Molecular Aspects of the Mechanism of NH₃‐SCR on Tungsten‐Loaded Ceria from Modulated Excitation DRIFTS

Abstract Tungsten‐loaded ceria is a potential alternative catalyst for the selective catalytic reduction of NO x by NH 3 (NH 3 –SCR). In this work, we carried out operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) experiments using concentration modulation excitation (ME) coupled with phase sensitive detection (PSD) analysis to study key transient adsorbates on a W(10 wt%)/CeO 2 catalyst. During NO oxidation, NO 2 produced by NO oxidation is adsorbed on the catalyst, and the adsorbed NO 2 (NO 2ad ) undergoes disproportionation to yield NO + and NO 3 − , accompanied by consumption of the bridged OH groups on the CeO 2 surface. During NH 3 ‐SCR, NH 3 adsorbed on a Ce 4+ Lewis acid site (L‐NH 3 ) reacts with NO to yield Ce 3+ site, N 2 , H 2 O, and H + (Brønsted acid site). A portion of the initially adsorbed L‐NH 3 desorbs and subsequently re‐adsorbs onto the newly created Brønsted acid site, generating what we term B‐NH 3 . Consequently, the Ce 3+ species undergoes oxidation, facilitated by O 2 and H + , resulting in the regeneration of Ce 4+ species as well as the formation of H 2 O. This oxidation process coincides with the depletion of the tentatively formed Brønsted acid site (B‐NH 3 ).