Assessment of the Single-Site Kinetic Model for NH3-SCR on Cu-Chabazite for the Prediction of NOx Emissions in Dynamometer Tests

  • Selmi Erim Bozbağ
  • Mutlu Şimşek
  • Onur Demir
  • Deniz Şanlı
  • Barkın Ozener
  • Gokhan Hisar
  • Can ErkeyEmail author
Original Paper


A transient single-site kinetic model consisting of NH3-SCR (selective catalytic reduction) related reactions (NH3 adsorption/desorption, NH3 oxidation, NO oxidation, standard SCR, fast SCR, NO2-SCR, NH4NO3, and N2O formation) on a commercial multi-site Cu-Chabazite washcoated monolith was developed using laboratory scale synthetic gas bench (SGB) data and its potential towards predicting the downstream NOx concentrations was assessed using SGB and dynamometer tests. Kinetic model described the transient and steady-state data obtained for the model development in the SGB well. Single-site nature of the model enabled the prediction of the reactivity of the lower temperature active Cu site much better than the activity associated with higher temperature Cu sites. Validation experiments in the SGB at 185 °C which consisted of varying NH3 and NO2/NOx ratios were very well predicted. The kinetic model was also successful in predicting the instantaneous NOx emissions and cumulative NOx and N2O amount released in real-size SCR reactors during World Harmonic Transient Cycle (WHTC) in the 220–290 °C range. Model was in slight disagreement with measured cumulative NO but was in good in agreement with NO2 for the World Harmonic Stationary Cycle (WHSC) tests in dynamometer and 235–339 °C range, respectively. The developed model was found sufficient for both design and calibration of aftertreatment systems (ATS).


Cu-chabazite NH3-SCR Kinetic model Dynamometer WHTC 



active site density for reaction j, (molsite x m−3 catalyst)


active site density for coverage k, (mol x m−3 catalyst)


pre-exponential factor for reaction i


intraporous concentration of species i (mol x m−3)

Di, m

binary diffusion coefficient of species i in the mixture (m2 x s−1)

De, i

effective diffusivity for species i (m2 x s−1)

DKn, i

Knudsen diffusion coefficient for species i (m2 x s−1)


hydraulic diameter (m)


washcoat pore size available for gas diffusion (m)


activation energy for reaction j (kJ x mol−1)


activation energy for reaction j at zero coverage (kJ x mol−1)


solid fraction of washcoat


surface area per reactor volume (m−1)


turnover rate constant for the reaction j

km, i

external mass transfer coefficient for species i (kg x m−2 s−1)


molecular weight of species i (kg x mol−1)


reaction rate for reaction j (mol x s−1 x molsite−1)


gas constant (J x mol−1 x K−1)


species mass rate for generation or consumption (kg x m−3 x s−1)


stoichiometric coefficient of species i for reaction j


Sherwood number


diffusion volume for species i (cm3 x mol−1)


interstitial velocity (m x s−1)

Greek Letters


coverage dependence


washcoat thickness (m)


void fraction of reactor


void fraction of washcoat


density of bulk gas in reactor channels (kg x m−3)


density of gas at catalyst surface (kg x m−3)


intraporous mass fraction of species i

ωg, i

mass fraction of species i in the bulk gas

ωw, i

mass fraction of species i in the gas-solid interface


surface coverage of species k


stoichiometric coefficient of coverage i in reaction k


Compliance with Ethical Standards

Conflict of Interest

The authors declare that they have no competing interests..


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Authors and Affiliations

  1. 1.Department of Chemical and Biological EngineeringKoç UniversityIstanbulTurkey
  2. 2.Ford Otosan R&D CenterIstanbulTurkey

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