Mechanochemical In Situ Assembly of Organourea-Containing Ionic Polymers within Mesoporous SiO ₂ for Efficient CO ₂ Fixation to Cyclic Carbonates

Mechanochemistry offers an environmentally benign and highly efficient route to heterogeneous catalysts. In this work, mesoporous SiO 2 serves as both a ball-milling aid that enhances grinding efficiency and a porous support for the in situ generation and immobilization of organourea-containing ionic polymers. During the mechanochemical process, the polymers are assembled within the mesopores and onto the external surface of SiO 2, thereby improving the accessibility of ionic active sites for catalysis. This solvent-free strategy eliminates the need for toxic organic solvents and significantly reduces synthesis time compared with conventional solvothermal or reflux routes that typically require several hours to days, while exploiting the synergistic interactions between the SiO 2 support and the ionic polymer matrix. The optimized catalyst, denoted TEB-O@Si-8(50%), achieves 99% conversion of various epoxides to the corresponding cyclic carbonates under mild conditions (100 °C, 1 MPa CO 2, 12 h) and retains high catalytic activity over five consecutive cycles. Kinetic studies and in situ FTIR spectroscopy reveal that urea and hydroxyl groups polarize the C–O bond of the epoxide through hydrogen bonding, while bromide ions facilitate nucleophilic ring-opening. This work overcomes the prolonged synthesis times and reliance on volatile solvents associated with conventional catalyst preparation and provides a sustainable, scalable route to high-performance heterogeneous catalysts for CO 2 conversion.