Catalytic CO₂ Fixation via Glycerol Carbonate Synthesis: Review of Silica Hybrids and Ionic Liquid Advancements

This review explores the catalytic conversion of carbon dioxide (CO₂) into glycerol carbonate (GC), positioning this pathway as a sustainable strategy that couples environmental mitigation with the valorization of surplus glycerol from biodiesel production. Glycerol carbonate maintains extensive industrial utility as a green solvent, chemical intermediate, and functional component in polymers, cosmetics, and packaging. Distinct from prior literature, this study specifically evaluates the use of amorphous silica from rice husk ash (RHA) as a sustainable, low-cost support, analyzing the synergistic effect between Nb₂O₅, NiO, and ionic liquids in hybrid catalyst architectures. The review evaluates diverse catalytic frameworks, with a primary focus on heterogeneous systems. Silica-based materials are highlighted, particularly those synthesized from rice husk ash, which is an abundant amorphous silica source. The sol–gel method is identified as a robust route for engineering porous matrices with high surface areas and tunable structural properties. Furthermore, the doping of silica with metal oxides, such as niobium oxide (Nb₂O₅) and nickel oxide (NiO), is discussed as a strategic approach to introduce synergistic acid–base sites and redox properties that facilitate CO₂ activation. The integration of ionic liquids into hybrid systems is also examined as a promising frontier to enhance reaction kinetics and selectivity. Finally, this review delineates the nexus between agro-industrial waste management and the reduction in greenhouse gas emissions, proposing a circular economy framework for the biodiesel value chain.