Chemical Engineering Science 59 (2004) 5301 – 5309 www.elsevier.com/locate/ces SCR-DeNO x for diesel engine exhaust aftertreatment: unsteady-state kinetic study and monolith reactor modelling Cristian Ciardelli a , Isabella Nova a , ∗ , Enrico Tronconi a , Brigitte Konrad b , Daniel Chatterjee b , Karlheinz Ecke b , Michel Weibel b a Dipartimento di Chimica, Materiali e Ingegneria Chimica “G. Natta”, Politecnico di Milano, Piazza Leonardo Da Vinci 32, 20133 Milano, Italy b DaimlerChrysler AG Abteilung RBP/C, HPC: 096-G206, D-70546 Stuttgart, Germany Received 29 February 2004 Available online 23 August 2004 Abstract The kinetics of NH 3 adsorption–desorption and of the NO + NH 3 /O 2 Selective Catalytic Reduction (SCR) reaction were studied in the 50–450 ◦ C T -range in the presence of water over a commercial powdered V 2 O 5 –WO 3 /TiO 2 catalyst loaded in a micro-reactor, following the temporal evolution of the outlet species concentrations by a mass spectrometer. The influence of water and oxygen feed contents was examined. Different Transient Response Techniques were applied to investigate the SCR dynamics in view of applications to vehicles. The experimental results were analysed by means of a dynamic one-dimensional heterogeneous PFR model, and fitted by multiresponse nonlinear regression to provide estimates of the rate parameters. Such parameters, as well as the relevant geometrical and morphological characteristics, were then used to simulate transient SCR runs performed over an extruded honeycomb sample of the same commercial catalyst. The satisfactory match obtained between model predictions and monolith data validates the proposed rate equations.  2004 Elsevier Ltd. All rights reserved. Keywords: Diesel-urea; DeNO x -SCR; Catalysis; Environment; Transient response; Dynamic simulation 1. Introduction The selective catalytic reduction (SCR) of NO x with NH 3 is well established as the most effective technol- ogy for the abatement of NO x emissions from stationary sources (Forzatti et al., 2002). Nitrogen oxides present in the flue gases (about 95% NO) react with O 2 and injected NH 3 according to the following stoichiometry: 4NO + 4NH 3 + O 2 → 4N 2 + 6H 2 O. Commercial catalysts, in the form of honeycomb monoliths, are made of a TiO 2 anatase carrier supporting the active components, i.e. V 2 O 5 and WO 3 . At present the SCR process is also regarded as a promis- ing technique for the removal of nitrogen oxides from the exhausts of heavy-duty diesel vehicles (Koebel et al., 2000), ∗ Corresponding author. Tel.: 39-02-2399-3228; fax: +39-02-70638173. E-mail address: isabella.nova@polimi.it (I. Nova). 0009-2509/$ - see front matter  2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.ces.2004.07.016 as they have to meet more and more stringent emission stan- dards for both NO x and particulate matter. Thus, extensive work is being currently devoted by the motor industry to adapt the SCR process to the specific demands of mobile applications; for example, mobile applications rely on the use of urea as reducing agent, which is hydrolized on-board to give ammonia. In the past work at Politecnico di Milano the SCR-DeNO x reaction over commercial V 2 O 5 –WO 3 /TiO 2 catalysts was studied under transient conditions in order to develop a dy- namic kinetic model applicable to NO x removal from the stack gases of power stations (Lietti et al., 1997, 2000a,b; Tronconi et al., 1998, 1999). Based on this experience, a new research has recently started in collaboration with Daimler- Chrysler aimed at developing an unsteady model of the SCR process for mobile applications: the first results are herein reported. In order to investigate the dynamics of the SCR reaction, kinetic runs were performed over a commercial powdered