Induced Infrared Absorption of Molecular Oxygen Sorbed in Exchanged A Zeolites. 1. Intensity Analysis

Abstract

This paper presents induced infrared spectra of oxygen sorbed in two calcium exchanged A zeolites. Changes of the vibrational band upon adsorption include two effects: the appearance of an induced band, due to the electric field of the zeolite, and a frequency shift of this band, due to the interaction. An analysis of the evolution of the intensity of the IR band with respect to the number of sorbed molecules is performed, yielding a value of the intensity of the electric field at the adsorption site of O2 in CaA. The value of 2.8 × 1010 V/m derived from this analysis is very high compared to the electric field observed in other zeolites (0.8 × 1010 V/m in NaA obtained with nitrogen or 1.1 × 1010 V/m with methane). It probably reflects the large effective charge of the Ca cation in CaA and its position in an 8-ring window of the cavity. This analysis also indicates that the oxygen molecule coordinates end-on, in a linear or somewhat bent manner, to the Ca2+.