Copper sites in zeolites : quantitative IR studies

Quantitative IR studies were realized in order to determine the concentration of various kinds of Cu sites in zeolites CuZSM-5, CuITQ-2, CuTNU-9, and CuY. These zeolites contained Cu in the form of $Cu^{2+}$, $Cu^{+}$ (in the form of exchange cations $Cu^{+}_{ex.}$ and oxo-form $Cu^{+}_{ox}$) and metallic $Cu^{o}$ (in reduced samples). The experimental conditions in which known amounts of CO (used as probe molecule) reacted with each kind of Cu sites in CuZSM-5 were elaborated and subsequently the extinction coefficients of IR band of CO in $Cu^{n+}$(CO) adducts were established. Following values of the extinction coefficients of monocarbonyl bands were obtained: 0.11$cm^{2}$/$\mu$mol for $Cu^{2+}$(CO), 1.30$cm^{2}$/$\mu$mol for $Cu^{+}_{ex}$(CO), 0.91 $cm^{2}$/$\mu$mol for $Cu^{+}_{ox}$(CO), and 0.79$cm^{2}$/$\mu$mol for $Cu^{o}$(CO). The procedure elaborated for CuZSM-5 was also applied for other zeolites. Consequently, the concentrations of $Cu^{2+}$, $Cu^{+}$ both in exchange positions and oxo-forms, as well as of $Cu^{o}$ were determined in CuZSM-5 treated at various conditions (reduced, oxidized and treated with $H_{2}O$) as well as in zeolites CuZSM-5, CuITQ-2, CuTNU-9, and CuY.