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.