José J. Fripiat

Active sulfated alumina catalysts obtained by hydrothermal treatment

AbstractThe structural and surface properties of sulfated γ -Al 2 O 3 prepared by hydrothermally aging precipitates obtained from aluminum sulfateand ammonia have been studied. The Lewis sites are formed on coordinately unsaturated fourfold alumina. No pentacoordinated aluminumhas been found, probably as a consequence of the aging process. Residual sulfate is distributed among several species characterized by theirdesorption temperatures. Bronsted sites of high strength are probably located on sulfate species desorbing between 900 and 1000 ◦ C. Theymay have the following schematic structure (O=) 2 S(–OH)(–O–Al). The decomposition of 4-methylpentan-2-ol shows clear differencesaccording to the types of acidity present on the surface. The sulfated aluminas have favorable textural properties: pore size ∼=50 nm andspecific surface area ∼=200 m 2 / g stable up to more than 700 ◦ C.  2003 Elsevier Inc. All rights reserved. Keywords: Sulfated alumina; Hydrothermal preparation; Acid sites; Catalytic properties

Dealumination and surface fluorination of H-ZSM-5 by molecular fluorine

Abstract At room temperature, framework aluminum (FAl) is extracted rapidly from the lattice of H-ZMS-5 by molecular fluorine. Ionic fluoro-complexes containing octahedral aluminum are formed within the micropores of the zeolite. The structure remains intact while the Si/FAl increases, for instance from 27 to 233 or from 55.2 to 382. As shown previously, the behavior of HY with respect to molecular fluorine is similar. The terminal SiOH in H-ZSM-5 are also fluorinated. The extent of this reaction was negligible in the case of HY. The quantitative distinction between the fluorine atom in SiF and the aluminum fluoro-complexes is possible using 19 F MAS NMR, HETCOR and TRAPDOR. The good agreement between 27 Al and 19 F NMR data and the quantitative analysis of the infrared spectra in the OH stretching region is outlined. In particular, the disputed assignment of the 3700 cm−1 band to OH on non-framework aluminum moieties is elucidated.

29Si MAS-NMR study of the silica condensation in the synthesis of mesoporous materials

A series of silica mesoporous materials was prepared adding ammonium sulfate into reaction mixture. The 29 Si MAS NMR showed that the Q 4 signal increased when the sulfate content in the synthesis mixture increased thus suggesting that the OH/Si of the material decrease hence confirming that silica had a higher degree of condensation. Accordingly, an increase in the unit cell parameters and in the wall thickness of the synthesized materials was observed.

Physicochemical properties of FSM-16 modified by fluoride and HPA

Mesoporous material FSM-16 has been modified by addition of ammoniumfluoride into the sysnthesis mixture (in-situ modification).After calcination at 863 K the samples were impregnated by phosphotungstic acid (HPA) and characterizedby XRD, FT-IR and 31 P MAS NMR. The long-range order of the impregnated samples were improved. In addition, HPA promotes the formation of both Bronted (B) and Lewis (L) acid sites. The presence of both F and HPA modifiers increases the B acid sites density, and the catalytic activity performance. Agood correlation between the B sites density and conversion ofn-hexane activity was observed.

Role of Na in the ionic equilibrium ruling the synthesis of mesoporous FSM-16 materials

FSM-16 was prepared from sodium disilicate. In the synthesis mixture, the Na/Si ratio was varied in order to study the effect of Na on the formation and stability of mesoporous materials while the surfactant/Si was maintained constant. Increasing the sodium content in the precursor favors the formation of a pure hexagonal phase. The thermal structural stability is correlated with the OH density.

Synthesis conditions and properties of Ti-MCM-41

Abstract A series of mesoporous Ti-MCM-41 materials was prepared at hydrothermal conditions (HT) as well as room temperature (RT). A constant Si/Ti ratio (26.1) in the initial gel and varying amounts of ammonium sulfate (SO 4 /Si = 0, 0.01, 0.1, 0.3, 0.5) were used. For solids prepared at SO 4 /Si below 0.3 their XRD spectra showed the pattern of a MCM-41 hexagonal array. The structural order decreased as the amount of sulfate increased. In materials prepared at RT higher sulfate concentrations favored the insertion of Ti and the wall thickness while the surface area decreased.