Triazole-Based Protic Ionic Liquid Grafted onto Mesoporous SiO₂ as a Metal-Free Catalyst for CO₂ and Epoxide Coupling...

3-Amino-1,2,4-triazole-5-carboxylic acid was transformed into triazolium-based protic ionic liquid (TzPIL) via one-step acid-base neutralization. TzPIL was then immobilized onto a mesoporous SiO₂ (mSiO₂) support through quaternization, affording a mSiO₂-supported protic ionic liquid catalyst (TzPIL-4-mSiO₂) with multiple hydrogen-bond donor sites. Benefiting from its nitrogen-rich units and mesoporous structure, TzPIL-4-mSiO₂ exhibited an excellent CO₂ adsorption capacity. Under metal- and solvent-free conditions, this catalyst efficiently promoted the coupling reaction of CO₂ with propylene oxide, affording propylene carbonate in 98% yield at 90 °C and 1.0 MPa within 6 h. Moreover, after six consecutive cycles, the propylene carbonate yield remained 94%, demonstrating excellent recyclability. Finally, a plausible mechanism for the catalytic reaction was proposed: the protic hydrogen atoms and -COOH groups in TzPIL-4-mSiO₂ cooperatively activated the epoxide; Br^- sites served as nucleophile to initiate ring-opening, while the -NH₂ and -NH- groups in TzPIL facilitated CO₂ adsorption and activation.