(292d) Supported Bimetallic Cu/Ni Core-Shell Nanoparticles: Controlled Synthesis and Catalytic Activity in Water-Gas-Shift Reaction

Abstract: Recently, the water-gas shift (WGS) reaction has attracted renewed attention because of production of high purity H2 in conjunction with fuel cell power generation. It has been predicted that Cu and Ni are promising active transition metals for the water-gas-shift reaction based on theoretical (DFT) calculations. Supported bimetallic nanoparticles with a core-shell structure are being considered as new and promising catalysts with enhanced catalytic activity and improved selectvitiy. Thus, the goal of this work is to explore supported bimetallic nanoparticle catalysts comprising a Cu core coated with Ni shells (or vice versa) for the WGS reaction. The activity and selectivity in many metal-catalyzed reactions were shown to be dependent on the size, structure and composition of metal particles on the nanoscale. For these reasons, we investigated the effect of size and structure for three sets of supported Cu-Ni nanoparticles, namely, containing (a) a Cu core and Ni shell (Cu@Ni), (b) Ni core and Cu shell (Ni@Cu), and (c) Cu-Ni mixed alloy nanoparticles on their catalytic properties in the WGS reaction. The supported bimetallic Cu@Ni, Ni@Cu, and CuNi alloy nanoparticles were synthesized by a successive chemical reduction, a redox-transmetallation method, and simultaneous reduction, respectively. These catalysts were characterized by scanning electron microscopy (SEM), high resolution transmission electron microscopy (HRTEM), scanning transmission electron microscopy (STEM) equipped with an HAADF detector, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis (TGA), CO chemisorption, UV-vis spectroscopy. The size and shape of supported Cu@Ni and Ni@Cu nanoparticles were determined by HRTEM and STEM. The metal composition distributed in the core and shell regions were characterized by HAADF-STEM. The X-ray diffraction clearly showed the formation of Cu or Ni core structures. These catalysts were evaluated for the WGS reaction at 423-673 K under normal atmospheric pressure in a fixed-bed glass reactor connected to a gas chromatograph. Supported Cu@Ni and Ni@Cu nanoparticles showed much greater WGS activities, as compared to traditional CuNi nano-alloys. Specifically, the Cu core with an approximately 1-2 monolayer thick Ni shell exhibited a greater WGS activity as compared to traditional CuNi nano-alloys.