Evaluation of Cu/SAPO-34 Catalysts Prepared by Solid-State and Liquid Ion-Exchange Methods for NO Removal by NH₃-SCR

Cu/SAPO-34 catalysts are prepared using solid-state ion exchange (SSIE) and liquid ion exchange (LIE). SSIE is conducted by calcining a physical mixture of H-SAPO-34 zeolite and CuO nanoparticles at elevated temperatures (500-800 °C). The conventional LIE method is conducted by exchanging Na-SAPO-34 with Cu(COOCH₃)₂ aqueous solution with a final calcination step at 500 °C. Catalysts were fully characterized, focusing on Cu species identification. The NH₃-SCR activity is evaluated for NO removal. Cu/SAPO-34 catalysts synthesized by SSIE at 700 °C achieved an optimal reaction rate, which was correlated with a higher proportion of Cu²⁺ ions. The activation energies of Cu/SAPO-34 catalysts prepared by SSIE and LIE with varying copper loadings are 32-38 and 42-47 kJ mol^-1, respectively. The SSIE catalysts achieve higher turnover frequency than LIE catalysts for a similar copper content, which decreases on increasing the copper loading. These results provide evidence that Cu ions exchanged into the Cu/SAPO-34 catalysts synthesized by SSIE present higher activity than those prepared by LIE for NO removal by NH₃-SCR.