【作者】 祝新利；

【导师】 刘昌俊；

【作者基本信息】 天津大学 ， 化学工艺， 2007， 博士

【摘要】 随着世界石油资源的消耗,天然气（主要成分是甲烷）的化学利用日益提上了日程。从经济上考虑,甲烷经过合成气（氢气和一氧化碳）步骤,来间接合成液体燃料和含氧化合物的途径更具有应用前景。甲烷重整制合成气有三条路径:水蒸气重整,二氧化碳重整和部分氧化。现在工业上运行的水蒸气重整是一个能量密集过程,有很多不足。相对水蒸气重整,二氧化碳重整和部分氧化有各自的优势,比如甲烷二氧化碳重整具有温室气体的利用,甲烷部分氧化具有需要能量少、操作空速大等优点。对二氧化碳重整和部分氧化催化剂的基础研究具有重大的理论和实际意义。使用等离子体处理加焙烧的方法制备的Ni/Al₂O₃催化剂在甲烷二氧化碳重整反应中显示出高于常规催化剂样品的活性,并且在750 ?C保持50 h稳定。程序升温氧化反应5 h的催化剂样品,发现等常规催化剂样品的积碳量是等离子体处理样品的5.1倍。透射电镜观察发现,在反应10 h的常规样品中有大量的包埋碳和胡须碳,而在反应50 h后的等离子体样品中没有发现这些积碳。这些结果表明等离子体处理的样品大大抑制了这些对催化剂有害的积碳的生成。对催化剂的表征发现等离子体处理的样品中,Ni的平均颗粒直径比较小且分布均匀、Ni与载体的作用较强、Ni颗粒的表面比较平整。这些结构有效地降低了甲烷裂解产生积碳的速度,从而有效地抑制了胡须碳和包埋碳的成长。而较高的分散性提高和Ni富集在表面的特性提高了催化剂的活性。使用一氧化碳作为探针分子的漫反射红外光谱是研究催化剂结构的有效手段。在等离子体处理的Ni/Al₂O₃处理样品中观测到归属于一氧化碳桥式吸附在三个Ni原子上的特征峰,而在常规样品中没有观测到。这说明常规样品的Ni颗粒更加的粗糙,含有更多的缺陷位;而在等离子体处理的样品比较平整,含有较多的密集平面。等离子体处理制备的Pt/ZrO₂催化剂在甲烷二氧化碳重整反应中显示出高于常规催化剂的活性。初步研究表明等离子体处理提高了高温还原以后表层的Pt浓度,增强了Pt-ZrO₂的相互作用。使用各种表征手段,证明Ar辉光放电等离子体还原Pt催化剂的有效性,并且等离子体还原的催化剂在甲烷部分氧化反应中显示出与氢还原催化剂相近的活性。等离子体处理制备的Pt/ZrO₂催化剂在甲烷部分氧化反应中显示出优于常规催化剂的稳定性。催化剂的失活不是因为积碳而是因为Pt聚集引起的。使用CO吸附的漫发射红外光谱研究表明,等离子体处理的样品具有更好的高温临氧抗聚集性能。更多还原

【Abstract】 With the depleting of oil resource in the world, the utilization of natural gas （main component is methane） resources to useful chemicals has becoming important. From the economic consideration, it is more promising to use methane for syntheses of liquid fuels and oxygenated hydrocarbons via synthesis gas （H₂ and CO）. There are three approaches to produce synthesis gas from methane, namely, reforming with H₂O （steam reforming）, with CO₂ （CO₂ reforming）, and partial oxidation. Steam reforming is currently carried out in the industry with some drawbacks, for example, intense energy input. Compared to steam reforming, CO₂ reforming and partial oxidation have some advantages, for example, utilization of greenhouses gases, lower energy input and higher space velocity for partial oxidation. Therefore, it is of great importance for the studies of CO₂ reforming and partial oxidation.The Ni/Al₂O₃ catalyst prepared using plasma treatment followed by calcination method shows excellent stability and superior reactivity for CH₄/CO₂ reforming, compared with the non-plasma treated sample. The activity did not decline during 50 h time on stream at 750 ?C. Temperature programmed oxidation results show that the amount of carbon formed over the non-plasma treated sample during CH₄/CO₂ reforming at 750 ?C for 5 h was 5.1 times larger than that for the plasma treated sample. The TEM observations do not reveal obvious filamentous carbon or encapsulating carbon for the plasma treated sample even after 50 h time on stream. Whereas these carbon species are clearly observed for the non-plasma treated sample after 10 h time on stream. These results indicates that the greatly inhibition of filamentous carbon and encapsulating carbon formation over the plasma treated sample. Various characterizations illustrate the smaller particle size of Ni, the stronger interactions between the Ni and alumna support, and the flatter morphology of Ni particle result in the superior anti carbon property of plasma treated sample.CO adsorbed diffuse reflectance Fourier transform infrared （DRIFT） spectroscopy is a powerful way to study the structure of supported catalysts. A band centered at 1887 cm-1, which can be assigned to CO bridged bonded to three nickel atoms, is observed for the plasma treated Ni/Al₂O₃ sample. However, it is absent for the non-plasma treated sample. This result suggests that the nickel particle of the non-plasma treated sample is more rough, containing more defect sites; whereas, it is more flat, containing more close packed planes for the plasma treated sample. The Pt/ZrO₂ catalyst prepared using the plasma treatment and calcination method shows higher reactivity for the CH₄/CO₂ reforming with regard to the sample without plasma treatment. We tentatively ascribe the result to higher exposed Pt concentration after high temperature reduction and stronger Pt-ZrO₂ interactions for the plasma treated sample.Various approaches were used to confirm the validation of Ar glow discharge plasma reduction of supported Pt catalysts. And the plasma reduced supported Pt catalysts show comparable reactivity during partial oxidation of methane.The Pt/ZrO₂ catalyst prepared using the plasma treatment and calcination method shows higher stability for the partial oxidation of methane with respect to the sample without plasma treatment. The deactivation of the catalyst is not due to coke formation but Pt sintering in the presence of O2. CO adsorbed DRIFT study shows that the plasma treated sample is more resistance to sintering at higher temperature in the presence of O2.更多还原