Reducibility and Catalytic Activity of Nickel-platinum Composite Oxide Catalysts

Abstract

The reduction characteristics of silica supported nickel-platinum composite oxide catalysts were investigated by a thermal analysis method. The catalysts were prepared by an impregnation. The reduction peak of platinum oxide was found at 70°C and that of a mechanical mixture of NiO and PtO₂ was found at 70°C and 240°C. However, the nickel-platinum composite oxide showed a single reduction peak, at a temperature lower than that for nickel oxide. The results suggest that the phenomenon is attributable to hydrogen spillover from Pt (or Pd) to nickel oxide or the formation of a Ni-Pt composite oxide.
The catalytic activity was tested with the hydrogenation of ac etone. The nickel catalyst, when reduced at temperatures higher than 400°C, showed a remarkable decrease in the catalytic activity, while a nickel catalyst with a small addition of PtO₂ (0.01%) showed a considerable thermal stability for the aboye reaction. The catalysts containing 4% or more of PtO₂ showed no catalytic activity wheh they were reduced at temperatures lower than 400°C. However, when reduced at higher temperatures, they showed a gradual increase in the catalytic activity. The gas chemisorption (H₂ or CO) data also indicated a peculiar characteristic similar to the catalytic activity. This peculiarity was considered to be related with the formation and decomposition of the intermetallic compounds of nickel-platinum.