Comparative study of natural and synthetic clinoptilolites containing silver in different states

The crystalline structure of the Ag-synthetic clinoptilolite was not affected by the thermal reduction of Ag; however, the Ag-natural clinoptilolite samples were less thermally stable. In synthetic and natural clinoptilolites after reduction at 100 °C, small clusters (radius of <0.5 nm) located inside the channels along with metal particles (with radius <7 nm) on the external surface were observed. In Ag-natural clinoptilolite reduced at 100 °C, along with the small Ag2+ and Ag4δ+ clusters stabilized inside clinoptilolite pores, large Ag80 and Ag8δ+ clusters can be formed inside large mordenite channels or in the interstitial spaces of the particles that compose this mineral. Reduction at 400 °C leads to disappearance of silver clusters and large particle formation. In both supports the particles cannot be located in the zeolite cavities, which are much smaller.