Influence of crystal structure of Y-doped ZrO₂ as support oxide on the three-way catalytic performance of supported Rh catalyst

抄録

The effect of crystal structure of Y-doped ZrO₂ as support on the three-way catalytic performance of Rh catalyst was investigated. Rh catalyst supported on 3Y-ZrO₂ with tetragonal phase showed higher activity than that on 3Y/ZrO₂ with monoclinic phase. The difference in the Rh–support oxide interaction was suspected from the measurements of temperature-programmed reduction by CO (CO-TPR). The use of Y-doped ZrO₂ as support was found to contribute to the formation of easily reducible Rh species, resulting in high catalytic activity. Rh species can more strongly interact with 3Y/ZrO₂ than with 3Y-ZrO₂, resulting in the formation of catalytically active reducible Rh species in Rh/3Y-ZrO₂, which showed the highest activity. From Fourier transform infrared (FT-IR) spectroscopy following CO adsorption, no qualitative difference in the surface valence state of Rh particles irrespective of crystallite structure of Y-doped ZrO₂ was observed. On the other hand, a large fraction of the surface of Rh particles in Rh/3Y-ZrO₂ was found to be Rh⁰ sites rather than Rh⁺ sites. This is related to the interaction of Rh particles with Y species in tetragonal 3Y-ZrO₂. We concluded that the tetragonal structure of 3Y-ZrO₂ with which Rh can interact via Y species is a key-factor to obtain highly active Rh catalysts.