TS-1沸石的孔结构调控和表面化学修饰及其对大豆油的高效、清洁催化环氧化

The epoxy soybean oil (ESO) is a high value-added fine chemical product, which can be obtained from the soybean oil by oxidizing the C=C double bond of the soybean oil (SO) molecule. At present, in traditional ESO production process, the sulfuric acid and organic peroxides are usually used as the catalysts for the oxidation reaction of soybean oil, which presents various defects, such as the severe corrosion of equipment, the multiple byproducts, and the separation difficulty of products, etc. Therefore, it is very urgent that synthesis of non-acid and heterogeneous catalyst for efficient catalytic SO epoxidation reaction in industry. In this project, in order to promote the molecular diffusion of SO on the catalyst, a series of pore structural control (diameter, length, regularity, etc) of mesopore and nano TS-1 zeolite catalysts will be designed and synthesized on basis of the unique catalytic oxidation properties of the tetrahedral coordination Ti4+ in TS-1, complex molecular structure of SO and the mechanism of the epoxidation of C=C bond. Furthermore, the surface of mesopore and nano TS-1 zeolite will be chemically modified through the introduction of polyoxometalates (POM) when the tetrahedral coordination Ti4+ are well kept in these zeolite, which will be propitious to achieve high efficiency epoxidation of SO. The structure and properties of the catalysts will be analyzed by many characterization methods, and we will systematically investigate the mesopore structure and morphology and the Ti4+ coordination environment, as well as the promotion mechanism of the POM on the epoxidation reaction.

采用化学氧化法将大豆油分子中的C=C双键转化为环氧乙烷基是制备高附加值环氧大豆油的重要过程。目前以硫酸、过氧有机酸为催化剂的反应体系存在腐蚀设备、副产物多、产品分离困难等问题。为此，创制非酸性、非均相催化剂，实现环氧大豆油的高效、清洁生产是工业上的迫切需要。本项目提出：利用TS-1沸石四配位Ti4+物种的独特催化性能，结合大豆油（含三条C18支链）的复杂分子结构及C=C双键的氧化机理，制备多孔或纳米TS-1沸石，并调控沸石的介孔结构（孔径、长度、规则度等），使其有利于大豆油分子的扩散；保持TS-1沸石介孔和外表面Ti物种的四配位形态，进一步引入具有氧化活性的杂多阴离子对其表面进行化学修饰，实现大豆油的高效环氧化。通过多种表征手段和方法对催化剂的结构和性质进行分析，重点研究催化剂的介孔孔道结构和形貌、Ti物种配位状态，以及杂多阴离子对大豆油环氧化反应催化活性的促进作用机制。

设计、合成有利于大豆油分子扩散的、高活性位点数量和表面化学修饰的钛硅（TS-1）沸石催化剂，对实现大豆油的高效、清洁催化环氧化制备高附加值的环氧大豆油具有重要的理论和实践意义。本项目主要研究内容集中在利用有机碱后处理法和水蒸气辅助晶化法合成含有大量多级孔的介孔TS-1（MTS-1）和小粒径的纳米TS-1（TS-1-s）催化剂，再在TS-1催化剂表面引入金属物种（例如：Cd、Mo等）制备了负载型TS-1催化剂，用于高效催化大分子原料（大豆油或油酸甲酯）环氧化反应中。活性结果显示，对比传统微孔TS-1催化剂，TS-1-s和金属负载型TS-1催化剂均表现出更高的催化活性，但MTS-1却展现了较低的催化活性；另外，环氧大豆油的选择性差别不大（约85%），金属负载TS-1催化剂的活性稍下降。进一步通过多种表征手段（XRD、N2-物理吸附、SEM、XPS、TEM、Mapping、IR、UV-vis、ICP、TGA等）对催化剂的微观结构进行系统地分析，结合催化活性数据发现四配位骨架Ti是TS-1催化剂的主要活性中心，又因为大豆油分子尺寸较大但分子极性较小，其不能进入TS-1和TS-1-s微孔以及在MTS-1的介孔中扩散阻力很大且容易吸附在沸石孔内。因此，大量的催化反应发生在催化剂的外表面，导致MTS-1的催化活性下降，然而小晶粒的TS-1-s具有更大的外表面以显示更高的催化活性；尤其是在TS-1-s表面引入活性金属物种后，该金属物种可协调并改善TS-1催化剂中Ti物种催化系统微环境，使其表现出更佳的催化性能。期望这些研究能够为大分子环氧化反应制备高活性TS-1催化剂提供一种新的策略。

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