropsch process

Speight, R. J., Rourke, J. P. ORCID: https://orcid.org/0000-0002-8961-1021, Wong, A., Barrow, N. S., Ellis, P. R., Bishop, P. T. and Smith, M. E. 2011. (1)H and (13)C solution- and solid-state NMR investigation into wax products from the Fischer-Tropsch process. Solid State Nuclear Magnetic Resonance 39 (3-4) , pp. 58-64. 10.1016/j.ssnmr.2011.03.008

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Abstract

1H and 13C solid- and solution-state NMR have been used to characterise waxes produced in the Fischer–Tropsch reaction, using Co-based catalysts either unpromoted or promoted with approximately 1 wt% of either cerium or rhenium. The aim was to measure average structural information at the submolecular level of the hydrocarbon waxes produced, along with identification of the minor products, such as oxygenates and olefins, which are typically observed in these waxes. A parameter of key interest is the average number of carbon atoms within the hydrocarbon chain (NC). A wax prepared using an unpromoted Co/Al2O3 catalyst had NC∼20, whilst waxes made using rhenium- or cerium-promoted Co/Al2O3 catalysts were found to have NC∼21. All three samples contained small amounts of oxygenates and alkenes. The subtle differences found in the waxes, in particular the minor species produced, demonstrate that the different promoters have different effects during the reaction, with the Re-promoted catalyst producing the fewest by-products. It is shown in 13C solid-state NMR spectra that for that for longer chain (compared to the lengths of chain in previous studies) waxes that the lack of resolution and the complexities added by the differential cross-polarisation (CP) dynamics mean that it is difficult to accurately determine NC from this approach. However the NC determined by 13C CP magic angle spinning NMR is broadly consistent with the more accurate solution approaches used and suggest that the wax characteristics do not change in solution. On this basis an alternative approach for determining NC is suggested based on 1H solution state NMR that provides a higher degree of accuracy of the chain length as well as information on the minor constituents.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Chemistry
Publisher:	Elsevier
ISSN:	0926-2040
Last Modified:	03 Apr 2023 13:45
URI:	https://orca.cardiff.ac.uk/id/eprint/155217

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