I. Hannus

Dealumination of zeolites with phosgene

Abstract A novel dealuminating procedure with phosgene was applied to synthetic and natural zeolites, and the resulting changes in composition, structure and adsorption properties were assessed. The dealuminated samples were investigated by i.r. and X-ray spectroscopy, the adsorption Of nitrogen and elemental analysis. A new i.r. absorption band was observed at 930 cm −1 in the case of mordenite, in good correlation with the degree of dealumination. The highest adsorption capacity was attained at a dealumination temperature of 873 K; this was due to the removal of the impurities, while the nearly perfect crystallinity of the natural zeolites was maintained.

Adsorption and transformation of halogenated hydrocarbons over zeolites

Abstract The chloroflurocarbons (CFCs) are weakly adsorbed in the internal channels of the zeolite resulting in small wavenumber shifts on zeolites possessing no Bronsted acid centers, but hydrogen bonded adsorbed species are formed on Bronsted acidic samples. Some decomposition of CFCs was found upon adsorption at room temperature (RT) for HCFC 22, but CFCs having no hydrogen proved to be more stable against fragmentation. At higher temperature, fundamental interactions take place between the reactant and the zeolite, which can be followed easily by multinuclear ( 29 Si, 27 Al, 23 Na) solid state MAS NMR spectroscopy. The surface intermediate for the destruction of hydrogen containing reactant, i.e. HCOCl, is unstable and decomposes to CO and HCl as final products of the reaction. For CFCs known as more stable derivatives of the CFC family, phosgene was the surface intermediate. For this reaction, CO 2 and HCl or NaCl were the final products, depending on which (H + or Na + ) is the charge compensating cation. The complex feature of the destruction reaction of CFCs over zeolites is reflected by the appearance of different CFCs as products of dismutation reactions. A general observation was that AlCl 3 fall-out appeared in the cold part of the reactor or spectroscopic cell as a product of the dealumination of zeolites at higher temperature. The destruction of zeolites proved to be less pronounced in the presence of oxygen and/or in the case of a zeolite which has a higher Si to Al ratio than Y-FAU zeolites like mordenite or ZSM-5 zeolites.

Infrared spectroscopic study of adsorption and reactions of methyl chloride on acidic, neutral and basic zeolites

Abstract Infrared (IR) spectroscopic investigations were performed of the adsorption and surface reactions of CH3Cl over acidic, basic and neutral zeolite catalysts. In each case, the spectral changes reflected the appearance of the Fermi resonance phenomenon. The resonance parameters determined pointed to a decreasing extent of resonance in consequence of the adsorption. No influence of the acidity of the adsorbents was observed. The formation and consumption of HCl and OH groups were established at elevated temperatures. The reactions assumed to have occurred are described and explained.

Thermal stability of hydroxy groups in dealuminated mordenites

Abstract Results obtained by proton magnetic resonance and derivatographic measurements permitted the following conclusions regarding the thermal stability of OH groups in the framework of dealuminated mordenites: 1. (1) after vacuum pretreatment at room temperature, the adsorbed water molecules are removed. OH groups exist either in completely filled OH nests at the sites of aluminium vacancies, or as structural and terminal OH groups; 2. (2) the thermal stability of the OH nests is low, for after pretreatment at about 500 K, such nests could be detected neither with n.m.r., nor with derivatographic methods.

A novel method for the dealumination of zeolites

A wide range of halogen containing reagents (metal halides, oxyhalides, acid halides, etc.) are found to interact from the gas phase with exchange ions of zeolites and to effect dealumination at elevated temperatures. The incorporation of extraneous ions into the framework by this technique is not impossible theoretically. The importance of the method in the preparation of dealuminated and/or metal containing catalysts is discussed.AbstractЩыло найдено, что большое число реагентов, содержащих галогены (галогениды металлов, оксигалогениды, кислотные галогениды), взаимодействуют из газовой Фазы с цеолитами, приводя к обмене ионов и вытеснению алюминия. Происходящее при этом внедрение наружных ионов в решетку возможно и теоретически. Обсуждается значение метода в приготовлении катализатора без алюминия и/или катализаторов, содержащих металл.

Synthesis, Characterization and Catalytic Activity of V-Zsm-5 Zeolites

Abstract A V-ZSM-5 sample with a Si/V = 42 was synthetized outgoing from VO(COO)2 and Q-brand sodium silicate using TPA-Br as template. ESR spectroscopy proved that vanadium(IV) ions in the zeolitic framework exhibit a distorted square planar symmetry. Upon heat treatment a part of the framework vanadium ions migrate to extra-framework positions. After dehydration no Bronsted acidity was found. Treatment in oxygen and hydrogen above 570 K revealed the redox character of the V-ZSM-5 sample. In oxidation of n-butane (as catalytic test reaction) the V-ZSM-5 zeolite exhibits selective dehydrogenation and aromatization activity.

Reactions of cyclopropane over zeolite catalysts

The reaction of cyclopropane on NaY, CaNaY, and NaHY zeolites yielded isobutane, 2-methylbutene, propane, isobutene, 2-methylbutane, 2-methylpentane, and heptanes among the minor products, probably as a result of complex oligomerization, isomerization, and cracking processes of a propylene intermediate.

Investigation of NaN3 salt occlusion in the framework of Y zeolites

The interaction between sodium atoms (obtained by thermal decomposition of NaN3) and acidic OH groups of the zeolite, leading to the elimination of H+ ions, is accompanied by the occlusion of the NaN3 in the zeolitic framework. This salt occlusion process was investigated using X-ray, thermogravimetric, i.r. and visible spectroscopic methods. NaN3 occluded in the zeolite framework does not decompose at 773 K, though this temperature is higher than the decomposition temperature of the pure NaN3. It was found that nearly two N−3 ions per u.c. were occluded in the framework without destroying the crystal structure of the zeolite.

Step towards nanoscale Fe moieties: Intercalation of simple and Keggin-type iron-containing ions in-between the layers of Na-montmorillonite

The synthesis and characterization of iron-containing Na-montmorillonite prepared by various techniques are reported. Methods include ion exchange by Fe(II) ion and pillaring by partially hydrolysed Fe(II) salt or by Al13O407+ where the substitution of Fe(III) for Al(III) was attempted. Substances were characterized by elemental analysis, thermogravimetry, X-ray diffractometry (XRD), 27A1 and 29Si MAS NMR, FT-IR spectroscopies, and BET measurements. The coordination and oxidation states of iron were deduced from 57Fe Mossbauer spectra. Ion exchange resulted in the incorporation of polynuclear hydrous Fe(III) oxides characterized by octahedral coordination in significant amounts. In contradiction to earlier reports, we find no evidence for isomorphous substitution of iron for aluminium in Al13O407+ Keggin ions. Instead, mixed pillars were formed containing Al13O407+ Keggin ions and hydrous iron oxide oligomers. After reduction, large magnetite patches kept the layers apart when the partially hydrolysed pure iron salt was used for pillaring. Heat treatment influenced the water content of the intercalated species. The oxidation state of iron could be significantly influenced by reduction with hydrogen at various temperatures depending on the method of preparation.

The thermal behaviour of sodium azide in zeolites

Abstract Upon thermal treatment, NaN3-doped zeolite transforms stepwise. After endothermic dehydration, the NaN3 decomposes exothermically in air and under N2 flow. The temperature of decomposition is higher than that of the pure azide. Part of the sodium azide remains intact up to 1000 K. The process was also monitored by IR spectroscopy. 23Na NMR measurements revealed that metallic sodium clusters were formed.