Enriching framework Al sites in 8-membered rings of Cu-SSZ-39 zeolite to enhance low-temperature ammonia selective catalytic reduction performance

A research team led by Prof. Jihong Yu and Prof. Wenfu Yan (Jilin University, State Key Laboratory of Inorganic Synthesis and Preparative Chemistry) recently developed a potassium-based Cu-SSZ-39 catalyst (Cu-SSZ-39-K) with an increased concentration of Al in the 8-memberedrings. This design promotes the formation of more [Cu(OH)]⁺-Z species, resulting in nearly double the NO_x conversion at 150-225°C and excellent retention of activity after hydrothermal ageing at 800°C. The work was published inthe Chinese Journal of Catalysis (DOI: 10.1016/S1872-2067(25)64800-5).

Nitrogen oxides (NO_x) isone of the major contributors to air pollution. In 2023, more than 60% of China's total NO_x emissions originated from mobile sources, particularly diesel engine exhaust. During the cold-start phase of diesel operation, up to 80% of total NO_x emissions in the test cycle are released. Enhancing the low-temperature performance of NH₃-SCR catalysts is therefore critical for effective NO_x mitigation.

Cu-SSZ-39 is a promising NH₃-SCR catalyst because of its superior hydrothermal stability compared with Cu-SSZ-13. However, its low-temperature activity remains insufficient, especially under increasingly stringent emission regulations that require stronger NO_x control during cold-start. To address this challenge, the team used K⁺instead of Na⁺ during SSZ-39 synthesis to tune the framework Al distribution. This approach produced SSZ-39-K, which contained 37.6% more Al-pairs in the 8-memberedrings than conventional SSZ-39 (SSZ-39-T). DFT calculations and H₂-TPR measurements showed that this modification significantly increased the formation of [Cu(OH)]⁺-Z species after Cu exchange, thereby enhancing the low-temperature activity. After hydrothermal ageing at 800 °C for 16 h, Cu-SSZ-39-K maintained high-temperature activity comparable to Cu-SSZ-39-T, while its NO_x conversion at 150-225 °C was nearly twice as high. The synthesis method also delivered a 65% yield of SSZ-39-K—double the highest value (33%) previously reported—high lighting its promise for industrial-scale production.

This work presents an effective strategy for tailoring Al distribution in zeolites and offers a practical route to improving the low-temperature NH₃-SCR performance of Cu-SSZ-39 catalysts.

About the journal

Chinese Journal of Catalysis is co-sponsored by Dalian Institute of Chemical Physics, Chinese Academy of Sciences and Chinese Chemical Society, and it is currently published by Elsevier group. This monthly journal publishes in English timely contributions of original and rigorously reviewed manuscripts covering all areas of catalysis. The journal publishes Reviews, Accounts, Communications, Articles, Highlights, Perspectives, and Viewpoints of highly scientific values that help understanding and defining of new concepts in both fundamental issues and practical applications of catalysis. Chinese Journal of Catalysis ranks among the top six journals in Applied Chemistry with a current SCI impact factor of 17.7.

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