Study On The Preparation And Catalytic Performance Of Metal Nanoparticles Supported On MOFs Via Mechanochemical Method

Metal-organic frameworks (MOFs) have emerged as a new class of porous crystalline materials with numerous potential applications in gas separation and storage, catalysis, sensors, drug delivery. MOFs have attacted in heterogeneous catalysis due to their many advantages, such as highly ordered pore structure and pore highly dispersed, low density and large surface area and diverse structure. Over the past decade, immobilization of noble metal nanoparticles (e.g., Pd, Au, and Pt) on MOFs by employing various preparation methods, such as impregnation, solid grinding, and chemical vapor deposition have been reported. In mechanochemical synthesis, chemical reactions are induced through the input of mechanical energy with little or no solvent. The mechanochemical method has potential advantages for large scale production to produce quantitative yield and to avoid from using large quantities of solvent and high temperature.This thesis is devided into two parts. Firstly, Pd2+/ZIF-8 was prepared by in situ mechanochemical method mixing ZnO and 2-methyl imidazole with PdCl2 according to a certain proportion. Then Pd2+/ZIF-8 was reduced by NaBH4. Highly dispersed palladium nanoparticles (Pd NPs) supported on zeolitic imidazolate frameworks ZIF-8 (Pd/ZIF-8) have been prepared. The Pd/ZIF-8 were characterized by XRD, N2 adsorption, TEM, ICP-AES and XPS, respectively. The conditions of this catalyst system have been optimized with bromobenzene as substrate for Suzuki coupling reaction. And under the best conditions,different substrates have been studied as well as the recyclability of the catalyst. Secondly, this work represents the first example of an active catalyst by using effect of ZnO which is not only can reduce noble metal NPs under UV irradiation, but also can construct ZIF-8 with 2-methyl-imidazole ligand. The catalysts were characterized by XRD, N2 TEM, respectively. And the conditions of this catalyst system have been optimized with 4-NP as substrate for redox reaction of 4-NP. And then, different substrates have been studied as well as the recyclability of the catalyst.The main conclsions obtained are as followed. Firstly, bulk production of highly dispersed palladium nanoparticles can be achieved by mechanochemical method. Moreover, the obtained Pd/ZIF-8 exhibits high activity for Suzuki-Miyaura cross-coupling reaction and can be easily recovered and reused. Secondly, Ag/ZIF-8 also exhibits high activity for redox reaction of 4-NP and can be easily recovered and reused.The innovation of this thesis is as followed. (1) Mechanochemical synthesis is an environmentally benign approach. It is clean, fast and energy efficient. (2) Ag nanoparticles in site supported on ZIF-8 by effects of ZnO for the first time. And this method may provide a new way that loading MOFs with metal nanoparticles.