Redox behaviour of transition metal ions in zeolites. Part 4.—Kinetic study of the reduction and reoxidation of copper–Y zeolites

Abstract

The uptake of hydrogen and oxygen by (Cu, Na)–Y zeolites has been followed kinetically in a volumetric system. The temperature region investigated was between 273 and 773 K. The influence of several parameters on the reducibility of Cu²⁺ has been investigated: the degree of cation exchange, the presence of Cu²⁺ complexing ligands, the procedure of sample preparation and degassing.

The formation of Cu⁺ ions is determined mainly by the mobility of Cu²⁺ ions in the zeolite. The preparational and degassing procedure has a drastic influence on the reducibility of the Cu²⁺ species. The rate of formation of Cu^° is determined by the diffusion of the reactant through the pores.

Cu⁺ ions and small Cu^° clusters are reoxidized reversibly, the mobility of Cu⁺ ions determining the rate of the process. The reoxidation of Cu^° external to the zeolite consists of a homothetic attack of oxygen on the Cu^° particles.