Department of Chemistry, Iowa State University, Ames, Iowa 50011, USA.
Nanoscale. 2019 Mar 21;11(12):5336-5345. doi: 10.1039/c8nr10067e.
The outstanding catalytic activity and chemical selectivity of intermetallic compounds make them excellent candidates for heterogeneous catalysis. However, the kinetics of their formation at the nanoscale is poorly understood or characterized, and precise control of their size, shape and composition during synthesis remains challenging. Here, using well-defined Pt nanoparticles (5 nm and 14 nm) encapsulated in mesoporous silica, we study the transformation kinetics from monometallic Pt to intermetallic PtSn at different temperatures by a series of time-evolution X-ray diffraction studies. Observations indicate an initial transformation stage mediated by Pt surface-controlled intermixing kinetics, followed by a second stage with distinct transformation kinetics corresponding to a Ginstling-Brounstein (G-B) type bulk diffusion mode. Moreover, the activation barrier for both surface intermixing and diffusion stages is obtained through the development of appropriate kinetic models for the analysis of experimental data. Our density-functional-theory (DFT) calculations provide further insights into the atomistic-level processes and associated energetics underlying surface-controlled intermixing.
金属间化合物卓越的催化活性和化学选择性使它们成为多相催化的优秀候选者。然而，它们在纳米尺度上形成的动力学过程还了解甚少或尚未得到明确的描述，并且在合成过程中精确控制其尺寸、形状和组成仍然具有挑战性。在这里，我们使用在介孔硅中封装的具有明确结构的 5nm 和 14nm 的 Pt 纳米颗粒，通过一系列的时间分辨 X 射线衍射研究，在不同温度下研究了从单金属 Pt 到金属间 PtSn 的转变动力学。观察结果表明，在初始阶段，Pt 表面控制的混合动力学起中介作用，随后进入具有明显转变动力学的第二阶段，这对应于金斯丁-布朗斯坦（G-B）类型的体扩散模式。此外，通过为实验数据分析开发适当的动力学模型，获得了表面混合和扩散两个阶段的激活能垒。我们的密度泛函理论（DFT）计算为表面控制的混合相关的原子级过程和相关能量学提供了进一步的见解。
