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Open AccessArticle

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