自模板法制备多级结构TS-1沸石及其催化氧化脱硫性能研究

Deep desulfurization of fuels is one of the key steps in the national strategy for the environmental pollution control, in which the high performance catalyst is of vital importance. TS-1 zeolites, due to their remarkable catalytic performance in selective oxidation of organic compounds with dilute H2O2 solution under mild conditions, such as in the epoxidation of alkenes, hydroxylation of aromatics and ammoxidation of ketones, have attracted the increasing interest in recent years. However, suffering from the diffusion limitation in the sole microporous system of purely TS-1 zeolites, their performance needs to be further improved, especially when bulky species, such as benzothiophene (BT), dibenzothiophene (DBT) and their derivatives, are involved. On the other hand, although amorphous mesoporous titanosilicates show the improved desulfurization activity towards the bulky BT and DBT molecules, their stability and catalytic activity towards thiophene (Th) species are inferior. In order to alleviate these problems, the design of newly structured titanosilicate zeolites and synthesis methodology are highly desired. In this project, based on the structural and composition design of nanosized SiO2-TiO2@SiO2 core/shell precursors, it is proposed to carry out the study of synthesis of hierarchically micro/mesoporous structured TS-1 zeolites (TS-1 HSZs) by a new self-template method and their catalytic performance in oxidative desulfurization for the production of clean fuels. Moreover, the new concepts about in situ crystal seeds and gradient-composition TS-1 HSZs will have been built and verified for the first time. The controllable synthesis of high-quality and single-crystalline TS-1 HSZs is one of the main research targets. Specifically, research interests would be focused on the effect of the microstructure and composition of inorganic nanosphere template precursors and the detailed conditions of steam-assisted crystallization process on the product crystallinity, textural properties and active framework titanium distribution/concentration in the synthesized materials. And then, it would be discussed about the formation mechanism of TS-1 HSZs with this new self-template synthesis method. In addition, the synthesized TS-1 HSZs would be explored for catalytically oxidative desulfurization for the production of ultra-low sulfur fuels. Aiming at the superior activity towards the inert Th species and bulky BT and DBT ones, atom economy, long-term stability and recyclability, study of structure-performance relationship of synthesized TS-1 HSZs catalyst would be carried out, which would also direct the followed optimization of structural design of newly gradient-composition TS-1 HSZs and the corresponding synthesis procedure. In summary, the project production would offer the experimental and theoretical supports for the development of new-concept gradient-composition HSZs and the application research of novel catalytic oxidation materials.

燃油深度脱硫是实现国家治理大气污染战略的重要步骤，这其中高性能催化材料是关键。TS-1钛硅沸石是一类重要的催化氧化材料，但由于单一微孔孔道的扩散限制，其在燃油深度脱硫中的应用有待于材料新结构的设计与高效制备。针对这一问题，本项目基于SiO2-TiO2@SiO2核-壳结构纳米微球前驱体的结构与组成设计，提出开展自模板法梯度组成多级结构TS-1沸石的制备科学与催化氧化脱硫性能研究。项目以高质量、单晶型多级结构TS-1沸石的可控制备为主要目标之一，通过探讨影响合成材料微/介孔结构、骨架活性钛组成/分布的关键因素，阐释自模板新方法制备多级结构沸石的形成机理；面向钛硅沸石在燃油催化氧化脱硫中的应用，以高活性、原子经济性、高稳定性为目标，开展合成多级结构TS-1沸石的构效关系研究。项目的实施将为新概念多级结构沸石制备科学的发展及新型催化氧化材料的应用研究提供理论和实验基础。

燃油深度脱硫是实现国家治理大气污染战略的重要步骤，这其中高性能催化材料是关键。TS-1钛硅分子筛是一类重要的催化氧化材料，但由于单一微孔孔道的扩散限制，其中燃油深度脱硫中的应用，特别是对于较大分子的噻吩类物质的催化氧化脱除，依赖于多级孔新材料的设计与制备。本项目首先基于蒸汽辅助晶化转化与碱刻蚀后处理的两步设计，制备了具有超高比表面积（大于600 m2/g）的TS-1纳米晶多级孔结构材料，阐释了纳米晶沸石刻蚀过程中的杂原子导向、晶粒尺寸效应等新机制。其次，制备的TS-1纳米晶多级孔结构材料保持了微孔分子筛固有的疏水性特性，以纳米晶nanoTS-1(40)和多级孔结构材料nanoTS-1(40)_D为例，两者显示近似苯酚羟基化催化活性，苯酚转化率分别为32.9%和26.1%，但对于更大分子尺寸的环辛烯环氧化反应，多级孔材料具有更高的转化率达到12.9%，是前者4.8%转化率的2.5倍，体现了介孔结构在较大分子催化反应的优势；以模拟燃油中的噻吩(Th)、苯并噻吩(BT)、二苯并噻吩(DBT)等含硫化合物催化氧化脱除为模型反应，多级孔结构材料nanoTS-1(40)_D均具有近100%的催化氧化脱除效果，相比较而言，纳米晶nanoTS-1(40)对较小分子的噻吩虽然具有类似或略高的脱硫能力，但对于较大分子尺寸的BT和DBT则仅为57%和61%，进一步证明了介孔结构对于燃油中较大分含硫化合物催化氧化脱除的重要作用。最后，面向丙烷脱氢制丙烯催化应用，项目制备了PtSn负载的TS-1纳米晶复合催化剂，丙烷初始转化率达到53.6%，失活速率常数仅为0.008 h-1，对于多级孔TS-1复合催化剂，初始转化率进一步提升至55.6%，而近似组分的微米级TS-1复合催化剂丙烷初始转化率仅为31.2%且失活速率常数高达0.073 h-1。项目还研究了Ti掺杂ZSM-5对催化剂表面酸性质及催化剂甲醇制丙烯性能（MTP）的影响，结果表明，Al、Ti共掺杂赋予了材料表面适量的L酸，能够抑制MTP反应中的芳烃循环，延长催化剂寿命。