H. Kessler

New Route to Pentasil-Type Zeolites Using a Non Alkaline Medium in the Presence of Fluoride Ions

Silica-rich, Al-, B- and (Al + B) MFI zeolites called Zeosilites, Aluzeosilites, Borozeosilites and Aluborozeosilites respectively were obtained by hydrothermal crystallization at 60–200°C from mixtures containing F anions and tetra-, tri- and di-propylamraonium cations as templates; pH values were 3–10. Crystal size is a function of the Si substitution degree, it may reach 800 um in some cases. DSC, DTA and TG curves corresponding to the decomposition of the templates occluded as fluoride salts are different from those observed for samples obtained in alkaline medium. Mass spectrometer analysis shows that the presence of fluoride in the as-synthesized samples leads to organic fluro compounds formation on calcination. High resolution 29 si-, 27 Al- and 11 B magic angle spinning NMR evidences Si substitution by Al and B in the zeolite framework.

Synthesis and structure of the [AlPO4]12 Pr4NF molecular sieve with AFI structure

Large single crystals (500 × 80 μm) of the structure type AFI have been obtained at 170°C using a synthesis medium containing F− anions. The new as-synthesized phase [AlPO4]12 Pr4NF crystallizes in space group P6cc with a = 13.740(5) A and c = 8.474(4) A (Z = 1). The crystal structure has been refined to Rw = 0.042. The Pr4N+ cations are in the large 12-ring channels of the framework, their fourfold inversion axis coinciding with the sixfold axis of the lattice. The F− anions are located in the “wall” of the framework between two (Al,P)O4 4-rings. This unusual position could be confirmed by 31P MAS n.m.r. spectroscopy.

Thermoanalytical characterization of MFI-type zeolites prepared either in the presence of OH− or of F− ions

Thermoanalytical techniques (d.t.a., t.g., d.s.c.) were used in inert atmosphere to investigate the decomposition of organic templates (primarily the tetrapropylammonium cation) incorporated in MFI-type zeolites prepared in various media (acid or alkaline pH, in the presence or absence of F− ions and MIII substituents of silicon). The information derived from the position and the extent of the endothermal peaks recorded by d.t.a. and d.s.c., makes it possible to determine whether the templates is present in the form of ion pairs (TPAOH or TPAF) or of cations (TPA+) compensating the negative charges induced by the possible substitution of SiIV by trivalent elements MIII (Al or B). The value of the SiIVMIII molar ratio in the tetrahedra can also be derived from thermoanalytical data, with increased precision for samples prepared in fluoride medium.

Synthesis and characterization of cloverite: a novel gallophosphate molecular sieve with three-dimensional 20-membered ring channels

Abstract Cloverite, a novel cubic microporous gallophosphate, with three-dimensional channels circumscribed by 20-membered rings in the shape of a four-leafed clover, was synthesized in the presence of fluoride ions and quinuclidine. It is stable to at least 500°C in a dry atmosphere and shows high adsorption capacity for n -hexane, xylene, and mesitylene. By 13 C n.m.r., it was found that quinuclidine is protonated, thus compensating the negative charge of fluoride located in the double four-rings. The 31 P and 71 Ga MAS n.m.r. results are in agreement with the crystal structure analysis.

27Al MAS NMR characterization of AlPO4-14 enhanced resolution and information by MQMAS Dr. Hellmut G. Karge on the occasion of his 65th birthday

Abstract The crystalline microporous aluminophosphate AlPO4-14 was studied using 27Al NMR spectroscopy, with both conventional MAS and two-dimensional multiple-quantum MAS (MQMAS) techniques. Data obtained for the four non-equivalent framework aluminum atoms detected in AlPO4-14 are reported. They are found to occur with the ratio 1:1:1:1 according to the proposed crystal structure. The aim of this paper is also to compare the NMR methods used in this work with those found in literature. It is concluded that the new MQMAS method is by now the best approach to distinguish easily the non-equivalent Al atoms in the structure of such materials. It is also very efficient to obtain rapidly the necessary information about distribution of chemical shifts and quadrupolar interactions.

N.m.r. and i.r. study of B and BAl substitution in zeolites of the MFI-structure type obtained in non-alkaline fluoride medium

Pure boron and boron—aluminium MFI-type zeolites have been obtained by heating non-alkaline reaction mixtures containing F− instead of OH− anions and tetrapropylammonium bromide as a template. High resolution solid state magic angle spinning (MAS) 29Si-, 27Al- and 11B-n.m.r., and i.r. spectroscopy have indicated the incorporation of the trivalent elements in the zeolite framework. BO4 and AlO4 groups were shown to be present in the as-synthesized samples. For the dehydrated calcined samples, it is suggested that boron is in a trigonal environment still in the framework.

Synthesis, characterization, and catalytic activity of SAPO-34 obtained with piperidine as templating agent

The synthesis of SAPO-34 in the presence of a new templating agent, namely piperidine, was investigated. The effects of the gel composition, the template concentration, the time and temperature of crystallization on the degree of crystallinity and the purity of the crystalline phase were examined. It was found that SAPO-34 and SAPO-20 are competing phases at high piperidine concentrations, whereas SAPO-34, SAPO-17 and SAPO-35 are the phases present at low template concentrations. Pure SAPO-34 with high crystallinity was obtained at a piperidine/Al2O3 ratio of 1.1:1.0. An optimal synthesis procedure giving an homogeneous SAPO-34 framework without Si islands, consists of heating a gel of composition 1.0Al2O3/0.6P2O5/1.1Pip./0.8SiO2/100H2O at 200 °C for 4–8 days. Such a reproducible procedure gives rise to an acidic catalyst active in the aldol condensation of acetaldehyde with formaldehyde.

Synthesis of microporous titanosilicate ETS-10 with TiF4 or TiO2

Abstract Engelhard titanosilicate number 10 (ETS-10) was synthesized using titanium(IV) fluoride as the titanium source, both with and without the organic additive tetramethylammonium chloride. Compared with TiCl 3 and TiCl 4 , which are commonly used in the synthesis of ETS-10, TiF 4 is not sensitive to moisture in the ambient air, and therefore, its use makes the preparation of the synthesis gels more convenient and simpler. Pure ETS-10 was obtained with TiF 4 by heating at 200°C for 168 h both with and without the organic additive. For comparison, another convenient Ti source, i.e. P25, a mixture of anatase and rutile, was used. X-ray pure ETS-10 was obtained by heating at 200°C for 42 h, whereas heating for 168 h produced pure ETS-4. The ETS-10 samples obtained with TiF 4 and P25 were thoroughly characterized by powder X-ray diffractometry, scanning electron microscopy, thermal analysis, n -hexane adsorption, diffuse reflectance UV/VIS, FT-IR spectroscopy and solid state 29 Si, 19 F MAS NMR.

I.r. spectroscopy of single zeolite crystals. Part 1: Thermal decomposition of the template in MFI-type materials

The thermal decomposition of tetrapropylammonium fluorides in ZSM-5 crystals was studied by means of time resolved i.r. spectroscopy. For the first time, in situ transmission measuresments on single crystals are reported. Three different processes have been observed, i.e., increasing of the mobility of the tetrapropylammonium cations and oligomerization of the template or parts of the template, and decomposition of the template via two different mechanisms. The rate-determining step for the decomposition is the reaction producing the dipropylamine or a dipropylammonium ion. The weight of the ionic or nonionic mechanism in the decomposition of the template is strictly dependent upon the aluminum concentration in the zeolite.

Nanosized Zinc Sulfide Obtained in the Presence of Cationic Surfactants

O WILEY-VCH Verlag GmbH, D-69469 Weinheim, 1998 0935-9648/98/1208-0946