Zeolite-catalysed olefin carbonylation based on tuning spatial confinement.

Carbonylation is an important process used to produce aldehydes, carboxylic acids and esters1-5 that is usually catalysed by homogeneous metal complexes with ligands and iodide promoters6-12. Koch has reported that protons of mineral acids can also catalyse carbonylation13. Previous studies have demonstrated that Brønsted acidic zeolites can act as a heterogeneous, Koch-type catalyst for carbonylation of alcohols and olefins, but the products in this case are limited to tertiary carboxylic acids14-18. Here we show that targeted use of spatial confinement in a zeolite together with a high CO/olefin ratio can help break this limitation. We report that, with FER zeolite and a CO/olefin ratio of 360, olefin carbonylation can produce primary and secondary carboxylic acids as the main products; ethylene carbonylation to propanoic acid (PA) is achieved with 80% selectivity over 100 h and propylene carbonylation to isobutyric acid (IBA) is achieved with 95% selectivity over 750 h. The propylene and ethylene carbonylation selectivities decrease to 61% and 57%, respectively, as the CO/olefin ratio decreases to 24 and 90, respectively. Experiments in combination with theoretical calculations suggest that T2-O5 in eight-membered ring (8-MR) cavities of FER zeolite are the primary active sites for ethylene carbonylation and T3-O1 in ten-membered rings (10-MRs) are the primary active sites for propylene carbonylation. Our findings open new directions for olefin carbonylation and provide critical insights into the prerequisites for developing new zeolite-based carbonylation processes.