Dynamic Cu pairing within SSZ-13 zeolites: balancing low-temperature activity and hydrothermal stability for NH₃-SCR

Cu/SSZ-13 serves as the benchmark catalyst for ammonia selective catalytic reduction (NH₃-SCR) of NO_x from diesel engine exhaust, yet its further development is constrained by the trade-off between low-temperature activity and hydrothermal stability. Recent mechanistic advances reveal that the active Cu sites are not static isolated ions, but dynamically evolving NH₃-solvated species capable of migration and transient pairing within CHA cages. Under reaction conditions, NH₃ solvated Cu ions become mobile and undergo transient pairing, governing efficient low-temperature redox cycling through multinuclear Cu intermediates. However, excessive mobility may also accelerate Cu aggregation and hydrothermal deactivation. Balancing Cu mobility and stability therefore emerges as the central challenge in next-generation Cu/SSZ-13 catalysts. In this review, we discuss how Cu speciation, Al distribution, framework composition, and secondary cations govern the mobility-pairing-stability relationship in Cu-SSZ-13. We further highlight emerging strategies for balancing the Cu mobility and anchoring strength and outline future opportunities for designing the next-generation dynamic single-site zeolite catalyst beyond conventional static active-site models.