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? Minerals2018, 8, 105.
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.
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. Acknowledging the possibility of microbial catalysis and the difficulty of identifying a direct organic geochemical source of the lighter n-alkanes, 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 substantiate the presence of the PGE in solution predicted by soil geochemistry and illustrate processes involving the PGE. Graphical Abstract
n-alkanes, platinum, catalyst, soil, humic acid, Freetown Intrusion, Sierra Leone
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