Structure, Activity, and Stability of Triphenyl Phosphine-Modified Rh/SBA-15 Catalyst for Hydroformylation of Propene: A High-Resolution Solid-State NMR Study

A ligand (triphenyl phosphine, PPh3)-modified heterogeneous PPh3-Rh(CO)/SBA-15 catalyst and supported Wilkinson complex HRh(CO)(PPh3)(3)/SBA-15 catalyst were prepared and examined in the hydroformylation of propene. Heterogeneous PPh3-Rh(CO)/SBA-15 catalyst showed much higher activity and stability in this reaction. Multimuclear H-1, Si-29, P-31, and O-17 MAS NMR and two-dimensional O-17 MQ MAS NMR together with XRD and N-2 adsorption were employed to study the local structures of these two catalysts. Quantitative H-1 and Si-29 MAS NMR and qualitative one- and two-dimensional O-17 MAS and MQ MAS NMR indicate that in the presence of CO the silanols on the surface of SBA-15 can react with rhodium carbonyls to form the Si-O-Rh bonds at the interface between the catalyst and the support. IT MAS NMR spectra demonstrate a similar Wilkinson complex structure is produced on the heterogeneous PPh3-Ph(CO)/SBA-15 catalyst. The formation of Si-O-Rh bonds at the interface may immobilize the Rh complex during the long reaction. These may be correlated to the higher performances of heterogeneous PPh3-Rh(CO)/SBA-15 catalyst in propene hydroformylation.