The performance of platinum-tin catalysts, supported on Al2O3 and SiO2 and subjected to reduction prior to use, has been studied. The catalysts were characterized in reduced forms by X-ray diffraction (XRD) and XPS. The surface properties were determined by N-2 BET specific surface area and CO chemisorption. The model compounds were 4,6-dimethyldibenzothiophene (4,6DMDBT) and carbazole. The PtSn catalysts supported on either Al2O3 or SiO2 were characterised by high activity, but the catalyst PtSn/SiO2 Was found the most effective, even more effective than the commercial KF848 catalyst. Both PtSn catalysts studied were more effective in the reaction of 4,6DMDBT hydrogenation, the dominant product obtained with the use of PtSn/Al2O3 was methyl-cyclohexyltoluene (MCHT) and with PtSn/SiO2 the dominant product was dimethylbicyclohexyl (DMBCH). The amount of dimethylbiphenyl (DMBPh) obtained was small and practically independent of the contact time. In the HDN reaction of carbazole the most active was PtSn/SiO2. It was also more active in the consecutive reaction of isomerisation of the main product of the HDN reaction, bicyclohexyl (BCH) to methylcyclopentylcyclohexane (MCPCH). The large differences shown in the hydrotreating activity specially in the HDN reaction between PtSn catalysts supported on Al2O3 and SiO2 result from the physicochemical properties of both samples. The significantly higher CO chemisorption for PtSn/SiO2 indicates the presence of larger amount of metallic species and better hydrogenation properties so important for deep hydrotreating process. (c) 2007 Elsevier B.V. All rights reserved.