Encapsulation Of Atomically Metal Clusters In Metal-Organic Frameworks And Their Heterogeneous Catalytic Properties

Metal nanoparticles can be capsulated in Metal-Organic Frameworks(MOFs) because MOFs possess large internal surface areas, uniform tunable cavities and tailorable chemistry. Compared with the traditional organic materials, these MOFs have the following advantages:1) the composites composed of metal nanoparticles (NPs) and MOFs possess high stability and high metal NPs dispersion. Therefore, MOFs have been an excellent support to stabilize various metal NPs.2) Many MOFs have unique catalytic activities in many chemical reactions. The metal NPs with catalytic activities have been loaded in MOFs and improved the catalytic activities caused by "synergistic effect". Metal NPs and MOFs have also been verified to form various bi-functional catalysts, which expand the application of these composites. So far, metal NPs@MOFs catalysis have achieved great progress, researchers encountered difficulties in understanding the catalytic mechanism, which due to the indeterminacy of the structure of metal NPs.Recently, with the development of metal nanoclusters(NCs) with particle size less than 3nm, the precise structure and the organic ligand surrounded, the atomic level and atom precise metal NCs aroused the interests of many researchers. The encapsulation of metal NCs in MOFs is worthy of study and a new research aspect. The introduction of metal NCs into MOFs and the application of metal NCs@MOFs catalysis still remain challenges because of the instability and low yield of metal NCs and surrounded by ligands. Herein, using the in situ reduction method, we prepared the metal NCs encapsulated in the pores of MOFs and the "confined synthesis" method provided a new idea for the synthesis of metal nanoclusters. Then the metal NCs@MOFs composites have been applied in heterogeneous catalysis. These results will provide more opportunities in understanding the mechanism of catalytic reaction. The main content includes:1. Au nanoclusters have been successfully encapsulated into the pores of ZIF-8 using the proper solvent and in situ reduction method. The Au NCs released from ZIF-8 have been characterized by UV-vis and ESI-TOF measurements. ZIF-8 acts not only a desirable support but also acts the microreactor, and the high purity Au11 was obtained. The catalytic activity of benzyl alcohol oxidation over the composite of Au11and ZIF-8 and the stability and recyclability was studied in this paper.2. Encouraged by the success of Au11 encapsulation in ZIF-8, we designed a MOFs with mesoporous channel as the template and a metal nanocluster with larger size can be incorporated in the MOFs. Then the AuAg NCs with high purity have been prepared in mesoporous MIL-101(Cr). The structure of Au13Ag12 NCs was confirmed by X-ray single crystal diffractometer. The composite of Au13Ag12 NCs@MIL-101(Cr) was determined to catalyze the benzyl alcohol oxidation and the stability and recyclability of the catalysts were further measured.3. The excellent catalytic properties of Ni aroused the attention of researchers. Herein, Ni nanocluster was synthesized in the amino-functioned MOF(UIO-66(NH2)). In addition, the structure of Ni NCs was predicted by MALDI,UV-vis and the TG analysis. The catalytic activity and selectivity of Ni NCs@UIO-66(NH2) composite in the nitrobenzene hydrogenation. Significantly, Ni NCs@UIO-66(NH2) catalyst changed the selectivity for the nitrobenzene hydrogenation product in comparison to the bare Ni NCs. Furthermore, the ligand-off of Ni@UIO-66(NH2) catalysis and the ligand-on catalyst properties were then investigated. The stability and recyclability of catalysts was finally determined in this paper.