限域纳米孔道内Fe基仿酶催化剂的分子创制及其催化氧化反应性能的研究

By biomimetic studies of model metalloproteins on the geometric structure of metal sites and its contribution to physical properties and reactivity, the preparation of the analogous active sites at supported catalysts is of great importance in heterogeneous catalysis but remains a challenge.The mononuclear, binuclear heme and non-heme iron enzymes have been shown to carry out a variety of different reactions through activation of dioxygen.In this proposal, using iron enzymes as model complexes, the targeted iron-based biomimetic heterogeneous catalysts with mono- and bi nuclear metal active sites will be design synthesized at a molecular level by surface grafting technique in combination with co-condensation strategy using unique mesoporous silica as a confined nanospace; Their electronic and geometric structures in the catalytic active site will be studied by various characterization techniques, such as UV, EPR, Raman, EXAFS, solid NMR and Mössbauer spectrum; a group of key hydrocarbon substrates with different C-H bond dissociation energies, including of cyclohexane, cyclohexene, toluene, ethylbenzene, and cumene is used to test the chemical reactivity of the obtained catalysts. The influence of key experimental parameters, including of the spatial distribution and self-assembling of organic functions (i.e., ligands to metals), surface hydrophilicity-hyfeophobicity, fabrication of weak interaction (such as H-bond interaction), and pore structures, on the coordination environment of Fe active sits and oxygen binding mode, will be systematically investigated. Elucidation of the unique spectral and structural features of these active sites provides detailed insights into the nature of these sites that can be applied toward greater understanding their contributions not only to the structure/function correlations over the classical catalysis, but also to the unique catalytic functions in biology.

研究金属酶的结构与功能，合成它们的模拟物，实现可控制备具有类似酶结构特征的高效、稳定的活性中心，一直是多相催化领域的重要研究挑战。本课题以Fe基金属蛋白酶作为模型配合物，利用共缩聚和表面嫁接相结合的分子表面功能化技术在纳米孔道内进行单/双核Fe基催化活性位的构筑，进而实现分子氧的有效活化和烃类的高效催化氧化转化。重点考察咪唑和卟啉等有机官能团的复配、孔道内疏水化程度、弱作用力的构筑（如氢键）以及孔道结构等关键因素对Fe金属离子配位状态的影响，从而深入了解分子氧的键合模式，以期望实现温和条件下分子氧的高效活化。通过对限域纳米孔道内Fe金属配合物活性位点微结构控制的系统研究，不仅可以加深传统多相催化剂构效关系的理解，也可以在分子水平上深入了解生物酶的催化作用机制，从而为新型多功能仿生催化剂的设计合成提供更多的实验和理论依据。

分子氧参与的C-H和C-O的活化一直是均相和多相催化反应的核心研究课题。由于同时涉及到反应底物以及小分子的氧的活化，因此对一些特定惰性反应底物选择性氧化的效率比较低，如环己烷和苯甲醇的选择性氧化。 本课题利用介孔材料丰富的孔道结构以及大的比表面和孔容，企图模拟自然界中金属酶的结构，构筑过渡金属活性中心结构，实现环己烷和环己醇的高效催化活化转化。以此为目标，发展了新颖的软模板合成策略实现了不同孔道结构和尺寸的介孔二氧化硅纳米颗粒的精准、有效合成；构筑了负载型过渡金属基多相催化剂。在相对温和的反应条件下，通过液固和气固相反应高效长寿命的实现了环己烷和肉桂醛的选择性氧化，气固相催化反应的寿命达到500小时，是当前已报道催化剂的最长反应寿命。结合超快时空分辨的光化学和光物理谱学表征手段，确定了表面界面态的存在及其本质，提出了全新的界面态理论，在分子水平上催化反应的过渡态及吸附本质。