Awaruite and Tetrataenite Driven NH3 Synthesis

Abstract:

The deep biosphere hypothesis postulates that life emerged from a hydrothermal system beginning with small molecules such as CO₂, N₂, H₂, CO, and CS₂. (M. J. Russell, A. J Hall, and W. Martin, Geobiology, 2010, 8, 355). Key catalysts/surfaces at the ocean crust boundary would have interacted with these dissolved gases, giving rise to larger biomolecules and ultimately life. Among the catalysts found at present in hydrothermal system, Ni₃Fe (Awaruite) and NiFe (Tetrataenite) stand out because they convert simple di and triatomic molecules to more complex structures; for example, Awaruite has been shown to produce NH₃ from hydrogen and nitrogen precursors (Alexander Smirnov, Douglas Hausner, Richard Laffers, Daniel R Strongin, and Marton AA Schoonen, Geochemical Transactions, 2008, 9:5).

The goal of this study is to examine the role of iron nickel clusters with Awaruite and Tetrataenite stoichiometries in converting atomic nitrogen and hydrogen to ammonia. Using a basin-hopping algorithmic procedure, the global minima of Awaruite and Tetrataenite clusters with up to 35 atoms have been identified along with their affinity to nitrogen and hydrogen attachment has been examined (i.e. atom position, cluster edges, and surface sites). Preliminary results indicate that atomic nitrogen attaches onto mixed iron nickel cluster surface sites, with distinct discontinuities in the binding energy profile at magic cluster number positions. We also studied the effects of cluster composition on the affinity of nitrogen and hydrogen to attach to Ni_13-xFe_x with up to x=13. These results, for both scenarios (size and compositional variation), indicate that nano-sized iron-nickel clusters would drive the initial transformation of nitrogen and hydrogen toward NH_3, with important implications for the chemistry of Earth's early atmosphere.