高稳定性金属纳米粒子/ZSM-5分子筛双功能催化剂构筑及其催化转化轻质正构烷烃作用机制研究

Light normal alkanes (C4-C6) are a kind of industrially typical carbon-based energy and resources. Because of the high thermal stability, they are not fully utilized in chemical industry. The effective activation and evolution regulation of C-C and C-H bonds in light n-alkanes constitutes the academic frontier of and the challenge for modern chemistry and chemical engineering. In this project, catalytic cracking route is suggested for the conversion of light normal alkanes into light olefins and high octane number aromatics. Given the situation that metal subcomponent in typical metal/zeolite bifunctional catalyst is prone to sintering and coking at high temperatures, leading to low catalytic efficiency and also hindering the studying of structure-property relationship of catalysts, in combination with the unique features of atomic layer deposition technique in the construction of model catalysts, the introducing of metal oxide interfacial layer on metal/zeolite bifunctional catalyst or bimetallic subcomponent on zeolite, i.e. the construction of stable metal and bimetallic nanoparticles on zeolite is proposed. Effects of the electronic and geometric factors of metal nanoparticles on the catalytic performances of the catalysts will be studied. On this basis, the method for synergistic regulation of the thermal stability & selective dehydrogenation of metal subcomponent and the cracking function of zeolite counterpart will be determined. It is expected that the present research will promote the design of advanced catalysts for efficient catalytic cracking of light alkanes. Meanwhile, it is also of practical significance for the production of light olefins and high octane number aromatics, achieving the enhanced utilization efficiency of petroleum resources.

轻质正构烷烃(C4-C6)是一类工业典型的碳基能源，由于其高度稳定，目前化工利用率低，其C-C键和C-H键高效活化和演变调控是目前化学化工领域的研究前沿和重要挑战。本课题致力于采用催化裂解路线将轻质正构烷烃转化为低碳烯烃和高辛烷值芳烃研究，针对当前金属/分子筛双功能催化剂中金属组分易高温烧结、积炭导致催化剂效率降低以及构效关系难以深入研究的现状，结合原子层沉积技术在模型催化剂构建上的独特优势，提出在金属/分子筛双功能催化剂中引入氧化物界面层或在分子筛上引入双金属，构建高稳定性金属/分子筛双功能催化剂体系。研究催化剂电子、几何效应等与催化性能的关系，确定金属高温热稳定性、选择性脱氢及其与分子筛酸性裂解整体协同调控的方法。本课题研究不仅有助于推动轻质烷烃催化转化高效催化剂的设计，而且还对以轻质烷烃为原料制备高附加值低碳烯烃和高辛烷值芳烃组分、提高石油资源利用率具有直接和现实的意义。

轻质正构烷烃结构稳定，化工利用率低，催化裂解轻质烷烃是其高值利用的一个重要途径，该反应的难点在于提高原料转化率同时，如何有效抑制较活泼目的产物低碳烯烃的过度转化。本项目致力于高稳定性与良好双功能特性兼具的Pt/ZSM-5基催化剂构建及其催化作用机制研究。项目采用两步原子层沉积（ALD）法，在Pt与ZSM-5界面、Pt表面引入多孔TiO2及Al2O3层，通过组合金属-载体强相互作用和物理沉积调控等，实现了Pt抗烧结及催化剂良好双功能特性。研究发现，所制备催化剂中可控高比例的不饱和配位Pt有助于正丁烷探针原料C-H键的活化，提高中间产物丁烯的生成速率，从而提高目的产物乙烯丙烯的收率。金属氧化物前驱体在不同配位Pt表面吸附能的差异以及样品制备过程的还原处理等均会影响不饱和配位Pt的暴露比例，因而可通过所沉积氧化物类型、ALD工作参数以及制备过程还原处理对其比例进行调控，从而实现对催化剂反应性能和产物分布的可控调节。双功能催化剂上脱氢与裂解匹配关系研究结果表明，分子筛引入金属后，高硅铝比分子筛上活化能降低的更多，脱氢/裂解指数提高的更多，脱氢效应更强，金属的引入使得高硅铝比分子筛上倾向于生成丁烯，而低硅铝比分子筛上倾向生成乙烯。上述ALD构建双功能催化剂的方法可拓展至有良好传质性能的介孔ZSM-5分子筛，项目还制备了Pt-Sn/ZSM-5、Pt-Pd/ZSM-5催化剂，上述催化剂在正丁烷催化转化反应中均表现出优异的催化性能。本项目研究结果对于新型高效双功能催化剂的设计及轻质烷烃的高效转化具有指导意义。围绕项目及相关研究内容，共发表SCI标注论文7篇，申请国家发明专利3项。