A Carbon-Neutral CO 2 Capture, Conversion, and Utilization Cycle with Low-Temperature Regeneration of Sodium Hydroxide

A highly efficient recyclable system for capture and subsequent conversion of CO to formate salts is reported that utilizes aqueous inorganic hydroxide solutions for CO capture along with homogeneous pincer catalysts for hydrogenation. The produced aqueous solutions of formate salts are directly utilized, without any purification, in a direct formate fuel cell to produce electricity and regenerate the hydroxide base, achieving an overall carbon-neutral cycle. The catalysts and organic solvent are recycled by employing a biphasic solvent system (2-MTHF/H O) with no significant decrease in turnover frequency (TOF) over five cycles. Among different hydroxides, NaOH and KOH performed best in tandem CO capture and conversion due to their rapid rate of capture, high formate conversion yield, and high catalytic TOF to their corresponding formate salts. Among various catalysts, Ru- and Fe-based PNP complexes were the most active for hydrogenation. The extremely low vapor pressure, nontoxic nature, easy regenerability, and high reactivity of NaOH/KOH toward CO make them ideal for scrubbing CO even from low-concentration sources-such as ambient air-and converting it to value-added products.