Serpentinization: Connecting Geochemistry, Ancient Metabolism and Industrial Hydrogenation

Rock–water–carbon interactions germane to serpentinization in hydrothermal vents have occurred for over 4 billion years, ever since there was liquid water on Earth. Serpentinization converts iron(II) containing minerals and water to magnetite (Fe(3)O(4)) plus H(2). The hydrogen can generate native metals such as awaruite (Ni(3)Fe), a common serpentinization product. Awaruite catalyzes the synthesis of methane from H(2) and CO(2) under hydrothermal conditions. Native iron and nickel catalyze the synthesis of formate, methanol, acetate, and pyruvate—intermediates of the acetyl-CoA pathway, the most ancient pathway of CO(2) fixation. Carbon monoxide dehydrogenase (CODH) is central to the pathway and employs Ni(0) in its catalytic mechanism. CODH has been conserved during 4 billion years of evolution as a relic of the natural CO(2)-reducing catalyst at the onset of biochemistry. The carbide-containing active site of nitrogenase—the only enzyme on Earth that reduces N(2)—is probably also a relic, a biological reconstruction of the naturally occurring inorganic catalyst that generated primordial organic nitrogen. Serpentinization generates Fe(3)O(4) and H(2), the catalyst and reductant for industrial CO(2) hydrogenation and for N(2) reduction via the Haber–Bosch process. In both industrial processes, an Fe(3)O(4) catalyst is matured via H(2)-dependent reduction to generate Fe(5)C(2) and Fe(2)N respectively. Whether serpentinization entails similar catalyst maturation is not known. We suggest that at the onset of life, essential reactions leading to reduced carbon and reduced nitrogen occurred with catalysts that were synthesized during the serpentinization process, connecting the chemistry of life and Earth to industrial chemistry in unexpected ways.