Formation and Effect of NH4 + Intermediates in NH3–SCR over Fe-ZSM‑5 Zeolite Catalysts

With the help of a technique combining in situ electrical impedance spectroscopy and DRIFT spectroscopy, we observed directly the formation of ammonium ion (NH4 +) intermediates resulting from the interaction of NO and NH3 on Fe-ZSM-5 catalysts for selective catalytic reduction by NH3 (NH3–SCR). The formed NH4 + intermediates, indicating the activation of NO in the presence of adsorbed NH3, were found to be strongly related to the NH3–SCR activity of Fe-ZSM-5 catalysts at low temperatures. These findings, which are not easily achievable by conventional methods, provide new and important perspectives to understand mechanistically the NH3–SCR reaction over Fe-zeolite catalysts.