Executive Summary : | Using inexpensive, harmless, and abundantly available CO₂ as C1 feedstock for fuel and chemical synthesis can mitigate the problem of global warming and decrease our dependence on petrochemicals. The transformation of CO₂ into chemicals is difficult due to its thermodynamic stability and chemical inertness. Among various CO₂ transformations, the cycloaddition of CO₂ with small membered ring compounds (e.g., epoxides and aziridine derivatives) is an efficient method to generate important organic compounds such as cyclic carbonates and oxazolidinones derivatives that are important for fine chemical, petrochemical and pharmaceutical industries. Various homogenous catalysts, including α-amino acids, alkali metal halides, ionic liquids, and iodine, have been investigated to activate highly inert CO₂ molecules. Homogenous catalyst has been commercialized to form cyclic carbonates from CO₂ and epoxides. Researchers also reported a series of heterogeneous catalysts such as zeolites, mixed oxides, metal complexes, organic polymers, zeolitic imidazolate frameworks, MOF, etc. However, the requirement of toxic organic solvents and co-catalysts, high reaction temperature, significant CO₂ pressure, prolonged reaction time, and inherent limitations of homogeneous catalysts such as tedious recovery and non-recyclability are bottlenecks to accomplish adequate performance. Integrating acid and basic groups in a single heterogeneous catalyst for performance enhancement is challenging and promising for a low carbon future. Accordingly, in the proposed research, we mainly intended to develop bifunctional (acid-base) hybrid (organic-inorganic) nanoporous transition metal (Zr, Ti, Ni, Fe, Cu) phosphonates with low cost, high performance, strong co-ordinations, and robust properties that are efficient under challenging conditions such as diluted CO₂, mild temperature, and presence of moisture and impurities. The metal phosphonates will be synthesized by hydrothermal and sonochemical methods. The synthesis time can be reduced through the ultrafast sonochemical process. After thorough characterization, the catalyst will be evaluated for the cycloaddition of CO₂ with small membered rings under ambient and solvent-free conditions. Both basic and acidic active sites will facilitate the activation of CO₂ and small ring compounds without needing a co-catalyst. The porous structure is advantageous for fast mass transport due to the accessibility of a large number of active sites per unit area. The acidity/ basicity and textural properties of the resulting catalyst will be fine-tuned by using different organic linkers and soft templates. It is also planned to assess the long-term activity and stability of these phosphonates as it is crucial for its implication on an industrial scale. Furthermore, in-situ reaction monitoring for the mechanism of the reaction and structure-property relationship will be performed during the course of the proposed work. |