ESR studies of silver clusters in the isostructural A and ZK-4 molecular sieves

Cationic silver clusters formed in γ-irradiated Ag⁺-exchanged Linde 4A zeolite and isostructural synthetic ZK-4 zeolite with Si/Al ratio of 1.2 and 2.4 have been studied by electron spin resonance (ESR) spectroscopy. Whereas dehydrated AgNa-A zeolite shows remarkable ability for stabilization of Agⁿ⁺₆ clusters in AgNa-ZK-4 zeolites hexameric silver clusters are not formed at all. In ZK-4 samples exposed to water or methanol tetrameric silver clusters Ag³⁺₄ are efficiently produced. Although geometrical size constraints play a crucial role with respect to cluster nuclearity and stability, in this paper we show that other factors like total cation capacity and/or the presence of molecular adsorbates can affect the silver agglomeration process to a great extent.