Insight into solid-state ion-exchanged Cu-based zeolite (SSZ-13, SAPO-18, and SAPO-34) catalysts for the NH3-SCR reaction: The promoting role of NH4-form zeolite substrates

In this paper, Cu-exchanged SSZ-13, SAPO-18, and SAPO-34 were synthesized via a novel green and sustainable solid-state ion-exchange (SSIE) route with excellent NH3-SCR activities, which could simplify the preparation process and reduce the wastewater production in comparison to conventional aqueous ion-exchange route. The results also proved that Cu-exchanged zeolites synthesized by SSIE technology presented higher Cu ion-exchange (IE) levels and better SCR activities than those prepared via the traditional incipient impregnation route. In the case of SSIE, the usage of NH4-form substrates could achieve more Cu2+ ions and fewer CuOx than those H-form substrates since the formation of Cu(NH3)(x)(2+) intermediate could promote the Cu2+ mobility to facilitate Cu2+ occupying IE sites, which was favorable for the SCR reaction. The combined DFT data confirmed the SSIE reaction energy barriers between Cu(NO3)(2) and the NH4-form substrates were almost identical, whereas the higher reaction energy was required for H-form substrates. In-situ DRIFTS results manifested the labile species like NH4+ , -NH2 , NO2- , NO3- , NO2, etc were the reaction intermediates over the catalysts prepared from NH4-form substrates. The Langmuir-Hinshelwood (L-H) and Eley-Rideal (E-R) mechanisms contributed collectively over both Cu-SSZ-13 and Cu-SAPO-18 in the SCR reaction, however, the L-H mechanism dominated over CuSAPO-34.

Automated summary

Cu-exchanged zeolites synthesized via the solid-state ion-exchange (SSIE) route exhibited excellent NH3-SCR activities and higher Cu ion-exchange levels compared to traditional methods. NH4-form substrates promoted Cu2+ ion mobility and facilitated Cu2+ occupying exchange sites, beneficial for SCR reactions. Reaction intermediates like NH4+, -NH2, and NO2- were observed on catalysts prepared from NH4-form substrates.