Controlled synthesis of Cu-based SAPO-18/34 intergrowth zeolites for selective catalytic reduction of NO by ammonia.

Cu-based SAPO-18, SAPO-18/34 intergrowth and SAPO-34 zeolites were applied for the selective catalytic reduction of NO by ammonia (NH-SCR) catalysts. Comprehensive characterization results revealed that the SAPO-18/34 with higher amount and strength of acid sites could facilitate the generation of more isolated copper ions (Cu and Cu) and suppress the formation of CuO, which might account for the fact that intergrowth crystal structure of Cu-SAPO-18/34 exhibited higher fresh NH-SCR activity, more robust hydrothermal durability and better SO-resistance ability than that Cu-SAPO-18 and Cu-SAPO-34. In situ DRIFTS results provided the formation of reaction intermediates, such as -NH, NH, NO, NO, etc. Eley-Rideal (E-R) and Langmuir-Hinshelwood (L-H) reaction mechanisms were both involved in Cu-based SAPO-18 and SAPO-18/34 intergrowth zeolites, but the L-H mechanism dominated the NH-SCR reaction, in addition, Cu-SAPO-34 only followed "L-H" mechanism.