Infrared-spectroscopic detection and distinction of indium cations of different oxidation states in zeolites

In⁺ cations introduced by reductive solid-state ion exchange into zeolites (Y, ZSM-5, mordenite) and cationic InO⁺ species created by oxidation of the incorporated univalent cations were found to be detectable and distinguishable by IR spectroscopy using pyridine as probe molecule. Relatively weak interactions of In⁺ lattice cations with pyridine give rise, after degassing at temperatures not higher than 370 K, to typical bands at 1446 and 1599 cm⁻¹. After oxidation to InO⁺, these bands are shifted to 1452 and 1610 cm⁻¹, being significantly more resistant towards degassing. Because of restrictions in the accessibility of InO⁺ to pyridine, the respective bands are absent in the spectra of mordenite.