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

Abstract

Cu-SSZ-13 (CHA zeotype) zeolites are commenly used in diesel engines for the selective catalytic reduction (NH3-SCR) of nitrogen oxides (NOx). 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 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 OSDA, enabling rapid crystallization of SSZ-13. The resulting Cu-SSZ-13 demonstrated comparable NH3-SCR performance to conventionally synthesized Cu-SSZ-13 (Cuconv-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 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 Ce(III) precursor inhibited CuOx formation during hydrothermal ageing, while the Ce(IV) precursor favored the formation of CeO2, decreasing zeolite stability and promoting CuOx 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.