4.8 Article

First-Principles Microkinetic Model for Low-Temperature NH3-Assisted Selective Catalytic Reduction of NO over Cu-CHA

Journal

ACS CATALYSIS
Volume 11, Issue 23, Pages 14395-14407

Publisher

AMER CHEMICAL SOC
DOI: 10.1021/acscatal.1c03973

Keywords

first-principles microkinetic modeling; Cu-CHA; NH3-SCR; N2O formation; entropy evaluation

Funding

  1. Swedish Energy Agency [47110-1]
  2. AB Volvo
  3. ECAPS AB
  4. Johnson Matthey AB
  5. Preem AB
  6. Scania CV AB
  7. Umicore Denmark ApS
  8. SNIC grant

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The study shows that NH3-SCR on Cu-CHA is facilitated by NH3-solvated Cu sites, promoting the selective reduction of NO; NH3 adsorption inhibits the reaction at low temperatures; the successful formulation of a first-principles microkinetic model links kinetic behavior with materials properties.
A first-principles microkinetic model is developed to investigate the low-temperature ammonia-assisted selective catalytic reduction (NH3-SCR) of NO over Cu-chabazite (Cu-CHA). The reaction proceeds over NH3-solvated Cu sites by the formation of H2NNO and HONO, which decompose to N-2 and H2O over Bronsted acid sites. Nonselective N2O formation is considered by H2NNO decomposition over the Cu sites. The adsorption of NH3 at oxidized Cu sites is found to inhibit the reaction at low temperatures by hindering NO adsorption. For the reactions, we find positive reaction orders with respect to NO and O-2, whereas the reaction order with respect to NH3 is negative. The reaction orders and the obtained apparent activation energy are in good agreement with experimental data. A degree of rate control analysis shows that NH3-SCR over a pair of Cu(NH3)(2)(+) is mainly controlled by NO adsorption below 200 degrees C, whereas the formation of HONO and H2NNO becomes controlling at higher temperatures. The successful formulation of a first-principles microkinetic model for NH3-SCR rationalizes previous phenomenological models and links the kinetic behavior with materials properties, which results in unprecedented insights into the function of Cu-CHA catalysts for NH3-SCR.

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