V. Mavrodinova

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.

Influence of the Lewis acidity of indium-modified beta zeolite in the m-xylene transformation

Abstract The catalytic performance of NH4-beta zeolite containing different amounts of indium, introduced as In+ cations by the method of reductive solid-state ion exchange (RSSIE), has been studied in the m-xylene conversion. It has been shown that In cations regarded as coordinatively unsaturated species possessing Lewis acidity substantially change the catalyst stability and the selectivity of the reaction when performed in an inert atmosphere. An acceleration of the side reactions of disproportionation and coking has been observed on the In-modifications of zeolite beta and a mechanism of hydride ion abstraction and faster benzylic cation formation on them have been supposed. In presence of H2 these reactions are strongly suppressed at the expense of the main reaction of isomerisation. On the completely In-exchanged beta zeolite a partial bimolecular mechanism of isomerisation is suggested.

Toluene conversion on the zeolites offretite, omega and ZSM-5

Abstract The conversion of toluene and the accompanying formation of coke has been studied on the H-forms of the zeolites offretite, omega and Z5M-5. A qualitative correlation between the initial activity, the acidity and coke formation could be established. The p-selectivity of the ZSM-5 sample remains constant over a long time on stream. The selectivity of omega, and especially that of offretite increases with decreasing activity. As an explanation for these effects an increase of the diffusion paths by a closure of the pore entrances for the ZSM-5 and the interior of the pores of the omega and the offretite is discussed together with transition state selectivity. The results are further compared with (a) the selectivities of a number of other zeolites and (b) the results of theoretical calculations by Wei8,9.

Incorporation of cationic indium species into zeolite beta by template-induced reductive solid-state ion exchange

Reductive solid-state ion exchange (RSSIE) was found to proceed in mechanical mixtures of crystalline In2O3 and as-synthesized precursors of zeolite beta (TEA-beta) during thermal decomposition of the template (TEA) in an inert gas atmosphere or high vacuum. It was evidenced that gaseous decomposition products of the template play the decisive role as reductants in this process, which results in the incorporation of univalent indium cations into the zeolite structure. Accordingly, no reaction between In2O3 and the zeolitic component was observed during template decomposition in an oxidizing atmosphere. After RSSIE associated with thermal template decomposition both In+ and InO+ lattice cations could be detected by typical IR spectroscopic bands attributed to interactions of these ions with adsorbed pyridine. The trivalent indium species are probably formed by a redox process involving the reduction of protons (internal silanol groups) to H2 and oxidation of In+ into InO+. In line with this conclusion is the finding that part of the In+ cations are converted into InO+ upon contact with water.

Factors influencing the conversions of alkylaromatic hydrocarbons on high-silica zeolites: Part II. Presence of extralattice Al

Abstract The effect of different amounts of dislodged Al present in hydrothermally treated Y-type zeolites has been studied in the conversions of toluene, m -xylene, and alkylation of benzene with ethylene. T.p.d. of NH 3 is used to explain changes in the catalytic activity and modification of the strength and number of acid sites occurring in relation to the extralattice Al content. No indications for direct participation of the nonframework Al in the alkylaromatic conversions have been observed.

Solid-state ion exchange in beta zeolites. I: Alkaline chlorides/NH4-β

Abstract Solid-state ion exchange between Na and Cs chloride and two NH 4 -β zeolites with different SiO 2 /Al 2 O 3 ratios proceeding during heat treatment in He has been studied. Temperature-programmed gas evolution monitored by mass spectrometry (TPE/MS) and thermogravimetric analysis combined with 1-propylamine adsorption (DTG/1-PA) reveals differences in the rate of the reaction and the degree of exchange depending on the host zeolite and the guest salt used. The interaction is controlled not only by the temperature and the ability of the salt to disaggregate, but also by the type of exchangeable sites formed during the post-synthesis treatments.

Factors influencing the conversions of alkylaromatic hydrocarbons on high-silica zeolites: Part I. Structure and density of the active centers

Abstract High-silica faujasites prepared through hydrothermal treatment are compared with HZSM-5-type catalysts with almost the same Si Al lattice ratios in the conversions of toluene, m -xylene, and alkylation of benzene with ethylene. Disproportionation of m -xylene proceeds more intensively on Y-type zeolites than on ZSM-5 materials having practically equal or even higher active center concentration. The results confirm the predominant importance of the structural characteristics over the density factor for determining the differences in the disproportionation ability of these two types of zeolite catalysts with respect to alkylaromatics.

Solid-state encapsulation of Ag and sulfadiazine on zeolite Y carrier

HYPOTHESIS A new simplified procedure for encapsulation of antibacterial silver nanoparticles by Solid-state Ion Exchange (SSIE) procedure over zeolite Y, followed by deposition of sulfadiazine (SD) by dry mixing was examined for the preparation of topical antibacterial formulations. The ion-exchange and adsorptive properties of the zeolite matrix were utilized for the bactericidal Ag deposition and loading of antibiotic sulfadiazine. EXPERIMENTS Assessment of the encapsulation efficiency of both active components loaded by solid and liquid deposition methods was made by X-ray diffraction, TEM, FT-IR spectroscopy and thermogravimetric analysis (TGA). SD release kinetics was also determined. FINDINGS Sustained delivery of sulfadiazine has been observed from the Ag-modified zeolites compared to the parent HY material. It was found that if SD was loaded in solution, part of the zeolite silver ions was released and interacted with SD, forming AgSD. By solid-state SD deposition, the reaction between the drug and the silver was restricted within the limits of inter-atomic interaction, and total but prolonged drug release occurred.

On The Nature of the Catalytic Activity of SAPO-5

Abstract An attempt to estimate the nature of the catalytic activity of SAPO-5 was made by means of the “inner standard” approach. SAPO-5 materials were compared with model mixtures of HY introduced into an AlPO-5 matrix as well as with HZSM-5 and highly dealuminated HY. The selectivity patterns in m-xylene conversion support the assumption of a relatively homogeneous Si-incorporation. The generated active centers are situated far from each other as in the case of the highly dealuminated faujasite.