Investigation of Low-Temperature OHC and RHC in NH 3 –SCR over Cu-CHA Catalysts: Effects of H 2 O and SAR

作者：Nicole Daniela Nasello, Umberto Iacobone, Nicola Usberti, Andrea Gjetja, Isabella Nova, Enrico Tronconi, Roberta Villamaina, Maria Pia Ruggeri, Djamela Bounechada, A. York, Jillian Collier · 发表于：ACS Catalysis · 年份：2024 · DOI：10.1021/acscatal.4c00118 · 被引用次数：39 · 研究领域：Catalytic Processes in Materials Science、Nanomaterials for catalytic reactions、Advanced Photocatalysis Techniques

A transient kinetic approach was applied to independently investigate the oxidation half-cycle (OHC) and reduction half-cycle (RHC) of NH 3 –selective catalytic reduction (SCR) at low temperature (150–200 °C). Three model Cu-exchanged chabazite (Cu-CHA) samples with fixed Cu loading (∼1.8% w/w) and different silica-to-alumina ratios (SARs = 10-17-25) were investigated under dry and wet conditions. We confirmed the following: (i) OHC proceeds via second- and first-order kinetics in Cu I and O 2, respectively, with O 2 (+H 2 O) alone able to completely reoxidize Cu I sites; (ii) RHC proceeds via second- and first-order kinetics in Cu II and NO, respectively, according to a Cu/NO = 1:1 stoichiometry. Notably, coupling RHC and OHC rates resulted in an accurate prediction of the steady-state standard SCR conditions, providing the consistent closure of the SCR redox chemistry. Unexpectedly, we revealed the impact of H 2 O to vary depending on the catalyst formulation. At high SAR, water inhibits the RHC and promotes the OHC. As a result, a limited impact was observed on steady-state deNO x activity, while the Cu-oxidation state was significantly enhanced by H 2 O. With decreasing SAR, however, the H 2 O effect on RHC gradually shifts from inhibition to promotion, while the OHC is always promoted. At fixed water content, we revealed the RHC rate to decrease with decreasing Al density, with minor influence observed on the OHC; as a result, a lower deNO x activity was observed upon in...