Mathematics – Logic
Scientific paper
Jan 2012
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2012gecoa..76...14f&link_type=abstract
Geochimica et Cosmochimica Acta, Volume 76, p. 14-28.
Mathematics
Logic
Scientific paper
In order to evaluate the oxidation effect of dissolved hydrogen peroxide and the catalytic role of iron oxides on the kinetics of formic acid decarboxylation, a series of flow-through hydrothermal experiments was conducted at temperatures ranging from 80 to 150 °C and pressures of 172-241 bar. δ13C composition of residual HCOOH(aq) was also monitored to examine kinetic isotope effects associated with oxidation processes. Our results reveal that decomposition of H2O2(aq) in presence of magnetite follows pseudo first order kinetics, highly enhanced relative to the homogeneous H2O2(aq)-HCOOOH(aq)-H2O system, which possibly reflect synthesis of hydroxyl radicals (OH) through Fenton processes. The kinetic rate constants of HCOOH(aq) decarboxylation to CO2(aq) are also elevated relative to those previously measured in H2O2(aq) free experiments. However, reaction kinetics are slightly slower in the case of H2O2(aq) aqueous solutions coexisting with magnetite than in the absence of mineral phases. This behavior is attributed to the possible formation of Fe-bearing hydroxyl formate aqueous species that could serve as stable transition states leading to a decrease in the activation entropy of formic acid decomposition.δ13C values of residual formic acid in the homogeneous H2O2(aq)-HCOOH(aq)-H2O system are consistent with previous studies. However, magnetite-bearing experiments produce a negative shift in δ13C of residual formic acid, perhaps specific to OH-imposed oxidation of organic compounds. This would indicate that isotopic fractionations by this oxidation pathway are opposite to kinetic fractionation effects expected in biologically driven oxidation processes. This could have important implications for putative H2O2(aq)-bearing Martian subsurface environments and the evolution of organics at low-temperature hydrothermal conditions.
Foustoukos Dionysis I.
Stern Jennifer C.
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