Preparation, Characterization And Catalytic Properties Of Metal-Organic Framework Materials

Metal—organic frameworks (MOFs) are a new category of inorganic-organic hybrid materials comprised of ordered networks formed from organic bridging ligands of oxygen or nitrogen and inorganic transition metal cations. MOFs have been emerging as very promising functional materials for gas storage, adsorption and separation, sensing and heterogeneous catalysis due to their high surface area, porosity, and chemical tunability. Among various MOFs materials, MIL-101(Cr) with mesoporous structure and ZIF-8 with a good chemical and thermal stability are the two more extensively studied and apllied MOFs. In this paper, the works are based on the following aspects:i) the catalytic properties of MIL-101 (Cr) in the reaction system with with H2O2 as oxidant and the influences of synthesis conditions on the structure and catalytic properties of the as-synthesized MIL-101 (Cr); ii) ZIF-8 as a host for encapsulation of metal complexes. Specific works and results are as follows:Ⅰ. Preparation, characterization and catalytic performances of MIL-101 (Cr)(1) MIL-101(Cr) was synthesized by the hydrothermal method. The synthesized MIL-101(Cr) samples were characterized by XRD, FT-1R, TG-DTA, SEM, UV-VIS and catalytic reaction. The results show that crystallization time and concentration influence the crystallinity, morphology and catalytic performances of the synthesized MIL-101(Cr) at a certain extent. The MIL-101(Cr) sample synthesized at 8 h crystallization time,210℃ and 370 of H2O/Cr molar ratio not only had a higher specific surface area and crystallinity, but also exhibited higher catalytic activity in cyclohexane oxidation with H2O2 than those synthesized under other conditions.(2) The catalytic activity of MIL-101 (Cr) in cyclohexane oxidation with H2O2 are closely related to the reaction temperature, time, solvent and other factors. The optimum reaction conditions were as follows:reaction time 4 h, reaction temperature 70℃,15.1 weight ratio of cyclohexane to catalyst, MeCN as reaction solvent,1 molar ratio of H2O2 to cyclohexane.(3) The structural changes of MIL-101(Cr) after reaction were characterized by XRD, FT-IR and UV-Vis techniques in detail. MIL-101(Cr) was not stable in cyclohexane oxidation with H2O2 and Cr leaching was observed. The crystalline structure of MIL-101 (Cr) was completely destroyed and it became amorphous after reaction. The formed amorphous material exhibited much higher catalytic activity than the fresh MIL-101(Cr), and could be reused several times without significant change in its catalytic efficiency. Ⅱ. Preparation, characterization and catalytic performances of metal complexes/ZIF-8ZIF-8 is one of the most studied prototypical ZIF compounds and has exhibited potential applications as host for immobilized metal nanoparticles because of its high specific surface area, large pore and porosity as well as thermal stability. Based on this, the exploring work on preparation, characterization and catalytic performances of metal complexes/ZIF-8 composites are carried out. Cu(Ⅱ)-1·10-phentantroline complexes had been successfully immobilized in the zeolitic metal-organic framework ZIF-8 by introduction of Cu(Ⅱ) in the process of ZIF-8 formation followed by coordination with 1·10-phentantroline ligand. The characterization results of XRD、FT-IR. TG-DTA. SEM and UV-VIS reveal that encapsulation of Cu(Ⅱ)-1·10-phentantroline complexes within the cages of ZIF-8 by keeping the host framework intact. The encapsulated Cu complexes show much higher catalytic activity than homogeneous Cu complexes and those encapsulated in zeolite Y in oxidation of cyclohexane with H2O2. The prepared catalysts are stable and can be reused at least for five times without loss of activity.