Selective Catalytic Reduction (SCR) Mechanistic Model Development and Application over a Cu-CHA Catalyst

• Author / Creator

  Bendrich, Michelle

• Mechanistic proposals for the different selective catalytic reduction (SCR) subreactions are integrated into one surface reaction mechanism that describes the main SCR reactions (Standard SCR, Fast SCR, NO2 SCR), transient effects due to
  nitrate storage, as well as the production of the side product N2O over a copper chabazite (Cu-CHA) catalyst. The mechanism is parameterized to steady state and
  transient experiments, and is shown to predict the behaviour of the catalyst during a driving cycle, without any refitting of kinetic parameters.

  Surprisingly, although a significant amount of inhibitive ammonium nitrate is modelled to form during low temperature Fast and NO2 SCR steady state experiments, almost no ammonium nitrate is predicted to form during a hot and cold
  driving cycle, thus allowing for a higher reaction activity than predicted based on steady state data. To validate whether the minimal formation of ammonium nitrate during transient driving cycles holds true, an experimental method and simulations are applied to compare the amount of ammonium nitrate stored during steady state and transient tests over the Cu-CHA catalyst. The results demonstrate that little
  ammonium nitrate accumulates on the catalyst surface during multiple cold world harmonized transient cycles (WHTCs) with a high cumulated NO2/NOx ratio owing to the slow accumulation of ammonium nitrate and rapidly fluctuating inlet conditions.

  Finally, the Cu-CHA mechanistic model, as well as an Fe-zeolite global model, are used as the SCR washcoat for an SCR and ammonia slip catalyst (ASC) configuration, to investigate whether the ASC’s ability to minimize ammonia slip can
  result in a more aggressive dosing strategy during a driving cycle, which can help increase the NOx conversion. Overall, it is shown that the true value of an ASC is its ability to limit ammonia slip when an error in dosing occurs, rather than allow for a more aggressive ammonia dosing strategy to increase the overall NOx conversion of the catalytic converter system.

• Subjects / Keywords

  • Copper chabazite
  • Kinetic model
  • Driving cycle
  • Ammonium nitrate
  • SCR mechanism

• Graduation date

  Fall 2018

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3BZ61Q8K

• License

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