Dehydrogenation dynamics of NH4+ intermediates direct N2 selectivity in high-temperature zeolite SCR

In zeolite catalysis, the evolving composition of acid-relevant intermediates crucially influences the selective reduction of nitrogen oxides (NO x ). This process faces challenges, notably the undesired oxidation of NH 3 to NO x at high temperatures (>500 °C). Herein, we employ transient gas pulse spectroscopy to probe the behavior of NH 4 + species and related ligands in H- and Fe-exchanged zeolites. The synthesized HSSZ-13 exhibited an intrinsic de-NOx efficiency of 71.0 % and a N 2 selectivity of 99.4 % at 800 °C. A direct correlation between acid-related intermediate intensities and reaction rates was identified, varying with zeolite structure. In-situ spectroscopy and theoretical calculations revealed that the conjugation unit at the Brønsted site stabilizes the occupied π-orbital of NH 4 + , maintaining a moderate energy barrier for dehydrogenation and suppressing over-oxidation, thereby enhancing NH 3 adsorption and activation. These findings provide new implications for modulating NH 4 + intermediates and Fe-coordinated complexes within zeolites, enabling a more efficient redox cycle for high-temperature SCR applications.