F. Fajula

Comparison of two MCM-41 grafted TEMPO catalysts in selective alcohol oxidation

A new heterogeneous system for catalytic oxidations has been developed by immobilising TEMPO onto ordered mesoporous silica (MCM-41-type). The immobilisation was performed according to different methods: (i) direct grafting of the silica surface with 3-(trimethoxysilyl)propyloxy-TEMPO obtained by coupling 4-hydroxy-TEMPO and allyl bromide followed by hydrosilylation; (ii) coupling of 4-carboxy-TEMPO with 3-aminopropylsilane previously grafted on the mesoporous silica surface; (iii) coupling of the N-succinimide ester of 4-carboxy-TEMPO with the same previously grafted 3-aminopropylsilane. Efficiency and anchoring of the TEMPO were studied by various spectroscopic techniques. The textural characteristics of the mesoporous support were preserved during the different modifications. Catalytic tests on the use of the materials in the oxidation of primary alcohols proved their activity and stability under the reaction conditions.

Butene oligomerization over mesoporous MTS-type aluminosilicates

Abstract The oligomerization of butene at 423 K and 1.5–2 MPa has been investigated over a series of zeolite, amorphous silica–alumina (ASA) and ordered mesoporous aluminium-containing micelle templated silica (MTS) catalysts. While olefin oligomerization into strongly adsorbed residue and fast deactivation prevailed on microporous catalysts and ASA, mesoporous aluminosilicates with uniform pore openings near 3 nm in size exhibited high selectivity and good stability with time for the production of branched dimers. The characterization of the surface properties of the solids, the nature of the adsorbed residue on the spent catalysts, and the identification of reaction intermediates by in situ infrared spectroscopy of co-adsorbed acetonitrile and butene, suggest that the unique catalytic behaviour of MTS-type catalysts is related to the moderate strength and the high dispersion of the acid sites in the mesoporous structure.

Factors affecting the steam dealumination of zeolite omega

Abstract Three samples of zeolite omega with varying residual contents of sodium have been dealuminated by combined steam and acid treatments. The hydrolysis of the AlO bonds is a fast process that occurs mainly during the initial period of heating above 500° under steam. Sodium ions inhibit the reaction. The steamed solids contain mesopores ≅ 100 A in diameter, but their porosity is not available to sorbents because of the presence of debris in which aluminum is in tetrahedral and octahedral configurations. Acid leaching removes all the nonframework tetrahedral aluminium and part of the octahedral one. This removal permits access to the microporous and mesoporous voids. Increasing the severity of the steam treatment increases the quantity of the disloged material that cannot be removed by the acid, but has little effect on the texture of the final solids. The TEM observations and the volumetric measurements suggest that the mesopores are not directly linked to the surface of the grains and are connected to each other by narrow necks.

Functionalization of Y zeolites with organosilane reagents

Abstract Y-type zeolites with different Si/Al ratios, surface areas and pore volumes havebeen modified by grafting with organosiloxane molecules. Volumetry, 13C NMR and infrared spectroscopy, thermal and elemental analyses confirm the covalent attachment of the organic species inside the micro- and mesopore voids. The grafted species are strongly bound to the surface and can be readily functionalized by further reaction with suitable reagents to generate imino and benzamido groups.

Ethylene oligomerization over Ni-containing mesostructured catalysts with MCM-41, MCM-48 and SBA-15 topologies

Nickel ion exchanged MCM-41, MCM-48 and SBA-15 mesostructured materials with a controlled concentration of nickel and acidic sites were prepared, characterized, and successfully used as catalysts in the ethylene oligomerization performed in slurry batch mode (T = 150°C, p = 3.5 MPa). Larger pores or a 3D pore system, as well as an equilibrated balance between acid and nickel ion sites were very favorable for the oligomerization process.

Dissipative water intrusion in hydrophobic MCM-41 type materials

Texture-related features of water intrusion in hydrophobised MCM-41 silicas render these materials especially suitable for energy dissipation in mechanical dampers.

Isomerization of meta-xylene over offretite catalysts

Abstract The conversion of meta -xylene has been investigated over offretites with different levels of ion exchange. The ratio isomerization/disproportionation increases with the degree of exchange, most probably due to an increased accessibility of the reactant to the internal surface and to a higher number and strength of acid sites. The addition of a hydrogenation function, in H 2 atmosphere, slightly increases the activity and decreases the deactivation as a function of time. The conversion of 1−3-dimethylcyclohexene-1 yields experimental evidence that a bifunctional path exists for the reaction in these conditions. The supposed intermediate olefin isomerizes and disproportionates faster than meta -xylene, but the ortho/para selectivity remains unchanged.

29-O-02 Towards total hydrophobisation of MCM-41 type silica surface

Publisher Summary This chapter presents the refinement of the procedure for MCM-41 surface fictionalization with various octylsilanes to obtain a maximum surface coverage. Two different types of surface modification using different grafting agents are performed on micellar templated silica (MTS) samples. MTS samples possessing three different pore sizes are functionalized by the hydrolysis and polymerization of pre-adsorbed monolayer of octylsilanes on MTS surface or by chlorine substitution from chlorooctylsilane with nucleophilic assistance. The effect of various experimental parameters on the hydrophobicity and the grafted chain loading is also analyzed.

Grafting of nitroxyl (TEMPO) radical on the surface of silical gel and micelle-templated silica (MTS)

Abstract Grafting of TEMPO on MCM-41-type silica (MTS) and on silica gel was achieved through amide bond on previously grafted amino chains by two different procedures. The spin labeling materials were characterized by various physicochemical methods (XRD, nitrogen sorption volumetry, thermogravimetry, IR, NMR, EPR and UV-Vis spectroscopies). The main conclusion drawn from UV-Vis spectroscopic studies on reaction of TEMPO- immobilized species with electron-acceptor properties is that functionalization of mineral support through coupling reaction on previously anchored organic chains would not necessarily lead to fully grafted species. Special attention should be focused on the control of anchoring in immobilized catalysts.

Synthesis of Aluminium-rich Zeolite Beta

Hydrothermal synthesis of zeolite beta carried out at low alkalinity levels(OH-SiO2<0.25) from aluminium-rich media(SiO2/Al2O3<19) yielded zeolite beta with an aluminium content higher than 8 atoms per tetragonal unit cell(SiO<2/Al2O3=16). 29Si and 27 Al MAS NMR spectroscopy indicate that all aluminium occupy framework tetrahedrally coordinated sites. The framework negative charge of these aluminium-rich solids is compensated for by sodium and tetraethylammonium cations.