Characteristics of adsorbed CO and CH3OH oxidation reactions for complex Pt/Ru catalyst systems

Pt/Ru powder catalysts of the same nominal Pt to Ru composition were prepared using a range of methods resulting in different catalyst properties. Two PtRu alloy catalysts were prepared, one of which has essentially the same surface and bulk Pt to Ru composition, while the second catalyst is surface enriched with Ru. Two powders consisting of non-alloyed Pt phases and surfaces enriched with Ru were also prepared. The oxidation state of the surface Ru of the latter two catalysts is mainly metallic Ru or Ru-oxides. The catalyst consisting of Ru-oxides was formed at 500 °C. Part of this catalyst was then reduced in a H2 atmosphere under “mild” conditions, thus catalyst properties such as particle size are not changed, as they are locked in during previous high temperature treatment. The oxidation kinetics of adsorbed CO (COads) and solution CH3OH were studied and compared to the Ru ad-metal state and Pt to Ru site distribution of the as-prepared catalysts. The kinetics of the COads oxidation reaction were observed to be slower for the catalyst containing Ru-oxides as opposed to mainly Ru metal. The CH3OH oxidation activities measured per Pt surface area, i.e., the catalytic activities are better (by ca. seven times) for the alloy catalysts than the non-alloyed Pt/Ru catalysts. The latter two catalysts showed essentially the same catalytic CH3OH oxidation activities, i.e., independent of the Ru ad-metal oxidation state of the as-prepared catalysts. Furthermore, it is shown that COads oxidation experiments can be used to extract characteristics that allow the comparison of catalytic activities for the COads oxidation reaction and Pt to Ru site distribution for complex catalyst systems.