Bimetallic PdZn catalysts for the steam reforming of methanol

ZnO-supported palladium-based catalysts have been shown in recent years to be both active and selective towards the steam reforming of methanol, although they are still considered to be less active than traditional copper-based catalysts. In this work, we prepared Pd/ZnO/Al₂O₃ catalysts which were exposed to in-situ oxidation reduction cycles, and were characterized by XRD, TEM, EDS, and FTIR in order to elucidate their bulk and surface characteristics. We show that our Pd-based catalysts are not only more active than Cu-based catalysts after the initial 48 hour deactivation period, but they can be easily regenerated by oxidation in air at 420°C followed by re-exposure to reaction conditions at 250°C. Reduction at high temperatures (>420°C) led to Zn loss from the alloy nanoparticle surface resulting in lowered catalyst activity. However, the catalysts exhibited self-healing properties as activity was regained with time on stream under reaction conditions alone. These findings illustrate that the nanoparticle surface is dynamic and changes drastically depending on the environment leading to highly stable catalysts, and that elevated reduction temperatures are not necessary to achieve high CO₂ selectivity as commonly believed for PdZn alloy catalysts.