Synthesis Of Heterogeneous Catalysts For Olefin Hydroformylation

Hydroformylation reaction involves the addition of H₂ and CO to olefins, yielding aldehydes in one-step fashion. Since firstly discovered by Roellen in 1938, the hydroformylation has became one of the most important syngas-related reactions, and the formed aldehydes are valuable final products and intermediates in the synthesis of bulk chemicals like alcohols, esters and amines, which can be further produced to plasticizer, surfactant and additive. Theoretically, all the â…§ group metals can be used as active component. But now, only cobalt and rhodium are used in industrial practice due to the relatively high activity in olefin hydroformylation. Supported cobalt catalyst and homogeneous rhodium-based catalyst are widely used in industrial process, but there are some problems about these two kinds of catalysts, such as relatively low activity for supported cobalt catalyst and the loss of active component for homogeneous catalyst after reaction. Some attempts have been made to avoid these disadvantages. For example, pretreatment of support and addition of noble metal would increase the activity of supported cobalt catalyst and immobilization of homogeneous catalyst on support would decrease the amount of leached rhodium. The following is the main contents in this work:1. SiO₂ supported cobalt catalysts, prepared by the incipient wetness impregnation method, were used in 1-hexene hydroformylation reaction. The promotional effects of ethylene glycol （EG） pretreatment and Ru addition on the catalytic performances of the obtained catalysts were also studied. The results indicated that pretreatment SiO₂ with EG significantly enhanced the interaction between cobalt precursor and support, resulting in high dispersion but low reduction degree. Addition of trace amount of noble metal Ru could improve the reduction degree of supported cobalt remarkably. Under the synergetic effects of EG and Ru, Co-Ru/SiO₂ （EG） catalyst exhibited 3 times higher 1-hexene conversion and 16 times higher heptanal yield than the conventional Co/SiO₂ catalyst, which was due to the high dispersion and reduction degree of supported cobalt particles. Addition of Pd or Pt would increase the dispersion and reduction degree of supported cobalt particles, but the promotional effect of Ru on reduction degree was more significant than that of Pd or Pt. Therefore, the activity of the catalyst promoted by Pd or Pt was lower than that promoted by Ru.2. Q-100 support with large pore size was pretreated by incipient wetness impregnation （IWI） method and slurry impregnation （SI） method. The effect of pretreating manner （including pretreating method, temperature and solvent） on the particle size and the activity of supported cobalt catalysts in 1-hexene hydroformylation were investigated. The results indicated that pretreatment of Q-100 support by IWI method had almost no effect on the surface properties of Q-100, but the interaction between Q-100 and supported cobalt particles was significantly strengthened after pretreating Q-100 with SI method. Moreover, this interaction would increase with the pretreating temperature or the number of hydroxyl in pretreating solvent. When Q-100 support was pretreated by SI method with propanetriol （PTO） at 333 K, the obtained supported catalyst Co/Q-100 （PTO, SI-333） exhibited the highest activity in 1-hexene hydroformylation and the heptanal yield of it was almost 13 times higher than that of Co/Q-100 catalyst.3. The hydrolysis of tetraethyl orthosilicate （TEOS） was used to prepare SiO₂ particles and magnetic silica support （Fe3O4@SiO₂） which was obtained by the coating of SiO₂ layer on Fe₃O₄ microspheres. Fe₃O₄ was synthesized by solvothermal method and the size of it could be controlled by the kind of chemical additives and the composition of solvent used in solvothermal process. Both of the obtained Fe₃O₄ and Fe3O4@SiO₂ microspheres exhibited superparamagnetic property and relatively high saturation magnetization. The prepared SiO₂ particles with size of 169 nm and Fe3O4@SiO₂ microspheres with size of 256 nm were used as supports to anchor active component. Homogeneous catalyst Rh（PPh3）3Cl was successfully immobilized on these supports by two different methods:coordination effect （CE） and Friedel-Crafts alkylation （F-C）. The activities of these obtained heterogeneous catalysts in 1-hexene hydroformylation were relatively high and not affected by the supports. Although the heterogeneous catalyst immobilized by CE showed a little higher activity than that by F-C, the leached rhodium content of latter catalyst was less in the resulting mixture after reaction.1-decene and styrene hydroformylation reactions were also carried out and the results indicated that the immobilized catalysts （CE） exhibited high activities in these two reactions. However, the activities of heterogeneous catalysts immobilized by F-C in 1-decene hydroformylation were much higher than that in styrene hydroformylation, which was due to the little flexibility of active species in these immobilized catalysts and the smaller space hindrance of 1-decene. Homogeneous catalysts HRh（CO）（PPh₃）₃ could also be immobilized on these two supports by CE and F-C method, which indicated that these two methods could also be used to immobilize other catalysts. After each reaction, the heterogeneous catalysts immobilized on Fe₃O₄@SiO₂ support could be easily recovered from the resulting mixture taking advantage of magnetic decantation in applied magnetic field without using filtration or centrifugation, which would be of great importance in industrial practice.