Synergistic Effects of Silica-Supported Iron-Cobalt Catalysts for CO₂ Reduction to Prebiotic Organics

To test the ability of geochemical surfaces in serpentinizing hydrothermal systems to catalyze reactions from which metabolism arose, we investigated H₂-dependent CO₂ reduction toward metabolic intermediates over silica-supported Co-Fe catalysts. Supported catalysts converted CO₂ to various products at 180 °C and 2.0 MPa. The liquid product phase included formate, acetate, and ethanol, while the gaseous product phase consisted of CH₄, CO, methanol, and C₂-C₇ linear hydrocarbons. The 1/1 ratio CoFe alloy with the same composition as the natural mineral wairauite yielded the highest concentrations of formate (6.0 mM) and acetate (0.8 mM), which are key intermediates in the acetyl-coenzyme A (acetyl-CoA) pathway of CO₂ fixation. While Co-rich catalysts were proficient at hydrogenation, yielding mostly CH₄, Fe-rich catalysts favored the formation of CO and methanol. Mechanistic studies indicated intermediate hydrogenation and C-C coupling activities of alloyed CoFe, in contrast to physical mixtures of both metals. Co in the active site of Co-Fe catalysts performed a similar reaction as tetrapyrrole-coordinated Co in the corrinoid iron-sulfur (CoFeS) methyl transferase in the acetyl-CoA pathway. In a temperature range characteristic for deeper regions of serpentinizing systems, oxygenate product formation was favored at lower, more biocompatible temperatures.