Being a major poison, SO(2) is often avoided for selective catalytic reduction (SCR) of NO with ammonia at low temperatures. In the present work, we report a V(2)O(5)/CNT catalyst with high NO catalytic activities tolerant to SO(2), moreover, whose SCR activity is promoted by the SO(2) at proper low temperatures. When the reacting temperature is higher than 200 degrees C, SO(2) improves the SCR activity, while it is lower than 200 degrees C, SO(2) deactivates the V(2)O(5)/CNT catalysts. It seems that the reacting temperature behaves like a switch, capable of turning on and off the poisoning reactions. Furthermore, the promoting effect of SO(2) exhibits a magnified tendency with decreasing V(2)O(5) loadings. TEM and EDS results indicate that the vanadium oxides should molecularly anchor on the surface of CNTs. X-ray photoelectron spectroscopy, ammonia temperature-programmed desorption, temperature-programmed decomposition and temperature-programmed surface reaction results show that the promoting effect of SO(2) on SCR activity originates from the formation of sulfate species on the catalyst surface. Based on these findings, a promoting process is also proposed. More importantly, the V(2)O(5)/CNTs catalysts show a great stability under the SO(2)-containing conditions after being operated for 100 h. (C) 2010 Elsevier B. V. All rights reserved.