Department of Chemical and Biological Engineering, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
J Am Chem Soc. 2010 Jun 2;132(21):7418-28. doi: 10.1021/ja101108w.
We report on the first-principles-guided design, synthesis, and characterization of core-shell nanoparticle (NP) catalysts made of a transition metal core (M = Ru, Rh, Ir, Pd, or Au) covered with a approximately 1-2 monolayer thick shell of Pt atoms (i.e., a M@Pt core-shell NP). An array of experimental techniques, including X-ray diffraction, Fourier transform infrared spectroscopy, high resolution transmission electron microscopy, and temperature-programmed reaction, are employed to establish the composition of the synthesized NPs. Subsequent studies of these NPs' catalytic properties for preferential CO oxidation in hydrogen-rich environments (PROX), combined with Density Functional Theory (DFT)-based mechanistic studies, elucidate important trends and provide fundamental understanding of the reactivity of Pt shells as a function of the core metal. Both the PROX activity and selectivity of several of these M@Pt core-shell NPs are significantly improved compared to monometallic and bulk nonsegregated bimetallic nanoalloys. Among the systems studied, Ru@Pt core-shell NPs exhibit the highest PROX activity, where the CO oxidation is complete by 30 degrees C (1000 ppm CO in H(2)). Therefore, despite their reduced Pt content, M@Pt core-shell NPs afford the design of more active PROX catalysts. DFT studies suggest that the relative differences in the catalytic activities for the various core-shell NPs originate from a combination of (i) the relative availability of CO-free Pt surface sites on the M@Pt NPs, which are necessary for O(2) activation, and (ii) a hydrogen-mediated low-temperature CO oxidation process that is clearly distinct from the traditional bifunctional CO oxidation mechanism.
我们报告了一种基于第一性原理设计、合成和表征的核壳纳米粒子（NP）催化剂，该催化剂由过渡金属核（M=Ru、Rh、Ir、Pd 或 Au）组成，表面覆盖有约 1-2 个单层厚的 Pt 原子壳（即 M@Pt 核壳 NP）。采用了一系列实验技术，包括 X 射线衍射、傅里叶变换红外光谱、高分辨率透射电子显微镜和程序升温反应，以确定合成 NP 的组成。随后，对这些 NP 在富含氢气的环境中（PROX）优先氧化 CO 的催化性能进行了研究，并结合基于密度泛函理论（DFT）的机理研究，阐明了重要趋势，并提供了对 Pt 壳作为核金属函数的反应性的基本理解。与单金属和块状非分离双金属纳米合金相比，几种 M@Pt 核壳 NP 的 PROX 活性和选择性都得到了显著提高。在所研究的体系中，Ru@Pt 核壳 NP 表现出最高的 PROX 活性，其中 CO 氧化在 30°C（1000ppm CO 在 H2 中）完全完成。因此，尽管它们的 Pt 含量减少，但 M@Pt 核壳 NP 提供了更具活性的 PROX 催化剂的设计。DFT 研究表明，各种核壳 NP 的催化活性的相对差异源自于（i）M@Pt NPs 上 CO 自由 Pt 表面位点的相对可用性，这对于 O2 活化是必要的，以及（ii）一种明显不同于传统双功能 CO 氧化机制的氢介导的低温 CO 氧化过程。
