(296a) Supported Bimetallic Cu/Ni Nanoparticles for Low–Temperature Water-Gas-Shift Reaction

Recently, the water-gas shift (WGS) reaction has become very important 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. However, Ni-based catalysts also catalyze methanation side-reaction under water-gas-shift reaction conditions. It is expected that the Cu addition to Ni can modify the Ni ensemble properties and electronic structure by the Cu-Ni alloy formation to improve the WGS reaction and suppress the methanation reaction. The goal of this work is to explore supported bimetallic Cu-Ni nanoparticles for low temperature water-gas-shift reaction in order to suppress the undesirable methanation activity. The activity and selectivity in many metal-catalyzed reactions were shown to be dependent on the size and structure of metal particles on the nanoscale. For these reasons, we investigated the effect of size and chemical compositions of Cu/Ni nanoparticles on their catalytic properties in the WGS reaction.

The supported bimetallic Cu-Ni catalysts were synthesized in water-in-oil microemulsions and by a modified polyol route. These catalysts were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction, X-ray photoelectron spectroscopy (XPS), thermogravimetric analysis, N₂O and H₂ chemisorption, temperature programmed reduction (TPR) in H₂, and N₂ physisorption at 77K. The TPR analysis showed that the presence of Cu facilitated the reduction of Ni at lower temperatures, indicating a strong interaction between Cu and Ni leading to solid alloy formation. The X-ray diffraction indicated that the size of these alloy particles was in the 15-50 nm range depending on the Cu/Ni content. The size and shape of supported Cu-Ni nanoparticles were determined by TEM. These catalysts have been evaluated in the water gas shift reaction at 423-673 K under atmospheric pressure in a fixed-bed microreactor employing the feed of 10% CO and 20% H₂O (balance He). It was observed that the Cu/Ni=20/80 wt.% nanoparticle catalysts exhibited improved WGS and decreased methanation activity as compared to both pure Cu and Ni nanoparticle catalysts.