J.L. Bonardet

Nuclear Magnetic Resonance of Physisorbed 129Xe Used as a Probe to Investigate Porous Solids

Abstract Xenon is an inert gas with a large electronic environment that makes it sensitive to any interaction, even physical. In the case of 129Xe isotope (spin 1/2), the resulting electronic perturbation is directly transmitted to the nucleus and, therefore, affects the nuclear magnetic resonance chemical shift. In this review, we report exhaustively up to 1996 the many applications of this technique in both fundamental and applied research in the fields of microporous and mesoporous solids.

New Ti-SBA mesoporous solids functionnalized under gas phase conditions: characterisation and application to selective oxidation of alkenes

Functionnalization of mesoporous silica SBA15 with titanium oxide was carried out under gas phase conditions with TiCl4 as titanium source, between 473 and 673 K, followed by hydrolysis at ambient temperature. Spectroscopic characterisations (X-ray diffraction, XPS, IR, UV-Vis.) and porosimetry measurements showed that part of TiO2 is grafted on the internal surface of the pores. Catalytic activity was tested in selective oxidation of bulky alkenes. Several cycles of reaction showed that any leaching of Ti species is observed in the liquid phase.

129Xe NMR overview of xenon physisorbed in porous solids

Xenon is an inert gas whose large polarizability makes it very sensitive to electronic perturbation which is directly transmitted to the nucleus and therefore markedly affects the chemical shift. This overview, which is not exhaustive, presents some characteristic examples of the use of 129Xe NMR to study micro and mesoporous solids. Copyright

Mechanical properties of mesoporous silicas and alumina–silicas MCM-41 and SBA-15 studied by N2 adsorption and 129Xe NMR

Abstract Purely siliceous and Al-containing MCM-41 and SBA-15 materials have been prepared with pore diameters of 2.4–3.0 nm for MCM-41 and 6.5–7.5 nm for SBA-15. The effect of compression on the mesopore structure has been studied by N 2 adsorption–desorption, X-ray diffraction and 129 Xe NMR experiments. The pore size distributions obtained from N 2 adsorption data show that the mesopore structure is partially destroyed and that small size pores are formed at the expense of the original ones (in the loose powder) when the powder is compressed at high pressure (up to 520 MPa). The 129 Xe NMR spectra are interpreted in terms of an exchange between adsorbed Xe (in the channels) and gaseous Xe atoms (in the interparticle spaces), which depends on the particle size and the compaction of the powder. For both MCM-41 and SBA-15 materials, the Al-containing samples are more fragile than the purely siliceous materials.

Direct synthesis of AlSBA mesoporous molecular sieves: characterization and catalytic activities

Aluminium-incorporated SBA mesoporous materials have been obtained for the first time by direct synthesis; the resulting materials retain the hexagonal order and physical properties of purely siliceous SBA-15 and present higher catalytic activities in the cumene cracking reaction than AlMCM-41 materials.

Green and selective epoxidation of alkenes catalysed by new TiO2–SiO2 SBA mesoporous solids

New catalysts TiO2–SiO2 (Ti–SBA) with pore sizes of 37 and 65 A have been synthesized by grafting titanium on a structured mesoporous SBA15 (SBA for Santa BArbara and 15 for hexagonal structure) by means of titanium tetrachloride in the gas phase. These catalysts have been tested in the selective epoxidation of cyclooctene, cyclohexene, (R)-limonene and α-pinene. Whatever the oxidant, hydrogen peroxide (H2O2), tert-butyl hydroperoxide (TBHP) or cumyl hydroperoxide (CHP), the selectivity is 100%. However, the yield is low with H2O2 and the catalyst is partially leached out. In the case of TBHP and CHP the epoxide yields can reach practically 100% and no leaching of titanium is observed after four successive reaction cycles. An effect of pore size on the epoxidation kinetics of α-pinene and cyclooctene has been found.

Direct incorporation of A1 in SBA mesoporous materials: characterization, stability and catalytic activity

Abstract Aluminum-incorporated SBA mesoporous materials have been obtained by direct synthesis; the resulting materials retain the hexagonal order and physical properties of purely siliceous SBA-15 and present higher catalytic activity in cumene cracking reaction than A1MCM-41 solids. The stability of these mesoporous molecular sieves after various treatments (calcination, vapor treatment and treatment in solution at different pH) is also studied using XRD, 27 A1 MAS NMR and N 2 adsorption/desorption techniques. All results show that SBA after treatments has much higher stability than MCM-41 owing to its large wall thickness. The incorporation of aluminum into purely siliceous SBA-15 improves its stability. The stability of the state of aluminum coordination as well as the mesoporous structure of A1SBA is also higher than A1MCM-41, especially in the different pH solutions.

Surface acidity diagnosis and catalytic activity of AlSBA materials obtained by direct synthesis

Abstract The objective of this work is to give a characterization of aluminosilicate AlSBA materials in particular with respect to acidity and the nature of acid sites. The number of acidic centers and the strength of these sites are determined by ammonia adsorption and temperature-programmed desorption (TPD). The Bronsted acidity of AlSBA is also assessed by measuring the relative intensity of the laser-induced fluorescence (LIF) quinolinium ion band peaking at 390 nm when quinoline is adsorbed on the surface of the material. When Lewis acid sites are present, a complex formed between these sites and quinoline is observed. The AlSBA samples showed a high and durable activity in the cumene cracking.

A 129-Xe NMR study of the Co2+-Xe interactions in partiallyexchanged CoNaY zeolites: influence of the hydration level

Sodium Y zeolites partially exchanged with Co 2+ have been studied by 129-XeNMR spectroscopy. Large chemical shifts due to paramagnetic effects of Co 2+ ions are observed when the water concentration is less than 6 H 2 O/Co 2+ . The 0 term (σ value for zero xenon concentration) derived from a second-order polynomial expansion is characteristic of the Co 2+ -Xe interactions. This term increases exponentially when [H 2 O] decreases.

Oxidative ring opening of epoxides by tert-butyl hydroperoxide in the presence of AISBA-15

Oxidative ring opening of epoxides by tert -bytyl hydroperoxide was carried out in the presence of AISBA-15 under mild conditions (acetonitrile, 353 K). Various materials were prepared with different Si/Al molar ratio (5 to 20) in order to compare their catalytic activity. These solids were fully characterized especially by 27 Al NMR and NH 3 adsorption. This work emphasizes the influence of the method used for the incorporation of aluminium (grafting (AISBA(PS)) or direct synthesis (AlSBA(DS))) on the conversion of cyclohexene oxide to adipic acid. The best yields of the diacid (40–50%) were obtained in the presence of aqueous TBHP and AlSBA(DS) materials.