It has been challenging to synthesize palladium (Pd) and ruthenium (Ru) alloy nanoparticles of solid solution in atomic scale, thus preventing us to study the size effect on the catalytic activity. Here we reported the synthesis of PdRu alloy nanoparticles through polyol reduction method, with the size from 6.0 to 16.6 nm. Elemental mapping indicated that Pd and Ru with 1:1 ratio are evenly distributed over the alloy nanoparticles. XRD of PdRu alloy nanoparticles displayed the characteristic diffraction patterns of face centered cubic (fcc) of Pd and invariable inter plane distance of (1 1 1). The band width of valence state increased from 5.7 to 6.2 eV when the diameter of the nanoparticles increased from 6.0 to 16.6 nm. The size effect of PdRu alloys towards electrooxidation of formic acid was examined on the support of CNT. PdRu alloy nanoparticles with diameter of 15.6 nm performed best among all the samples, 5.7 times higher than that of commercial Pd/C with formic acid. PdRu alloy nanoparticles also demonstrated optimum catalytic activity towards methanol oxidation in alkaline medium solution and the best performance was achieved by PdRu alloy nanoparticles with diameter of 15.6 nm, which was 2.5 times that of Pd/C. A volcano shape dependence of catalytic activity towards both formic acid and methanol oxidation on the size of PdRu alloy nanoparticles was observed. This work provided a vial strategy for the size-controlled synthesis of alloy nanoparticles of solid solution in atomic scale, especially for those elements that are immiscible, unraveled the size effect on the electronic structure and catalytic activity on metal nanoparticles and may shed light on the optimization of alloy noble metal nanoparticles.

以原子尺度合成固溶体的钯（Pd）和钌（Ru）合金纳米颗粒一直是一项挑战，因此阻碍了我们研究尺寸对催化活性的影响。在这里，我们报道了通过多元醇还原法合成PdRu合金纳米粒子的过程，粒径在6.0至16.6 nm之间。元素映射表明，Pd和Ru的比例为1：1，均匀分布在合金纳米颗粒上。PdRu合金纳米粒子的XRD显示了Pd的面心立方（fcc）的特征衍射图和（1 1 1）不变的晶面间距。当纳米粒子的直径从6.0 nm增加到16.6 nm时，价态的带宽从5.7 eV增加到6.2 eV。在CNT的载体上检查了PdRu合金对甲酸电氧化的尺寸效应。直径为15.6 nm的PdRu合金纳米颗粒在所有样品中表现最佳，比市售含甲酸的Pd / C高5.7倍。PdRu合金纳米颗粒还表现出对碱性介质溶液中甲醇氧化的最佳催化活性，直径为15.6 nm的PdRu合金纳米颗粒的性能最佳，是Pd / C的2.5倍。观察到火山形态对甲酸和甲醇氧化的催化活性均与PdRu合金纳米粒子的大小有关。这项工作提供了一种小瓶策略，用于以原子级大小控制固溶合金纳米颗粒的尺寸控制合成，尤其是对于那些不混溶的元素，