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

Abstract

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.

Keywords: CO2 Fixation; Co−Fe Alloy; Hydrothermal Vent; Origin of Life; Promoter.