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, CulTQ-2, CuTNU-9, and CuY. These zeolites contained Cu in the form of Cu2+, Cu+ (in the form of exchange cations Cu-ex(+). and oxo-form Cu-ox(+)) and metallic Cu (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 Cun+(CO) adducts were established. Following values of the extinction coefficients of monocarbonyl bands were obtained: 0.11 cm(2)/mu mol for Cu2+(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 degrees(CO). The procedure elaborated for CuZSM-5 was also applied for other zeolites. Consequently, the concentrations of Cu2+, Cu+ both in exchange positions and oxo-forms, as well as of Cu were determined in CuZSM-5 treated at various conditions (reduced, oxidized and treated with H2O) as well as in zeolites CuZSM-5, CuITQ-2, CuTNU-9, and CuY. (C) 2012 Elsevier Inc. All rights reserved.