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.     

Catalytic Activity of Boron-Beta Zeolite Modified with Indium in the Epoxidation of Cinnamyl Alcohol

Liquid-phase epoxidation of cinnamyl alcohol was carried out with hydrogen peroxide as oxidizing agent using indium-containing boron- and aluminium-beta zeolites. It was proved that InO⁺ ions, created by oxidation of univalent indium cations incorporated into beta zeolite by reductive solid-state ion exchange, play an important role in the activation of hydrogen peroxide. The indium-hydroperoxo complex formed in beta zeolite pores was found to be accessible by the bulky cinnamyl alcohol molecules. Among the applied catalysts In/H[B]-beta (containing 7.6% In₂O₃/g) showed the highest selectivity in cinnamyl alcohol epoxidation.     

Study on the reactivity of In2O3 in mixtures with ammonium-zeolites

In ground mixtures of In₂O₃ and NH₄Y, incorporation of In⁺ cations into the zeolitic phase occurs upon thermal treatment by partial reductive solid-state ion exchange associated with oxidation of ammonium ions or released ammonia to N₂ and NH₂OH. Cationic InO⁺ species, created in zeolites by reductive solid-state ion exchange of In₂O₃/NH₄-zeolite mixtures in hydrogen atmosphere and subsequent oxidation of the In⁺ lattice cations by oxygen, do not undergo autoreduction up to 970 K. Reductive solid-state ion exchange easily proceeds in carbon monoxide atmosphere at temperatures between 620 and 770 K. The significance of these observations for the use of indium-containing zeolites as catalysts is discussed.