The catalytic activity of noble metal ion substituted in reducible oxide is much higher than the corresponding metal particles supported on oxides. We have studied Pt, Pd, Rh, and Cu metal ions substituted in CeO 2, TiO 2, and Ce1-xTixO 2. Pd ion substituted oxides are the best three-way catalysts for automotive exhaust applications. Noble metal ions in a number of new oxide supports such as Ce1-xAxO 2 (A ) Ti, Zr, Hf, Th,) can be developed. Substitution of first row transition metal ions in CeO 2 are amenable to redox coupling between M(3d) and Ce(4f). There are a number of other reducible oxide supports such as SnO 2 or V 2O 5. Redox properties of noble metal ions in first row transition metal oxides are not yet explored. Understanding the redox behavior of reducible metal oxides doped with more easily reducible noble metal ions would be a worthwhile area to pursue in catalysis combined with solid-state chemistry. © 2009 American Chemical Society.