Understanding the facet effects of heterogeneous Rh2P catalysts for styrene hydroformylation

Abstract

Heterogeneous hydroformylation reactions have attracted much attention and Rh-based phosphides are highly active in converting styrene to phenylpropionaldehyde. In this work, we combined the characterization results and density functional theory (DFT) calculations to reveal that (111)-terminated facets are the main active sites for Rh-based phosphide catalysts. The DFT calculation results indicated that the Rh₂P (111) facet is far more active than the (110) and (100) facets, due to its appropriate electronic structure and unique isolated Rh sites. Such well-defined compounds, containing only isolated monometallic active sites, have some similarities to single atom catalysts (SACs) and are named quasi single atom compounds (QSACs). We further considered the entropic contribution to the surface reactions on Rh₇Pd₁P₄ (111) and predicted the activation energy using the energetic span model, which was consistent with the previously reported results obtained from experimental fitting. This result further confirms that (111)-terminated facets are the main active sites for Rh-based phosphides in heterogeneous styrene hydroformylation.