Study On Reduction Of Noble Metal Catalysts Using Argon Glow Discharge Plasma At Room Temperature

The use of catalyst is one of principles of green chemistry. Exactly, the catalysis plays an extremely important role in the present chemical industries and will be even more important in the future. One of the basic operations for the catalysis is the reduction since many reactions require metallic nano-particles as the active species. The catalytic properties of metal species are closely related to the morphology and particle size, which are normally determined by the conditions of the catalyst reduction. Reducing catalyst should possess the following conditions: simple operation, low cost, environmental friendly, uniform distribution of the metal particles obtained, good dispersion, and having no negative effect on the carrier. In this work, we explore the reduction properties of noble metal-loaded catalysts treated by argon glow discharge plasma. With regard to energy and environment problem, catalytic methane conversion was selected for study. At the same time, the relationship between plasma-reduced noble metal catalysts and catalytic activities were analyzed.The catalyst preparation process through plasma includes: impregnation, drying, argon glow discharge plasma treatment and activation. From the surface colour change of the catalyst powder during plasma treatment and XPS, XRD, TEM, EDX characterization results, noble metal-loaded ions were reduced. For the different catalytic system, compared to hydrogen-reduced catalysts, different recuction effects were obtained.For Pd/HZSM-5 catalyst, highly dispersed Pd nano-particles were obtained through plasma treatment and the particle size was smaller than that of hydrogen-reduced. Carbon nanotubes prepared by catalytic methane decomposition with plasma-reduced catalyst were dense, smooth, and elastic.For Pd/γ-Al₂O₃ catalyst, after activation with protection of inert gas at elevated temperature, plasma-reduced Pd nano-particles aggregated and the particle size was much bigger than that of hydrogen-reduced. During the carbon dioxide reforming of methane, catalytic activities were much lower than that of hydrogen-reduced. Two kind of catalysts had different reaction mechanisms.For Rh/γ-Al₂O₃ catalyst, when the metal loading was 5wt%, plasma-reduced Rh nano-particles were much bigger than that of hydrogen-reduced. While the metal loading was 1wt%, the particle size was almost the same. During the carbon dioxide reforming of methane with 1wt%Rh, the catalytic activity and stability were the same for the two kinds of catalysts.For Ir/γ-Al₂O₃ catalyst, no matter how much loading, the particle size of plasma-reduced catalyst was smaller than that of hydrogen-reduced. During the carbon dioxide reforming of methane with 1wt%Ir, the higher activity and stability were obtained with plasma-reduced catalyst than hydrogen-reduced. Two kinds of catalysts had different reaction mechanisms.