【作者】 吴鹏；

【导师】 吴通好；

【作者基本信息】 吉林大学 ， 物理化学， 2005， 博士

【摘要】 本论文主要以MCM-22 族分子筛为载体的钼基催化剂为研究对象,围绕分子筛载体的合成规律及其孔道结构与甲烷无氧芳构化反应性能之间的关系等方面展开了以下工作: 研究了以六亚甲基亚铵(HMI)为模板剂的体系下各种分子筛的合成,对合成规律以及产物的物理化学性质进行了较深入的研究。为进一步研究催化性能提供了材料基础。采用多种大分子有机化合物分别对Mo/HZSM-5、Mo/HMCM-49、Mo/HMCM-22 催化剂载体的外表面酸性位进行毒化修饰。分析对比了修饰前后分子筛的物理化学性质及其钼基催化剂的甲烷无氧芳构化反应性能。研究发现,修饰后催化剂上的苯选择性均有明显的提高,而积碳和萘的生成得到了一定程度的控制。我们认为催化剂载体外表面的酸性位,由于缺少空间束缚,在芳构化反应中的作用主要是促进积碳等副产物的生成。通过对MCM-22 分子筛进行溶胀和柱撑,合成了不含超笼结构的MCM-36 分子筛,并以其为载体制备了Mo/HMCM-36 催化剂,考察了它的芳构化活性。研究发现,Mo/HMCM-36 催化剂的CO、萘和积碳的选择性明显高于Mo/HMCM-22,而苯选择性和甲烷转化率则低于后者。同载体结构相关联,我们认为,受10 元环孔口的影响,超笼结构可以一定程度地促进甲烷的转化和苯的生成。这为寻找新的催化剂载体提供了依据。在对Mo/HMCM-36 催化剂的外表面和介孔孔道进行硅烷化处理后发现,硅烷化处理大大抑制了Mo36 催化剂上积碳的生成,显著提高了产物中苯的选择性。因此我们认为,10 元环正弦孔道在甲烷芳构化反应中对苯具有良好的择形作用。更多还原

【Abstract】 Methane is the component of natural gas, its activation and conversion has received much attention in recent years. Considering the prospect, environment protection and scientific research, utilization of methane resource is of significance. Methane non-oxidative aromatization is one of the main routes for methane direct conversion, since first reported in 1993, many research has focused on the study of this reaction. It is proved that Mo/H-ZSM-5, Mo/H-ZSM-11,Mo/H-MCM-22 and Mo/H-MCM-49 are the best catalysts for methane aromatization at present. But up to now, there is not a detailed study on the role of different pore sites of zeolite supports in the titled reaction. Especially, there is not a suitable method to distinguish the role of the three pore systems in MWW structure zeolites. The purpose of this thesis lies in: first, modify the external surface of HZSM-5, HMCM-49 and HMCM-22 with larger molecule organic compounds to change the acidic properties of zeolites and the dispersion of Mo species, and synthesize the MCM-36 zeolite by swelling and pillaring the MCM-22 precursor to change the pore structure of zeolites, and thus analyze the connection of the pore systems and catalytic activities on methane conversion. The main results obtained are as follows: 1. The synthesis of catalyst supports and the study on the synthesis condition. In the presence of template HMI, several zeolite molecular sieves such as MCM-22, MCM-49, MCM-56, MOR, ANA has been synthesized by dynamic synthesis method through the control of Si/Al ratios, alkalinity, crystallization temperature, time and other reaction conditions. It was found that the Si/Al ratios of reactant mixture were determinative to the phases of the products, while the alkalinity of reactant mixture has no effect on the products in certain range. 2. The role of the external surface of Mo/HZSM-5 catalyst. The selective modification of the external surface of HZSM-5 by large organometallic complexes was used to reduce the densities of external acid sites and MoOx species retained at external surfaces during the exchange process. The amounts of acid sites and the catalytic properties for non-oxidative aromatization of methane over modified and unmodified samples were studied. It was found that acid sites and active MoOx species mainly located within the channels of the modified zeolites, and the modified Mo/HZSM-5 showed higher shape-selectivity to major product benzene and lower formation rates and selectivities for naphthalene and coke. So we consider that the role of external surface acid sites is to promote the formation of larger hydrocarbons. 3. The role of the external 12-ring pockets over Mo/HMCM-49 catalyst. Four kinds of large molecular organic compounds were used to modify the external pockets of HMCM-49, and the physical properties, acidic properties, Mo dispersion and catalytic activities of modified and unmodified samples were studied by XRD, IR, TPD, BET, ICP, TGA measurements. It was found that the modification of HMCM-49 reduced the acid sites, the surface area and the dimension of microporous channel accesses. Otherwise, the modified catalysts更多还原