Redox behaviour of transition metal ions in zeolites. Part 3.—Auto-reduction of cupric ions in Y zeolites

Abstract

In CuY zeolites degassed at temperatures above 650 K cupric ions are reduced to some extent to cuprous ions.

Evidence for this process of auto-reduction was taken from the decrease in weight of the sample, and the detection of a desorbing gas in a volumetric system. The latter was identified as oxygen. U.v. reflectance spectroscopy showed directly the decrease of the Cu²⁺ species upon outgassing and their increase after oxygen adsorption. Excitation spectra showed the presence of Cu⁺ ions after high temperature degassing. Infrared spectroscopic techniques showed that Lewis sites are also formed upon degassing. A mechanism is proposed that accounts for the observations.