R.M. Mihályi

Study of the reductive solid-state ion exchange of indium into an NH4-beta zeolite

Abstract 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 In 2 O 3 NH 4 NaY 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 (In(OH)2+) the acid strength of which is significantly weaker than that of ‘bridged’ hydroxyls. The reduction/reoxidation cycle proved to be fully reversible.

Transalkylation of toluene with cumene over zeolites Y dealuminated in solid-state: Part II. Effect of the introduced Lewis acid sites

The effects of the introduced Lewis acid sites of different kind (InO+ or AlO+) and the variation of InO+ concentration on the catalytic behavior of dealuminated in solid-state HY zeolites in the reaction of cumene–toluene transalkylation have been studied. The catalysts, indium modified HY(3.7) and ultra stable zeolite USY(3.4), containing essentially equivalent amounts of framework aluminum and Lewis acid sites (InO+ and AlO+, respectively), have been compared to the initial HY(3.7), not containing any extra-framework aluminum (EFAl). Strictly controlled conditions were used for the formation of Lewis acid sites: through reductive solid-state ion exchange (RSSIE) for InO+ or by steaming in the case of AlO+. The ratio between the Lewis and Broensted acid sites was varied by progressive replacement of the protons by InO+ cations in HY(5.6) zeolite. The zeolites modified by monovalent (InO+ and AlO+) have, as a result, an enhanced catalytic activity in comparison with HY(3.7). This effect is mainly due to intense side reactions of dealkylation, oligomerization, cracking and re-alkylation at the expense of the cymenes formation. The data for the distribution of the reaction products suggest a highly preferred mechanism of dealkylation/alkylation with the increase of the Lewis/Broensted acid site ratio. The presence of cation-connected Lewis acid sites is supposed to be responsible for the fast samples’ deactivation.

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.

Particular features of the introduction of In into MCM-41 by reductive solid-state ion exchange

Abstract The incorporation of indium cations into aluminum-containing mesoporous MCM-41 by reductive solid-state ion exchange (RSSIE) was studied by XRD, FTIR spectroscopy, TPR and TPDA techniques. It is shown that the RSSIE process proceeds as easily as in the case of zeolites. However, some typical differences associated with the specific acid properties of these molecular sieves were observed and are discussed in terms of the peculiar structure and composition of the framework.

Acidity modification of MCM-22 for selective p-xylene formation in toluene disproportionation

Improved p-xylene selectivity upon toluene disproportionation has been achieved with MCM-22 zeolite by controllable modification of its acidity through proton replacement with InO + and Cs + counter ions. The former cations were introduced by Reductive Solid-State Ion Exchange (RSSIE) starting from In 2 O 3 . The favorable effect of such modification has been compared with the merely proton replacement with cesium cations accomplished by Solid-State Ion Exchange (SSIE). It was found that the Lewis-connected InO + acid sites contribute to the enhanced release of the p-isomer.