Temperature programmed reduction of copper ions in zeolites

Abstract

Temperature programmed reduction (t.p.r.) has been used to study the redox behaviour of copper ions in X and Y zeolites. Two distinct Cu^II to Cu^I reduction processes are discernible in both X and Y zeolites. These two processes have been attributed to the reduction of Cu^II ions occupying sodalite and supercage sites; a small fraction of the Cu^II ions, assumed to occupy hexagonal prism sites, remain unreduced. At 773 K in nitrogen, autoreduction of both sodalite and supercage Cu^II occurs in X zeolite, while only supercage Cu^II ions are autoreduced in Y zeolite. The reductions are reversible in Y zeolite, but some CuO is formed in X which is subsequently reduced by a third process. Activation energies (kJ mol^–1) were obtained as follows: Cu^II to Cu^I(sodalite cages) 84 ± 13, Cu^II to Cu^I(supercages) 64 ± 10 and CuO to Cu⁰(X-type zeolite) 49 ± 7.