Promotion of Inorganic Phosphorus on Rh Catalysts in Styrene Hydroformylation: Geometric and Electronic Effects

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Abstract

Rh-based homogeneous catalysts with phosphine ligands are highly active in hydroformylation reactions. Using DFT calculations, we found a similar electronic effect of inorganic phosphorus in the Rh2P structure. The energy profiles demonstrated that Rh2P would significantly enhance the styrene hydroformylation activity in comparison with Rh, which was further confirmed by experiments. Triphenylphosphine (PPh3) was used as the phosphorus source, and Rh2P supported on silica was prepared by impregnation at a relatively low temperature (550 °C). The turnover frequency (TOF) of styrene hydroformylation was increased to 1496 h–1, which was comparable with some single atom catalysts (SACs). Recycling tests showed a good stability in five runs. Furthermore, HAADF-STEM, XPS, and other characterizations confirmed the synthesis of the Rh2P structure. The promotion effect of P was bifunctional. On the one hand, the doped P separated the surface Rh atoms, which eliminated the surface hollow sites and prevented excessively strong adsorption of the reactants. On the other hand, electrons transferred from Rh to P, causing the surface Rh atoms to be positively charged, which was favorable for hydroformylation reactions. The geometric effects improved the dispersion and the electronic effects changed the rate-determining step from CO insertion to phenylpropionyl hydrogenation, both leading to a higher hydroformylation activity.

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