Modulated excitation DRIFTS and steady-state isotopic transient kinetic analysis (SSITKA) of NH3-SCR-DeNOx on Cu-containing zeolite Y

Abstract

As-received commercial zeolite Y (in the forms of Na⁺, H⁺, and NH₄⁺) with an n(Si)/n(Al) ratio of about 2.6 modified with copper cations was investigated in the selective catalytic reduction of nitrogen oxide with ammonia (NH₃-SCR-DeNO_x). Operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFT) experiments using concentration modulation excitation (ME) coupled with phase-sensitive detection (PSD) analysis, together with steady-state isotopic transient kinetic analysis (SSITKA), were carried out to study key transient adsorbates on Cu-containing zeolite Y samples. We could observe different interactions between NO exposure to the NH₃ preadsorbed surface over the applied catalysts. For CuY_CBV100, NO exposure to an NH₃-preadsorbed surface leads to a decrease in NH₃ bound to Lewis acid sites (L-NH₃) and the formation of new Brønsted acid sites (B-NH₃). Part of the L-NH₃ migrates to these newly generated BAS. Based on the modulation excitation results, we could set the order of activity of the applied catalysts. For CuY_CBV500, the situation differs. A strong B-NH₃ peak indicates a high concentration of Brønsted acid sites on the CuY_CBV500 surface. NO can react with both L-NH₃ and B-NH₃, and the presence of B-NH₃ contributes to the high N₂ selectivity observed. SSITKA revealed that CuY_CBV100 exhibited a higher number of active centers on its surface, thus leading to higher NO conversion during NH₃-SCR-DeNO_x, but its reactivity is slightly lower than in the case of the other studied materials (especially CuY_CBV500).