The definition of experimental methods to be employed in the lab-scale for catalytic activity measurements for soot oxidation with either powder or coated catalysts is necessary before industrial applications. Characterisations of carbon black, a model soot of constant composition, have proved that mechanical grinding weakly affects its structure. The nature of carbon black can be modified by oxidation with O-2, H2O or H2O2 and confirmed by transmission electron microscopy (TEM). The temperature for half conversion of carbon (607-593 degreesC after treatment) has revealed also the chemical stability of the structure. Molybdenum oxide is used as catalyst for the oxidation of carbon black. The reaction is greatly affected by the quality of the mixture between the two solid materials. For the preparation method by grinding, the effects of the amount Of MoO3 and carbon black have been studied. At a high ratio of catalyst and carbon black (95/5), carbon black is well surrounded by MoO3 and the temperature for half conversion strongly decreases (from 607 to 459 degreesC). This sample preparation condition can be adopted for the classification of catalysts. (C) 2003 Elsevier B.V. All rights reserved.