Catalytic cycloaddition of CO2 and epoxides by sustainable metal-free N,O-enriched hydrochar

• Nitrogen-rich biomass is sustainably converted into hydrochar with both Lewis acid and base sites. • The hydrochar exhibits highly CO 2 conversion and up to 95 % yield of cyclic carbonate with no solvents or co-catalysts. • The improved catalytic performance is attributed to the abundant acid and base active sites that dominated by the doping oxygen and nitrogen groups, respectively. The cycloaddition of CO₂ and epoxides to produce cyclic carbonates offers an atom-economical route for carbon utilization, yet its industrial implementation is hindered by the scarcity of sustainable, efficient, and cost-effective catalysts. We herein develop a metal-free N/O-enriched hydrochar (NO-HC) through a one-pot synthesis using nitrogen-rich biomass precursors. The optimized NO-HC 100 catalyst achieves 95 % cyclic carbonate yield under solvent- and co-catalyst-free conditions, exhibiting exceptional substrate generality. It demonstrated that the improved catalytic performance is attributed to the abundant acid and base active sites that are dominated by the doping oxygen and nitrogen groups, respectively. This conclusion can be extended to the widely existing actual biomass, considering the composition and nitrogen content of biomass, as well as the corresponding pre-treatment methods (e.g., deash). This work provides a circular economy paradigm that synergistically valorizes nitrogen-containing biomass into functional carbocatalysts while converting CO₂ into value-added chemicals, achieving dual carbon mitigation through waste-to-resource conversion and greenhouse gas utilization. The excess emitted CO 2 is transformed by a combined biochemical and chemical method. One method fixes the CO 2 into the biomass through photosynthesis, and the other is catalyzed by the N-rich biomass-derived hydro char to produce cyclic carbonates.