For NOx/soot laboratory experiments, different carbon materials have been used as model soot. In this work, the behaviour of two carbon materials (a charcoal and a synthetic soot from Degussa) is compared with that of a real diesel soot. The performance of the three carbon materials in synthetic air and in an O-2 + NO gas mixture was compared, both in the presence and in the absence of the KCu2/Al2O3 catalyst. The properties of the carbon materials, including microstructure, elemental analysis, ash content and ash composition determine its reactivity, which is higher in NO, atmosphere than in synthetic air. The use of the KCu2/Al2O3 catalyst increases the NO., reduction, the soot consumption rate and the selectivity towards N-2 and CO2. Charcoal A3 and Printex-U can be accepted as model substances representing upper and lower limits of diesel soot reactivity. (c) 2007 Elsevier B.V. All rights reserved.