Rapid synthesis and hydrothermal stability enhancement of Cu-SSZ-13 zeolites for nitrogen oxide removal

Abstract

Cu-SSZ-13 (CHA topology) zeolites are commonly used in diesel engines for the selective catalytic reduction (NH₃-SCR) of nitrogen oxides (NO_x). However, their synthesis typically requires long crystallization times and their durability in NH₃-SCR is limited. Herein, we achieved a significant reduction in crystallization time, synthesizing SSZ-13 zeolites in just 6 h by using SAPO-18 seeds and a minimal amount of an organic structure-directing agent (OSDA). The OSDA/Si ratio was reduced by a factor of 16 compared to conventional methods. Crystallization studies revealed that SAPO-18 seeds promoted the formation of four-membered rings (4MRs), which quickly combined into double 6-membered rings (D6Rs) with the assistance of the OSDA, enabling rapid crystallization of SSZ-13. The resulting Cu-SSZ-13 demonstrated comparable NH₃-SCR performance to conventionally synthesized Cu-SSZ-13 (Cu_conv-SSZ-13). Moreover, we introduced Ce ions into Cu-SSZ-13 to enhance its hydrothermal stability and explored the effects of different metal precursors on the catalytic performance. The optimized CuCe(III)_0.5-SSZ-13 exhibited superior hydrothermal stability compared to Cu-SSZ-13. Conversely, CuCe(IV)_1.0-SSZ-13 and CuCe(III)_0.5Ce(IV)_1.0-SSZ-13 displayed reduced hydrothermal stability. Characterization revealed that using the Ce(III) precursor inhibited CuO_x formation during hydrothermal ageing, while the Ce(IV) precursor favored the formation of CeO₂, decreasing the zeolite stability and promoting CuO_x formation. This work presents a novel approach for rapid SSZ-13 synthesis and highlights the critical role of metal precursors in the performance of bimetallic SSZ-13 zeolites.