The effect of soot on ammonium nitrate species and NO2 selective catalytic reduction over Cu-zeolite catalyst-coated particulate filter

Journal article, 2016

A selective catalytic reduction (SCR)-coated particulate filter was evaluated by means of dynamic tests performed using NH3, NO2, O-2 and H2O. The reactions were examined both prior to and after soot removal in order to study the effect of soot on ammonium nitrate formation and decomposition, ammonia storage and NO2 SCR. A slightly larger ammonia storage capacity was observed when soot was present in the sample, which indicated that small amounts of ammonia can adsorb on the soot. Feeding of NO2 and NH3 in the presence of O-2 and H2O at low temperature (150, 175 and 200 degrees C) leads to a large formation of ammonium nitrate species and during the subsequent temperature ramp using H2O and argon, a production of nitrous oxides was observed. The N2O formation is often related to ammonium nitrate decomposition, and our results showed that the N2O formation was clearly decreased by the presence of soot. We therefore propose that in the presence of soot, there are fewer ammonium nitrate species on the surface due to the interactions with the soot. Indeed, we do observe CO2 production during the reaction conditions also at 150 degrees C, which shows that there is a reaction with these species and soot.