De Novo Synthesis of Metal Nanoparticles Embedded Metal-Organic Frameworks (MOFs) and their Derivatives for Catalytic Reactions

• Main Authors: Yu-Te Liao, 廖祐德
• Other Authors: Chia-Wen Wu
• Format: Others
• Language: en_US
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/zy9m37

博士 === 國立臺灣大學 === 化學工程學研究所 === 106 === Supported catalyst has been involved in most of industrial production owing to the benefits of long-term stability and easy recycle. The aggregation, deactivation and random distribution of metal nanoparticles during procedures are three issues in the preparation of supported metal catalysts. In this dissertation, a novel synthetic methodology called de novo approach is proposed to improve the quality of supported catalyst. Metal-organic frameworks (MOFs) are a porous structure composed of abundant metal joints and organic ligands which serve as self-template for porous carbon structure and metal oxide structure. We successfully use MOFs as the host and different metal precursors as metal sources to synthesize metal nanoparticles embedded MOF by de novo approach, and further converted the MOF composite into MOF-derived substrates with even metal nanoparticles distribution. The development of supported catalyst, MOFs and its derivatives are introduced in Chapter 1. Five kinds of metal nanoparticles embedded, MOF-derived supported catalyst would be discussed from Chapter 2 to Chapter 5. The synthesized supported catalysts showed apparently better performance on different catalytic reactions than those prepared by general post-treatment methods owing to the homogeneous substrate precursor on framework of MOF and strong interaction between metal composites and substrates contributed by de novo approach. Nitrogen-rich zeolitic imidazolate framework-8 (ZIF-8) is selected as the host material, and Au and Pd precursors are introduced into ZIF-8 structure using de novo method to prepare Au@ZIF-8 and Pd@ZIF-8, respectively. After pyrolysis, ZIF-8 framework would become nitrogen-contained carbon framework and the resulting nitrogen doped, Au nanoparticles embedded nanoporous carbon nanoparticles (namely Au@NC) showed excellent performance (specific conversion rate [SC]: 1185 g-1s-1) on reduction of 4-nitrophenol due to N-rich carbon framework originated from 2-methylimidazole. Similarly, the Pd@ZIF-8 can be carbonized into even Pd-Zn anchored nanoporous carbon nanoparticles (namely PdZn@NC), which also shows good performance (SC:1344 g-1s-1) on reduction of 4-nitrophenol owing to N-rich carbon substrate and the synergistic effect of Pd-Zn alloy. Finally, Au and Pd co-loaded ZIF-8 is carbonized into Au-Pd alloy embedded nanoporous carbon nanoparticles (namely AuPd@NC), demonstrating tunable composition of alloy and synergistic effect of alloy on the oxidation of benzyl alcohol. The detail is included in chapter 2 and chapter 3. Another MOF material (i.e. MIL-125) is selected as the host material because it contains titanium in the framework. Cu precursor is then introduced into MIL-125 by de novo method, and the synthesized copper ion encapsulated MIL-125 is calcined into CuO-loaded mesoporous titania tablets (namely CuO@MT). The results of H2-TPR and XAS show that part of CuO are inserted in TiO2 layer. The resulting CuO@MT catalysts demonstrate enhanced hydrogen evolution in methanol-containing solution (4760 mol h-1) owing to even distribution of CuO embedded in titania and effectively interfacial charge transfer between CuO and TiO2. The detail of experiment and discussion is included in chapter 3. A Co-containing MOF (ZIF-67) is selected as the host material. Both Au and Pd precursors are introduced into ZIF-67 during assembly, and the resulting composites are calcined into Au-Pd alloy nanoparticles embedded cobalt oxide cages (namely AuPd@Co3O4). XPS spectrum shows the appearance of highly active Au+ on the interface of catalyst and substrate. The AuPd@Co3O4 cages are then applied as an efficient solid catalyst for H2O2-assisted conversion of hydroxymethyl furfural (HMF) to 2,5-furandicarboxylic acid (FDCA). The results show a high yield of FDCA (95%) is achieved under atmosphere in one hour, which is attributed to the hydroperoxyl radicals, synergistic effect of Au-Pd alloy, strong interaction between Co3O4 and Au nanoparticles. The detail of experiment and discussion is included in chapter 5. In summary, metal nanoparticles encapsulated MOFs are synthesis with de novo approach, and the composites are further converted into supported catalyst. We demonstrate a reliable methodology (i.e. de novo approach) for synthesis of supported catalyst with enhanced activity on various catalytic reactions. The future works and perspective of this new method is described in Chapter 6.