The presence of basic centers in some oxides has been recognized for a long time as being important in catalysis [1-4]. Usually both basic and acid sites exist simultaneously. The two centers may work independently or in a concerted way. For instance, in alcohol transformation, dehydration is favored on acidic sites and dehydrogenation on basic centers [3,5]. A large variety of materials are cited as having basic character. They include single-metal oxides (MgO, CaO, ZnO), supported alkali metals (Na/MgO, K/K2CO3), mixed-metal oxides (MgO-A12O3, ZnO-SiO2, MgO-TiO2), zeolites (X and Y saturated with alkaline cations of low electronegativity), hydrotalcite-type anionic clays, asbestoslike materials, carbon-supported basic catalysts, and basic organic resins. ∗ Present address: 16 rue Francois Gillet, 69003 Lyon, France.

Basic zeolites : Characterization and uses in adsorption and catalysis

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.

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

We fabricated bare and Pd-decorated SnO2 nanowires (NWs) for comparative study of hydrogen sensing. A selective vapor-liquid-solid method was used for fabricating SnO2 NWs and a UV reduction method was used to decorate Pd NPs on the surfaces of the fabricated NWs. Sensing studies showed that decorating the surfaces of SnO2 NWs with a noble metal increased the response to 1 ppm H2 gas from 6.88 to 16.95 at an optimal working temperature of 300 °C. Furthermore, Pd decoration also increased the selectivity. The enhanced sensing properties of the Pd-decorated sensor are related to the Pd NPs’ catalytic effect and the formation of Schottcky junctions. This study demonstrated the possibility of a high performance H2 sensor created by combining metal oxide NWs with a catalyst such as Pd.

Improving the hydrogen sensing properties of SnO2 nanowire-based conductometric sensors by Pd-decoration

Investigation of competitive adsorption is carried out using the Xe–Ar mixture in zeolite NaA as a model system. The Xen clusters are trapped in the alpha cages of this zeolite for times sufficiently long that it is possible to observe individual peaks in the NMR spectrum for each cluster while the Ar atoms are in fast exchange between the cages and also with the gas outside. The 129Xe nuclear magnetic resonance spectra of 12 samples of varying Xe and Ar loadings have been observed and analyzed to obtain the 129Xe chemical shifts and the intensities of the peaks which are dependent on the average argon and xenon occupancies. The detailed distributions, f(XenArm), the fractions of cages containing n Xe atoms and m Ar atoms cannot be observed directly in this system, that is, individual peaks for XenArm mixed clusters are not observed in the NMR spectrum. This information is, however, convoluted into the observed 129Xe chemical shifts for the Xen peaks and the distributions Pn, the fraction of cages contain...

http://www.stemwomen.org/topics/pubs/V150.pdf

Competitive adsorption of xenon and argon in zeolite NaA. 129Xe nuclear magnetic resonance studies and grand canonical Monte Carlo simulations

Nanoporous photocatalysts have been designed to exhibit unique photocatalytic activities through framework substitution of titanium species or surface immobilization of rhenium complex onto mesoporous silica. This article summarizes recent work on the synthesis, characterization and photocatalytic activities of the designed porous photocatalysts performed by the present authors. Various spectroscopic investigations revealed that the photo-excited states of these catalysts play a vital role in the photocatalytic reactions and their photocatalytic reactivities are strongly dependent on structures of active sites, which are confined and immobilized in the restricted framework structure of the mesoporous silica. Highly dispersed titanium oxide species incorporated in the framework of mesoporous silica exhibited high and unique photocatalytic reactivity for the reduction of CO2 with H2O to produce CH4 and CH3OH under UV irradiation, its reactivity being much higher than bulk TiO2. The cationic rhenium(I) complex was encapsulated into a mesoporous AlMCM-41 material by ion-exchange method, yielding a visible light photocatalyst to be active for photocatalytic reduction of CO2.

Photoreduction of Carbondioxide on Surface Functionalized Nanoporous Catalysts

N.m.r. investigation of benzene adsorption on a dehydrated NaY zeolite

The sorption and transport properties of benzene on dehydrated NaX and NaY zeolites have been investigated directly by 1 H and 13 C NMR measurements of the adsorbed benzene and probed indirectly by 129 Xe NMR of the coadsorbed xenon. Dehydrated NaX and NaY zeolite adsorbate samples containing various adsorbate concentrations and having various sample bed configurations, which were subjected to different preparatory and experimental conditions, have been examined. Thermal treatment at a temperature (>250 °C) much greater than the boiling point of bulk benzene (80 °C) for an extended period of several hours is indispensable to ensure a homogeneous benzene distribution within the supercages of the faujasite-type zeolites.

NMR Studies of Benzene Adsorbed on Synthetic Faujasite-Type Zeolites

Homogeneous Adsorption of Benzene on NaX and NaY Zeolites

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N.m.r. investigation of benzene adsorption on a dehydrated NaY zeolite

NMR Studies of Benzene Adsorbed on Synthetic Faujasite-Type Zeolites

Homogeneous Adsorption of Benzene on NaX and NaY Zeolites