Effect of Alkali- and Alkaline-Earth-Metal Promoters on Silica-Supported Co-Fe Alloy for Autocatalytic CO2 Fixation.

Hydrothermal vents harbor numerous microbial communities rich in reduced carbon species such as formate, acetate, and hydrocarbons. Such essential chemicals for life are produced by H2 -dependent CO2 reduction, where serpentinization provides continuous H2 and thermal energy. Here, we show that silica-supported bimetallic Co-Fe alloys, naturally occurring minerals around serpentinite, can convert CO2 and H2 O to key metabolic intermediates of the acetyl coenzyme A pathway such as formate (up to 72 mM), acetate, and pyruvate under mild hydrothermal vent conditions. Long-chain hydrocarbons up to C6 including propene are also detected, just as in the Lost City hydrothermal field. The effects of promoters on structural properties and catalytic functionalities of the Co-Fe alloy are systematically investigated by incorporating a series of alkali and alkaline earth metals including Na, Mg, K, and Ca. Alkali and alkaline earth metals resulted in higher formate concentrations when dissolved in water and increased reaction pH, while alkaline earth metals also favored the formation of insoluble hydroxides and carbonates similar to the constituent minerals of the chimneys at the Lost City hydrothermal fields.

Direct Synthesis of Formamide from CO2 and H2O with Nickel-Iron Nitride Heterostructures under Mild Hydrothermal Conditions.

Formamide can serve as a key building block for the synthesis of organic molecules relevant to premetabolic processes. Natural pathways for its synthesis from CO2 under early earth conditions are lacking. Here, we report the thermocatalytic conversion of CO2 and H2O to formate and formamide over Ni-Fe nitride heterostructures in the absence of synthetic H2 and N2 under mild hydrothermal conditions. While water molecules act as both a solvent and hydrogen source, metal nitrides serve as nitrogen sources to produce formamide in the temperature range of 25-100 °C under 5-50 bar. Longer reaction times promote the C-C bond coupling and formation of acetate and acetamide as additional products. Besides liquid products, methane and ethane are also produced as gas-phase products. Postreaction characterization of Ni-Fe nitride particles reveals structural alteration and provides insights into the potential reaction mechanism. The findings indicate that gaseous CO2 can serve as a carbon source for the formation of C-N bonds in formamide and acetamide over the Ni-Fe nitride heterostructure under simulated hydrothermal vent conditions.

Influence of Composition of Nickel-Iron Nanoparticles for Abiotic CO2 Conversion to Early Prebiotic Organics.

Abiotic synthesis of formate and short hydrocarbons takes place in serpentinizing vents where some members of vent microbial communities live on abiotic formate as their main carbon source. To better understand the catalytic properties of Ni-Fe minerals that naturally exist in hydrothermal vents, we have investigated the ability of synthetic Ni-Fe based nanoparticular solids to catalyze the H2 -dependent reduction of CO2 , the first step required for the beginning of pre-biotic chemistry. Mono and bimetallic Ni-Fe nanoparticles with varied Ni-to-Fe ratios transform CO2 and H2 into intermediates and products of the acetyl-coenzyme A pathway-formate, acetate, and pyruvate-in mM range under mild hydrothermal conditions. Furthermore, Ni-Fe catalysts converted CO2 to similar products without molecular H2 by using water as a hydrogen source. Both CO2 chemisorption analysis and post-reaction characterization of materials indicate that Ni and Fe metals play complementary roles for CO2 fixation.

Ambient temperature CO2 fixation to pyruvate and subsequently to citramalate over iron and nickel nanoparticles.

The chemical reactions that formed the building blocks of life at origins required catalysts, whereby the nature of those catalysts influenced the type of products that accumulated. Recent investigations have shown that at 100 °C awaruite, a Ni3Fe alloy that naturally occurs in serpentinizing systems, is an efficient catalyst for CO2 conversion to formate, acetate, and pyruvate. These products are identical with the intermediates and products of the acetyl-CoA pathway, the most ancient CO2 fixation pathway and the backbone of carbon metabolism in H2-dependent autotrophic microbes. Here, we show that Ni3Fe nanoparticles prepared via the hard-templating method catalyze the conversion of H2 and CO2 to formate, acetate and pyruvate at 25 °C under 25 bar. Furthermore, the 13C-labeled pyruvate can be further converted to acetate, parapyruvate, and citramalate over Ni, Fe, and Ni3Fe nanoparticles at room temperature within one hour. These findings strongly suggest that awaruite can catalyze both the formation of citramalate, the C5 product of pyruvate condensation with acetyl-CoA in microbial carbon metabolism, from pyruvate and the formation of pyruvate from CO2 at very moderate reaction conditions without organic catalysts. These results align well with theories for an autotrophic origin of microbial metabolism under hydrothermal vent conditions.

Effects of Silica Modification (Mg, Al, Ca, Ti, and Zr) on Supported Cobalt Catalysts for H2-Dependent CO2 Reduction to Metabolic Intermediates.

Serpentinizing hydrothermal systems generate H2 as a reductant and harbor catalysts conducive to geochemical CO2 conversion into reduced carbon compounds that form the core of microbial autotrophic metabolism. This study characterizes mineral catalysts at hydrothermal vents by investigating the interactions between catalytically active cobalt sites and silica-based support materials on H2-dependent CO2 reduction. Heteroatom incorporated (Mg, Al, Ca, Ti, and Zr), ordered mesoporous silicas are applied as model support systems for the cobalt-based catalysts. It is demonstrated that all catalysts surveyed convert CO2 to methane, methanol, carbon monoxide, and low-molecular-weight hydrocarbons at 180 °C and 20 bar, but with different activity and selectivity depending on the support modification. The additional analysis of the condensed product phase reveals the formation of oxygenates such as formate and acetate, which are key intermediates in the ancient acetyl-coenzyme A pathway of carbon metabolism. The Ti-incorporated catalyst yielded the highest concentrations of formate (3.6 mM) and acetate (1.2 mM) in the liquid phase. Chemisorption experiments including H2 temperature-programmed reduction (TPR) and CO2 temperature-programmed desorption (TPD) in agreement with density functional theory (DFT) calculations of the adsorption energy of CO2 suggest metallic cobalt as the preferential adsorption site for CO2 compared to hardly reducible cobalt-metal oxide interface species. The ratios of the respective cobalt species vary depending on the interaction strength with the support materials. The findings reveal robust and biologically relevant catalytic activities of silica-based transition metal minerals in H2-rich CO2 fixation, in line with the idea that autotrophic metabolism emerged at hydrothermal vents.

Role of geochemical protoenzymes (geozymes) in primordial metabolism: specific abiotic hydride transfer by metals to the biological redox cofactor NAD.

Hydrogen gas, H2 , is generated in serpentinizing hydrothermal systems, where it has supplied electrons and energy for microbial communities since there was liquid water on Earth. In modern metabolism, H2 is converted by hydrogenases into organically bound hydrides (H- ), for example, the cofactor NADH. It transfers hydrides among molecules, serving as an activated and biologically harnessed form of H2 . In serpentinizing systems, minerals can also bind hydrides and could, in principle, have acted as inorganic hydride donors-possibly as a geochemical protoenzyme, a 'geozyme'- at the origin of metabolism. To test this idea, we investigated the ability of H2 to reduce NAD+ in the presence of iron (Fe), cobalt (Co) and nickel (Ni), metals that occur in serpentinizing systems. In the presence of H2 , all three metals specifically reduce NAD+ to the biologically relevant form, 1,4-NADH, with up to 100% conversion rates within a few hours under alkaline aqueous conditions at 40 °C. Using Henry's law, the partial pressure of H2 in our reactions corresponds to 3.6 mm, a concentration observed in many modern serpentinizing systems. While the reduction of NAD+ by Ni is strictly H2 -dependent, experiments in heavy water (2 H2 O) indicate that native Fe can reduce NAD+ both with and without H2 . The results establish a mechanistic connection between abiotic and biotic hydride donors, indicating that geochemically catalysed, H2 -dependent NAD+ reduction could have preceded the hydrogenase-dependent reaction in evolution.