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.