| Author: | Chen, Tianxiang |
| Title: | Precise synthesis of Cu-based metal nanoclusters in zeolites and the structure-catalysis investigations |
| Advisors: | Lo, Benedict (ABCT) Yu, Wing Yiu (ABCT) |
| Degree: | Ph.D. |
| Year: | 2022 |
| Subject: | Nanostructured materials Metals -- Microstructure Metal clusters Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Applied Biology and Chemical Technology |
| Pages: | x, 271 pages : color illustrations |
| Language: | English |
| Abstract: | Supported single-atoms (SAs) and metal nanoclusters (NCs) are well-known as next-generation nanomaterials. Great efforts have been made to engineer the electronic and geometric properties of the metal moiety(ies) in SAs and NCs, for instance, the coordination environment, metal compositions, and host materials. Contributing to the development of advanced characterisation techniques, a thoughtful understanding of the electronic and geometric properties of SAs and NCs can be obtained. This thesis therefore focuses on the precise synthesis of supported NCs with high precision. Exploiting the underlying principles of coordination chemistry and solid-state chemistry, we proposed a stepwise assembly strategy for the synthesis of multinuclear copper-based NCs within zeolite supports. Using state-of-art structural elucidation techniques, the electronic and geometric structures of the NCs have been revealed, and their structure-activity relationships have been discussed at an atomic level. Recent advances in the electronic and geometric structures of single-atom and nanocluster catalysts have been introduced in Chapter 1. The precursor materials and characterisation techniques used in this thesis have been provided in Chapter 2. Chapter 3 reports the first stepwise assembly of supported atom-precise bimetallic ligand-mediated metal clusters (LMMCs). Lewis di-basic imidazolates have been used to bridge multiple Cu2+ and M2+ (M = Co, Ni, Cu, and Zn) within ZSM-5 zeolites. Excitingly, we have directly observed the metal constituent composition of the LMMCs by mass spectroscopy. The adjacent metal nuclei in the LMMCs offer substantial synergistic effects that enhance the catalytic performance by at least an order of magnitude in the model catalytic 'click' reaction. Chapter 4 presents the direct amination of C(sp2)-H of unprotected phenols over related Cu-M LMMCs on USY zeolites. The catalytic process is highly efficient and sustainable with an isolated yield of greater than 80% at room temperature over Cu-Co-Y and Cu2-Y in the absence of any additional additives, which is a nearly two-fold magnitude more superior than the single-atom analogues. Gram-scale production has been achieved in a regular scale-up experiment. The combined bulk crystallographic and theoretical approach revealed the structural characteristics of the immobilised LMMCs in the confined zeolitic space, which has unraveled a new route of cooperative catalysis that involves a classical 'co-adsorption-co-activation' catalytic model with multiple substrates. Chapter 5 reports the preparation of multinuclear copper clusters (with direct M-M bonding) supported by ZSM-5 zeolites. Direct visualisation of the trinuclear copper cluster has been obtained, which reveals that the trinuclear copper cluster was formed directly by metal-metal bonds. The trinuclear copper clusters, Cu3/Z, achieve a hydrogen yield of 3365.9 μmol/gcat in the methanol reaction (methanol-to-hydrogen), which is 21.2 times more superior to the mononuclear analogues Cu1/Z. The structure-activity relationship has also been studied, which demonstrated the adsorption configuration of methanol on trinuclear copper clusters possesses lower energy, supporting more efficient methanol activation for hydrogen formation. |
| Rights: | All rights reserved |
| Access: | open access |
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