ORIGINAL PAPER A System Simulation Study of the Enhanced-SCR Reaction F. Marchitti 1 • I. Nova 1 • P. Forzatti 1 • E. Tronconi 1 • S. Adelberg 2 • V. Strots 2 Ó Springer Science+Business Media New York 2016 Abstract This study addresses fundamental and practical aspects of the Enhanced-SCR reaction over a Fe-zeolite SCR catalyst. The key mechanistic steps responsible for the improvement of the DeNO x activity at low temperatures are analysed, and a system simulation model is developed to assess its potential for NO x conversion improvement in heavy-duty aftertreatment systems. It was found that the ammonium nitrate additive can dramatically improve the low-temperature DeNO x activity of a Fe-zeolite catalyst, by generating in situ NO 2 readily. Such NO 2 can then react in the Fast-SCR reaction, which explains the enhanced low-T SCR activity. The simulation of a complete heavy-duty aftertreatment system with a dedicated AN injection showed the potential of the apparatus, in both cold and hot WHTC. Keywords NH 3 /urea SCR Á Ammonium nitrate Á Enhanced-SCR Á Fe-zeolite Á Simulation 1 Introduction NH 3 /urea SCR is nowadays a well-established technology for the control of NO x emissions from diesel vehicles, but the reduction of the emission limits and the lower exhaust temperatures due to more efficient engines require more effective DeNO x systems, especially at low temperatures. It has been demonstrated [1, 2] that addition of aqueous solutions of NH 4 NO 3 (AN) to a NO–NH 3 containing feed results in the ‘‘Enhanced-SCR’’ (E-SCR) reaction, 2NH 3 + 2NO + NH 4 NO 3 ! 3N 2 þ 5H 2 O; ðR:1Þ over V 2 O 5 –WO 3 /TiO 2 and Fe-zeolites. The E-SCR reac- tion is associated with high DeNO x efficiencies, similar to those of the Fast-SCR, in the 180–350 °C T-range without upstream oxidation of NO–NO 2 . The aim of the present work is to clarify both fundamental and practical aspects of the E-SCR reactivity, with particular focus on the key mechanistic steps responsible for the improvement of the DeNO x activity. Further, a system simulation model is developed to semi-quantitatively describe the E-SCR chemistry and to assess its potential for NO x conversion improvement in heavy-duty aftertreatment systems. 2 Materials and Methods 2.1 Lab Scale Test Rig Runs The catalytic material used for the investigation herein reported is a commercial Fe-zeolite SCR catalyst, coated on a 400 cpsi honeycomb substrate and provided by Umicore. The tested sample was a small core monolith cut down from the central part of the original brick. The tested sample had a square cross section (6 9 6 cells, 7.7 9 7.7 9 65 mm 3 ). In order to fully analyze the Fe-zeolite catalyst behavior with and without the ammonium nitrate (AN) additive, both steady-state and transient runs were performed. First, the catalyst behavior was characterized under pure NH 3 - SCR conditions, collecting a complete SCR baseline data set. Then, proceeding according to a hierarchical approach, an increasing amount of AN was added to the reacting system. During the investigation, the following effects on & V. Strots vadim.strots@iav.de 1 Laboratory of Catalysis and Catalytic Processes, Dipartimento di Energia, Politecnico di Milano, Via La Masa 34, 20156 Milan, Italy 2 IAV GmbH, Carnotstrasse 1, 10587 Berlin, Germany 123 Top Catal DOI 10.1007/s11244-016-0568-0