Factors Influencing the Activity, Selectivity, and Stability of Rh-Based Supported Ionic Liquid Phase (SILP) Catalysts for Hydroformylation of Propene

An investigation has been carried out on the effects of catalyst preparation on the activity and stability of supported ionic liquid phase (SILP) catalysts for propene hydroformylation. Catalyst activity and stability were found to be strongly influenced by ligand and ionic liquid composition, ligand-to-rhodium ratio, and the surface density of silanol groups on the silica support. Highest activity was achieved using rhodium sulfoxantphos (SX) complexes in the presence of [bmim][OctSO4]. In situ FT-IR and solid-state 31P and 29Si MAS NMR characterization suggest that active Rh centers are not present as homogeneous complexes dissolved in an ionic liquid film, instead are present as HRh(CO)2SX complexes bound to the support by interactions of the sulfonate groups of SX with silanol groups of the support. The function of the ionic liquid is to inhibit undesired interactions of SX ligands, since such interactions render the phosphine groups unavailable for interaction with the Rh+ cations. Catalyst deactivation is attributed mainly to the formation of catalytically inactive [Rh(CO)(μ-CO)SX]2 or HRh(SX)2 complexes when the SX/Rh ratio is too low or high, respectively.