MECHANISTIC AND KINETIC ANALYSIS OF THE NO2 SCR REACTION AND N2O FORMATION OVER Fe AND CuZEOLITE CATALYSTS FOR THE AFTERTREATMENT OF DIESEL EXHAUSTS

Urea/NH3-SCR is presently considered a key technology for the control and abatement of NO emissions from Diesel engines; the presence of a DOC catalyst upstream from the SCR unit warrants significant amounts of NO2 entering the SCR reactors together with NO. In this work new zeolite-based catalysts promoted by Fe and by Cu were investigated: reactivity tests were performed to allow a quantitative comparison, whereas systematic mechanistic experiments were run to elucidate the major reaction pathways, with particular focus on the NO2/NH3 reacting system and on formation of N2O. The bulk of information was then used to develop a dynamic kinetic model in close agreement with all the details of the SCR catalytic chemistry.