【作者】 潘大海；

【导师】 马静红； 李瑞丰；

【作者基本信息】 太原理工大学 ， 化学工艺， 2004， 硕士

【摘要】 本文以微孔沸石分子筛（Y型和Beta型）和中孔材料MCM-41为载体，运用真空浸渍法制备负载纳米Pt金属簇催化剂。结合XRD，低温N₂吸附，NH₃-TPD和TEM等现代物化表征技术对各种载体的结构和表面性质以及金属粒子在载体表面上的分散状态进行了考察。在此基础上，将这些催化剂用于甲烷的两步等温转化反应，系统地考察了中微孔分子筛的结构和表面性质对催化反应的影响。 首先，通过离子交换对沸石分子筛表面酸性进行调节，并以此为载体负载Pt金属簇。主要考察了催化剂中载体酸性对甲烷低温两步反应的影响。研究发现，随载体酸性的增强，甲烷催化反应活性明显增加，产物中生成高碳烷烃的选择性逐渐增大，但由于载体酸性可同时加快副反应（高碳烷烃产物氢解反应）的速度，从而表现出催化剂Pt／HY对生成C₆₊烷烃的选择性较催化剂Pt／HNaY的低。此外，在采用程序升温加氢反应（TPH）对甲烷吸附裂解中间产物CHx的分布及加氢反应性进行考察时发现，虽然在各种催化剂上碳物种生成的形式相似，但各碳物种的生成量及加氢反应性均随载体酸性的增强而增大。 其次，通过水热晶化法制备出纯硅及不同Si／Al比的MCM-41试样，采用先经各种抽提液（纯乙醇或含NH₄NO₃，太原理工大学硕士研究生学位论文HAc和NaN03的醇溶液）处理后焙烧的方式脱除MCM一41孔道内的模板剂，并以此作为负载R金属簇的载体。研究结果表明，使用含盐或酸的乙醇溶液可有效脱除MCM一41孔道内的大部分模板剂分子而不会对孔道结构造成任何破坏。此外，在经酸性乙醇溶液处理Al一MCM一41的过程中，可同时进行离子交换反应，形成具有质子酸的HMCM一41。另一方面，在MCM一41制备过程中，通过改变配料Si/A1比可达到调节材料孔径的目的，即随Si/A1的增加，载体孔径逐渐减小而比表面逐渐增大。 最后，选取系列催化剂P灯MCM一41进行甲烷低温两步反应，考察了载体MCM一41的结构及表面性质对甲烷同系聚合催化反应的影响。研究发现，纯硅MCM一41因其具有最高的比表面和较小的孔径，有利于R粒子以较小的粒径在其内表面高度分散均匀，从而表现出对甲烷转化具有最高的催化活性。另外，就经酸性抽提液处理的Al一MCM一41负载催化剂而言，甲烷催化转化活性亦随载体酸性的增强而增大。同时，在对CHx物种加氢反应性进行考察时发现，MCM一41载体酸性对碳物种的分布具有选择性，即酸性载体有利于促进CQ和Cp的生成以及C一C键的增长。更多还原

【Abstract】 Well-dispersed and stable nanoclusters supported on mesoporous materials and zeolite have been prepared by vacuum impregnation technique. The pore structure and the surface electronic properties of supports and the state of Pt dispersed on the support surface have been investigated by modern characterization techniques, such as XRD, N2 adsorption-desorption, NH3-TPD and transmission electron microscopy (TEM) methods. Meanwhile, it was studied that the influence of the support effects in different catalysts on the catalytic reaction of methane.First of all, the acidity of supports was changed by ion exchange to study the influence of electronic properties of platinum particles on two-step isothermal conversion of methane to higher hydrocarbons. The catalytic results showed that the activity of catalyst increased with the increase of support acidity and the selectivity of C2-C6 products varied with support acidity. Moreover, the distribution and the reactivity of surfacecarbonaceous species chemisorbed on catalysts, generated from the methane decomposition at first step were characterized by temperature programmed hydrogenating (TPH). The formation of C a species, which is known to give C2+ hydrocarbons on hydrogenation, and reactivity of surface carbon are enhanced on acidic support compared to neutral supports.Secondly, mesoporous molecular sieves MCM-41 were synthesized by hydrothermal method. The template in MCM-41 can be removed by extraction with solutions of an acid or salt in ethanol. When extracting with acidic ethanol, ion exchange of sodium ions for protons was achieved simultaneously. As a result, the supports had different acidities. On the other hand, with the increase of Si/Al ratio of materials, the pore diameter was reducing gradually and the surface area was increasing obviously.Finally, a series of MCM-41 mesoporous materials with different Si/Al ratio were used as supports for Pt-supported catalysts. Thesis catalysts showed the obviously different catalytic behaviors for methane conversion to higher alkanes through two-step procedure. The results of experiments suggested:1. Pure silica MCM-41 had the largest surface area and smaller pore diameter, which was better for the higher dispersion of Pt particles with smaller particle size. As a result, the catalyst Pt/MCM-41 presented a superior activity for C2+ formation.2. The total amount of methane converted to C2+ hydrocarbon was increasing with the increase of support acidity. The change ofcatalytic properties is due to electron deficient nature of platinum particles on acidic support from the interaction of metal and support.3. By studying the distribution and hydrogenation reactivity of surface carbonaceous species chemisorbed on catalysts, it was found that the acidity of MCM-41 would strengthen the hydrogenation reactivity of carbonaceous species and promote the production of C a & C .更多还原