Sulaiman Kazeem O, Zubair Muhammad, King Graham, Bedford Nicholas M, Scott Robert W J
Department of Chemistry, University of Saskatchewan, 110 Science Place, Saskatoon, Saskatchewan S7N 5C9, Canada.
School of Chemical Engineering, University of New South Wales, Sydney, New South Wales 2052, Australia.
Phys Chem Chem Phys. 2022 Oct 19;24(40):24834-24844. doi: 10.1039/d2cp02682a.
Synchrotron X-ray total scattering measurements and accompanying pair distribution function (PDF) analyses are an excellent characterization technique to complement both transmission electron microscopy (TEM) and extended X-ray absorption fine structure (EXAFS) spectroscopy methods for detailed structural studies of atom-precise metal clusters. Herein, we study the thermal activation of Au(SR) and Ag(SR) clusters on alumina supports differential PDF (dPDF) analyses to compare structural changes in the metal clusters upon thermal activation in air. The metal-metal interatomic distances in Au(SR) and Ag(SR) clusters as measured by the dPDF method are comparable with those measured single-crystal crystallographic and EXAFS methods. Compared to EXAFS analysis, dPDF data can also provide high-temperature, non-element specific, longer range structural information with excellent temporal resolution. TEM and dPDF results show that Ag(SR) systems behave significantly differently than analogous Au(SR) systems upon thermal activation. Atom-precise Au clusters on alumina supports show continuous growth in particle size with increasing activation temperature due to particle coalescence upon thermal deprotection, and grow to an average size of 11.2 ± 2.1 nm for samples thermally activated at 650 °C. Conversely, analogous Ag clusters on alumina supports show particle size growth to mid-sized particles (3.2 ± 0.4 nm) at activation temperatures of 450 °C, beyond which the Ag particles then undergo thermal degradation to give smaller Ag clusters with an average size of 1.4 ± 0.2 nm for samples thermally activated at 650 °C. The significant difference in the behaviours of atom-precise, thiolate-protected Au and Ag clusters upon thermal activation emphasizes the development of distinct activation protocols for different metal cluster systems.
同步加速器X射线全散射测量及伴随的对分布函数（PDF）分析是一种出色的表征技术，可补充透射电子显微镜（TEM）和扩展X射线吸收精细结构（EXAFS）光谱方法，用于对原子精确的金属簇进行详细的结构研究。在此，我们通过差分PDF（dPDF）分析研究了氧化铝载体上Au(SR)和Ag(SR)簇的热活化，以比较金属簇在空气中热活化时的结构变化。通过dPDF方法测量的Au(SR)和Ag(SR)簇中的金属-金属原子间距离与通过单晶晶体学和EXAFS方法测量的结果相当。与EXAFS分析相比，dPDF数据还可以提供具有出色时间分辨率的高温、非元素特异性、更长范围的结构信息。TEM和dPDF结果表明，热活化时Ag(SR)体系的行为与类似的Au(SR)体系有显著不同。氧化铝载体上原子精确的Au簇由于热脱保护时颗粒聚结，随着活化温度升高，粒径持续增长，对于在650°C热活化的样品，平均粒径增长到11.2±2.1nm。相反，氧化铝载体上类似的Ag簇在450°C的活化温度下粒径增长到中等尺寸颗粒（3.2±0.4nm），超过该温度后，Ag颗粒会发生热降解，对于在650°C热活化的样品，会生成平均尺寸为1.4±0.2nm的较小Ag簇。原子精确的、硫醇盐保护的Au和Ag簇在热活化时行为的显著差异强调了针对不同金属簇体系开发不同活化方案的必要性。
