Soot oxidation with NO (in the absence of gas phase O(2)) on potassium-supported Mg-Al hydrotalcite mixed oxides (K/MgAlO) was studied using a temperature-programmed reaction and in situ FTIR techniques. Nitrite and the ketene group were identified as the reaction intermediates and thus a nitrite-ketene mechanism was proposed in which surface active oxygen on K sites of K/MgAlO is transferred to soot by NO through nitrites. In the absence of gas phase O(2), soot oxidation with NO at lower temperatures (below 450 degrees C) is limited by the amount of active oxygen on the K sites. This kind of active oxygen is not reusable but can be replenished in the presence of gas phase O(2).