Boosting the low-temperature activity of fast-synthesized Cu-SAPO-18 for NH3-SCR by hydrothermal treatment

Cu-SAPO-18 catalysts attracts increasing attention in the reaction of selective catalytic reduction (SCR) of nitrogen oxides (NOx), but the catalyst synthesis process is complicated and time-consuming. Also, it is urgent to enhance the low-temperature catalytic conversion of NOx for practical applications. Herein, we reported a fast synthesis method to prepare the Cu-SAPO-18 catalysts in 32-80 h, and the catalysts showed an excellent catalytic performance of over 80 % NO conversion at 260-480 degrees C. The crystalline of the catalysts was improved in short crystallization time and high crystallization temperature, accelerating the NH3-SCR reaction. The low temperature activity of all catalysts was improved after hydrothermal treatment, and the temperature range of over 80 % NO conversion was extended to 190-515 degrees C for the optimized catalyst, which was due to the increasing active Cu2+ species (ZCuOH and Z2Cu, where Z represents an anionic site on the zeolite framework). The redox cycle of Cu2+/Cu+ was accelerated and more Lewis acid sites on the catalyst enhanced the NO/NH3 adsorption and activation, promoting the low-temperature catalytic activity. Furthermore, after hydrothermal treatment, part of Z2Cu species converted to ZCuOH species, which exhibited stronger NO adsorption energies (-2.06 eV) than that of Z2Cu (-1.38 eV) based on theoretical calculation. Both fresh and aged catalysts showed remarkable SO2/H2O resistance. This work reveals the effects of hydrothermal treatment on the Z2Cu and ZCuOH species, which is helpful to prepare the fast-synthesized zeolite catalysts with excellent low-temperature SCR performance.