Ch. Minchev

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.

Thermochemical and acidic properties of the zeolites offretite, omega and ZSM—5

Abstract The thermochemical and acidic properties of offretite, omega and ZSM—5 have been compared by thermal and X-ray analysis, infrared spectroscopy and temperatureprogrammed desorption of ammonia. It has been established that the temperature range of the decomposition of the organic cation depends on the zeolite structure, and is wider in the case of offretite. The decomposition of the NH 4 -forms of the three types of zeolites proceeds at higher temperatures than in the case of NH 4 -Y and also for the decomposition of the organic cation. The appearance of a high-temperature part in the t.p.d. curves of the samples is attributed to their stronger acidic properties after deammoniation. With respect to the strength of ammonia adsorption at 573 K, the decationized forms of the zeolites showed the sequence omega ∼ offretite>ZSM—5.

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.

Thermal decomposition of tripropylamine as a template in MeAPO-5 molecular sieves

The thermal decomposition of tripropylamine as a template occluded in the pores of MeAPO-5 aluminophosphate molecular sieves was investigated by means of TG, DTG and DTA. The effects of the incorporation of metal ions [Be, Mg, Ca, Ni, Fe(II), Fe(III) and Zn] in the crystal framework on the complete removal of template molecules and on the thermal stability of the samples were considered.ZusammenfassungMittels TG, DTG und DTA wurde die thermische Zersetzung von Tripropylamin, eingeschlossen in den Poren von MeAPO-5 Aluminophosphat-Molekularsieben untersucht. Es wurde weiterhin der Einfluß der Einlagerung von Metallionen [Be, Mg, Ca, Ni, Fe(II), Fe(III) und Zn] im Kristallgitter auf die vollkommene Abgabe der eingeschlossenen Moleküle und auf die thermische Stabilität der Proben untersucht.

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.

Thermal decomposition of organic templates in silicoaluminophosphate molecular sieves with various structures

The decomposition of organic templates in molecular sieves SAPO-5, SAPO-11, SAPO-20, SAPO-34 and SAPO-37 was investigated by TG, DTG and DTA. In the case of SAPO-S, the decompositions of various organic templates were studied. The effects of the type of crystal structure, the pore size and the channel system on the complete removal of the organic material were considered.ZusammenfassungMittels TG, DTG und DTA wurde die Zersetzung von organischen Modelle in SAPO-5, SAPO-11, SAPO-20, SAPO-34 und SAPO-37 Molekularsteben untersucht. Im Falle von SAPO-5 wurde die Zersetzung verschiedener organischer Modelle untersucht. Weiterhin wurde auf den Einflu\ von Kristallstruktur, Porengrö\e und Kanalsystem auf das vollstÄndige Austragen des organischen Materiales eingegangen.

Solid state modification of as-synthesized SAPO molecular sieves withindium

Solid state ion exchange of the protonic acid sites in SAPO-5, SAPO-34 and SAPO-37 molecular sieves with indium can be accomplished via thermal treatment of mechanical mixtures of as-synthesized SAPOs with In 2 O 3 in an inert gas. The organic template acts as a reducing agent in respect to the indium oxide and the volatile In 2 O is likely the intermediate species that further interacts with the SAPO protonic sites. The catalysts produced by this procedure possess very similar properties to the materials obtained through reductive solid state ion exchange of template free SAPOs that have been converted in an H + form and mixed with In 2 O 3 prior to the reduction with H 2 . Both acidity and catalytic activity in proton catalyzed reactions such as m-xylene and methanol conversions strongly decrease upon modification with indium. The novel procedure of template induced solid state ion exchange may be useful for modification of materials like SAPO-37 whose template free forms are less stable than the corresponding as-synthesized form.

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.

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.

Effect of the different modifications of A1PO-5 molecular sieve on its acidity and catalytic properties in methanol conversion to hydrocarbons

An AlPO-5 molecular sieve has been isomorphously substituted by one (Co or Si) or two (Co and Si) elements and studied in the catalytic conversion of methanol to hydrocarbons. The effect of different modifications on both acidity and catalytic behavior of this material was established and further discussed.