Pt/CuO/Al2O3 catalysts with 20 wt% CuO and 0.5-4 wt% Pt were prepared and used for the selective catalytic oxidation of ammonia in wet and dry gases and in synthetic biogas with CO, hydrogen, and methane. Imaging of the catalysts with HREM and STEM, combined with elemental analysis, reveals that copper is well dispersed and Occurs in the form of patches on the support. Platinum in the form of nanometer-sized particles are localised on copper-rich areas. The activity measurements show that Pt/CuO/Al2O3 is active and selective for the oxidation of ammonia to form nitrogen. Compared with dry feeds, the catalyst shows higher selectivity for nitrogen when the feed is wet. Pretreatment of the catalyst with SO2-containing gas produces an improved catalyst with a selectivity for nitrogen of about 97-98% at complete ammonia conversion. Pt/CuO/Al2O3 shows good performance also for the oxidation of ammonia to nitrogen in the presence of biogas components including water. However, the performance is not as good under dry conditions, giving either low selectivity for nitrogen or low conversion of the ammonia, depending on the partial pressure of oxygen. (C) 2004 Elsevier Inc. All rights reserved.