L.C. de Ménorval

Synthesis and characterization of pillared clays containing both Si and Al pillars

Abstract A Wyoming montmorillonite clay has been intercalated using the competitive ion exchange of aluminum hydroxy polycations and oligosilsesquioxanes. Whereas the intercalation of montmorillonite by the products of hydrolysis of trichlorosilylethylpyridine yields an heterogeneous solid, with a large fraction non-intercalated, the X-ray diffraction shows that competitive intercalation permits a nearly complete intercalation of the material. The lattice spacing of 21.4 A after ion exchange, is determined by the size of the largest oligosilsesquioxane cations. It is reduced to 17.4 A after calcination at 873 K where 29 Si and 27 Al MAS-NMR show the existence of the two types of pillars with respectively the siloxane and Al 13 structure. After calcination at 973 K, a clear 001 XRD line is observed, and the microporous volume is 0.13 ml g −1 , thus showing a good thermal stability. The number and strength of acid sites determined by adsorption of ammonia is comparable to that of HY zeolites. This strong acidity is related in part to the stability of the structure, and to the retention of the individuality of the Al 13 pillars. The tetrahedral aluminum atom of the pillars is assumed to be responsible for this strong acidity.

Characterization of montmorillonites pillared by cationic silicon species using129Xe-NMR spectroscopy

The l”‘Xe-NMR technique has recently been extensively used to probe the porosity of zeolites, the location of metal clusters and cluster precursors as a function of calcination conditions in NaY zeolite-supported platinum catalysts, as well as the arrangement of organic molecules within the zeolite Y supercages [l--4]. It is of interest to investigate whether xenon can be used to characterize other microporous systems. The aim of this work was to study the microporosity of a new class of materials, pillared interlayered clays (PILC ). We have found that 12’Xe-NMR is sensitive to the microporosity between the pillars and to some extent to the partial crystallinity of these materials.

29Si and 129Xe NMR of Mn2+ doped silica xerogels

Abstract Paramagnetic Mn2+ ions were incorporated in silica gel during the preparation of the sol. Doped silica xerogels were obtained by heat treatment at different temperatures and studied by 29Si and 129Xe nuclear magnetic resonance (NMR) experiments. Comparison between 29Si NMR magic angle spinning (MAS) spectra of doped and undoped xerogels showed that there is a significant effect of the paramagnetic probe on Q2, Q3 and Q4 peaks. Reduction of the 29Si-T1 relaxation time in the presence of the Mn2+ probe was observed. 129Xe NMR spectra were recorded on the xerogels at variable Xe pressures. Results were consistent with 29Si NMR data and confirmed the localization of the paramagnetic probe in surface sites as shown by electron paramagnetic resonance (EPR) of Mn2+.

Diels-Alder Condensation of Methyl and (-)-Menthyl Acrylates with Cyclopentadiene over Zeolites and Cation Exchanged Clays

Abstract Clays exchanged by different cations have been compared to HY and HBEA zeolites for Diels Alder condensation of methyl and (-)-menthyl acrylates with cyclopentadiene. Two reactions are in competition: the Diels Alder reaction and diene polymerisation which deactivates the catalysts and consumes the reactant. Polymerisation is catalysed either by protons or reducible cations. With methyl acrylate polymerisation is minimised, and activity is related to the number of acid sites. Selectivity is comparable for zeolites or clay catalysts with the two acrylates, then concentration effects or confinement in micropores play a negligible role.

K10 Montmorillonites as catalysts in Diels-Alder reactions: influence of the exchanged cation

Abstract K10 montmorillonites exchanged with different cations, dried at 120°C or calcined at 550°C, are used as catalysts in Diels-Alder reactions of methyl and (-)-menthyl acrylates with cyclopentadiene. In general, calcined clays give rise to better conversions and selectivities. Zr(IV) and specially Ti(IV) clays display the best catalytic activities. However, the best asymmetric induction is achieved with Cr(III) and Ca(II) calcined clays. Clays containing easily reducible cations behave differently due to the cyclopentadiene polymerization via radical cations.

Characterization of MFI/αAl2O3 and V-MFI/αAl2O3 composite membranes by 129Xe NMR

Abstract 129 Xe NMR was investigated in order to study both the compositional and structural homogeneity of composite MFI zeolite membranes. Interaction of the αAl 2 O 3 support by incorporation of Al in the MFI structure has been pointed out. The MFI zeolite layer grown on the top of the support does not contain Al, although the MFI zeolite grown inside the support contains about of 2.2 Al atoms by unit cell. This result is in a good keeping with those published in the literature and obtained by TEM/EDS. A quantitative evaluation of the inserted vanadium species could also be possible if reference curves were available. Results show that the V-MFI structure quality is different inside and outside the support. The double NMR signal specifically observed for V-MFI-out was attributed to structural defects. The results of this study on the composition and homogeneity of composite zeolite/alumina membranes are helpful for better understanding their properties and performance.

Photoluminescence properties of fullerene C60 confined in microporous VPI-5 zeolite.

Abstract Andersons method of incorporation of C 60 within the cages of a VPI-5 zeolite has been used as well as a chemical vapor deposition procedure. 129 Xe NMR has confirmed that, starting from an organic solution of fullerene, C 60 , was actually incorporated into the molecular cages of the inorganic matrix. Thermal analysis and X-ray diffraction showed that the treatment does not affect the integrity of the crystalline structure of VPI-5. Photoluminescence experiments gave similar results as those already mentioned by other authors indicating the probable confinement effect of the inorganic matrix on the C 60 isolated molecules.

Study of the molecular diffusion in the internal porosity of ZSM-5 and H-MOR zeolites

Summary In this work we have applied a 129Xe-NMR spectroscopic technique using liquid octamethylcyclotetrasiloxane (OMCTS) as a pore blocking agent to study the molecular diffusion of xenon within different zeolite catalyst samples. We were able to extract important information about the microporosity and the xenon molecular diffusion in individual crystallite particles.

Formation of alkali nanoparticles in NaY zeolite cages and in AlPO4-5 molecular sieves: NMR studies

Summary Dehydrated NaY zeolite and AlPO 4 -5 molecular sieves have been reacted with sodium, rubidium and cesium metal vapor and sodium metal vapor, respectively. Using 129 Xe, 23 Na, 87 Rb and 133 Cs solid state NMR technique, we were able to characterize the sodium nanoparticles and Na-M bimetallic alloys (M=Rb, Cs) formed in the cavities of NaY zeolite and in the channels of AlPO 4 -5 molecular sieves.

Potentialities of an innovative technique like {sup 129}Xe NMR and of SAXS for the characterization of microporous sol-gel derived SiO{sub 2}

Addition of surfactants in TEOS derived sols leads to micro- or mesoporous materials whose porous texture can be varied by changing the surfactant quantity and/or chain length. This series of materials, with a relatively narrow pore size distribution, is well adapted to study the potentialities of an innovative characterization technique like {sup 129}Xe Nuclear Magnetic Resonance in comparison with Small Angle X-ray Scattering and N{sub 2} adsorption. SAXS revealed a high surface rugosity of the materials and a good correlation with pore hydraulic radius distributions measured by N{sub 2} adsorption. Using {sup 129}Xe NMR, the authors have studied the Xe chemical shifts ({delta}{sub Xe}) as a function of p{sub Xe} and have pointed out several original results showing the importance, for microporous materials, of the NMR line shapes and of the slope of the lines {delta}{sub Xe} = f(p{sub Xe}).