Synthese, Structure Characterization Of Metal-Organic Frameworks Catalysts And Their Catalytic Performance

Metal-organic frameworks (MOFs), a kind of compound with three-dimensional porous structure, are combined by metal or metal clusters with organic ligands. Due to large specific surface area, tunable pore size and easy functionalization, it has been widely focused on all over the world. Ascribe to the various structures, especially in the catalytic area, MOFs could be designed according to the demand of experiments, or functionalized by catalytic active components. For example, the catalytic active group could be grafted on the surface of MOFs. The active metal or cluster could be loaded in the pore of MOFs. Moreover, the active sites in MOFs could also improve the catalytic reaction. Besides, the organic ligands in MOFs could be favor some reaction, too.Recently, MOFs as heterogeneous catalysts were usually applied in solid-liquid catalytic reactions. However, the problems of reparation and recycling were inevitably during the experiment operation. For example, the centrifugation may lead to the demolishing of MOFs during the procedure, and the loss of MOFs catalysts during this process was also unavoidable. Both of the above showed the minus effect to the activity of the reactions. If the magnetic carrier could be encapsulated in MOFs, the separation of catalysts would be easier due to the external magnetic fields. This could simplify the experiment process and decrease the loss the catalysts. Hence, the magnetic MOFs could be the promising catalysts for solid-liquid reactions.The magnetic carrier and MOFs were combined in this literature, and prepared a series of magnetic MOF-5@SiO2@Fe3O4, Zn-BTC@SiO2@Fe3O4, ZIF-8@SiO2@Fe3O4and Cu-BTC@SiO2@Fe3O4composite catalyst. The structure and property of the above catalysts was characterized by SEM, TEM, XRD, FT-IR, N2adsorption-desorption, VSM and temperature program dsorption. Finally, the catalytic activity of the above catalysts was evaluated by Friedel-Crafts alkylation, Friedel-Crafts acylation, Knoevenagel condensation and Pechmann reaction. The main works are as followings:1. Fe3O4was synthesized by Solvo-thermal method, and then hydrolysis method was used to encapsulate a compact layer of SiO2on the surface of Fe3O4particles. Finally, four kinds of magnetic MOFs@SiO2@Fe3O4samples were prepared by coating different contents of MOFs (MOF-5, Zn-BTC, ZIF-8and Cu-BTC) on the surface of SiO2@Fe3O4support in situ method.2. The structure as-synthesized samples were characterized by TEM, SEM, XRD, FT-IR, N2adsorption-desorption, VSM and NH3-TPD. The catalytic activity of MOF-5@SiO2@Fe3O4was evaluated by the reaction of toluene with benzoyl chloride. The results showed that MOF-5@SiO2@Fe3O4catalysts exhibited superparamagnetic property, and could be separated by a magnet from the liquid reaction system. The conversion of toluene was increased gradually with the increase of catalyst contents and reaction temperature, respectively.97%conversion of toluene has been achieved by using26.8%MOF-5@SiO2@Fe3O4catalyst at120℃for6h. Furthermore, electron-donating group, such as OCH3, CH3and H, exhibited affirmative effect. Besides, the catalyst could be easily separated from the reaction mixture after the reaction and reused for five times without significant decrease in activity.3. SEM, TEM, XRD, IR, NH3-TPD and VSM were used to character the structure of magnetic Zn-BTC@SiO2@Fe3O4catalysts. The acylation reaction of toluene with p-toluoyl chloride was evaluated over magnetic Fe3O4@SiO2@Zn-BTC catalysts. The results showed that a certain content of Zn-BTC in Zn-BTC@SiO2@Fe3O4catalysts exhibited superparamagnetic property and excellent acidity. In addition, Zn-BTC@SiO2@Fe3O4catalysts showed favorable acylation catalytic activity, and the conversion of toluene gradually increased with the increasing of Zn-BTC contents. Take36.7wt%Zn-BTC@SiO2@Fe3O4catalyst (the content of Zn-BTC was36.7%) as sample, the conversion of toluene could reach78.8%at120℃. the selectivity was about79.9%. Zn-BTC@SiO2@Fe3O4catalysts could be recycled through external magnetic field after the reaction. After reused for five times, the conversion of toluene was not apparently decreased. This novel magnetic Zn-BTC@SiO2@Fe3O4catalyst has a potential application in heterogeneous acylation reaction.4. The structure of the as-synthesized catalysts were characterized by TEM, SEM, XRD, FT-IR, VSM, N2adsorption-desorption and CO2-TPD technology. The catalytic activity and recovery properties of the catalysts for the Knoevenagel reaction of p-chlorobenzaldehyde with malononitrile were evaluated. The results showed that as-synthesized magnetic ZIF-8@SiO2@Fe3O4catalysts had the larger surface areas and the suitability superparamagnetism. In the ZIF-8@SiO2@Fe3O4catalysts when the content of the ZIF-8was more than3.22%the catalysts exhibited a good catalytic activity for the Knoevenagel reaction. The conversion of p-chlorobenzaldehyde could reach98.24%and the selectivity of the production could reach99.85%under the condition of25℃and4h. The as-synthesized magnetic ZIF-8@SiO2@Fe3O4catalysts had also a good the substrates adaptation. Besides, the electron-accepting groups could benefit the reaction, and the electron-donating group could show the negative effect to the reaction. Especially, after the reaction the magnetic ZIF-8@SiO2@Fe3O4catalyst could be easily separated by an external magnet. The conversion of p-chlorobenzaldehyde could keep over90%after the catalyst was recycled for five times.5. The structure of magnetic Cu-BTC@SiO2@Fe3O4catalysts were characterized by TEM, SEM, XRD, FT-IR, VSM, N2adsorption-desorption and CO2-TPD technology. The catalytic activity and recovery properties of the catalysts for the Pechmann reaction of1-naphthol and ethyl acetoacetate were evaluated. The results showed magnetic Cu-BTC@SiO2@Fe3O4catalysts exhibited superparamagnetic property, and could be separated by an external magnet. The above catalysts present acidity and could catalyze the reaction of1-naphthol with ethyl acetoacetate. The conversion and the selectivity of the above reaction were96.12%and98.31%, respectively. Besides, the magnetic catalyst exhibited excellent reuse property, and the conversion could keep nearly90%after recycle for five times. At the same time, the selectivity of the above reaction was also maintained98%.