Rapid and Efficient CO₂ Conversion to Cyclic Carbonates under Ambient Conditions Using a Fe₃O₄@SiO₂-Immobilized Cobalt Nanocatalyst

The present study describes the synthesis, characterization, and application of an efficient magnetically recoverable and reusable heterogeneous catalyst for the conversion of CO₂ into cyclic carbonates by utilizing epoxides under mild conditions. The catalyst Fe₃O₄@SiO₂@Propyl@L^ABP@Co is fabricated through anchoring the amido-bis(phenolate) cobalt complex on a modified surface of silica that is coated with magnetic Fe₃O₄ nanoparticles. The structural and morphological properties of the catalyst are well-characterized by state-of-art techniques such as Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), Brunauer-Emmett-Teller (BET) analysis, field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDX), transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and inductively coupled plasma-optical emission (ICP-OES), respectively. The synthesized catalytic system of Fe₃O₄@SiO₂@Propyl@L^ABP@Co has exhibited high efficiency in converting CO₂ and epoxides into cyclic carbonates with excellent yield (99%) and high turnover number (TON, 900). The catalyst has been successfully tested with various epoxides including aliphatic, aromatic, cyclic, and acyclic epoxides. The conditions for the catalytic conversion of CO₂ into cyclic carbonates have extensively been investigated to confirm the occurrence of this transformation that is facilitated through tetrabutylammonium bromide (TBAB) under 1.0 bar of CO₂ pressure, room temperature, and stirring for 6 h. The catalyst is also efficient for the fixation of CO₂ into cyclic carbonate under stimulated flue gas (30% of CO₂ in N₂ v/v) conditions. The recyclability test for this catalytic system has shown that the low catalyst loadings (0.11 mol % of Co) could be reused up to five times in the conversion of styrene oxide and CO₂ into cyclic carbonate 4-phenyl-1,3-dioxolan-2-one, without a noticeable decrease in activity.