| Cinnamaldehyde is one of typicala, β-unsaturated aldehydes having C=C and C=O conjugated double bonds. The half-hydrogenated product hydro-cinnamaldehyde (HCAL) of C=C, as an important chemical raw material and intermediate, finds its wide applications in the production of perfumes and pharmaceuticals, especially the lilacs, jasmine and rose scent flavor. On the other hand, the other half-hydrogenated product cinnamyl alcohol (COL) of C=O is also an important intermediate for the synthesis of fine chemicals, such as flavors, perfumes, and pharmaceuticals. Consequently, both of the half-hydrogenated products of cinnamaldehyde are of significance for industrial applications and the selective hydrogenation of cinnamaldehyde has aroused great concern in the field of catalysis. Due to the high boiling point of cinnamaldehyde, the hydrogenation is often conducted in a batch reactor through a liquid-phase reaction system. The recovery of catalyst based on filtration and separation faces some drawbacks such as low efficiency, low recovery, and easy loss of active components. Preparation of magnetic responsive hydrogenation catalysts could significantly improve the catalyst recovery through the rapid separation from the liquid reaction system under the help of external magnetic field. In this thesis, we prepared two magnetic responsive catalysts with different structures using Fe3O4particles as magnetic phase and Pt or Pd as activities. The catalysts were characterized by various techniques such as XRD, SEM, TEM, XPS and ICP etc. Furthermore, the liquid phase selective hydrogenation of cinnamaldehyde on the magnetic catalysts was also investigated. This thesis mainly consists of three parts as follows:1) A stepwise method was applied to prepare a magnetic Pt/Fe3O4-MCNT catalyst by depositing the as-prepared Fe3O4and Pt nanoparticles onto multi-walled carbon nanotubes (MCNT). It is indicated that the as-prepared Fe3O4and Pt nanoparticles are well dispersed on the MCNT. The magnetic measurements show that both fresh and recycled magnetic Pt/Fe3O4-MCNT catalysts display excellent superparamagnetic properties at room temperature. The selective hydrogenation of cinnamaldehyde to cinnamylalcohol was performed on the magnetic Pt/Fe3O4-MCNT catalyst, showing a superior activity in the hydrogenation of the C=O bond and a selectivity of96%to cinnamyl alcohol with a cinnamaldehyde conversion of about50%. Additionally, the catalyst can be easily recovered from the reaction medium under the external magnetic field and maintain their catalytic properties after used for several recycles.2) Magnetically recyclable Pd/Fe3O4@C catalysts have been successfully prepared by depositing Pd nanoparticles onto the surface of Fe3O4@C composites, which were prepared by coating carbon on the Fe3O4spheres prepared by the solvent thermal method. Various techniques such as XRD, SEM, TEM, SQUID etc. have been used to characterize the composite catalysts. The obtained catalysts, consisting of core-shell structured microspheres with high uniformity, show a good superparamagnetic property. The selective hydrogenation of cinnamaldehyde on the magnetic catalysts has been investigated, achieving about70%selectivity to hydrocinnamaldehyde at100%conversion. Moreover, the magnetic catalyst can be easily recovered under an external magnetic field and reused for7cycles without any degradation in activity.3) Two type core-shell structured magnetic catalysts of Pt/Fe3O4@Cå'ŒPt-Fe3O4were prepared by the deposition-reduction method in an ethyl glycol reduction system. The hydrogenation of cinnamaldehyde was performed on the two prepared catalysts, indicating that Pt-Fe3O4exhibit a higher selectivity to cinnamyl alcohol (99.1%) than Pt/Fe3O4@C (97.6%) while the latter has a higher activity. The magnetic responsive catalysts can be rapidly separated from liquid reaction system under the exteranl magnetic field and show a good reusage property. |
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