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 Cu(2+)) as probe molecules. Two zeolites were studied: one of them contained mostly Cu(+)(exch.), whereas another one contained mostly Cu(2+) 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(2+)(exch.) was reduced in the first order before Cu(2+)(ox.) Ethanol reduced mostly Cu(2+) and, also, some amounts of Cu(+). The treatment with oxygen caused the oxidation of Cu(+) (both Cu(+)(exch.) and Cu(+)(ox.)) to Cu(2+). The adsorption of NO at 190K produced Cu(+)(NO)(2) dinitrosyls, but heating to room temperature transformed dinitrosyls to mononitrosyls and increased the Cu(2+) content.