CeO₂–ZrO₂solid solutions supported with Rh and Pt are investigated as catalysts for reduction of NO by CO. The incorporation of ZrO₂into the CeO₂framework strongly promotes the reduction of Ce⁴⁺in the bulk of the support. The effects of the reduction temperature are investigated and it is shown that when bulk oxygen vacancies are formed in the reduced CeO₂–ZrO₂solid solution, NO is efficiently decomposed on the support to give N₂O and N₂. The presence of bulk oxygen vacancies is indicated as the driving force for NO dissociation, suggesting their indirect participation in the catalytic cycle.