Cu-ZSM-5 catalyst synthesis via ion-exchange with ammonia solution of copper hydroxysalts

• Published in: Microporous and mesoporous materials 2024-03, Vol.367, p.112966, Article 112966
• Main Authors: Yashnik, S.A., Surovtsova, T.A., Salnikov, A.V.
• Format: Article
• Language: English
• Subjects: Copper dihydroxycarbonate; Copper trihydroxynitrate; Copper-ammonia complex; Cu-ZSM-5; DeNOx
• ISSN: 1387-1811
• DOI: 10.1016/j.micromeso.2023.112966

The properties of dihydroxycarbonate (malachite) and trihydroxynitrate of copper were studied in order to apply their ammonia solutions for the synthesis of copper-substituted ZSM-5 zeolites. Copper concentration and NH4OH/Cu2+ ratio in the solutions varied 1–12 g/l and 6–30, respectively. The parameters of Langmuir, Freundlich, Dubinin-Radushkevich, and Temkin isotherms revealed the favorability of the chosen conditions and the chemical nature of [Cu(NH3)n]2+ ions sorption by zeolite. For both copper salts, the sorption capacity of H-ZSM-5 for Cu2+ ions was higher in the solutions having NH4OH/Cu2+ = 6–10 compared to 30. To identify the synthesis and structure – activity relationship correlations, the ammonia solution and Cu-ZSM-5 samples were characterized by EPR, UV–visible spectroscopy, temperature-programmed reduction by hydrogen (H2-TPR). The calcined Cu-ZSM-5 samples produced at NH4OH/Cu2+ = 6–30 contained two types of the isolated Cu2+ ions (bare Cu2+ and [Cu(OH)]+), differing in their Redox properties. Their reducibility improved with an increase in the copper loading and with a decrease in NH4OH/Cu2+. At NH4OH/Cu2+ = 6–10, the samples additionally comprised the structures of Cu2+ ions with extra-lattice oxygen (ELO), which were formed due to hydrolysis of [Cu(NH3)n(H2O)]2+ to [Cu(NH3)n(OH)]+ and then to [Cu(OH)2Cu]2+. Cu2+–ELO structures possessed a greater ability to complete reduction than both types of isolated Cu2+ ions. Correlations with DeNOx properties in selective catalytic reduction (SCR) of NO by propane and ammonia are discussed. [Display omitted] •Synthesis of ion-exchanged Cu-ZSM-5 using ammonia solutions of copper hydroxysalts.•NH4OH/Cu2+ in solution affect copper content and type of Cu-ions loaded in ZSM-5.•At NH4OH/Cu2+ = 30, there is 2 types of isolated Cu2+ ions differing in Redox.•At NH4OH/Cu2+ = 6–10, reducibility is improved due to Cu2+–ELO structures.•Cu2+–ELO structures enhance SCR NO performance compared with isolated Cu2+ ions.