【作者】 赵瑜；

【导师】 刘昌俊；

【作者基本信息】 天津大学 ， 化学工艺， 2007， 博士

【摘要】 使用催化剂已经被公认为绿色化学基本原则之一。确切地说,催化在当前化学工业中起了非常重要的作用,将来也会变得越来越重要。催化过程的基本操作之一就是把催化剂进行还原,因为许多反应需要金属纳米颗粒作为活性物种。金属活性物种的催化性能与催化剂还原条件下决定的金属颗粒形貌及颗粒大小密切相关。进行催化剂还原应具备以下特点:操作简单,成本低,环保、不对环境造成危害,获得的金属颗粒分布均一、分散性好,不对载体产生负面影响。本文探索了氩气辉光放电等离子体对负载贵重金属催化剂的还原性能,同时,鉴于能源和环境问题日益严峻,选取了催化甲烷转化为研究对象,并分析了等离子体法制备的贵重金属催化剂和催化活性之间的关系。等离子体法制备催化剂的过程包括:浸渍、干燥、氩辉光放电等离子体处理、活化。通过等离子体处理后催化剂粉末表面颜色的变化及XPS、XRD、TEM、EDX表征技术分析可知,负载的贵重金属离子得到了还原。并且对于不同的催化体系,和常规氢气还原相比,等离子体还原的效果各不相同。对还原的Pd/HZSM-5催化剂表征发现,等离子体还原的Pd纳米颗粒在载体上高度分散,比常规氢气还原的金属颗粒小,催化甲烷分解制备的碳纳米管稠密、平滑且有弹性。对还原的Pd/γ-Al₂O₃催化剂表征发现,等离子体还原的Pd纳米颗粒,经过在惰性气体中活化后,金属颗粒长大,比常规氢气还原的颗粒尺寸大很多。在催化甲烷二氧化碳重整反应中,催化活性比氢气还原的低很多,并且催化反应机理和常规催化剂不同。对还原的Rh/γ-Al₂O₃催化剂表征发现,在高载量5wt%时,等离子体还原的纳米颗粒比常规氢气还原的大很多;在低载量1wt%时,和常规氢气还原的颗粒大小基本一样。1wt%Rh用于甲烷二氧化碳重整反应中,等离子体还原的催化剂具有常规氢气还原的催化剂相同的催化活性和稳定性。对还原的Ir/γ-Al₂O₃催化剂表征发现,不管是高载量5wt%还是低载量1wt%,等离子体还原的金属纳米颗粒尺寸比常规氢气还原的小很多。1wt%Ir用于甲烷二氧化碳重整反应中,等离子体还原的催化剂比常规氢气还原的活性高很多,且很稳定。催化作用机理与常规催化剂不同。更多还原

【Abstract】 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.更多还原