Preparing Novel Noble Metal Catalytic Materials With High Performance For CO And HCHO Oxidation

Noble metal catalytic materials have received great attentions, and have been widely studied for decades, due to their excellent performance as catalysts in chemical industry, environmental protection and energy production. However, due to the limited source and high cost of noble metals and their relative low thermal stability, it is currently a critical issue and hot research topic on how to design and prepare catalysts with high dispersion and low noble metal loadings. Aim to improve the utilization efficiency of noble-metals, a series of systematic works have been performed in this thesis, with the main results summarized here:In the first part, Pd@SiO₂ core-shell nanomaterials have been synthesized through various methods, and Pd/SiO₂ was prepared by conventional impregnation for comparison. With an improved one-step reverse micelle method, Pd@SiO₂-RM with thermally stable, 1.1 nm ultra-small Pd nanoparticles were prepared in one-pot. HRTEM results reveal that the ultra-small Pd nanoparticles are embedded in the bulk of the silica nanospheres around 30 nm to form a multi-core shell structure. Therefore, the migration and agglomeration of the ultra-small Pd nanoparticle cores can be impeded effectively at elevated temperatures. Compared with Pd/SiO₂-IMP prepared by impregnation, core-shell Pd@SiO₂-ST and Pd@SiO₂-ME catalysts prepared by St?ber and regular micro-emulsion processes, Pd@SiO₂-RM possesses a much higher metal surface area. As a consequence, this catalyst shows remarkable activity and superior thermal stability for CO oxidation. It is concluded that the Pd grain size and metal surface area are the determining factors for the activity, as evidenced by the strict linear relationship between the differential rates and the Pd sizes/metal surface areas.In the second part, a high surface area?572 m2/g? dendritic silica?KCC-1? was synthesized successfully, and used as a support to prepare nanoparticle Pt-Ni bimetallic catalysts. SEM and TEM results have revealed that the Pt-Ni alloy particles are highly dispersed with an average size of 3 nm, because of the strong confinement effect from the dendritic KCC-1 support. In addition, the combination of Pt and Ni together with a suitable ratio can induce synergetic effect between Pt and Ni. As a consequence, the CO oxidation activity of the prepared Pt-Ni bimetallic catalysts is improved significantly in comparison with the single Pt/KCC-1 and Ni/KCC-1 catalysts. Over Pt₇Ni₃/KCC-1, the best catalyst in this study, 100% CO conversion was achieved at 100?. Apparently, the incorporation of Ni into Pt can reduce its amount to get catalysts with even improved activity, which could be an efficient way to improve the noble-metal utilization efficiency in designing novel CO oxidation catalysts with low precious metal loading.The third part investigated the effects of La₂O₃, a rare earth metal oxide, on the performance of Pt/TiO₂ catalysts for low concentration HCHO oxidation at room temperature. The HRTEM,HAADF-STEM and CO-TPD results showed that the grain size of Pt nanoparticles were reduced from 2.2 nm to 1.7 nm after modified by La₂O₃, which leads to higher Pt-dispersion and promoted catalytic activity. In addition, metal-support interaction was enhanced after modification, resulting in more adsorbed oxygen species. Therefore, the superior activity for indoor low concentration HCHO oxidation was obtained. Furthemore, the 3%La/TiO₂ was wash coated on cordierite monolith and then very small amount of Pt was supported on it. This cordierite monolith catalyst was then evaluated in a simulated indoor HCHO elimination environment, which displayed very highly purifying efficiency and stability.