调控性芳构化类沸石咪唑酯骨架化合物（ZIFs）催化剂的制备及其催化机理研究

Increased environmental consciousness and development of bio-energy crisis have aroused a growing interest focus by industry and academia on utilizing renewable glycerol, the major by-product of biodiesel production. It has a positive meaning for chemoselective catalytic conversion of glycerol into high value-added aromatics, which can enhance the economic profits in biodiesel and biomass industry chain. Nevertheless, there are severe problems such as serious deactivation and low activity for the catalyst currently used in this reaction due to the limited loading active metal species on HZSM-5 zeolites. This proposal is to design a catalyst with high catalytic activity, selectivity and stability for glycerol to aromatics. Zeolitic imidazolate frameworks (ZIFs) with appropriate channel structure and acidity for aromatization are prepared using aromatization-functional promoted hybrid metals as metal frameworks. And the prepared ZIFs material is post-synthesized to further improve its aromatization performance. The porous structure, acidity and incorporated metals, which have impact on the control activation and selective conversion of aromatization, is analyzed through studying the internal relations between composition distribution of aromatization product and composition-structure of catalyst. Meanwhile, the synergetic effect of hybrid metal nanoparticles and interaction between metals and support are discussed in detail with relation to the aromatization of glycerol. Then the formation process of aromatization product is deduced according to the above results, and the catalytic mechanism of GTA on ZIFs is explored on the basis of aromatization experimental results. The proposed research will provide scientific evidences and direction for further developing efficient, stable and useful catalysts for aromatization reaction, and help to lay a foundation for the development of industrial application for aromatization of crude glycerol.

随着环境污染的不断加剧与生物质能源的逐步开发，生物柴油副产物甘油成为新的研究热点。将粗甘油芳构化可以有效提高生物柴油及生物质产业链的利润。由于通常芳构化反应所采用的HZSM-5分子筛上所负载的活性金属含量是有限的，这使得甘油芳构化反应活性、稳定性较低。本课题提出采用一种或多种具有芳构化催化活性的金属（如Zn、Sn）为骨架来制备具有适合进行芳构化反应的孔结构与酸性的ZIFs材料，并通过对ZIFs中未与金属配位的有机配体进行硅烷化、质子化等修饰来进一步提高其催化芳构化性能。通过研究甘油芳构化过程中产物的组成及分布与ZIFs催化剂的成分、结构、形貌、孔道、酸性的内在联系，解析甘油在ZIFs材料上进行芳构化反应的机理与ZIFs催化剂的催化芳构化机制，为设计制备高效、稳定、实用的芳构化催化剂提供科学依据和指导，也为粗甘油芳构化的工业化应用奠定重要的研究基础。

随着生物柴油的开发利用，其副产物甘油成为一种新兴的可再生化工原料。将甘油芳构化可以降低石油依存度，同时完善生物柴油产业链，促进生物柴油产业的发展。本项目首先研究了甘油在HZSM-5上的芳构化反应路径，提出该转化过程由液相路径和气相路径组成。催化剂的弱酸位更有利于液相路径的进行，但过弱的酸性会导致C9+芳烃的大量增加，结焦加剧，催化剂寿命缩短；强酸位更有利于气相路径的进行，但是过强的酸性会导致过度裂解生成C1小分子，因此适当的酸强度对于目标产物苯、甲苯、二甲苯（BTX）的生成至关重要。通过对HZSM-5粒径、孔分布及引入金属的研究，发现较小的粒径、适当的介孔数量以及Sn、Zn有利于甘油芳构化过程及抗结焦。同时发现不同方式引入的Zn物种的芳构化活性不同，同晶替代法制备的催化剂具有最高的BTX收率和最长的寿命。基于此，采用ZIF-8为模板制备了ZF/HZSM-5，其中ZIF-8用量为0.45时，所得0.45-ZF/HZSM-5均为小纳米晶，并且具有适宜的酸强度和酸分布，此时ZnOH+物种、晶间介孔、HZSM-5纳米晶之间具有最佳的协同催化效果，催化剂的BTX收率、总芳烃收率和催化寿命分别提高至36.7%、59.5%和11h。提出了ZF/HZSM-5催化的甘油芳构化可能机制。采用ZIF-8焙烧后的金属碳材料为模板剂，制备得到的Zn改性多级孔HZSM-5催化剂，活性与寿命显著高于非ZIF-8模板引入Zn的HZSM-5催化剂,催化剂的BTX收率、总芳烃收率和催化寿命分别达到了34.6%、54.7%、8.5h。。采用ALD在负载Sn的HZSM-5表面引入ZnO，二者的协同作下，芳烃总收率可以达到56%，BTX碳收率可以达到40%。以双金属ZIF-8为模板剂制备了一系列同时含有Zn金属和杂金属的双金属ZF/HZSM-5催化剂，其中La/Zn掺杂摩尔比为1:1时制备的La-Zn/ZF/HZSM-5催化剂具有最佳的催化活性和稳定性, 反应进行至7h时，La-Zn/ZF/HZSM-5仍具有64.5%的总芳烃收率，明显高于ZF/HZSM-5在此时的总芳烃收率（54.6%）。

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