One-dimensional metal oxide nanostructures for heterogeneous catalysis

• Main Author: Zhang, Qian
• Other Authors: Yang Yanhui
• Format: Theses and Dissertations
• Language: English
• Published: 2015
• Subjects: DRNTU::Engineering::Materials::Nanostructured materials
• Online Access: http://hdl.handle.net/10356/63283
• Institution: Nanyang Technological University

Metal oxides are of paramount importance in heterogeneous catalysis as either supports or active phases. Controlled synthesis of metal oxide nanostructures has received enormous attention in heterogeneous catalysis due to the possibility of tailoring the properties of metal oxides by tuning their shapes, sizes, and compositions. For instance, through the well-defined nanocrystals, the catalytic activity and selectivity can be enhanced by selectively exposing a specific facet. The research work presented in this thesis focuses on the synthesis of novel metal oxide with one-dimensional nanostructures, including TiO2, MnO2 and CuO, and their applications as catalytic materials for a series of selective oxidation reactions, with the aim of introducing new insights into the heterogeneous catalyst design. Firstly, large quantities of high-quality, single-crystalline rutile TiO2 nanowires with controllable dimensions were synthesized by a molten-salt route and the catalytic applications were demonstrated in benzyl alcohol oxidation under the radiation of solar light. The surface structure of rutile TiO2 was reconstructed via the formation of surface complex by adsorbing benzyl alcohol molecules or its derivatives, to better utilize visible-light irritation. The photo-catalytic activity could be efficiently improved on TiO2 nanowires by exposed more {100} active facets. Secondly, a simple hydrothermal method was proposed to synthesize 1D MnO2 nanowires (-phase) and 2D MnO2 nanosheets (-phase). The catalytic properties of as-synthesized MnO2 nanowires in the selective oxidation of 5-hydroxymethylfurfural (HMF) were evaluated. The effects of phase structure of the as-synthesized MnO2 nanomaterials on the catalytic activity were investigated. -MnO2 exhibited a higher activity than -MnO2 in selective oxidation of HMF because -MnO2 could be reduced more easily than that of -MnO2. In addition, it was found that the catalytic activity was mainly influenced by the unique crystal forms and anisotropic structure of MnO2 nanowires. The catalytic activity of MnO2 could be improved by increasing the aspect ratio of -MnO2 nanowires to expose more high-energy active sites. Lastly, a facile hydrothermal method was developed to synthesize one-dimensional Cu2(OH)3NO3, and subsequent calcination deposition process afforded CuO nanowires with specific anisotropic nanostructures. The as-prepared CuO 1D material, with controllable anisotropic structure by tuning the decomposition temperature, exhibited enhanced catalytic activity in CO oxidation and selective epoxidation of trans-stilbene, compared to its bulk phase counterpart. In summary, the research findings in this thesis have attempted the great potential of synthesizing 1D metal oxide nanomaterials for improved catalytic activities in selective oxidation reactions. The enhanced physicochemical properties of 1D nanomaterials achieved by proper nanostructure design made them potential candidates for large-scale applications in heterogeneous catalysis.