Surface oxidic phases of binary and ternary zirconia-supported metal catalysts investigated by Raman spectroscopy

Abstract

The prevailing zirconia modification in a series of metal/ZrO₂ catalysts has been investigated by Raman spectroscopy. Activation of an amorphous Cu₇₀Zr₃₀ alloy, or coprecipitation of zirconium dioxide with either copper, nickel or silver oxides at constant pH results in amorphous solids containing varying fractions of monoclinic or tetragonal zirconia. The cubic ZrO₂ modification is not present in significant concentrations according to the Raman results. For Cu/ZrO₂, strong Raman signals of Cu₂O are detected, which indicate an enrichment of this compound on the catalyst surface. Copper and nickel ions apparently stabilize the tetragonal zirconia modification, whereas in the presence of palladium or silver, the formation of monoclinic zirconia domains is favoured. In ternary systems, the addition of 5 at.% of either Ag or Pd results in pronounced changes in the structure of Cu/ZrO₂: Raman signals of monoclinic zirconia are observed for Ag(5%)/Cu(45%)/ZrO₂ and Pd(5%)/Cu(45%)/ZrO₂, and at the most only traces of surface Cu₂O are detected.