Selective carboxylation of alkenes with CO2 to form unsaturated carboxylic acid on Sc-exchanged MFI zeolite

Abstract

Utilization of CO₂ in chemical synthesis as C1 carbon feedstock to introduce a carboxylic group into alkene is valuable for producing unsaturated carboxylic acids. Selective carboxylation of alkenes at targeted positions can be used to regulate the production of such specific unsaturated carboxylic acids or functionalize hydrocarbon plastics that possess residual CC double bonds. In this study, we investigated the carboxylation of 1-butene and 2-butene (as representative alkene) with CO₂ on Sc-exchanged MFI zeolites using density functional theory calculations. We find that similar to ethylene, the carboxylation of butene is also rate-limited by the β─H transfer. We examined carboxylation at the C1 and C2 positions of 1-butene and cis and trans isomers for 2-butene. Based on activation barriers of the β─H transfer, our results demonstrate that Sc-MFI zeolite preferably carboxylates at the terminal position of butene. In the case of 2-butene, carboxylation of the trans isomer is more favorable than the cis isomer. Furthermore, We show that the energy of degenerate orbitals of C, O and H atoms (involved in the β─H transfer) in the metallalactone ring regulates the activation energy of the β─H transfer.