A series of catalysts of manganese oxide, manganese-cerium and iron-manganese oxide supported on USY (ultra-stable Y zeolite) were studied for the low-temperature selective catalytic reduction (SCR) of NO with ammonia in the presence of excess oxygen. It was found that MnOx/USY have high activity and high selectivity to N-2 in the temperature range 80-180 degreesC. The addition of iron and cerium oxide increased NO conversion significantly although the single-component Fe/USY and Ce/USY catalysts had low activities. Among the catalysts studied in this work, the 14% Ce-6% Mn/USY showed the highest activity. The results showed that this catalyst yielded nearly 100% NO conversion at 180 degreesC at a space velocity of 30 000 cm(3) g(-1) h(-1). The only product is N-2 (with no N2O) below 150 degreesC. The effects of the concentration of oxygen, NO and NH3 were studied and the steady-state kinetics were also investigated. The reaction order is 1 with respect to NO and zero with respect to NH3 on the 14% Ce-6% Mn/USY catalyst at 150 degreesC.