Synthesis and characterization of Al2O3 and ZrO2–TiO2 nano-composite as a support for NOx storage–reduction catalyst

To improve the thermal stability of NOx storage–reduction catalysts, a novel support containing Al2O3, ZrO2, and TiO2 was synthesized by the coprecipitation method. The XRD and TEM results indicated that primary particles of γ-Al2O3 and a solid solution of ZrO2–TiO2 coexisted as secondary particles, that is, the synthesized support was a nano-composite of γ-Al2O3 and ZrO2–TiO2. The synthesized support had a characteristic single meso-pore, derived from the structure of the secondary particle. The basicity of the synthesized support was lower than that of the physically mixed oxide. After thermal treatment, aggregation of the ZrO2–TiO2 particles in the support was inhibited relative to that in the mixture of Al2O3 powder and ZrO2–TiO2 powder. This was attributed to the diffusion barrier (against ZrO2–TiO2) created by primary Al2O3 in the synthesized support. After a thermal aging test, the NOx storage–reduction catalyst containing the synthesized support had a larger NOx storage capacity than the catalyst containing the physically mixed oxide.