Strong activity of a Cu-V-K-Cl/TiO2, catalyst for soot oxidation was found by comparing results of constant temperature carbon oxidation tests in the presence and in the absence of catalyst. In addition, temperature programmed reductions (TPR) with different reductants (H-2 or soot) and re-oxidations (TPO) with air were carried out. Mass-spectrometric (MS) analyses of the gaseous products of the mentioned TPR and TPO processes were also performed on line. The aim was to investigate the behaviour of the catalyst under reducing and oxidising environments in order to draw indications on the role of the redox properties in the catalytic reaction mechanism. Results showed that the catalyst can be reduced and re-oxidised under proper environments. In particular, the catalyst delivers oxygen in the whole range of temperatures from 480 to 1000K when carbon or H-2 are employed as reducing substances. The relevant differences between the two cases are the main products of the reductions (H2O with H-2 and CO2 with soot) and the high HCl desorption in the case of reduction by H-2. In addition, the temperature range within which the catalyst re-oxidises after such a reduction is practically coincident with those where soot catalytic oxidation occurs. (C) 2003 Elsevier Science B.V All rights reserved.