Aqueous Phosphine-Rh Complexes Supported On Nano-SiO₂ For Olefin Hydroformylation

Many kinds of catalysts active for hydroformylation of olefins have been developed in the last more than sixty years. These are including the hydrophobic Rh-TPP [TPP: triphenylphosphine, P(C6H5)3] complexes, the supported liquid phase catalysts (SLPC), the water-soluble phosphine-Rh complexes containing TPPTS [TPPTS: trisodium salts of tri-(m-sulfophenyl)-phosphine, P(m-C6H4SO3Na)3] ligand and the supported aqueous phase catalyst (SAPC). As for all homogeneously catalyzed reactions the problem of separating the homogeneously dissolved catalyst is immanently disadvantageous. The difficult separation between the catalyst like Rh-TPP and the reaction products after reaction could only be overcome by expensive recycle process. The SLPC greatly facilitates the separation of catalyst-products and the recycling use, but it shows the drop of catalytic activity due to the mass transfer in heterogeneous catalysis and the rhodium leaching from its carriers.The application of water-soluble metal-complexes as catalysts since 1973 offered the chance to separate catalyst and reaction products just by decantation. The new technology commercially applied for hydroformylation of propene by employing the water-soluble phosphine-Rh complex i.e., HRh(CO)(TPPTS)3, as catalyst was firstly reported by Ruhrchemie/Rhone-Poulenc (RCH/RP process) with great success in 1984. The advantages of this technique economically and ecologically compared to the corresponding homogeneous process make the biphasic catalyst system become increasingly important both for industrial application and for new reactions and new products, and thus become one of the most active research fields currently. The problem of low reactivity of higher olefin hydroformyylation using two-phase catalyst due to the low solubility of thehigher olefins in the water phase, however, remains to be solved. There are several attempts to overcome the problem of low reaction rate in the higher olefin hydroformylation using biphasic catalyst system. Here are summarized briefly as followings: (1) use of amphiphilic water-soluble ligands, (2) use of co-solvent or surfactant (for example: CTAB), (3) temperature controlled switch of the catalyst system from the aqueous phase to organic phase, (4) use of SAPC. The results in literature showed that the SAPC, which integrated the advantages of the higher reactivity in the homogeneous catalysis into the easy separation of catalyst and reaction products in the heterogeneous catalysis, was applicable for hydroformylation of lower and higher olefins.The present work shed some light on the improvement and development of SAPC system for the hydroformylation of higher olefins by using nanometer silicas as supports. Works in the present thesis were focused on the catalytic performance and mechanism of the nano-SiOa-SAPC for the reaction. Several significant results are described as follows.(1) The catalytic activity of nano-SiO2-SAPC was 1-10 times higher than that of conventional porous-SiOa-SAPC and that of biphasic catalyst system under the identical reaction conditions, but slightly lower than that of biphasic-CTAB-system. While the rhodium content in the product phase in the case of nano-SiO2-SAPC was about one magnitude lower than that in the case of biphasi-CTAB-system.(2) The nano-SiO2-SAPC could be operated effectively in a wide range of support hydration range (ranging scope of 15-20 wt%), yielding a high reaction rate and selectivity, while only a very narrow range of water hydration did the conventional porous-SiCVSAPC show a maximum of activity. The best hydrationin the nano-SiCVSAPC was found to be almost independent of the type of nano-SiC>2 and the L/Rh ratio under the present experiments.(3) The characterizations of SAPC and the nanometer silicas by means of BET, SEM, TEM, 31P-NMR and pyridine-TPD techniques revealed that there existed abundant one-dimensional mesopores in the nanoparticles of silicas and that the water-soluble complex HRh(CO)(TPPTS)3 in the nano-SiO2-SAPC kep...