In Situ XAS Diagnostics of Reductive Hydroformylation Reaction in Segmented Flow Under Elevated Pressure and Temperature

Abstract

Homogeneous hydroformylation is an important industrial reaction for the production of aldehydes and alcohols. Rh metal complexes modified with tertiary amine ligands allow tandem one-pot reactions for converting olefins directly into alcohols, and more often, such reactions are performed in microfluidic flow regimes relevant to both academic research and industrial automatization. The reaction yield depends on the coordination of Rh atoms or the formation of Rh clusters; therefore, knowledge about the local atomic and electronic structure of active sites under industrial conditions is important. Rh K-edge X-ray absorption spectroscopy (XAS) is a unique tool to probe Rh coordination; however, to date, there have been no reports of the application of this methodology to hydroformylation in microfluidic biphasic flow. Our work demonstrates the experimental setup and transmission cell developed for segmented flow operando measurements. Quantitative analysis of XAS data was performed with the library of theoretical spectra computed for relevant monomeric, dimeric, and small cluster species. As found recently by EXAFS analysis for autoclave, we demonstrate that under segmented flow, the presence of amine species in the reaction prevents the formation of Rh clusters in favor of Rh dimers.