The chemical state and Cu plus stability for three-way catalytic performance of Cu-added Al2O3 catalysts

Cu-added gamma-Al2O3 (CuAl) catalysts having varying Cu loadings (3, 5, 8, and 10 mol%) were prepared at 900 degrees C. The effects of the copper oxidation states and the stability of these states under oxidizing and reducing atmo-spheres were examined. The use of these materials as three-way catalysts (TWCs) was also assessed. Analyses by X-ray diffraction and transmission electron microscopy indicated that copper oxide species were well dispersed and formed a solid solution in a surface layer of the gamma-Al2O3. The TWC activity was found to increase with the addition of copper, and the 8 mol% CuAl catalyst showed very high performance despite being heat-treated at high temperatures. In the case of the 10 mol% CuAl catalyst, the excess Cu loading resulted in the precipitations of copper species on the gamma-Al2O3 surface, which decreased catalytic activity. The oxidation states also differed between these catalysts. X-ray absorption fine structure and temperature-programmed reduction data demon-strated variations in copper oxidation states among the catalysts before and after oxidation and reduction treatments. The 8 mol% CuAl catalyst had a high Cu+/Cu2+ ratio and contained stable Cu+ species during both oxidation and reduction trials. The stability of the copper oxidation states is evidently a factor affecting catalytic activity.

Automated summary

Cu-added gamma-Al2O3 catalysts were prepared with varying Cu loadings and the effects of copper oxidation states on catalytic activity were investigated. The results showed that the addition of copper increased the catalyst activity, but excessive copper loading decreased catalytic activity. XRD and TEM analysis indicated the formation of a solid solution of copper oxide species on the surface of gamma-Al2O3. XAS and TPR data demonstrated variations in copper oxidation states among the catalysts.