Location of extra-framework Co2+, Ni2+, Cu2+ and Zn2+ cations in natural and dealuminated clinoptilolite

Abstract In the present work a combination of chemically constrained Rietveld refinement and computer simulation is used for the determination of the positions of the extra-framework cations Co 2+ , Ni 2+ , Cu 2+ and Zn 2+ in the channels of clinoptilolite. The analysis of the metal rich clinoptilolites with two different Si/Al ratio (4.7 and 7.8) demonstrates that most of the cations are located in two extra-framework sites, the first one in the center of channel A and the second one in the center of channel B . In the case of the Cu 2+ exchanged zeolite with high Si/Al ratio (4.7), a third site is found. This site is located at 1.65 A of the center of the A channel and can be considered as a highly disordered first site. All the metal ions are coordinated to water molecules with no coordination to the zeolite framework. The presence of hydronium cations controls the relative occupancy of the transition metals in the observed sites.