Molecular aspects of the mechanism of NH3‐SCR on Tungsten‐loaded ceria from modulated excitation DRIFTS

Tungsten‐loaded ceria is a potential alternative catalyst for the selective catalytic reduction of NOx by NH3 (NH3‐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%)‐CeO2 catalyst. During NO oxidation, NO2 produced by NO oxidation is adsorbed on the catalyst, and the adsorbed NO2 (NO2ad) undergoes disproportionation to yield NO+ and NO3‐, accompanied by consumption of the bridged OH groups on the CeO2 surface. During NH3‐SCR, NH3 adsorbed on a Ce4+ Lewis acid site (L‐NH3) reacts with NO to yield Ce3+ site, N2, H2O and H+ (Brønsted acid site). A portion of the initially adsorbed L‐NH3 desorbs and subsequently re‐adsorbs onto the newly created Brønsted acid site, generating what we term B‐NH3. Consequently, the Ce3+ species undergoes oxidation, facilitated by O2 and H+, resulting in the regeneration of Ce4+ species as well as the formation of H2O. This oxidation process coincides with the depletion of the tentatively formed Brønsted acid site (B‐NH3).