Preparation Of Novel Zeolitic Imidazolate Framework Materials And Evaluation Of Their Catalytic Activities

Metal organic framework (MOF) is a novel kind of functional crystal microporous materials, which is formed by transition metal ions or metal clusters and organic ligands through complexation. Recent years, it has been developed very fast in the coordination chemistry, relating to inorganic chemistry, organic chemistry and coordination chemistry. There are many advantages of MOF, for example, the specific pore, the regular framework, a wide range of metal ions and organic ligands, unsaturated metal coordination and larger specific surface area. However, the thermal stability and chemical stability of MOF materials is poor, which limits its application in a certain extent. Zeolitic imidazolate framework (ZIF) is a branch of MOF, and imidazole organic ligand(IM) replaces O of the traditional zeolite, while transition metal (M) replaces Si/Al atoms of the zeolite. Interesting, the angle of M-IM-M in the topology of ZIF is close to the angle of Si/Al-O-Al/Si in the zeolite (145°). ZIF combines the advantages of MOF and the traditional zeolite. Due to the strong interaction between the metal ion and imidazole, ZIF has good chemical stability and thermal stability. Some ZIF can exist stably in the boiling organic solvent or boiling water, and thermal stability can be as high as 400℃.In this work, we focus on the preparation and modification of several typical ZIF materials, while the structure, morphology, BET specific surface area and acid-base properties of the ZIF materials were characterized. Then we select three typical acid-base catalysis reaction, including the ester exchange reaction, the cycloaddition reaction of CO2 and the Knoevenagel coupling reaction, as the probe experiments for exploring the acid-base properties of the ZIF materials. In addition, we studied the modified ZIF-8 as the photocatalyst of organic dye.Firstly, the preparation, modification, and characterization of the selected ZIF catalytic materials: ZIF-8 and ZIF-68 were synthesized by the solvent thermal method, while ZIF-7, ZIF-8, and ZIF-67 were prepared by mixing at room temperature. Then we explored the effects of different metal salts on the morphology of ZIF-7 and ZIF-8 crystals, the influence of ammonia deprotonation reagent on the preparation and morphology of the ZIF-7 crystal. In the aspect of modified catalytic materials, ICP-AES and EDX were used to test the amount of W in the ZIF-8 supported phosphotungstic acid. ZIF-8 was modified in situ by polyvinylpyrrolidone-Pt, increasing the adsorption capacity of CO2, and then improving the catalytic activity of CO2 cycloaddition. The powder X ray diffraction, N2 adsorption desorption test, scanning electron microscopy, temperature programmed desorption, thermogravimetric analysis, infrared spectroscopy, ultraviolet visible spectroscopy analysis and laser raman spectroscopy were used to characterize the prepared catalysts, respectively. In addition, ZIF-8, ZIF-67, and ZIF-68 materials belong to the acid-base bifunctional catalyst through CO2-TPD and NH3-TPD verification.Secondly, ester exchange reaction catalyzed by ZIF-67:this paper studied the ester exchange reaction of dimethyl carbonate and diethyl carbonate, while ZIF-67 was used as the catalyst. The result shows that the EMC yield was up to 83.39% at 100℃ for 24 hours by gas chromatography, which was much better than that when ZIF-8 as catalyst. In addition, ZIF-67 catalyst has good performance of stability and recycled in the reaction.Thirdly, Pt/ZIF-8 and ZIF-68 catalyzed the cycloaddition reaction of CO2:in this study, Pt/ZIF-8 and ZIF-68 were used to catalyzed the synthesis of cyclic carboxylic acid ester from CO2 and styrene. The results show that the catalytic activity of modified ZIF-8 was improved and the catalyst can be recycled, but the catalytic result is not enough high. When ZIF-68 was used as the catalyst, the yield of SC was up to 93.34% in solvent free and no co-catalyst. Furthermore, ZIF-68 has good performance of stability and recycled in the reaction.Forthly, ZIF-8 catalyzed the Knoevenagel coupling reaction:in this paper, a series of different size porous ZIF-8 was synthesized at room temperature using mixing method, the experimental results show that the smallest ZIF-8 particles was prepared when Zn (NO3)2·6H2O as the zinc salt. Then we used the smallest ZIF-8 particles to catalyzed the Knoevenagel coupling reaction of benzaldehyde and malononitrile. The results show that the benzaldehyde was conversed completely at room temperature for 2 hours. Moreover, ZIF-8 had no obvious decrease in the activity when recycling, while the leaching test shows that the reaction was a heterogeneous catalytic reactionFifthly, ZIF-8 photocatalytic the degradation of methylene blue dye:a novel photocatalyt -ic materials PTA/ZIF-8 was prepared by supporting phosphotungstic acid on the frameworks of ZIF-8 materials, then was used in the reaction of methylene blue photo degradation. The results show that the rapid multi electron transmission of phosphotungstic acid makes the PTA/ZIF-8 be an excellent photocatalyst, and the methylene blue was degraded completely for 20 minutes.