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Minerals 2018, 8(3), 105; https://doi.org/10.3390/min8030105

C14–22 n-Alkanes in Soil from the Freetown Layered Intrusion, Sierra Leone: Products of Pt Catalytic Breakdown of Natural Longer Chain n-Alkanes?

1
School of Earth and Environmental Sciences, University of Manchester, Manchester M13 9PL, UK
2
UF Chimie, Collège Sciences et Technologies, Université de Bordeaux, 33405 Bordeaux, France
3
Consultant Geochemist, 3 Kingsway, Frodsham WA6 6RU, Cheshire, UK
*
Author to whom correspondence should be addressed.
Received: 26 January 2018 / Revised: 26 February 2018 / Accepted: 27 February 2018 / Published: 6 March 2018
(This article belongs to the Special Issue Geomicrobiology and Biogeochemistry of Precious Metals)
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Abstract

Soil above a platinum-group element (PGE)-bearing horizon within the Freetown Layered Intrusion, Sierra Leone, contains anomalous concentrations of n-alkanes (CnH2n+2) in the range C14 to C22 not readily attributable to an algal or lacustrine origin. Longer chain n-alkanes (C23 to C31) in the soil were derived from the breakdown of leaf litter beneath the closed canopy humid tropical forest. Spontaneous breakdown of the longer chain n-alkanes to form C14–22 n-alkanes without biogenic or abiogenic catalysts is unlikely as the n-alkanes are stable. In the Freetown soil, the catalytic properties of the PGE (Pt in particular) may lower the temperature at which oxidation of the longer chain n-alkanes can occur. Reaction between these n-alkanes and Pt species, such as Pt2+(H2O)2(OH)2 and Pt4+(H2O)2(OH)4 can bend and twist the alkanes, and significantly lower the Heat of Formation. Microbial catalysis is a possibility. Since a direct organic geochemical source of the lighter n-alkanes has not yet been identified, this paper explores the theoretical potential for abiogenic Pt species catalysis as a mechanism of breakdown of the longer n-alkanes to form C14–22 alkanes. This novel mechanism could offer additional evidence for the presence of the PGE in solution, as predicted by soil geochemistry. View Full-Text
Keywords: n-alkanes; platinum; catalyst; soil; humic acid; Freetown intrusion; Sierra Leone n-alkanes; platinum; catalyst; soil; humic acid; Freetown intrusion; Sierra Leone
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Bowles, J.F.W.; Bowles, J.H.; Giże, A.P. C14–22 n-Alkanes in Soil from the Freetown Layered Intrusion, Sierra Leone: Products of Pt Catalytic Breakdown of Natural Longer Chain n-Alkanes? Minerals 2018, 8, 105.

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