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DB-FTIR Spectroscopy Unravels Confinement-Driven Modulation of Cu Species in Zeolite Catalysts for Low- Temperature NH3-SCR of NOx

Abstract

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 NOx, 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 NOx abatement technologies to meet increasingly stringent emission regulations.