小尺寸金纳米粒子的稳定化与催化功能化设计及其催化中高温反应探索

The poor thermal stability of gold nano-catalyst inhabits not only the commercial use but also the application in catalytic reactions at high temperatures. The applicant have successfully stabilized gold nanoparticles by using magnesium gallate spinel as support based on the proposed strategy of constructing lattice matched epitaxial interface between metal and oxide support. The sizes of gold nanoparticles on magnesium gallate spinel remain at about 3 nm after aging at 800 ºC for 28 days! In this proposal, the stable gold-spinel ensemble will be studied as a catalyst directly and as a component for furthering combing with typical “active support” oxide to form new catalytic active structures, in which way the stabilization and catalytic functionalization of small-sized gold nanoparticles can be realized simultaneously. Probe reactions like CO oxidation and methanol selective oxidation will be used to determine the effect of introducing specific oxide onto the gold-spinel ensemble. The relationships between the structures of modified catalysts and their catalytic function will be established and used to guide further optimizations. For the purpose of extending the application of gold nano-catalysts, selected catalysts will be applied in conversions of resource small molecules at high temperatures, for example, dehydrogenation of light alkane to alkene. With successful execution of this project, a universal method for rational constructing of gold nano-catalysts with high activity and high stability can be established. Moreover, this will provide critical guidance for design on the stabilization and catalytic functionalization of other metal nanoparticles.

纳米金催化剂热稳定性差的缺点不但制约了其工业化进程，也限制了其在中高温催化反应中的应用。申请人基于其首倡的构筑晶格匹配的金属与载体氧化物外延界面策略，研究发现镓酸镁尖晶石可有效稳定金纳米粒子，经800℃焙烧28天后金粒子尺寸仍可小于3纳米。本申请基于金与镓酸镁尖晶石这一稳定组合，拟将其直接用作催化剂，或将其作为被稳定的金纳米粒子继续与常规“活性载体”氧化物复合以形成新的催化活性结构，以期同时实现小尺寸金纳米粒子的稳定化与催化功能化。以CO氧化和甲醇选择氧化作为探针反应，探测活性氧化物引入对其催化功能的调控规律，建立催化剂结构与功能关系，并用于指导催化剂结构优化；将优选的催化剂用于催化中高温资源小分子转化，如低碳烷烃脱氢制烯烃反应，拓展纳米金催化剂应用领域。本项目的实施，有望建立一种普适的高活性和高稳定性金纳米催化剂的创制方法，并对其他金属纳米粒子的稳定化和催化功能化设计提供理论指导。

本项目成功制备了一系列抗高温烧结的以MgGa2O4尖晶石为载体的负载型贵金属催化剂。通过多种表征手段和密度泛函理论（DFT）计算揭示了该催化剂体系的稳定结构和稳定机制，以CO氧化、丙烯燃烧和甲醇选择性氧化以及丙烷脱氢制烯烃为探针反应考察了催化剂结构和功能的关系。提出了金属-氧化物“异质孪晶”稳定机理并发展和验证了“先稳定、再活化”这一金纳米粒子稳定化及催化功能化的普适方法。由于纳米Au催化剂具有显著的载体效应，氧化还原性的载体负载的Au纳米催化剂往往可表现出较高的催化活性。我们发现在高温抗烧结的Au/MgGa2O4催化剂表面进行CeO2助剂的修饰可显著提高Au/MgGa2O4催化水汽变换、甲烷燃烧以及CO氧化的反应活性。对水汽变换反应而言，CeO2助剂的添加可将Au/MgGa2O4-800oC-5h样品在450 oC温度下的CO转化率由~1.5%提高至~34.0%；对甲烷燃烧和CO氧化反应而言，CeO2助剂的添加可将甲烷和CO的起燃温度分别降低80 oC和100 oC左右。金基双金属催化剂能显著提高催化活性和选择性以及稳定性，例如，Au-Pt/MgAl2O4催化剂催化丙烷脱氢和Au-Ni/MgAl2O4催化剂催化干甲烷化反应都表现出显著的双金属协同作用。