EPR study of Cr5+ and Cu2+ in some zeolites introduced by solid- and liquid-state reactions

Abstract

This study reports on the EPR of Cr5+ and Cu2+ ions, introduced by solid- and liquid-state reactions with the synthetic zeolites 3A, 4A and 5A, and the natural zeolite clinoptilolite. Cr3+ was oxidized to Cr5+ in the samples, the coordination around Cr5+ being square pyramidal. Superhyperfine (shf) interaction of Cr5+ with Al-27 nucleus was observed in both solid- and liquid-state-introduced 5A zeolite, whereas this shf could not be observed for the solid-state introduced 4A zeolite. The liquid-state Cr-introduced 4A zeolite needed a heat treatment at 473 K for 1/2 h for the appearance of shfs. Furthermore, it has been found that the coordination structure around the Cu2+ is square pyramidal in solid-state introduced samples, whereas it is octahedral in the liquid-state introduced ones.