Carbon dioxide utilization in plastic production: Development of a nickel catalyst



Carbon dioxide emissions, known to exacerbate climate change, have been increasing rapidly over the past century. One strategy to alleviate this issue is carbon capture and utilization (CCU), in which some of the abundant atmospheric CO2 is used as a carbon source for the production of valuable compounds. An attractive target is sodium acrylate, the building block of superabsorbent sodium polyacrylate found in hygiene products and many other common goods. Currently, sodium acrylate is synthesized by sequential oxidations of propylene over heterogeneous catalysts at high temperatures. Researchers have instead sought a one-step process coupling CO2 and ethylene, which is more sustainable and uses much less expensive starting materials. This method could consume a large quantity of atmospheric CO2. However, coupling with ethylene is not spontaneous. Homogeneous nickel catalysts have shown great promise for enabling this reaction, but the reported systems suffer from low efficiency. The main obstacle is a very stable nickelalactone intermediate, which contains a rigid Ni–pre-acrylate ring that resists the release of free sodium acrylate from the catalyst. My project aims to develop nickel complexes which include an N-heterocyclic carbene (NHC) in a supporting bidentate ligand. The characteristic strong electron donation and steric imposition of NHCs are expected to destabilize nickelalactones and to promote ring-opening, thereby enabling efficient catalytic production of sodium acrylate. Initial results support the instability of a simple bis(NHC) nickelalactone, and experiments testing sodium acrylate production are underway. Computational investigation of NHC-containing ligands with varying electronic and steric effects also helps to elucidate their capability to support the target reaction. This family of ligands could be the key to efficient nickel catalysts coupling CO2 and ethylene for sodium acrylate production, thus contributing to global CCU efforts.

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