SBA-15-Supported Imidazolium Ionic Liquid through Different Linkers as a Sustainable Catalyst for the Synthesis of Cyclic Carbonates: A Kinetic Study and Theoretical DFT Calculations

Various cyclic carbonates were prepared by cycloaddition of carbon dioxide with different epoxides using imidazolium-based catalysts grafted on a mesoporous silica support through 3-aminopropyltrimethoxysilane and Br–(CH2)n–Br (n = 2 or 4) under efficient and mild conditions. The catalysts were characterized by various physicochemical techniques such as magic angle spinning (MAS) NMR, 1H NMR, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), Field-emission scanning microscopy (FESEM), thermogravimetric analysis (TGA), and Brunauer–Emmett–Teller (BET). The reactions were conducted under maximum carbon dioxide pressure of 2.0 MPa at the temperature range of 80–140 °C without using any solvent. The influence of different reaction parameters was investigated. The effects of the chain length and different anions on the catalyst activity were also studied. The mechanism of the reaction was investigated theoretically using density functional theory (DFT) calculations in the ONIOM scheme, and the influence of hydrogen bonding and the chain length of the linker on the transition state of the rate-determining step was also studied. The selected catalyst was used in subsequent runs without a significant loss of its reactivity.