Fabrication And Performance Investigation Of Pd, Pt And Ag-based Nanocatalysts

Owing to the distinct chemicophysical properties and excellent catalytic performance, noble metal nanomaterials (NMNMs) have become an active research topic in modern chemistry. The catalytic activity of NMNMs is strongly determined by their size and shape. So we can control any one of these parameters to improve their catalytic activity. Generally, NMNMs with a higher surface area will possess better catalytic activity. However, the large surface area of NMNMs often leads to their easy sintering and subsequent loss of catalytic activity during the catalysis process. Meanwhile, concerned with the high price of noble metal, therefore, developing strategies to improve the stability of NMNMs is crucial. Although different approaches have been taken to fabricate a series of NMNMs, industrial applications of the NMNMs are still limited because of the disadvantages of preparation, such as tedious synthesis, strict operation condition and unsuitable for large-scale production. In this thesis, we focused on the development of a simple, rapid and versatile method to synthesize the NMNMs with high activity and stability in catalysis. Suzuki coupling, oxidation of silanes and reduction of p-nitrosophenol were selected as the catalytic reactions to test the catalytic performance of the synthesized NMNMs.(1) We investigated the catalytic performance of highly dispersed γ-Al2O3-supported Pd nanoparticles for Suzuki coupling and silanes oxidation reactions. The highly dispersed Pd nanoparticles were fabricated through impregnation of γ-Al2O3 with the aqueous solution of PdCl2 followed by CO reduction at room temperature (Pd298 K/Y-Al2O3). Owing to the mild reaction condition, the Pd nanoparticles on Pd29g K/γ-Al2O3 have a smaller size, higher dispersion state and narrow size distribution than the Pd nanoparticles prepared by calcination in air at 773 K and Ar/H2 reduction at 623 K (Pd773 K/γ-Al2O3). Therefore, Pd298 K/γ-Al2O3 exhibited increased catalytic activity towards the Suzuki coupling and silanes oxidation reactions than the Pd773 K/γ-Al2O3. Furthermore, the Pd298 K/γ-Al2O3 catalyst could be reused at least five times without obvious loss of catalytic activity.(2) We developed simple and rapid route to fabricate PtAg hollow porous nanosphere shells (HPNSSs), and evaluated their catalytic performance for the oxidation of silanes in water. Firstly, Ag@Pt core-shell nanospheres (CSNSs) were fabricated via a one-pot approach of solvent-thermal process. Here the introduction of NH3H2O and Polyvinylpyrrolidone guaranteed the concentration of Ag+remained at a relatively low level to reduce the formation of AgCl. Next, the Ag core was etched with concentrated HNO3, then the PtAg HPNSSs were fabricated. Owing to their hollow, porous structure and rough surface, the PtAg HPNSSs exhibited high activity and selectivity for the oxidation of both aliphatic silane and phenyl silane to the corresponding silanols in water. What’s more, the special hollow structure make the PtAg HPNSSs own a high stability and they could be reused at least five times without significant loss in activity.(3) We fabricated the Au-SiO2 yolk-shell nanoparticals (YSNSs) and investigated their catalytic performance for the reduction of p-nitrosophenol. Here we simplified the traditional three-steps method for the synthesis of Au@M@SiO2-Firstly, Au@Ag core-shell nanospheres (CSNSs) were fabricated via a one-pot approach of solvent-thermal process, and next SiO2 coated on the Au@Ag, then Au@Ag@SiO2 was obtained. After HNO3 etched the Ag core, Au-SiO2 YSNSs were finally achieved. The Au-SiO2 YSNSs showed excellent catalytic activity and reusability for the reduction of p-nitrosophenol, and the activity of the catalyst remained stable after 5 times of recycle.