“Global warming” owing to the exponential rise of CO2 has forced researchers to explore possibilities for limited release of CO2. Sequestration of CO2 and its utilization to produce industrially important products are potential solutions. High thermodynamic stability (–△Hf = -394 kJ/mol) of CO2 is a bottleneck for its conversion to targeted products, hence, its activation by appropriate catalyst is required. Although metal-based catalysts are popular choices, requirement of co-catalysts and environmental concerns owing to metal ion leaching has encouraged to explore their metal-free counterparts. High surface area nanoporous materials especially enriched with heteroatoms are at the forefront in this research area owing to their superior performance demonstrated both theoretically and experimentally. In this direction, a generalized approach was explored to investigate the activation of CO2 and epoxides simultaneously by amine and hydroxyl functionalities of metal-free heteroatoms enriched high surface area heterogeneous catalysts for the formation of cyclic carbonates. Nitrogen-enriched nanoporous polymer (MNENP) and composite of polytriazine-SBA-16 (PT@SBA-16), both having amine and hydroxyl functionalities, were utilized for the synthesis of cyclic carbonates, keeping in mind that –OH will interact with the epoxide via H-bonding and the –NH groups activate the CO2 molecules by Lewis acid-base interactions. Almost complete conversion CO2 and epoxides to cyclic carbonates were observed when epichlorohydrin was reacted with CO2 at 100 °C within a reaction time of 20 and 16 h using MNENP and PT@SBA-16, respectively, at 4 bar CO2 pressure. Moreover, these catalysts are generalized for the conversion of five additional epoxides differ in the electronegativity of the substituents with good conversion and selectivity. Retention of almost 80% of its initial catalytic activity even after five consecutive cycles, easily recyclable, co-catalyst, and solvent-free conditions made these materials as efficient metal-free catalysts for the conversion of CO2 to cyclic carbonates, molecules of industrial importance.

Role of multifunctionalities in the metal-free heterogeneous catalysts for CO2 utilization

ACS Spring Meeting 2021

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