金基三元团簇的结构及其对氧气活化机制的理论研究

Recently, it has been observed experimentally that the Au-based trimetallic clusters (containing Au and other two different metal elements) often exhibit more unique physical and chemical properties, higher catalytic activity and selectivity in some oxidation reactions, than the traditional Au-based bimetallic clusters and the pure Au clusters. In this project, by means of density functional theory (DFT), we will conduct a systematical investigation regarding: i) the stable structures, electronic properties and bonding characters of the small- and medium-sized Au-based trimetallic clusters; ii) the relations between the reactivity of clusters towards O2 activation and the size, charge state, component of clusters, by using the dissociation of O2 as probe reaction; iii) the effects of the co-adsorption of reaction substrate (such as ethanol, formaldehyde, ethylene, water) on O2 activition. The quantum size effect of the activation and dissociation of O2 on Au-based trimetallic clusters will be discussed by changing the cluster size, the element type and the composition of the doped metal atoms; the formation of the possible oxidative species will be searched by simulating the cooperative adsorption of reaction substrate and O2 on clusters. Our theoretical results are expected to provide valuable information and guidance for designing and developing novel Au-based trimetallic clusters catalysts in oxidation reactions.

最近实验上发现当在金团簇中掺入两种不同的金属元素时，形成金基三元团簇具有比金基二元团簇（含一种掺杂原子）和单一金团簇更为独特的物理化学性质，在一些催化氧化反应中活性更高、选择性更强。本项目拟采用密度泛函方法，以中小尺寸金基三元团簇为研究对象，系统研究它们的稳定结构、电子性质和成键规律。进一步以O2的吸附解离为探针反应，研究金基三元团簇化学成分和电子结构特征与O2的活化、解离反应活性的关系，以及反应底物（如乙醇、甲醛、乙烯、水分子）的共吸附对O2活化机制的影响。通过改变金基三元团簇的尺寸、掺杂原子的种类和比例，探讨O2在金基三元团簇上活化和解离过程的量子尺寸效应; 模拟反应底物和O2在金基三元团簇表面的共同吸附，寻找反应底物存在情况下可能产生的活性氧物种，为实验上设计和发展新型金基三元团簇催化剂提供一定的理论基础。

由于增强的催化活性、改进的选择性，金基三元团簇物理及化学性质的研究目前已成为国际金催化领域的研究热点。本研究项目基于密度泛函理论计算，以金基三元团簇为研究对象，取得的主要研究成果概括为：（1）探讨了一系列金基三元团簇(Au/Pd/Pt、Au/Ag/Pt、Au/Ag/Pd、Au/Ag/Cu、Au/Pd/Cu)的结构、稳定性及电子性质随团簇化学成分、尺寸及电子态的演化关系；（2）研究了AuxPdyPtz(x+y+z=7)及AuxAgyCuz(x+y+z=3-6)三元团簇对O2分子的吸附行为和活化机制。结果表明与单一金团簇和金基二元团簇相比，金基三元团簇能更有效地活化O-O键，促进O2分子解离为O 原子；（3）模拟了H2分子在PdaCubAuc (a+b+c=7)三元团簇上的吸附行为。当团簇中Au、Pd、Cu三种原子比例接近时，团簇对H2分子的吸附能较高，对H-H的活化效应最为明显。本项目研究工作的开展为金基三元团簇物理和化学性质的深入研究、催化氧化反应中新型金基三元金属催化剂的设计和开发提供了一定的理论指导。