Judicious design of Cu-SSZ-39@ZSM-5 core–shell architectural catalyst for elevated hydrothermal stability in the NH3-SCR reaction

Abstract

Nitrogen oxides (NO_x) emitted from vehicle exhaust are major pollutants contributing to environmental and health challenges such as acid rain and photochemical smog. In response, NH₃ selective catalytic reduction (NH₃-SCR) stands out as one of the most practical denitrification technologies. The key to effective NH₃-SCR technology lies in the fabrication of highly efficient and stable catalysts. However, existing catalysts generally suffer from insufficient high-temperature hydrothermal stability. Herein, a Cu-SSZ-39@ZSM-5 catalyst with a core–shell architecture was prepared by a dual-template method with in situ Cu loading, followed by uniform coating of ZSM-5 shell. Characterization results indicated that the ZSM-5 shell mitigates Al leaching from the zeolite framework and retarded the deactivation of Cu species, thereby promoting the hydrophobicity and structural integrity of the catalyst. Catalytic performance tests revealed that the core–shell architecture significantly enhanced the high-temperature hydrothermal stability of the catalyst. After 12 hours of hydrothermal aging at 850 °C, the Cu-SSZ-39@ZSM-5 catalysts maintained NO_x conversion above 90% across a broad temperature window of 200–450 °C. Under severe operating conditions (i.e., 500 °C and 10% H₂O), the core–shell catalysts afforded over 10% higher activity compared to that of the uncoated counterpart. The correlations between catalytic performance (i.e., activity and stability) and shell thickness suggested an optimal shell thickness of approximately 20 nm for maximized overall performance. Therefore, this work provides a novel catalyst design with exceptional hydrothermal stability, offering a promising strategy for advancing NH₃-SCR technology in practical applications.