Institute for Integrated Catalysis, Pacific Northwest National Laboratory, Richland, WA, 99354, US.
School of Materials Science and Engineering, Tiangong University, Tianjin, 300387, China.
Nat Commun. 2023 May 6;14(1):2633. doi: 10.1038/s41467-023-38309-8.
Low-temperature standard NH-SCR over copper-exchanged zeolite catalysts occurs on NH-solvated Cu-ion active sites in a quasi-homogeneous manner. As key kinetically relevant reaction steps, the reaction intermediate Cu(NH) ion hydrolyzes to Cu(OH)(NH) ion to gain redox activity. The Cu(OH)(NH) ion also transfers between neighboring zeolite cages to form highly reactive reaction intermediates. Via operando electron paramagnetic resonance spectroscopy and SCR kinetic measurements and density functional theory calculations, we demonstrate here that such kinetically relevant steps become energetically more difficult with lower support Brønsted acid strength and density. Consequently, Cu/LTA displays lower Cu atomic efficiency than Cu/CHA and Cu/AEI, which can also be rationalized by considering differences in their support topology. By carrying out hydrothermal aging to eliminate support Brønsted acid sites, both Cu(NH) ion hydrolysis and Cu(OH)(NH) ion migration are hindered, leading to a marked decrease in Cu atomic efficiency for all catalysts.
低温标准 NH-SCR 在 NH 溶剂化的 Cu 离子活性位上以准均相方式发生。作为关键的动力学相关反应步骤，反应中间体 Cu(NH)离子水解为 Cu(OH)(NH)离子以获得氧化还原活性。Cu(OH)(NH)离子也在相邻沸石笼之间转移，形成高反应性的反应中间体。通过在位电子顺磁共振波谱和 SCR 动力学测量以及密度泛函理论计算，我们在此证明，随着支撑体 Brønsted 酸强度和密度的降低，这些动力学相关步骤变得更加困难。因此，Cu/LTA 比 Cu/CHA 和 Cu/AEI 的 Cu 原子效率更低，这也可以通过考虑它们的支撑拓扑差异来解释。通过进行水热老化以消除支撑体 Brønsted 酸位，Cu(NH)离子水解和 Cu(OH)(NH)离子迁移都受到阻碍，导致所有催化剂的 Cu 原子效率显著降低。
