A commercial zeolite-based catalyst for NOx removal via ammonia SCR has been studied in a synthetic flow very close to a real automotive exhaust mixture. Particular attention has been paid to reproduce effective temperatures and space velocities. The impact of the hydrocarbon presence towards the NH3-SCR efficiency has been investigated through the use of a mixture of representative hydrocarbons, i.e. propene, toluene and decane. It has been found that both decane and toluene produce a carbonaceous deposit, partially hindering the reaction by pore blocking. However, it also appears that decane is the most inhibiting compound for the deNO(x) activity due to a competitive adsorption with ammonia on the active sites, notably at low temperature. (C) 2010 Elsevier B.V. All rights reserved.