Controlled synthesis of Cu-based SAPO-18/34 intergrowth zeolites for selective catalytic reduction of NOx by ammonia.

Cu-based SAPO-18, SAPO-18/34 intergrowth and SAPO-34 zeolites were applied for the selective catalytic reduction of NOx by ammonia (NH3-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 (Cu2+ and Cu+) and suppress the formation of CuOx, which might account for the fact that intergrowth crystal structure of Cu-SAPO-18/34 exhibited higher fresh NH3-SCR activity, more robust hydrothermal durability and better SO2-resistance ability than that Cu-SAPO-18 and Cu-SAPO-34. In situ DRIFTS results provided the formation of reaction intermediates, such as -NH2, NH4+, NO3-, NO2-, 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 NH3-SCR reaction, in addition, Cu-SAPO-34 only followed "L-H" mechanism.