Single-Atom Titanium on Mesoporous Nitrogen, Oxygen-Doped Carbon for Efficient Photo-thermal Catalytic CO₂ Cycloaddition by a Radical Mechanism

Developing efficient and earth-abundant catalysts for CO₂ fixation to high value-added chemicals is meaningful but challenging. Styrene carbonate has great market value, but the cycloaddition of CO₂ to styrene oxide is difficult due to the high steric hindrance and weak electron-withdrawing ability of the phenyl group. To utilize clean energy (such as optical energy) directly and effectively for CO₂ value-added process, we introduce earth-abundant Ti single-atom into the mesoporous nitrogen, oxygen-doped carbon nanosheets (Ti−CNO) by a two-step method. The Ti−CNO exhibits excellent photothermal catalytic activities and stability for cycloaddition of CO₂ and styrene oxide to styrene carbonate. Under light irradiation and ambient pressure, an optimal Ti−CNO produces styrene carbonate with a yield of 98.3 %, much higher than CN (27.1 %). In addition, it shows remarkable stability during 10 consecutive cycles. Its enhanced catalytic performance stems from the enhanced photothermal effect and improved Lewis acidic/basic sites exposed by the abundant mesopores. The experiments and theoretical simulations demonstrate the styrene oxide⋅⁺ and CO₂⋅⁻ radicals generated at the Lewis acidic (Ti^δ+) and basic sites of Ti−CNO under light irradiation, respectively. This work furnishes a strategy for synthesizing advanced single-atom catalysts for photo-thermal synergistic CO₂ fixation to high value products via a cycloaddition pathway.