A novel heterogeneous catalytic process for styrene carbonate synthesis via CO2 utilisation

Olaniyan, Bisi and Kanmodi, Joshua and Saha, Basu (2022) A novel heterogeneous catalytic process for styrene carbonate synthesis via CO2 utilisation. In: International Conference on Ion Exchange - IEX 2022: A Vision for the Future, 2022-09-072022-09-09.

Text (63. Olaniyan Kanmodi Saha extended abstract submitted)
63._Olaniyan_Kanmodi_Saha_extended_abstract_submitted.docx - Accepted Version
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Abstract

In recent years, the growing emissions of anthropogenic carbon dioxide (CO2) into the atmosphere have reached an unsustainable level. As a result, the effective utilisation and management of CO2 emissions have brought to the spotlight of independent and government-sponsored research. One of the most innovative approaches to transform CO2 into useful chemicals is the synthesis of organic carbonates via CO2 and epoxides. Cyclic organic carbonates such as styrene carbonate and chloromethyl ethylene carbonate are widely used as polar aprotic solvents, electrolytes for lithium-ion batteries, automobiles, cosmetic, precursors of polymeric materials, and fine chemicals. In the last two decades, several attempts have been made to develop new catalytic systems for the chemical fixation of CO2, using both homogenous and heterogeneous catalysis. However, these attempts have failed to yield satisfactory results as most of these catalysts require high temperature and/or pressure (usually around 453 K and pressure higher than 8 atm), further separation and purification steps, poor reusability performance, and low product yield. Hence this research is directed at the use of metal organic frameworks (MOFs) catalysts as a relatively new and promising candidate that addresses these aforementioned shortfalls. Recently, the stability of MOFs for large-scale industrial applications has been questioned in much published literature. This is due to their weak thermal stability, partly because of the structure of inorganic bricks and the nature of the chemical bonds it forms with the linker. However, this research is focused on the use of zeolitic imidazolate framework-8 (ZIF-8) (a sub-class of MOFs) for the synthesis of organic carbonates. It aims to improve its thermal stability as well as its catalytic performance via doping with a well-known metal-based catalysts promoter. Zirconium (Zr4+) has been selected as a favoured dopant for this novel catalytic design due to its high thermal stability. Zr4+ has comparable ionic size to Zn2+ (i.e., 0.745 Å for Zr and 0.740 Å for Zn2+), which helps to minimise lattice distortion. It can also act as a dual donor, providing up to two extra free electrons per ion when substituted for Zn2+. Zirconium can also act as a phase stabilizer to increase the dispersion and stability of the active metal through strong metal-support interactions. Therefore, the development of a novel Zr/ZIF-8 catalyst has shown a good substrate tolerance towards styrene oxide. More importantly, the reaction has been carried out under solvent-free and co-catalyst conditions. The heterogeneity of the catalyst has been proven by recovering and reusing the catalyst up to seven times with no noticeable change in catalytic activity. Powdered X-ray diffraction (PXRD) analysis of the recycled catalyst shows that the catalyst framework is very stable after reusability performance. The high efficiency of the catalyst may also be ascribed to the ion-exchange effect between the strong Lewis acidic Zn2+ sites and the basic nitrogen atoms from the imidazolate ligands, which promotes the epoxy ring-opening. The high selectivity towards styrene carbonate, simple separation by centrifugation, and excellent reusability demonstrated that the catalyst is viable for large-scale industrial applications.