Reduction And Oxidation Of Cu Species In Cu-Faujasites Studied By Ir Spectroscopy

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, Cu-exch.(2+) was reduced in the first order before Cu-ox.(2+) 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.