自从单原子催化剂Pt1/FeOx在2011年被报道以来，单原子和单团簇催化剂在各种催化过程中被广泛研究：例如CO氧化、水煤气转化、甲烷转化、选择性加氢、析氢反应、氧还原反应等。单原子催化剂不仅使具备催化活性的原子利用率最大化，而且由于其活性中心的确切结构，也导致很好的选择性和活性。单原子催化剂的稳定性在很大程度上取决于单原子与底物载体之间的结合，特别是在实际催化条件下。本论文采用密度泛函理论和分子动力学模拟的理论计算方法，探究了氧化物负载的金单原子催化剂的稳定性规律；电化学剥离法制备单原子催化剂的理论方法；石墨炔负载的金属三原子团簇催化剂；金属单团簇催化合成氨的反应机理。我们对氧化铈负载的金单原子催化剂的热力学稳定性、动力学稳定性、催化性能等方面进行了深入的讨论，并设计了一种基于化学势的模型，分析实际反应条件对催化剂稳定性和反应活性的影响，如反应温度、分压、负载金属的大小和载体的可还原性。通过对化学势的比较，我们发现金单原子更倾向于吸附在CeO2台阶位。通过制备具有丰富台阶位置的CeO2载体，可以提高单原子催化剂的分散性和稳定性。在保持目标单原子和单团簇催化剂稳定的同时，我们发现存在一个重要的电化学电位窗口，利用单原子和单团簇之间化学势的差别，可以用电化学氧化刻蚀方法清除多余金属纳米颗粒。基于该方法，第一步可以预沉积任何金属，第二步控制电位进行电化学氧化刻蚀，使得生产高质量单原子和单团簇催化剂成为一条简单的途径。随后我们研究了以石墨炔为载体的三原子团簇催化剂的稳定性，电子结构和催化性能。通过研究单团簇的实际催化反应性质，我们考察Fe3单团簇的合成氨催化反应活性。Fe3团簇可以稳定地锚定在Al2O3(010)表面上，其氧化还原能力、高自旋极化特性和低氧化态使得其可以有效活化N2，在Fe3单团簇的缔合机理中，*NNH解离仅具有0.45 eV的势垒。这种缔合机制打破了制约氮气解离机理的Br?nsted–Evans–Polanyi (BEP)关系，从而绕过了火山曲线一侧的限制，为设计新型低温低压合成氨催化剂提供了理论指导。上述结果可以帮助理解单原子和单团簇催化剂在实际催化反应条件下的稳定性，为高稳定性、高活性、高选择性的单原子催化剂的设计和制备提供理论指导。
Single-atom catalysis has become a new frontier in heterogeneous catalysis since 2011. As a result, single atom catalyst (SAC) and single cluster catalyst (SCC) have attracted extensive attentions in recent years. It has been reported recently that SACs and SCCs could catalyze reactions with remarkable reactivity for, e.g., CO oxidation, water gas shift, methanol reforming, and ethanol dehydrogenation. SACs maximize the utilization of expensive metals by exposing every single metal atom to reactants. The configurations of SACs can be highly consistent, leading to excellent selectivity comparing to supported nanoparticles and metal surfaces that often feature multiple active sites. The stability of SACs strongly depends on the interaction between the single-atom (SA) and substrate used, especially in realistic catalytic reaction conditions. Based on Density Functional Theory (DFT) and ab initio molecular dynamics (AIMD) simulations, we first explored the stability of supported gold SACs. Then a general and efficient strategy is investigated for the synthesis of high-quality single-atom catalysts and single-cluster catalysts via an electrochemical route. And at last we explored oxides and carbon materials anchored Fe3 clusters as a heterogeneous catalyst for ammonia synthesis via an NNH associative mechanism. In the context of CO oxidation on ceria supported gold single atom catalysts, all the thermodynamic, reactive and kinetic aspects relative to the metal single atom catalysts are extensively discussed. Both the stability and reactivity are found to strongly depend on the realistic thermodynamic conditions such as reaction temperature, partial pressure, size of nanoparticles (NPs), and the reducibility of support. We propose an electrochemical route as a general method for preparing SACs with both high purity and high loading amount. Starting from the well-defined substrate with metal atoms pre-deposited by routine techniques that do not require precise control, we find that there exists a significantly large electrochemical potential window, with applied voltage in which all metal forms other than the strongly bound SAs are oxidized and leached out. Thus, this formulates an efficient and general strategy to prepare pure SACs with high loading amount of SAs. Then, we have investigated the graphdiyne supported metal trimer clusters and its stability, electronic structures, and reactivities.We propose a single-cluster catalyst with active center of Fe3 cluster that is anchored on the Al2O3(010) surface. In this work, it is shown that the direct dissociation of *N2 on this center is difficult. Instead, the adsorbed *N2 species is easily hydrogenated to form the *NNH species, which has a much lower N-N bond dissociation barrier than that of *N2. The large spin-polarization of Fe3 is also responsible for N2 activation, and the low oxidation state of Fe makes it work as an electron reservoir, regulating the charge variation of the whole process. The associative mechanism we found here bypasses the Br?nsted–Evans–Polanyi (BEP) relation and thus the limitation underlying one side of the volcano curve. Such an anchored Fe3? center bridges the gap between heterogeneous and homogeneous catalysts of iron, serving as a heterogeneous catalyst design that enables the associative mechanism.These results provide a new understanding of stability and activity of SACs and SCCs, as well as theoretical support for the design of stable catalysts with high loading concentration, activity and selectivity.
