纳米金/多级孔磷酸铝-氧化硅(APO-SiO2)复合材料制备及催化环己烷选择氧化研究

KA oil (cyclohexanone and cyclohexanol), prepared by cyclohexane selective oxidation using O2 as oxidant and homogeneous Co salts as catalyst, are important raw materials for adpic acid production, but low efficency and not environmentally friendly with the present industrial route make it urgently necessary be improved. nano gold heterogeneous catalysts can be prepared in a simple way and show high activity for cyclohexane selective oxidation. The methods for preparing nano gold heterogeneous catayst are by one-pot in-situ reduction or coordination with the organic ligand modified on support. These two methods suffer from the disadvantages such as low stablity with organic ligand and weak interaction between nano gold and support, which cause gradual growth of gold nanoparticles and loss of activity. The proposed nano gold /hierarchically porous APO-SiO2 heterogeneous catalyst in this project is prepared by self-assembling of nano gold collid in-situ reducted and stabilized by polyoxometalate, isopropyl alcohol aluminum, phosphoric acid, aminopropyl trimethoxysilane in solution promoted by long-chain aliphatic amine/triblock polymer P123 double template. Polyoxometalte as reductant and protecting reagent can effectively inhibit the agregation of gold nanoparticles, and the hierarchical structure of support has promotion effect on nanogold-support interaction and disperson of reactant and product molecules. This modified preparation of nano gold heterogeneous catalyst proposed in this project will effectively solve the problem of deactivation due to the agregation of gold nanoparticles, is meanful in realizing industrial application of green oxidation of cyclohexane using nano gold as catalyst. The computional chemistry study on the reaction mechanism of cyclohexane oxidation using nanogold/hierarchically porouos catalyst will further enrich the theory of gold catalysis in the field of catalytic oxidation.

KA油（环己酮和环己醇）是生产己二酸的重要原料，现有工业路线以均相钴盐为催化剂，氧气或空气氧化环己烷生产，效率低，能耗和污染大。纳米金多相催化剂制备简单，活性和选择性高，是实现环己烷绿色氧化的较好催化剂，但一锅法原位还原和载体修饰有机基团配位的制备方法，由于纳米金-载体作用弱和有机基团稳定性低，金纳米粒子易团聚长大导致活性下降。本项目以还原态杂多酸盐原位还原并稳定纳米金，在有机胺和三嵌段聚合物P123双模板作用下，和异丙醇铝、磷酸、硅酸乙酯、胺丙基三甲氧基硅烷自组装制备纳米金 /多级孔磷酸铝-氧化硅催化剂，杂多酸盐为稳定剂能有效抑制纳米金团聚，多级孔载体能促进载体-纳米金的相互作用。本项目对纳米金多相催化剂的制备改进有望有效解决纳米金团聚失活问题，在实现纳米金多相催化剂在环己烷氧化上的工业应用，促进KA油绿色生产方面有重要意义，对环己烷氧化机理的计算化学研究，将丰富纳米金催化氧化理论。

饱和C-H活化和选择性氧化获得单加氧产物一直是催化研究和工业应用领域中的研究重点。本项目研究的纳米金/分级多孔APO-SiO2复合催化剂，以杂多酸盐稳定纳米金为活性成分并以分级多孔结构APO –SiO2为载体，旨在解决纳米金多相催化体系中金纳米粒子易团聚失活问题，改善纳米金多相催化剂的稳定性和催化活性。本项目纳米金/分级多孔APO-SiO2催化剂由系列夹心型杂多酸盐稳定纳米金溶胶，再和可水解载体前驱体作用通过控制水解-水热法合成。对制备的催化剂进行了详细表征，结果表明纳米金粒径呈窄分布并保持高分散不易团聚，杂多酸盐和纳米金复合表现为正协同效应，促进活性协同增强和目标产物选择性提高。通过合成条件控制，催化剂的分级多孔结构成功形成，这一设计结构既能稳定活性成分不易流失，又能利于反应中心易接触，降低反应物和产物的扩散阻力。环己烷选择性氧化为复杂的自由基链式机理，在氧化还原性催化剂作用下，自由基和氧化还原中心通过电子转移作用可加速过氧化中间产物的分解生成单加氧目标产物。夹心杂多酸盐的配位能力和电子传递特性，能降低反应物分子的吸附和活化自由能，提高反应效率和目标产物选择性。在基金经费资助下，我们进一步研究了水解-缩聚条件的控制和材料微观结构的关系，发现通过控制水解反应条件和水解缩聚程度，相分离可控制在纳米维度内，从而形成均匀纳米复合结构，为了进一步探讨催化剂微观形貌控制和催化性能的关系，我们制备了具有微球形貌，和纤维堆积形貌的纳米金（钯）负载催化剂，表明改变多相催化过程的表面微环境，增加活性中心暴露，缩短扩散路径能一定程度提高催化效率。本项目的研究成果，在丰富C-H活化理论，对催化剂结构设计和控制，建立催化剂结构性能的构效关系方面具有一定科学意义，在发展纳米金多相催化剂在选择性氧化上的工业应用方面具有重要意义和应用前景。