DB-FTIR spectroscopy unravels confinement-driven modulation of Cu species in zeolite catalysts for low-temperature NH3-SCR of NOx

The confinement of active sites within zeolite frameworks critically governs the performance of Cu-based catalysts for low-temperature ammonia selective catalytic reduction (NH₃-SCR) of NO_x, but the mechanistic insights regarding the nature of active Cu species remain elusive. Here, we systematically elucidate the topology-driven modulation of Cu species by integrating advanced characterizations, including X-ray absorption spectroscopy, in situ dual-beam Fourier transform infrared spectroscopy, low-temperature CO/NO adsorption, and catalytic evaluations across Cu-SSZ-13, Cu-ZSM-5, Cu-Beta, and oxide-supported analogues. We demonstrate that, i) in comparison to MFI and BEA topologies, the strong spatial confinement within the CHA framework preferentially forms most abundant Cu⁺ sites with low-coordination numbers to carbonyl species, and stabilizes Z₂Cu²⁺ species in six-membered rings, enhancing Cu⁺/Cu²⁺ redox cycle and thus NO adsorption and nitrate turnover efficiency. ii) The ion-exchange and one-pot synthesis methods strongly influence the distribution and location Cu²⁺ species in Cu-SSZ-13 that further influence the activity. Mechanistic insights from in situ spectroscopy reveal that topology-governed Cu speciation dictates the formation and consumption of critical nitrate intermediates, enabling efficient low-temperature SCR cycles. These findings not only establish a clear topology-activity relationship for Cu-containing zeolite catalysts but also offer a mechanistic blueprint for the rational design of catalysts, advancing NO_x abatement technologies to meet increasingly stringent emission regulations.