Study of the reductive solid-state ion exchange of indium into NH4NaY zeolite

Quantitative data obtained by thermal analysis proved to be consistent with the stoichiometry expected for incorporation of indium(I) ions into Y zeolite by reductive solid-state ion exchange upon treatment of ground In2O3/NH4NaY mixtures in a hydrogen atmosphere at temperatures of 620-760 K. Detailed information on the complex process was obtained by IR spectroscopy. Both high frequency (HF) and low frequency (LF) hydroxyl groups are involved in the solid-state ion-exchange process, the HF ones showing higher reactivity. Reoxidation of the formed indium(I) lattice cations was found to proceed at relatively low temperatures (300-400 K) and to result, dependent on the excess of hydroxyl groups over In+ lattice cations, in the formation of In3+ and/or cationic In(III) species comprising 'extra-framework oxygen'. The cationic indium species obtained after reduction and reoxidation were characterized by their interaction with pyridine applied as probe molecule. Adsorption of water on the cationic indium(III) species results in the formation of Bronsted-acid sites (Zn(OH)(2)(+)) the acid strength of which is significantly weaker than that of 'bridged' hydroxyls. The reduction/reoxidation cycle proved to be fully reversible.