Henri Kessler

F-: A MULTIFUNCTIONAL TOOL FOR MICROPOROUS SOLIDS a) MINERALIZING, STRUCTURE DIRECTING AND TEMPLATING EFFECTS IN THE SYNTHESIS

ABSTRACT Three effects may be observed if fluoride anions are present in synthesis mixtures of microporous solids. The first one is a mineralizing (or mobilizing) effect: F allows crystallizing from a gel through a dissolution process. This effect applies especially for silica-based materials which thus may be prepared in media with pH lower than 10-11. The second one is a structure directing effect which means that its presence is necessary to obtain a material with a given structure and/or composition from a given reaction mixture. By this effect three entirely novel materials could be prepared (the silica form of the AST structure type, LTA-GaPO 4 and CLO-GaPO 4 ). The third one is a templating effect: F is incorporated into the framework interstices of the material and contributes strongly to the stabilization of the structure as do the organic template molecules. This effect is chiefly observed when the framework has no charges or if its charges are autocompensated.

Characterization of the acidity of Mu-14 by solid-state NMR and NH3-STD

The distribution and strength of the Bronsted acid sites in three Mu-14 (ITE structure type) samples with different Si/Al ratios (17, 28 and 35) were studied by 1H MAS (magic angle spinning), 1H-{27Al} TRAPDOR (transfer of population in double resonance), 1H-29Si CP-MAS (cross-polarisation magic angle spinning)/ HETCOR (two-dimensional heteronuclear correlation) NMR, and NH3-STD (stepwise thermal desorption). The 1H MAS NMR spectra exhibit two different types of bridging OH groups associated with proton chemical n shifts of ca. 4.2 and 5.3 ppm. From the 1H-29Si HETCOR experiments a single Bronsted [Si-(OSi)3(OAl)1] Q3 site resonating at δ(29Si) = n− 108 ppm, can be distinguished from two different [Si-(OSi)3(OH)1] Q3 sites, at δ(29Si) = n− 101 and − 104 ppm, and one of the Q4 sites resonating at δ(29Si) = n− 108.5 ppm. Aluminum is not randomly distributed in the structure of Mu-14, but rather sits at preferred places isolated from silanols. The acid strength of the Bronsted acid sites, n determined by NH3-STD, is slightly higher in Mu-14 than in a HZSM-5 with a similar Si/Al ratio.

Synthesis of Aluminosilicate Zeolites and Related Silica-Based Materials

Five important monographs are devoted to the synthesis of aluminosilicate zeolites. The first one, by Breck [1], is the most general in its content, since as well as syntheses which are reviewed until 1973, modifications and properties (ion exchange, adsorption) are also described. Barrer’s book [2] is fully devoted to the synthesis and transformation, with a complete survey up to 1981, of the results related to zeolites with low or medium Si/Al ratios. The third one, by Jacobs and Martens [3], presents exhaustive information about the preparation and identification of silica-rich zeolites. The two latest ones, by Szostak [4, 4a], contain in addition an important part on non-aluminosilicate molecular sieves.

Synthesis and characterisation of the novel GIS-type AlPO4: [NH2Me2][Al2P2O8F]

A novel fluorinated aluminophosphate with a framework topology closely related to zeolite gismondine is crystallized in the presence of dimethylformamide from a predominantly alcoholic system and its structure is determined from XRD powder data.

SYNTHESIS AND CHARACTERIZATION OF THE NOVEL GALLOPHOSPHATE CLOVERITE WITH 20-MEMBERED RING CHANNELS

ABSTRACT The influence of the synthesis conditions such as HF to quinuclidine ratio, gallium and silicon sources, pH and temperature were determined for the novel gallophosphate cloverite and the corresponding silicogallophosphate. For the latter, little Si was incorporated in the crystals (electron microprobe analysis). The thermal stability of the GaPO 4 form was determined by studying the variation of the adsorption capacity of n-hexane as a function of the calcination conditions. It is stable to at least 500°C. It was found that after calcination at 450°C, part of the fluoride was still present in the structure, in a slightly different environment ( 19 F MAS NMR). Presumably due to an amorphization reaction, NH 3 turned out to be an unsuited probe molecule for the determination of the acid properties of the materials.