Molar-scale formate production via enzymatic hydration of industrial off-gases

Abstract Decarbonizing the steel industry, a major CO 2 emitter, is crucial for achieving carbon neutrality. Escaping the grip of CO combustion methods, a key contributor to CO 2 discharge, is a seemingly simple yet formidable challenge on the path to industry-wide net-zero carbon emissions. Here we suggest enzymatic CO hydration (enCOH) inspired by the biological Wood‒Ljungdahl pathway, enabling efficient CO 2 fixation. By employing the highly efficient, inhibitor-robust CO dehydrogenase ( Ch CODH2) and formate dehydrogenase ( Me FDH1), we achieved spontaneous enCOH to convert industrial off-gases into formate with 100% selectivity. This process operates seamlessly under mild conditions (room temperature, neutral pH), regardless of the CO/CO 2 ratio. Notably, the direct utilization of flue gas without pretreatment yielded various formate salts, including ammonium formate, at concentrations nearing two molar. Operating a 10-liter-scale immobilized enzyme reactor feeding live off-gas at a steel mill resulted in the production of high-purity formate powder after facile purification, thus demonstrating the potential for decarbonizing the steel industry.