Dual-template-driven in situ synthesis of Cu-SSZ-39 catalysts: synergistic structure regulation for excellent NH3-SCR activity and hydrothermal stability

Abstract

The speciation and distribution of Cu in SSZ-39 zeolite have a significant influence on its catalytic activity and hydrothermal stability in NH₃-SCR. Herein, we report a dual-template-driven in situ synthesis strategy to fabricate Cu-SSZ-39 catalysts, where a N,N-dimethyl-3,5-dimethylpiperidinium cation (DMDMP⁺) and a copper ammonia complex (Cu–TETA) collaboratively regulate framework topology and copper speciation. A series of Cu-SSZ-39 catalysts with different Cu contents (1.3, 3.6 and 5.8 wt%) and similar cubic structures were prepared. Unlike conventional post-synthesis ion-exchange methods, this dual-template-driven in situ synthesis strategy enables the simultaneous crystallization of the SSZ-39 framework and incorporation of isolated Cu²⁺ ions at framework Al sites. The DEDMP⁺ template directs the formation of 8-membered ring micropores with enhanced structural crystallinity, while triethylene tetramine (TETA) coordinates with Cu ions to suppress CuO_x cluster formation. The dual-template synergy stabilizes [Cu(OH)]⁺ active sites while strengthening acid sites, which collaboratively facilitate the conversion of NO at low temperatures (<250 °C). The hydrothermal aging tests demonstrate that the in situ synthesized catalysts have higher hydrothermal stability, attributed to spatially confined Cu²⁺ ions that mitigate dealumination through strong Al–O–Cu bonding. As a consequence, the optimized Cu_3.6-SSZ-39 catalyst demonstrates exceptional NH₃-SCR performance, achieving >99% NO conversion between 225 and 525 °C (GHSV = 60 000 h⁻¹) and retaining >90% of its initial activity after hydrothermal aging at 750 °C for 10 h. This work establishes a paradigm for designing hydrothermal-resistant zeolite catalysts through synthesis control of active site architecture, providing critical insights for meeting stricter nitrogen oxide emission standards.