Iodide-induced differential control of metal ion reduction rates: synthesis of terraced palladium–copper nanoparticles with dilute bimetallic surfaces
Iodide-induced differential control of metal ion reduction rates: synthesis of terraced palladium–copper nanoparticles with dilute bimetallic surfaces
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DOI：
10.1039/c8ta06256k
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发表时间：
2018-11
影响因子：
--
通讯作者：
M. King;M. Personick
中科院分区：
文献类型：
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作者：
M. King;M. Personick
具有高密度的原子台阶和边缘位点的金属纳米颗粒提供了增加的配位不足的表面原子群体，与低折射率的多面或块状材料相比，这可以增强这些材料的催化活性。然而，简单地增加反应性可导致不期望的非选择性副产物的同时增加。在这些反应性阶梯特征处并入第二金属提供了精细衰减反应性以增加选择性的理想途径。合成具有可调表面特征的纳米材料的一个主要挑战是需要在含有贵金属和非贵金属的结构中弥合前体还原电位和金属晶格参数的差异，所述表面特征对于基础催化研究是理想的。我们报告使用低微摩尔浓度的碘离子作为一种手段，差分控制贵金属（钯）和非贵金属（铜）的相对还原率。该系统中的碘化物增加钯离子的还原速率，同时减慢铜离子的还原速率，因此提供了使用大多数其他报道的调节金属离子还原速率的方法无法实现的控制程度。由碘离子提供的金属离子还原的这种差异控制使得能够获得纳米颗粒生长条件，其中通过铜欠电位沉积控制钯纳米颗粒生长成为可能，从而产生独特的阶梯状纳米颗粒。由于它们的表面组成，这些阶梯状纳米颗粒在气相乙醇氧化中表现出对乙醛的选择性增加。
Metal nanoparticles possessing a high density of atomic steps and edge sites provide an increased population of undercoordinated surface atoms, which can enhance the catalytic activity of these materials compared to low-index faceted or bulk materials. Simply increasing reactivity, however, can lead to a concurrent increase in undesirable, non-selective side products. The incorporation of a second metal at these reactive stepped features provides an ideal avenue for finely attenuating reactivity to increase selectivity. A major challenge in synthesizing bimetallic nanomaterials with tunable surface features that are desirable for fundamental catalytic studies is a need to bridge differences in precursor reduction potentials and metal lattice parameters in structures containing both a noble metal and a non-noble metal. We report the use of low micromolar concentrations of iodide ions as a means of differentially controlling the relative reduction rates of a noble metal (palladium) and a non-noble metal (copper). The iodide in this system increases the rate of reduction of palladium ions while concurrently slowing the rate of copper ion reduction, thus providing a degree of control that is not achievable using most other reported means of tuning metal ion reduction rate. This differential control of metal ion reduction afforded by iodide ions enables access to nanoparticle growth conditions in which control of palladium nanoparticle growth by copper underpotential deposition becomes possible, leading to the generation of unique terraced bimetallic particles. Because of their bimetallic surface composition, these terraced nanoparticles exhibit increased selectivity to acetaldehyde in gas phase ethanol oxidation.