NH 3 /urea SCR is a very effective and widely used technology for the abatement of NO x from Diesel exhaust [1]. The SCR mechanism is well understood and the catalyst behavior can be predicted by mathematical models [2,3,4] -as long as operation above the temperature limit for AdBlue® injection is considered. The behavior below this level is less understood.During the first seconds up to minutes after cold start, complete NO x abatement can be observed over an SCR catalyst in test bench experiments, together with a significant increase in temperature after the converter (ca. 100 K).In this work these effects have been investigated over a monolith Cu-zeolite SCR catalyst. Concentration step experiments varying NO, NO 2 and H 2 O have been carried out in lab scale, starting from room temperature. Further, the interaction of C 3 H 6 and CO with NO x over the SCR has been investigated. The effects observed during cold start have been reproduced successfully at lab scale, providing insight into the prevailing mechanisms.It was found that low-temperature NO oxidation proceeds already at room temperature, showing a negative temperature dependence [5]. However, it is strongly inhibited by H 2 O. Thus, significant amounts of NO 2 can be produced over the SCR while H 2 O of the exhaust condenses on the cold devices upstream. Further, the SCR catalyst can store NO 2 efficiently, so that a major part of NO x disappears. Finally, upon addition of H 2 O-vapor to the gas, it adsorbs on the zeolite, causing a sudden temperature increase due to the heat of adsorption. The results show that this increase forces the stored NO 2 to desorb immediately. However, real engine cold start measurements show NO desorption instead. The reason can be reducing agents like CO and hydrocarbons, that were indeed proven able to reduce NO 2 to NO over the SCR. CITATION: Schmeisser, V., Weibel, M., Sebastian Hernando, L., Nova, I. et al., "Cold Start Effect Phenomena over Zeolite SCR Catalysts for Exhaust Gas Aftertreatment," SAE Int. J. Commer. Veh. 6(1):2013,
