Application Of Nobel Metal Catalysts Prepared By Plasma In Glucose Oxidation

The use of catalyst and renewable resources has been considered to be part of the twelve principles of green chemistry. Oxidation of glucose to gluconic acid is a typical example of these green chemistry principles. Gluconic acid, used as an intermediate in the chemical, food, pharmaceutical, and light industries, is a promising product for various applications. Nowadays, gold colloids as well as supported noble-metal and bimetal catalysts are employed in glucose oxidation, which is a structure-sensitive reaction. Therefore, different preparation conditions, especially the reduction methods, could result in variation in particle morphology and size, and then impact on the catalytic behaviors. In this dissertation, supported palladium catalysts and metal colloids prepared by glow discharge plasma were used in glucose oxidation.The Pd/γ-Al2O3 was successfully reduced by argon glow discharge plasma at ambient temperature. Comparing with conventional catalyst reduced by hydrogen at elevated temperature, the plasma reduced Pd/Al2O3 had the characters of smaller diameter, higher dispersion of Pd nanoparticles, and stronger interaction between metal and support. Because of the smaller size of Pd nanoparticles, the plasma reduced catalyst was easier to be deactivated by oxygen poisoning, which led to a lower conversion rate. However, after being calcined under Ar flow, the plasma reduced catalyst exhibited a larger particle size and possessed a higher activity than the hydrogen reduced catalyst. It was noteworthy that the stronger metal-support interaction induced by plasma reduction enhanced the stability of active metal loaded on the support. This effect avoided the irreversible deactivation caused by Pd leaching into chelate medium. Furthermore, the energy consumption and economy evaluation were conducted, which confirmed that the plasma reduction route was an energy efficient and economically effective approach for metal catalyst preparation.The glow discharge plasma was also employed to synthesize Pd catalyst loaded on ordered mesoporous silica support SBA-15. The long-range order hexagonal structure was well maintained during the plasma reduction. As a catalyst in glucose oxidation, Pd/SBA-15 showed much better catalytic activity than Pd/SiO2, because of the unique structure properties, such as the high surface area, large pore volume, and narrow distribution of pore diameter. Gold colloids were successfully synthesized at room temperature using glow discharge plasma within only 5 min. There was only one step in this simple method without any addition of reducing agent or stabilizer. The size of colloidal Au nanoparticles could be effectively tuned in the nanometer range by easily adjusting the initial concentration of aqueous HAuCl4 solution. The as-synthesized Au colloids exhibited good catalytic activity for glucose oxidation. Moreover, initial results indicated that this new synthesis method could be easily extended to the preparation of Pd colloids.