Formation of K clusters in K-form zeolite ZK-4ʹs with Si/Al>1

K atoms are dilutely adsorbed onto zeolite K-form ZK-4ʹs, which have an LTA type framework structure, with wide variation of Si-to-Al atomic ratios. Formation of cationic K clusters with a size of the α-cage is evidenced by both notable absorption bands observed at ca. 1 eV and no hyperfine structures in the ESR spectra.