Ethylene Dehydrogenation on Pt4,7,8 Clusters on Al2O3: Strong Cluster Size Dependence Linked to Preferred Catalyst Morphologies
Ethylene Dehydrogenation on Pt4,7,8 Clusters on Al2O3: Strong Cluster Size Dependence Linked to Preferred Catalyst Morphologies
复制标题
DOI：
10.1021/acscatal.7b00409
复制
发表时间：
2017-05-01
期刊：
影响因子：
12.9
通讯作者：
Anderson, Scott L.
中科院分区：
文献类型：
--
作者：
Baxter, Eric T.;Ha, Mai-Anh;Anderson, Scott L.
对Al_2O_3表面Pt_n（n = 4，7，8）团簇催化乙烯脱氢反应进行了实验和理论研究。簇的质量选择，沉积在氧化铝载体上，并探测低能量离子散射，程序升温脱附和反应的C2 D4和D-2，X射线光电子能谱，密度泛函理论和统计力学理论的组合。Pt-7被认为是最具催化活性的簇，而Pt-4和Pt-8表现出相当的活性。较高的活性可以与簇结构，特别是簇形态的分布在催化条件下与乙烯的温度和覆盖率。具体而言，虽然氧化铝上的Pt-7和Pt-8具有非常相似的棱柱形全局最小几何形状，但Pt-7在较高温度下也可获得单层异构体，其在增加乙烯覆盖率时在簇合物催化剂系综中变得越来越占主导地位。单层异构体的特征在于来自载体的更大的电荷转移和更多的激活乙烯脱氢而不是氢化或解吸的结合位点。还研究了尺寸依赖的对焦化和失活的敏感性。我们的研究结果表明，团簇的催化活性的大小依赖于不是一个简单的属性的单个团簇的几何形状，但在相关条件下的统计系综的平均值。为
Catalytic dehydrogenation of ethylene on size-selected Pt-n (n = 4, 7, 8) clusters deposited on the surface of Al2O3 was studied experimentally and theoretically. Clusters were mass-selected, deposited on the alumina support, and probed by a combination of low energy ion scattering, temperature-programmed desorption and reaction of C2D4 and D-2, X-ray photoelectron spectroscopy, density functional theory, and statistical mechanical theory. Pt-7 is identified as the most catalytically active cluster, while Pt-4 and Pt-8 exhibit comparable activities. The higher activity can be related to the cluster structure and particularly to the distribution of cluster morphologies accessible at the temperatures and coverage with ethylene in catalytic conditions. Specifically, while Pt-7 and Pt-8 on alumina have very similar prismatic global minimum geometries, Pt-7 at higher temperatures also has access to single-layer isomers, which become more and more predominant in the cluster catalyst ensemble upon increasing ethylene coverage. Single-layer isomers feature greater charge transfer from the support and more binding sites that activate ethylene dehydrogenation rather than hydrogenation or desorption. Size-dependent susceptibility to coking and deactivation was also investigated. Our results show that size-dependent catalytic activity of clusters is not a simple property of single cluster geometry but the average over a statistical ensemble at relevant conditions. for