Joël Patarin

Recent advances in the formation mechanisms of organized mesoporous materials

Since the discovery of the organized mesoporous solids by Mobil Oil Co. scientists, numerous patents and papers dealing with the synthesis, mechanisms of formation, properties and applications of these exciting solids have been published. A better understanding in the mechanisms of formation has been achieved through the use of in situ techniques of investigation. It appears that the mechanism depends much on the experimental conditions of synthesis. Even if the interaction between the inorganic precursor and the organic template is the key factor in the control of the formation of these materials, none of the proposed mechanisms provides an exclusive and definitive answer.

Synthesis, characterization, and catalytic properties of silica-rich faujasite-type zeolite (FAU) and its hexagonal analog (EMT) prepared by using crown-ethers as templates

High silica faujasite (FAU) and its hexagonal analog (EMT) were synthesized using 15-crown-5 and 18-crown-6, respectively, as templating agents. By mixing these two crown-ethers in the starting hydrogel, a material with a crystal morphology resulting from an overgrowth of both cubic and hexagonal structures was obtained. These three zeolites with a SiAl molar ratio close to 4 were ion-exchanged and transformed into their protonated forms. The samples were characterized by chemical analysis, 29Si, 27Al, and 23Na solid-state MAS n.m.r., and it was shown that the sodium removal was more complete in the hexagonal and overgrown samples. The acidity (determined by STD of ammonia) and the catalytic activity (evaluated by n-heptane cracking) are closely related to the residual amount of Na+, and they proved to be higher for the two latter samples.

Synthesis and characterization of zirconium containing mesoporous silicas: I. Hydrothermal synthesis of Zr-MCM-41-type materials

Abstract Zirconium containing MCM-41-type has been synthesized by a near neutral route. Various solids, with Si/Zr molar ratios ranging from 20 to ∞, were prepared. All these solids have high surface area and good crystallinity. Addition of zirconium results in a linear increase of both the Lewis and Bronsted acidities. At least one-third of zirconium is at the surface or near the surface, probably in the form of [(≡Si–O)3Zr–O−] species. As a consequence, introduction of zirconium on the surface results in the appearance of a negative charge, compensated by sodium ions which can be exchanged.

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.

Template synthesis of a new type of ordered carbon structure from pitch

New ordered nanoporous carbon materials can be synthesized using pitch and mesoporous silica materials as the carbon precursor and template, respectively. In this case, the silica material (type MCM-48 and SBA-15) is impregnated with pitch and further carbonized. After removal of the silica by acid treatment, a graphitizable carbon material with an ordered micro-mesoporosity is recovered. The preparation route as well as the characteristics of the carbon materials are presented in this paper. It appears that the use of pitch as the carbon precursor presents some advantages compared to carbon obtained by other methods. Moreover, study of the thermal stability of the carbon shows that the structural regularity is preserved upon heat treatment at 1675 K.

Synthesis and structure of Mu-4, the new layered aluminophosphate [(C2H5)2NH2]4[Al8P10O40H2]·[H2O]2.5

Abstract The title compound (named Mu-4) is a new layered aluminophosphate with a unusual A1/P ratio for this kind of materials. Mu-4 was obtained from a quasi non-aqueous mixture involving mainly diethylformamide (DEF) as solvent, in addition to limited amounts of water. DEF is decomposed during the synthesis and the resulting protonated diethylamine is occluded in the as-synthesized material. The crystal structure was determined by single crystal X-ray diffraction. The symmetry is triclinic, a=8.632(4) A, b=9.267(7) A, c= 17.461(10) A, α=86.66(5)°, β=82.20(4)° and γ=89.28(5)°, space group P-1. The structure consists of anionic double sheets essentially built from double 4-ring (D4R) units. The inorganic layers are in strong interaction with water and the protonated amine which is located in the interlayer spacing. Another type of diethylamine protrudes into the 8-membered rings (8-MR) present in the layers. The characterization of this new aluminophosphate by 13 C, 27 Al and 31 P solid state NMR spectroscopy is also reported.

Synthesis and characterization of high-silica zeolite RHO prepared in the presence of 18-crown-6 ether as organic template

Abstract Pure high-silica RHO-type zeolite samples with a framework Si Al molar ratio as high as 4.5 were prepared by using 18-crown-6 ether as an organic template from a starting aluminosilicate gel containing cesium cations. The solids were characterized by elemental analysis, scanning electron microscopy (SEM), X-ray diffraction (XRD) thermal analysis, solid-state nuclear magnetic resonance (NMR) spectroscopy and n-hexane adsorption. The NH3 stepwise thermal desorption (STD) curve of high-silica zeolite rho shows stronger acid sites than for a FAU-type material with similar Si Al molar ratio. High-temperature XRD analyses performed on the protonated hydrated form of high-silica zeolite rho showed no framework flexibility, presumably because of a higher covalent character of the framework.

Investigation of the mechanism of the surfactant removal from a mesoporous alumina prepared in the presence of sodium dodecylsulfate

Abstract The mechanism of the thermal decomposition of sodium dodecylsulfate occluded within a mesostructured alumina is studied by sample controlled thermal analysis. The alkyl chain of the surfactant is completely removed below 473 K whereas the sulfate head group is lost in the region between 673 and 823 K. The pore volume and the equivalent surface area increase as the alkyl chain is removed and decrease on removal of the sulfate head group. These results suggest a strong interaction between the sulfate head group and the alumina framework.

IM-19: a new flexible microporous gallium based-MOF framework with pressure- and temperature-dependent openings.

Five metal-organic frameworks (MOFs) based on the same three-dimensional gallium terephthalate network (IM-19) are described, and an incommensurate structure (for the as-synthesized form) as well as two remarkable guest-free polymorphs (open and closed) are highlighted.

First zeolite carbon replica with a well resolved X-ray diffraction pattern

The present study demonstrates that for the nanocasting process with zeolites, a careful choice of the zeolite structure type (EMT) allows the formation of faithful carbon replica exhibiting up to three well resolved XRD peaks.