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.

[Display omitted] • The solid-state ion-exchange technique achieved promoted Cu ion-exchange level. • The NH 4 - or H-forms zeolites led to various Cu ion-exchange levels. • The formation of Cu(NH 3) x 2+ was a critical factor for high Cu2+ dispersion. • The SCR reaction mechanisms were investigated by in situ DRIFTS. 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 NH 3 -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 NH 4 -form substrates could achieve more Cu2+ ions and fewer CuO x than those H-form substrates since the formation of Cu(NH 3) 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(NO 3) 2 and the NH 4 -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 NH 4 +, –NH 2 , NO 2 –, NO 3 –, NO 2 , etc were the reaction intermediates over the catalysts prepared from NH 4 -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 Cu-SAPO-34. [ABSTRACT FROM AUTHOR]