Global kinetic modeling of hydrothermal aging of NH3-SCR over Cu zeolites

Louise  Olsson, Chalmers University of Technology

Ammonia based selective catalytic reduction (SCR) is an important technology for removing NOx from lean burn diesel engines and Cu zeolites are commonly used for this system. We have previously studied the hydrothermal aging of Cu/BEA using both flow reactor experiments [1] as well as characterizing with XRD, BET, UV-vis [2] and H2 TPR [3]. The effect of hydrothermal aging on various catalytic functions, including NH3 storage, NOx conversion (over range of temperature, NO2/NOx ratio), NH3 oxidation, NO oxidation and N2O formation, was studied using flow reactor experiments. However, to our knowledge there are no kinetic models available in the literature that describes the hydro thermal aging of NH3-SCR over Cu-zeolites. The objective of this work was to develop a kinetic model for this. We have used micro calorimetry data for determining the dependence of heat of adsorption of ammonia with aging temperature. With the use of ?H, the NH3 storage and desorption was simulated as a function of time and aging temperature. Keeping the kinetic parameters for NH3 adsorption and desorption fixed, NH3 oxidation experiment was modeled after aging (500, 600, 700, 800 and 900°C). These results, together with a reaction step for NO oxidation were used in the development of the SCR aging mechanism. The aging model is developed for different NO2/NOx ratio (0, 0.5 and 0.75) and it was found that aging models with increased complexity was needed in order to describe SCR aging at higher temperatures.

[1] N. Wilken, K. Wijayanti, K. Kamasamudram, N.W. Currier, R. Vedaiyan, A. Yezerets, L. Olsson, Appl. Catal. B 111 (2012) 58.
[2] N. Wilken, R. Nedyalkova, K. Kamasamudram, J. Li, N.W. Currier, R. Vedaiyan, A. Yezerets, L. Olsson, Topics in Catalysis 56 (2013) 317.
[3] J. Li, N. Wilken, K. Kamasamudram, N.W. Currier, L. Olsson, A. Yezerets, Topics in Catalysis 56 (2013) 201.