Self-assembling of silver and copper small clusters within the zeolite cavities: prediction of geometry

The factors affecting a self-assembling of certain kind of silver and copper clusters during reduction of ion-exchanged forms of zeolites in hydrogen were studied. Conditions leading to the preferable M8 cluster formation were revealed. A matching of zeolite void and cluster sizes was found to be the key factor facilitating this process. Ag8 clusters can be easily stabilized in the zeolites with certain pore size (a cross-section in the range of 0.63–0.67 nm). Zeolites possessing voids wider than 0.70 nm stabilize these clusters only for low reduction temperatures. Small pores possessing at least one axis of pore cross-section ≤0.63 nm do not stabilize Ag8 clusters. Cu clusters assigned to Cu8 were predicted to be formed in narrow pores of erionite much easier than in mordenite voids. Comparison of experimental UV–Vis spectra with the results of ab initio calculations for selected M8 isomers was performed. The difference between Ag8 and Cu8 cluster models is discussed.