Direct Synthesis of Bimetallic Nanoalloys from Corresponding Bulk Alloys
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Direct Synthesis of Bimetallic Nanoalloys from Corresponding Bulk Alloys Chi-Kai Lin, Tao Xu* Department of Chemistry and Biochemistry, Northern Illinois University, DeKalb, IL 60115, USA *
Corresponding author Email: [email protected]
Abstract We report a transformative, all inorganic method-based synthesis of supported bimetallic alloy nanoparticles. We use Pd3Ag as a proof of concept. The method involves breaking down bulk Pd3Ag alloy into the nanoparticles in liquid lithium, converting metallic Li to LiOH, transferring Pd3Ag nanoparticles/LiOH mixture onto non-water soluble supports, followed by leaching off the LiOH with water under ambient conditions. The size of the resulting Pd3Ag nanoparticles was found narrowly distributed around 2.3 nm characterized by transmission electron microscope (TEM). In addition, studies by Xray diffraction (XRD) showed that the resulting Pd3Ag nanoparticles inherited similar structure as the starting bulk Pd3Ag. Introduction An important method of improving the activity of heterogeneous catalyst is to replace monometallic nanoparticles to binary or multi-metallic composition on various catalytic support.1-4 Often, nanoparticles of precious metal alloys exhibit enhanced catalytic selectivity and stability over the monometallic systems. Recent study suggested that the ensemble and/or ligand effects in alloy structures could effectively suppress the formation of undesired side reaction thus to enhance the selectivity of the catalysts. For example, in comparison with pure Pd catalysts, Ag in Pd–Ag catalyst not only increases the selectivity, stability and lifetime in partial hydrogenation of acetylene to ethylene, but also suppresses further hydrogenation of ethylene to ethane.5, 6 In these studies, the atomically intermixing of the different metal atoms were crucial to achieve the desired ensemble or ligand effects. The state-of-the-art synthetic routes for preparing supported nanoparticles of precious metal alloys adopt a bottom-up approach. In such approach, the mixture of the precursory metal ions and/or their ligated molecular complexes are used as the building blocks to construct the desired multimetallic nanoparticles.2, 3, 7-12 This bottom-up method is very successful in controlling the particle size and shape by varying the concentration and the nature of the ionic metal precursors, surfactants, reducing agents, and reaction conditions (temperature, current density, etc.)13-15 However, such approach also introduces many intrinsic complexities. For example, the difference in the reduction potentials of the precursory metal ions often leads to core-shelled structures instead of the alloy structures..2, 16,17 Additional tactics have to be applied such as annealing, selection of alternative precursors or reducing agents.18, 19 However, severe particle agglomeration and support sintering may occur when the annealing has to be carried out at elevated temperature.20, 21 In fact, many bulk precious metal alloys with atomically intermixed alloy structure could only be formed at extremely
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