Water-Induced Pseudocarboxylic-Mediated Hydroformylation in Zeolite Channel for Enhanced Linear Aldehyde Production

Increasing the reaction rate and linear-to-branched ratio (l/b ratio) of aldehydes is critical for efficient olefin hydroformylation, which is typically achieved by delicate catalyst design in industrialized homogeneous processes. Despite the fact that heterogenization of hydroformylation addresses critical challenges in catalyst recovery and reusability, it often compromises activity and regioselectivity due to the less-defined microenvironment surrounding active sites. To this end, most effort was dedicated to developing catalysts with high activity, chemoselectivity, and regioselectivity, while the intensification by enhancing reaction kinetics was relatively undertaken. Herein, we demonstrate a strategy beyond catalyst design to significantly increase the olefin conversion rate (from 179-221 to 371-408 mmol/(g_Rh·min)) and l/b ratio (from 10.1-19.3 to 25.3-67.0) by simply adding a trace amount of water to a series of heterogeneous hydroformylation systems using zeolite-confined Rh catalysts. Kinetic study, isotopic labeling experiments, and operando IR spectroscopy synergistically suggested that the presence of water induced an identical reaction pathway where water molecules enriched in zeolite channels and directly participated in the catalytic cycle of hydroformylation as a cocatalyst. Such a pathway resulted in a substantial decrease in the energy barrier for normal aldehyde formation (from 82.6 to 69.7 kJ/mol) and therefore selectively increased the formation rate of linear aldehyde (from 207 to 399 mmol/(g_Rh·min)). The results demonstrated the significance of intensifying heterogeneous hydroformylation in confined environments through the manipulation of reaction pathways.