Kinetic models for NH3 SCR over Cu-ZSM-5

Louise  Olsson, Chalmers University of Technology

Kinetic models for NH3 SCR over Cu-ZSM-5

Louise Olsson (a), Hanna Sjövall (a), Richard J. Blint (b) and Ashok Gopinath (c)

(a) Competence Centre for Catalysis, and Chemical Reaction Engineering, Chalmers University of Technology, SE-412 96 Göteborg, Sweden
(b) General Motors R&D Center, Chemical and Environmental Sciences Laboratory,30500 Mound Rd, Warren, MI 48090-9055
(c) General Motors R&D India Science Lab, Creator Building, International Tech Park, Whitefield Road, Bangalore 560 066, INDIA

We have developed both global [1] and detailed [2-4] kinetic models for ammonia SCR over copper zeolites. These models were developed for use in predicting NOx emissions from urea SCR automotive catalytic converters. The kinetics described in these models were developed using experimental data from coated monolith cores in flow reactor experiments, FTIR and TPD experiments. In addition two monolith samples (11 wt% washcoat and 23 wt.% washcoat) were used to evaluate the mass-transfer limits in the wash-coat. When holding the ratio between the total flow rate and the wash-coat amount constant, there were no differences in outlet NOx and NH3 concentrations indicating no significant mass-transfer limitations in the wash-coat layer. Ammonia temperature programmed desorption (TPD) experiments were used for investigating the adsorption and desorption of ammonia from the catalyst, which is crucial for simulating transient experiments. Further, the NO oxidation and NH3 oxidation submodels were examined separately. The global kinetic model also contains three steps for NH3 SCR: standard SCR (NO + O2 + NH3), rapid SCR (NO + NO2 + NH3) and NO2 SCR (NO2 + NH3) and one additional step for the N2O formation. 5% water was used in all experiments for the global model and the detailed model was developed both for dry and wet conditions. The global model was validated with six separate experiments including long steady state and short transient measurements. The NH3 concentration, NO concentration, and NO to NO2 ratio were varied and the model successfully predicted all the validation experiments. All global kinetic parameters and their 95% linearized confidence regions have recently been published [1].

[1] L. Olsson, H. Sjövall and R. J. Blint, Applied Catalysis B: Environmental, In press, 2008.
[2] H. Sjövall, R. J. Blint and L. Olsson, submitted, 2008.
[3] H. Sjövall, R. J. Blint and L. Olsson, submitted, 2008.
[4] L. Olsson, H. Sjövall, R. J. Blint, submitted, 2008.

Download Presentation: