Understanding the reaction kinetics of heterogeneous 1-hexene hydroformylation

Abstract

Since its discovery by Otto Roelen, hydroformylation has attracted extensive attention due to its ability to extend the carbon chain of olefins. Aldehydes, which are converted by the hydroformylation of olefins and syngas (CO/H₂), are not only high-value products, but also intermediates to produce fine chemicals, such as alcohols, esters and amines. The currently used homogeneous catalysts bring about the loss of precious metals and the discharge of phosphorus-containing waste. Therefore, heterogeneous catalysts are developed to simplify the separation process and enhance catalyst recovery. However, the reaction kinetics of heterogeneous hydroformylation, especially the hydroformylation of long-chain olefins, remains unclear. Unlike homogeneous hydroformylation, terminal olefins can be isomerized to internal olefins on heterogeneous catalysts, and can be further converted to different branched aldehydes. Thus, the reaction kinetics of heterogeneous hydroformylation is more complex. In this work, we established a kinetic model for the heterogeneous hydroformylation of long-chain terminal olefins on Rh-based phosphides, using 1-hexene as the model reactant. This kinetic model agrees well with the density functional theory (DFT) results, and can be used to predict the regioselectivity under different reaction conditions. This study reveals the kinetic mechanism of heterogeneous hydroformylation of long-chain terminal olefins, which paves the way for the rational design of heterogeneous catalysts and the theoretical optimization of reaction conditions.