Publication Date:
2020-02-24
Description:
Metal-catalysed CO2 hydrogenation is considered a source of methane in serpentinized (hydrated) igneous rocks
and a fundamental abiotic process germane to the origin of life. Iron, nickel, chromium and cobalt are the catalysts
typically employed in hydrothermal simulation experiments to obtain methane at temperatures 〉200°C.
However, land-based present-day serpentinization and abiotic gas apparently develop below 100°C, down to
approximately 40–50°C. Here, we document considerable methane production in thirteen CO2 hydrogenation
experiments performed in a closed dry system, from 20 to 90°C and atmospheric pressure, over 0.9–122 days,
using concentrations of non-pretreated ruthenium equivalent to those occurring in chromitites in ophiolites or
igneous complexes (from 0.4 to 76 mg of Ru, equivalent to the amount occurring approximately in 0.4–760 kg
of chromitite). Methane production increased with time and temperature, reaching approximately 87 mg CH4
per gram of Ru after 30 days (2.9 mgCH4/gru/day) at 90°C. At room temperature, CH4 production rate was
approximately three orders of magnitude lower (0.003 mgCH4/gru/day). We report the first stable carbon and
hydrogen isotope ratios of abiotic CH4 generated below 100°C. Using initial d13CCO2 of -40&, we obtained room
temperature d13CCH4 values as 13C depleted as 142&. With time and temperature, the C-isotope separation
between CO2 and CH4 decreased significantly and the final d13CCH4 values approached that of initial d13CCO2.
The presence of minor amounts of C2-C6 hydrocarbons is consistent with observations in natural settings. Comparative
experiments at the same temperatures with iron and nichel catalysts did not generate CH4. Ru-enriched chromitites could potentially generate methane at low temperatures on Earth and on other planets.
Description:
Published
Description:
438–452
Description:
7A. Geofisica di esplorazione
Description:
JCR Journal
Description:
restricted
Keywords:
abiotic methane, Sabatier reaction
;
04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry
Repository Name:
Istituto Nazionale di Geofisica e Vulcanologia (INGV)
Type:
article
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