A Pt/Al2O3 catalyst prepared by incipient wetness impregnation was used as a diesel oxidation model catalyst and tested in the simultaneous total oxidation of CO and C3H6. Sulphur incorporation by wet impregnation results in deactivation of the Pt/Al2O3 catalyst in both oxidation reactions. Characterization of the catalysts by evolved gas analysis by mass spectrometry (EGA-MS), X-ray diffraction (XRD), isotherm of adsorbed nitrogen, X-ray photoelectron spectroscopy (XPS), infrared spectroscopy of probe molecules (pyridine and carbon monoxide) and finally temperature-programmed surface reaction (O-2-TPSR of chemisorbed CO) demonstrated that the formation of aluminium sulphate modifies the acidic properties of the support and the electronic properties of the platinum particles. Thus, new Bronsted acid sites are formed and, moreover, the capacity of the Pt particles to chemisorb CO and O-2, the latter as strongly chemisorbed O species, is seriously deteriorated. The alteration of the electronic properties of the particles (they become electronically deficient) is related to the modification of the acidic properties of the support. Treatment of the deactivated catalysts by a reductive treatment at 873 K resulted in the removal of the sulphur due to decomposition of the aluminium sulphate. Thus, the original acidic properties of the support and the electronic properties of the Pt particles were largely recovered and a high degree of catalytic reactivation was achieved. (c) 2006 Elsevier B.V. All rights reserved.