Reduction and Oxidation of Cu Species in Cu-faujasites Studied by IR Spectroscopy

• Main Authors: Łukasz Kuterasiński, Jerzy Podobiński, Ewa Madej, Małgorzata Smoliło-Utrata, Dorota Rutkowska-Zbik, Jerzy Datka
• Format: Article
• Language: English
• Published: MDPI AG 2020-10-01
• Series: Molecules
• Subjects: CO/NO-IR spectroscopy; Cu sites; reduction; hydrogen; ethanol
• Online Access: https://www.mdpi.com/1420-3049/25/20/4765
• ISSN: 1420-3049

The process of reduction (by hydrogen and ethanol) and oxidation (by oxygen and NO) of Cu sites in dealuminated faujasite-type zeolites (of Si/Al = 31) was studied by infrared (IR) spectroscopy with CO (for Cu⁺) and NO (for Cu²⁺) as probe molecules. Two zeolites were studied: one of them contained mostly Cu⁺_exch., whereas another one contained mostly Cu²⁺and Cu⁺_ox.The susceptibility of various forms of Cu for reduction were investigated. IR experiments of CO sorption evidenced that Cu⁺_ox.was more prone for the reduction than Cu⁺_exch.According to NO sorption studies, Cu²⁺_exch.was reduced in the first order before Cu²⁺_ox.Ethanol reduced mostly Cu²⁺ and, also, some amounts of Cu⁺. The treatment with oxygen caused the oxidation of Cu⁺ (both Cu⁺_exch.and Cu⁺_ox.) to Cu²⁺. The adsorption of NO at 190K produced Cu⁺(NO)₂ dinitrosyls, but heating to room temperature transformed dinitrosyls to mononitrosyls and increased the Cu²⁺ content.