Efficient FeO/Fe Redox Cycle with Biomass Waste Glycerol for Net Carbon Benefit CO Reduction.

CO utilization is a critical aspect of achieving a sustainable carbon cycle, particularly in the context of global efforts to achieve carbon neutrality. Drawing inspiration from geological chemistry, Fe-based hydrothermal CO reduction into valuable chemicals has emerged as a promising CO utilization strategy. However, the lack of a sustainable and direct Fe regeneration approach presents a notable challenge to the widespread adoption of this strategy. Herein, we propose a method for the direct reduction of FeO to Fe using biodiesel-waste glycerol. This method yields a remarkable 97.9 wt % of reduced Fe, which exhibits a high activity for CO (HCO ) reduction to formic acid, maintaining a level of ~90 %. Our investigation reveals that the FeO reduction involves a direct hydrogen transfer from hydroxyl groups to lattice O atoms on the surface of FeO, forming reductive H species. The presence of a polyhydroxy structure in glycerol facilitates the stabilization of surface H species, thereby enhancing the reduction efficiency process. Based on this mechanism, we explore the potential of using various polyols derived from woody biomass, which exhibit similar capabilities for the reduction of FeO as glycerol. These findings establish an efficient and sustainable FeO/Fe redox cycle, which integrates waste biomass into circular carbon economy solutions and contributes to the overall net carbon benefit of CO utilization.