掺杂氧化铈-钼基分子筛催化剂的结构调控及其催化甲烷芳构化反应性能研究

Catalytic dehydroaromatization of methane opens a novel pathway to high-efficient production of aromatics, exhibiting particular economic, technological and environmental interest. The key aspects for a viable industrial application of this process are the development of a thermal stable catalytic material and the significant improvement of aromatics productivity. In this proposal, doped ceria—Mo-based zeolite will be developed as a highly effective bifunctional catalyst for the methane aromatization reaction. In this application, CeO2-based oxygen carrier will be introduced into the structure of Mo/HZSM-5 by the confinement effect of the mesoporous zeolite matrix. Here, the methane dehydrogenation will be performed over the Mo species, and the doped CeO2 components will catalyze the selective combustion of hydrogen, shifting the dehydrogenation equilibrium to the desired side. Furthermore, various dopants will be chosen in cerium oxides to further identify the effect of oxygen release kinetics on the selectivity and yield of aromatics in methane aromatization. In addition, various bifunctional catalysts with different structure, chemical state of active sites and molecule mobility will be obtained by tuning synthesis routes, and the relationship between these properties and the catalytic performances in dehydroaromatization of methane to aromatics will be established. In this regard, a highly effective bifunctional catalyst can be developed for methane aromatization, and the deep oxidation of hydrocarbons will be prevented, further enhancing the aromatics productivity. The aim of this application is to provide technical and theoretical guide for developing novel high-efficiency catalyst candidates for dehydroaromatization of methane and other catalytic systems.

通过甲烷芳构化过程实现芳烃的高效生产具有重要的理论和实际意义，提高催化剂的稳定性和芳烃产率是目前亟待解决的关键问题。本项目拟重点开发新型掺杂氧化铈-钼基分子筛双功能催化剂，并考察其催化甲烷芳构化反应活性和稳定性。通过在Mo/HZSM-5分子筛介孔孔道内引入CeO2基氧载体构筑双功能催化剂，其中Mo基活性组分催化甲烷脱氢反应，CeO2基氧载体可选择性燃烧H2。通过调变CeO2中掺杂金属的种类和含量等，阐释氧载体的释氧动力学行为对甲烷芳构化反应的影响。通过调变制备方法获得不同结构的双功能催化剂，并考察其催化性能，建立双功能催化剂的结构与甲烷芳构化反应性能之间的关系，从而获得高活性、高稳定性的甲烷芳构化反应用双功能催化剂，不仅能够避免烃类的深度氧化，同时可获得较高的芳烃产率。本项目的顺利实施可为甲烷脱氢芳构化技术的发展及相关催化剂体系的开发提供理论指导。

通过烷烃芳构化过程实现芳烃的高效生产具有重要的理论和实际意义，提高催化剂的稳定性和芳烃产率是目前亟待解决的关键问题。本项目一方面制备了具有纳米和介孔结构的分子筛，通过引入Zn等活性物种制备获得负载型分子筛催化剂，并考察了该催化剂在烷烃芳构化反应过程中的积炭行为。研究发现，与传统的Zn/HZSM-5分子筛催化剂相比，纳米和介孔的催化剂能够显著提高催化剂的稳定性，且能够保持更多的活性[ZnOZn]2+物种，芳烃和乙烯的总产率提高近3倍。拉曼和热重分析显示，纳米和介孔分子筛有利于低碳芳烃的传输，抑制该积碳前驱体进一步形成积碳，从而提高催化剂的稳定性。另一方面，通过进一步引入掺杂氧化铈或钙钛矿等作为载氧体，与分子筛催化剂复合制备复合型催化剂，并考察其烷烃芳构化反应性能。其中载氧体中的晶格氧能够原位移除分子筛催化剂上芳构化反应生成的H2，从而促进反应平衡向产物生成的正方向进行，提高了烷烃转化率。同时，H2燃烧反应原位生成的H2O能够减少反应过程中的积碳，提高催化剂的稳定性。例如，在甲烷芳构化反应中，反应100min时，载氧体的引入能够将CH4转化率和芳烃选择性分别提高~62%和83%，因此芳烃的产率提高了3倍以上。另外，基于载氧体的储放氧性能，我们可实现复合催化剂的间歇式反复循环再生，与未再生的复合催化剂相比，再生后催化剂能够保持CH4转化率提高2.5倍以上。本项目的顺利实施能够为烷烃芳构化技术的发展及相关催化剂体系的开发提供理论指导。