Fenton Oxidation of H2O2 under Low Temperature Hydrothermal Conditions: Implications for Organics on Mars

Details Fenton Oxidation of H2O2 under Low Temperature Hydrothermal Conditions: Implications for Organics on Mars Fenton Oxidation of H2O2 under Low Temperature Hydrothermal Conditions: Implications for Organics on Mars

Dec 2009

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009agufm.p41b..03g&link_type=abstract

American Geophysical Union, Fall Meeting 2009, abstract #P41B-03

Biology

[0456] Biogeosciences / Life In Extreme Environments, [1060] Geochemistry / Planetary Geochemistry, [5220] Planetary Sciences: Astrobiology / Hydrothermal Systems And Weathering On Other Planets, [6225] Planetary Sciences: Solar System Objects / Mars

Scientific paper

Evaluating the stability of organic compounds in the presence of oxidizing agents is essential to assess the potential habitability of present-day Mars. The residence time of CH4, for instance, may be greatly constrained by oxidants proposed to exist in Martian soil and atmosphere, in particular H2O2. Abiotic oxidation processes could play a key role in the removal of CH4 as recent studies suggest that CH4 sequestration in Martian environments occurs more rapidly than previously thought. Since CH4 evolution can be linked to possible subsurface liquid water, the formation of oxidants needs to be investigated under comparable hydrothermal conditions. To examine the possible formation of highly oxidizing hydroxyl radicals on Mars, a series of flow-through hydrothermal experiments involved decomposition of dissolved H2O2 in the presence of Fe-oxides (FeO, Fe3O4) via the Fenton reaction:

Fe2+ + H2O2(aq) ↔ Fe3+ + ●OH + OH- ○C, consistent with temperature conditions at which liquid water possibly exists at depth in the Martian crust. Results show that the addition of Fe-oxides does not appreciably change the activation energy, but significantly increases the preexponential factor (A), resulting in enhanced rates of H2O2 decomposition relative to the uncatalyzed H2O2-H2O system. Since A is related to activation entropy, higher values reflect an increase in the entropy of the transition state, which likely involves the metastable formation of hydroxyl radicals at rates closely linked to the surface area of mineral catalysts. To further probe the formation of these strong oxidants, the extent of dissolved formic acid oxidation was also evaluated. Preliminary findings from Fe-bearing experiments are indicative of enhanced HCOOH decomposition due to the presence of metastable ●OH. Considering the strong oxidation effects of radicals on organic compounds, constraints on the kinetics and metastable equilibria of the Fenton reaction under hydrothermal conditions would yield a better understanding of Martian habitability and allow us to assess the environmental conditions likely to sustain life.

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