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<p>Ammonia (NH<sub>3</sub>) inhibition during the selective catalytic reduction (SCR) of nitrogen oxides (NO<sub>x</sub>) over Cu-exchanged chabazite (Cu-CHA) catalysts limits low-temperature performance, yet its molecular origin remains unclear. Here we show that excess NH<sub>3</sub> selectively suppresses the oxidation half-cycle of the SCR reaction while leaving the reduction half-cycle largely unaffected. By combining kinetic measurements, operando electron paramagnetic resonance spectroscopy, and density functional theory calculations, we identify hindered mobility of Cu<sup>+</sup> ions as the key factor. Specifically, NH<sub>3</sub> coordination increases the energy barrier for Cu<sup>+</sup> diffusion, preventing the formation of reactive Cu<sup>2+</sup>-oxo dimer intermediates required for efficient oxidation. Spectroscopic measurements further reveal that the extent of inhibition depends strongly on temperature and copper loading. These insights provide a mechanistic basis for mitigating NH<sub>3</sub> inhibition, suggesting that improved catalyst design and optimized operating conditions can enhance low-temperature SCR performance in practical emission control systems.</p>

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Insights into the mechanisms of NH3 inhibition on Cu-CHA SCR catalysts

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2026年7月28日

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  • Dhruba J. Deka,
  • Mingyu Wan,
  • Garam Lee,
  • Eric Walter,
  • Fanglin Che,
  • Kenneth G. Rappe,
  • János Szanyi,
  • Yong Wang

摘要

Ammonia (NH3) inhibition during the selective catalytic reduction (SCR) of nitrogen oxides (NOx) over Cu-exchanged chabazite (Cu-CHA) catalysts limits low-temperature performance, yet its molecular origin remains unclear. Here we show that excess NH3 selectively suppresses the oxidation half-cycle of the SCR reaction while leaving the reduction half-cycle largely unaffected. By combining kinetic measurements, operando electron paramagnetic resonance spectroscopy, and density functional theory calculations, we identify hindered mobility of Cu+ ions as the key factor. Specifically, NH3 coordination increases the energy barrier for Cu+ diffusion, preventing the formation of reactive Cu2+-oxo dimer intermediates required for efficient oxidation. Spectroscopic measurements further reveal that the extent of inhibition depends strongly on temperature and copper loading. These insights provide a mechanistic basis for mitigating NH3 inhibition, suggesting that improved catalyst design and optimized operating conditions can enhance low-temperature SCR performance in practical emission control systems.