Reduction of N2 by Fe2+ via Homogeneous and Heterogeneous Reactions |
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Authors: | Matthew C. F. Wander Martin A. A. Schoonen |
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Affiliation: | (1) Penn State Astrobiology Research Center(PSARC), Department of Geosciences, Stony Brook University, Stony Brook, NY 11794-2100, USA |
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Abstract: | Because of their high kinetic barrier and thermodynamic favorability under moderately reducing atmospheric composition photochemical approaches appear to be ideally suited to the direct reduction of solvated nitrogen gas. Ferrous iron has been investigated as an electron donor, as it has a highly tunable redox character and is environmentally ubiquitous. Recent advances in mineralogy connected to the field of environmental remediation have led to the identification of an important class of rusts which have reductive potentials comparable to Fe(0). These materials possess redox couples that are, potentially, capable of overcoming the kinetic barrier to the production of NH3. In this study, we attempted to produce ammonia from N2 by oxidizing white rust both photochemically and in a dark reaction. All results indicated the reaction was inhibited by competing reactions; primarily the reduction of H2O to H2. However, the dark reactions showed limited potential for reduction up to 1.4 mM. As a result, we turned to the question of closure temperature; the minimum temperature of rapid reaction based on a choice of reductant, which we demonstrate a model for its estimation. Due to the high thermodynamic energy of the intermediate, we conclude that aqueous photochemical reduction under the conditions studied here is an unlikely prebiotic source for reactive, i.e. reduced, nitrogen. |
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Keywords: | Ammonia Ferrous iron Green Rust Heterogeneous Nitrogen Reduction Photochemistry Prebiotic chemistry White Rust |
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