Valorization of Iodine-doped Biochars for Conversion of Propylene Oxide with CO2 to Propylene Carbonate Under Mild Conditions

To cut down the atmospheric CO2 caused by human activities, it is crucial to develop effective carbon neutralization technologies. CO2 conversion through epoxide cycloaddition to cyclic carbonates is promising, but conventional catalytic systems are associated with limitations including harsh operating conditions, reliance on toxic solvents, the need for additional co-catalysts, and metal leaching. In this study, fruits of Liquidambar formosana Hance (LfH) were employed as biomass precursors to synthesize biochars (BC-T, T = 700–1000 °C) and iodine-doped biochars (I-BC-900-X, X = 4–12 M) through simple pyrolysis. The structural and surface characteristics of prepared catalysts were systematically analyzed by various spectroscopic and analytic measurements. The catalytic performance was evaluated in the cycloaddition of CO2 with propylene oxide to form propylene carbonate. Among the BC-T, the BC-900 exhibits the highest conversion (90%) and yield (90%) under mild conditions (90 °C, 3 kg cm− 2, 3 h) in the presence of co-catalysts, owing to its large surface area, high CO2 uptake, and abundant -OH/-COOH groups that promote epoxide activation. To further tackle the problems in product separations, I-BC-900-X biochars were prepared. Among these heterogeneous catalysts, the I-BC-900-8 achieves superior performance of 97% conversion and 87% yield without co-catalysts, which are attributed to enhanced hydrogen-bond donor groups and the triiodide anions facilitating epoxide ring-opening. These results demonstrate that biomass-derived and iodine-modified biochars represent efficient, sustainable, and environmental-friendly catalysts for CO2 utilization under cocatalyst-free and solvent-free conditions.