Bimetallic Cu/Pd Nanoparticles As Low Temperature Sulfur-Tolerant WGS Catalysts

Bimetallic Cu/Pd nanoparticles as low temperature sulfur-tolerant WGS catalysts

SeongUk Yun and Vadim V. Guliants

Chemical Engineering, University of Cincinnati, Cincinnati OH 45221

The global interest in the water-gas shift (WGS) reaction as a method of making hydrogen from coal-gasification products increased significantly in recent years. However, typical low temperature WGS catalysts are easily deactivated by sulfur compounds present in coal-derived syngas. According to recent theoretical predictions, Cu and Pd are expected to be promising sulfur-tolerant WGS catalysts. In addition, bimetallic Cu/Pd nanoparticles exhibiting bulk alloy, surface alloy, and core-shell structures are expected to show differences not only in the WGS activity, but also tolerance to sulfur.

Several bimetallic Cu/Pd catalysts were synthesized in our laboratory and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), physi/chemisorption, and temperature-programmed reduction (TPR) in H₂. The TPR analysis showed that the presence of Cu facilitated the reduction of active metals at lower temperatures. The TGA analysis revealed a strong interaction between Cu, Pd and oxide support suggesting solid alloy information. The XRD indicated that the size of these metallic nanoparticles was in the 15-20 nm range depending on the Cu/Pd ratio. The size and shape of supported Cu/Pd nanoparticles were determined by TEM. The WGS catalytic activity of catalysts have been evaluated in the WGS reaction at 398-723 K under atmospheric pressure in a fixed-bed microreactor employing the feed of 10% CO and 20% H₂O (balance He). Significant improvement in the WGS catalytic activity was observed by optimizing the Cu/Pd ratio. These novel bimetallic catalysts showed improved sulfur resistance during WGS reaction.