The effect of sulfur and copper contents on the activity of Cu/sulfated-zirconia (SZ) catalysts, in the selective reduction of NO by n-decane, were investigated in the 298-723 K temperature range. ZrO2 and SZ solids exhibited no activity below 773 K, Cu/ZrO2 is active and selective at low temperature (<600 K) but oxidises selectively NO to NO2 at higher temperatures. By contrast, whatever the temperature, a 100% selectivity to N-2 is obtained with Cu/SZ catalysts. The highest activity is reached with the catalyst containing the highest number of acid sites which corresponds to a sulfur content close to the amount required to form a sulfate monolayer. Acidity plays a significant role only at temperatures above 600 K, where it is concluded that a bifunctional mechanism governs the reduction of NO to N-2.