Department of Chemistry, State University of New York at Binghamton, Binghamton, NY 13902, USA.
Nanoscale. 2018 Feb 22;10(8):3849-3862. doi: 10.1039/c7nr08748a.
Nanoscale alloying constitutes an increasingly-important pathway for design of catalysts for a wide range of technologically important reactions. A key challenge is the ability to control the surface catalytic sites in terms of the alloying composition, thermochemical treatment and phase in correlation with the catalytic properties. Herein we show novel findings of the nanoscale evolution of surface catalytic sites on thermochemically-tuned gold-palladium nanoalloys by probing CO adsorption and oxidation using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) technique. In addition to the bimetallic composition and the support, the surface sites are shown to depend strongly on the thermochemical treatment condition, demonstrating that the ratio of three-fold vs. bridge or atop Pd sites is greatly reduced by thermochemical treatment under hydrogen in comparison with that under oxygen. This type of surface reconstruction is further supported by synchrotron high-energy X-ray diffraction coupled to atomic pair distribution function (HE-XRD/PDF) analysis of the nanoalloy structure, revealing an enhanced degree of random alloying for the catalysts thermochemically treated under hydrogen. The nanoscale alloying and surface site evolution characteristics were found to correlate strongly with the catalytic activity of CO oxidation. These findings have significant implications for the nanoalloy-based design of catalytic synergy.
纳米级合金化是设计各种技术上重要的反应催化剂的重要途径。一个关键的挑战是能够控制合金成分、热化学处理和相方面的表面催化位点，以与催化性能相关联。在此，我们通过原位漫反射红外傅里叶变换光谱（DRIFTS）技术研究了热化学调谐的金钯纳米合金表面催化位点的纳米演化，展示了新型发现。除了双金属成分和载体之外，表面位点强烈依赖于热化学处理条件，表明与在氧气下相比，在氢气下的热化学处理大大降低了三配位 Pd 位与桥位或顶位的比例。这种表面重构进一步得到了同步加速器高能 X 射线衍射与原子配分函数（HE-XRD/PDF）分析纳米合金结构的支持，揭示了在氢气下热化学处理的催化剂的随机合金化程度增强。纳米级合金化和表面位点演化特征与 CO 氧化的催化活性密切相关。这些发现对基于纳米合金的催化协同作用设计具有重要意义。
