Research On The Immobilized Rh-p Complex Catalyst For Olefin Hydroformylation

Currently as the largest homogeneous progress in industry, hydroformylation of olefins is an important reaction for producing aldehydes and alcohols, with its products widely involved in the production of plasticizer, fabric additives, surfactants, solvents and so on. Owing to the low solubility of higher olefin in water, the employment of industrial water-soluble Rh-P complex catalysts in hydroformylation of higher olefins is restricted. In the present study, Rh-P complexes were immobilized inside the pores of mesoporous molecular sieves via alkyl spacer. The effect of alkyl spacer length (or rather flexibility) on the immobilized catalyst activity as well as on the stability during catalyst cycles was investigated. The following is a summary of the present study.Mesoporous molecular sieves were first modified by haloalkyl silanes with different alkyl length. Lithium diphenylphosphide was then synthesized and diphenylphosphine ligands were connected to haloalkyl-modified support. Eventually rhodium precursor was immobilized on diphenylphosphinoalkyl- functionalized mesoporous molecular sieves via diphenylphosphinoalkyl-Rh coordination. X-ray diffraction, N2 sorption analysis, infrared spectroscopy, atomic emission spectroscopy and so on were applied to characterize the catalysts so as to infer the immobilized catalyst structure.The prepared immobilized catalysts were applied in hydroformylation of several olefins including 1-octene under autoclave operations. The influences of alkyl spacer with different length, different rhodium precursors, different supports and different olefin substrates on the catalyst activity and stability during catalyst cycles were investigated. Rh leaching during catalyst cycles and the surface properties of recycled catalysts were analyzed in order to explain the catalytic performances of the immobilized catalysts prepared by different supports and alkyl spacers.Shown by results, the immobilized catalyst activity was increased with the increasing alkyl spacer length. Catalyst prepared by undecyl as spacer showed a specific activity (shown as substrate turnover number, TON) comparable to corresponding rhdium precursor-catalyzed homogeneous process. Catalysts that were prepared by the same length of alkyl spacer and the same rhodium precursor revealed similar specific activity, independent on support pore size and structure. Rh leaching during the catalyst recycle was found very low, generally less than 0.5% for every catalyst cycle within eight to ten cycles. The dehydration product of the aldol condensation adduct of aldehydes formed anα,β-unsaturated aldehyde which, coordinated with Rh so as to poison it. Owing to the spatial hindrance, the catalyst prepared by undecyl as spacer showed capability of resisting the by-product poison as no obvious activity decrease was found in continuous eight-catalyst-cycle. Supports with difference pore size and surface curvature (SBA-15 or MCM-41) were employed and the employment of immobilized catalysts in hydroformylation of olefin substrates with difference length and structure were investigated so as to further prove the poison of the by-product.