Bogdan Sulikowski

Dealumination of zeolite Y by H4EDTA

Solid-state NMR shows that the treatment of zeolite Y by H4EDTA dealuminates the zeolite framework. Since no extra-framework aluminium is found, all the Al removed from the framework is subsequently washed out of the crystallites in the form of an H4EDTA complex. Unlike with hydrothermal dealumination or treatment with SiCl4, H4EDTA gives defective crystals in which framework vacancies created by the expulsion of aluminium are not healed by silicon from other parts of the framework. The likely reason for this is the slow intracrystalline diffusion of Si(OH)4 at low temperatures.29Si CP/MAS NMR and infrared spectra confirm the creation of hydroxyl nests in the zeolitic framework. A small amount of disordered siliceous phase responsible for a low intensity29Si MAS NMR shoulder at −110 ppm is produced in the process.

Preparation and characterization of titanosilicates with ZSM-5 structure

Abstract A titanosilicate with the crystal structure of zeolite ZSM-5 was prepared via the non-alkaline “fluoride” route using rutile as the source of titanium. The properties of the product are compared with those of silicalite, the purely siliceous analogue of ZSM-5, and a sample prepared by a post-synthesis treatment of silicalite with TiCl4. Zeolites [Si,Ti]-ZSM-5 selectively catalyse the liquid-phase oxidation of cyclohexanol to cyclohexanone.

Dealumination of zeolites with silicon tetrachloride vapour. Part 6.—Zeolites Li, Na-X and Li, Na-Y

The reaction of zeolites Li, Na-X and Li, Na-Y with SiCl4 vapour has been examined by IR spectroscopy, 29Si and 27Al magic-angle-spinning NMR (MAS NMR), X-ray diffraction and atomic absorption spectrophotometry. The aim was to prepare a fully crystalline and highly siliceous polymorph of silica with the faujasite structure. This can be achieved in single step when the starting material is the lithium form of zeolite Y. However, zeolite Li, Na-X cannot be similarly dealuminated with SiCl4 vapour. The reason for this is not the ‘screening’ of the framework by the charge-balancing cations, as previously suggested, but the presence in the framework of zeolite X of six-membered rings containing three aluminium atoms.

Template removal from molecular sieves by low-temperature plasma calcination

The oxidative removal of templates from crystals of MFI- and TON-type zeolites using low-temperature oxygen plasma at 370 K has been investigated. This treatment removes tetrapropylammonium inside 5 µm lengths of channels in the completely siliceous MFI structure (silicalite), and diethylamine to a depth of at least 70 µm in the channels of the completely siliceous TON structure. Substitution of B, Al or Fe into the framework of silicalite significantly obstructs the removal of tetrapropylammonium, but complete decomposition of the template can be accomplished in small samples of [Si, B]-MFI. A comparison of plasma calcination with thermal calcination in air indicates that the release of boron into extra-framework positions upon either treatment is caused by the slow desorption of water at the calcination temperature.

Low-temperature Plasma Calcination of Zeolite NH4, Na-Y

Abstract 70% Ammonium-exchanged zeolite NH 4 , Na-Y is completely deammoniated by low-temperature plasma calcination, while the crystallinity of the samples is not impaired. Neither the plasma calcined nor shallow bed treated material is “pure H-Y” zeolite, and 27 Al MAS NMR indicates a slight dealumination of the zeolitic framework in each case. Hydronium ion exchange to product H,Na-Y from Na-Y using highly dilute acidic medium also resulted in partial dealumination of the sample. Plasma calcination of 87% ammonium-exchanged NH 4 , Na-Y caused a severe loss of crystallinity, possibly because of mineral acid formation at inaccessible sites. Low-temperature plasma calcination is a mild technique for the oxidative removal of ammonia as long as oxidation products can easily leave the crystallite.

Structural and catalytic consequences of isomorphorus substitution of silicon by aluminium and vice versa in the framework of pentasil zeolites

Zeolite ZSM-5 was dealuminated to give material catalytically and structurally identical with silicalite; conversely Si → Al substitution was achieved in silicalite after completion of synthesis to produce ZSM-5 of high aluminium content.

Isomerization of Xylenes on Boroaluminosilicate Catalysts with the ZSM-5 Structure, Synthesized in Non-alkaline Media

We examined catalytic isomerization of xylenes at 300 and 445 C on zeolite [Si, B, Al]ZSM-5, prepared under non-alkaline conditions, on amorphous Si02 —A1203 and on the conventional zeolite H-ZSM-5. The reaction, known to proceed on Bronsted acid sites, is an excellent monitor of shape selectivity. Because of fast coking, the catalysts were examined in the pulse mode. The results, displayed using the Wei-Prater triangle plots, show that reaction paths on boroaluminosilicates lie in the region where diffusion effects arc present, and that shape selectivity contributes to the enhanced formation of p-xylene. The estimated Thiele modulus is 2:10 for boroaluminosilicates, zero for Si02

Trans-but-2-ene is the first hydrocarbon produced in the conversion of methanol to gasoline over zeolite H-ZSM-5

Abstract Careful gas Chromatographic studies reveal that, contrary to earlier reports,trans-but-2-ene and not ethene is the first hydrocarbon product desorbed from zeolite ZSM-5 in the catalytic conversion of methanol to gasoline at temperatures below 200 °C.

Synthesis of a novel gallosilicate with the ferrierite structure

Aluminium-free (Si, Ga)-ferrierite with Si/Ga = 6.6 has been prepared by direct synthesis and its orthorhombic unit cell parameters are a= 19.01(1), b= 14.15(1), and c= 7.481(3)A, the unit cell volume being 0.55% larger than for (Si, Al)-ferrierite; solid-sate n.m.r. spectroscopy shows that pyrrolidine, the template molecule, is essentially intact in the channels of the new material.

Synthesis of Novel Perfluoroalkylglucosides on Zeolite and Non-Zeolite Catalysts

Perfluoroalkylglucosides comprise a very important class of fluorine-containing surfactants. These compounds can be synthesized by using the Fisher reaction, starting directly from glucose and the required perfluoroalcohols. We wish to report on the use of zeolite catalysts of different structure and composition for the synthesis of perfluoroalkylglucosides when using glucose and 1-octafluoropentanol as substrates. Zeolites of different pore architecture have been chosen (ZSM-5, ZSM-12, MCM-22 and Beta). Zeolites were characterized by XRD, nitrogen sorption, scanning electron microscopy (SEM) and solid-state 27Al MAS NMR spectroscopy. The activity of the zeolite catalysts in the glycosidation reaction was studied in a batch reactor at 100 °C below atmospheric pressure. The performance of zeolites was compared to other catalysts, an ion-exchange resin (Purolite) and a montmorillonite-type layered aluminosilicate. The catalytic performance of zeolite Beta was the highest among the zeolites studied and the results were comparable to those obtained over Purolite and montmorillonite type catalysts.