【作者】 郭翠梨；

【导师】 王一平；

【作者基本信息】 天津大学 ， 化工过程机械， 2007， 博士

【摘要】 甲烷催化部分氧化具有能耗低、反应速率比水蒸气重整快几个数量级、生成的合成气中H2/CO比适合作甲醇及F-T合成等优点,因此近几十年一直为众多研究者所关注。镍基催化剂由于活性高和成本低而被认为是最有应用前景的催化剂之一,但由于其反应的稳定性差仍不能满足实际要求,因此探索如何提高催化剂稳定性是目前研究工作的重要内容。本文以BET、XRD、TPR、TG/DTA、SEM、XPS、反应活性评价等多种研究方法,重点考察了NiO/La₂O₃、LaNiO₃、La₂NiO₄催化剂的制备条件对其物化性质和甲烷部分氧化性能的影响,对LaNiO₃、La₂NiO₄物化性质和甲烷部分氧化性能进行了较为系统的比较,探讨了影响催化剂积碳和稳定性的因素。NiO/La₂O₃的研究结果表明,采用浸渍法制备的NiO/La₂O₃催化剂在经过高温焙烧后会形成LaNiO₃和La₂NiO₄;Ni含量为20～30%的催化剂具有相对较好的结构特征和催化活性;反应过程中生成的La₂O₂CO₃是有利于反应进行的物种,它能消除以金属碳化物形式存在的积碳,表现出良好的抗积碳性能。采用溶胶-凝胶法制备了钙钛矿型复合氧化物LaNiO₃。结果表明:制备过程中柠檬酸用量对催化剂的形貌及其甲烷部分氧化催化活性有很大的影响。当柠檬酸用量为La:Ni:CA=1:1:3时所制备的催化剂具有良好的结构形貌和催化活性。对于类钙钛矿复合氧化物La₂NiO₄,同样采用了溶胶-凝胶法制备。结果表明:当焙烧温度为850℃,柠檬酸用量为La:Ni:CA=2:1:3时,可以形成完整的、颗粒均匀的类钙钛矿型La₂NiO₄,而且甲烷部分氧化活性也良好。在500℃下用H2预还原处理后的催化剂活性明显高于未进行还原处理的催化剂。在甲烷部分氧化反应中,还原态Ni0是该催化反应的活性中心,La₂NiO₄上活性组分Ni0晶粒比LaNiO₃上的Ni0晶粒小,而且分散度要高,这也是La₂NiO₄甲烷部分氧化活性和稳定性比LaNiO₃好的主要原因。在甲烷部分氧化反应过程中,La₂NiO₄和LaNiO₃上都有积碳产生;La₂NiO₄产生的积碳主要以金属碳化物形式存在,而LaNiO₃产生的积碳以石墨碳为主;金属碳化物可以被反应过程中形成的La₂O2CO₃消除掉,而石墨碳活性低,不易被除去,这也是La₂NiO₄稳定性好而LaNiO₃稳定性差的原因。更多还原

【Abstract】 Partial oxidation of methane （POM） to syngas has attracted both academic and industrial interest. Compared with steam reforming, POM is more energy efficient and can be carried out with a much lower investment of capital. POM produces syngas with a H₂/CO ratio of ca. 2, which is suitable for use in the production of methanol and Fisher-Tropsch synthesis. Nickel-based catalysts are promising for its industrialization because of their high activity and relatively low cost. However, their application is limited due to their easy deactivation under reaction condition. Thus, it is important to develop the useful POM catalysts with ideal stability.In this work, the effects of different preparation condition on the structure and POM reactivity of NiO/La₂O₃, LaNiO₃ and La₂NiO₄ were examined. The structure and POM reactivity of LaNiO₃ and La₂NiO₄ were compared systemtically.NiO/La₂O₃ was prepared by wet impregnation method. The research on NiO/La₂O₃ showed that the provskite structure of LaNiO₃ can be formed after calcinations at high temperature, the NiO/La₂O₃ contained 20～30wt.% nickel exhibited good activity for partial oxidation of methane, La₂O₂CO₃ formed during reaction is probably species, which may favor removal of carbon deposition existed in MxC.LaNiO₃ and La₂NiO₄ were successfully prepared by a sol-gel method and used in partial oxidation of methane. The results showed that the amount of citric acid and calcination temperature have significant influence on the characteristics of the catalysts and their catalytic activity. The catalyst reduced in H2 at 500℃showed better POM performance.Ni0 is active site of the POM reaction, perovskite-like oxide La₂NiO₄ presents smaller nickel particle NiO after reduction treatment. Consequently the catalytic activity is higher than perovskite oxide LaNiO₃.The carbon deposition had formed on catalysts LaNiO₃ and La₂NiO₄ in POM reaction. Most of the carbon deposited on La₂NiO₄ was MxC, which can be removed by La₂O₂CO₃, while one on LaNiO₃ was graphite which is low active. So the stability of perovskite-like oxide La₂NiO₄ is better than perovskite oxide LaNiO₃.更多还原