Pt supported on CeO2 and 10 wt.% La3+-doped CeO2 catalysts have been prepared, characterised and tested for soot oxidation by O-2 in TGA. The reaction mechanism has been studied in a TAP reactor with labelled O-2. Isotopic oxygen exchange between molecular O-2, and 'O' on the support/catalyst was observed and soot oxidation is being carried out by lattice oxygen. TAP studies further show that Pt improves O-2 adsorption and, therefore, 5 wt.% Pt-containing catalysts are more active for soot oxidation than the counterpart supports. In addition, CeO2 doping by La3+ leads to an improved support, since La3+ stabilises the structure of CeO2 when calcined at high temperature (1000 degrees C) and minimises sintering. In addition, La3+ improves the Cc(4+)/Ce3+ reduction as deduced from H-2-TPR experiments and favours oxygen mobility into the lattice. A synergetic effect of Pt and La3+ is observed, Pt-containing La3+-doped CeO2 being the most active catalyst for soot oxidation by O-2 among the samples studied. (c) 2006 Elsevier B.V. All rights reserved.