Pd ion substituted CeO<SUB>2</SUB>: a superior de-NO<SUB>x</SUB> catalyst to Pt or Rh metal ion doped ceria

Pd, Pt and Rh ion doped CeO2, Ce1-xMxO2-&#948; (M = Pd2+, Pt2+, Rh3+) were synthesized by solution combustion synthesis method and the deNOx activity was investigated by NO + CO reaction. Ionically dispersed Pd in CeO2 was found to have better catalytic activity than ionically dispersed Pt or Rh in CeO2. High rates of NO conversion and high selectivity of N2 is observed over Ce0.98Pd0.02O2-&#948;. A bi-functional reaction mechanism is proposed, which fits very well with the experimental results. The oxide ion vacancy present in the CeO2 matrix seems to play an important role for product selectivity and high rate of reaction