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Vimont A Lavalley JC Sahibed-Dine A Otero Arean C Rodríguez Delgado M Daturi M 《The journal of physical chemistry. B》2005,109(19):9656-9664
By hydrolysis of an ethanolic gallium nitrate solution, gamma-Ga2O3 was prepared as a single-phase polymorph having a specific surface area of 160 m2 g(-1). Surface acidity and basicity of this material was studied by IR spectroscopy, using pyridine, 2,6-dimethylpyridine, acetonitrile, and carbon dioxide as spectroscopic probe molecules. For comparison, a gamma-Al2O3 sample having a surface area of 290 m2 g(-1) was also studied. On partially hydroxylated gamma-Ga2O3, the main O-H stretching bands were found at 3693 (sharp) and at 3660-3630 cm(-1) (broad), and the material proved (by adsorbed dimethylpyridine) to have a weak Br?nsted acidity. Surface Lewis acidity of gamma-Ga2O3 was revealed (mainly) by adsorbed pyridine, which gave the characteristic IR absorption bands of Lewis-type adducts at 1612, 1579, 1488, and 1449 cm(-1) (values noted under an equilibrium pressure of 1 Torr at room temperature); the corresponding Lewis acid centers (coordinatively unsaturated Ga3+ ions) were found to be weaker, although more abundant, than those present on the surface of gamma-Al2O3 (unsaturated Al3+ ions). Another significant difference between gamma-Ga2O3 and gamma-Al2O3 is the smaller thermal stability of pyridine and 2,6-dimethylpyridine Lewis adducts formed on the gallium oxide. The surface basicity of gamma-Ga2O3 was studied by using carbon dioxide and deuterated acetonitrile as IR probe molecules. Adsorbed CO2 gave carbonate and hydrogen-carbonate surface species similar to those formed by gamma-Al2O3. Adsorbed acetonitrile gave rise to acetamide species, which revealed the basic character of surface O2- ions. These acetamide species were found to be more abundant on gamma-Ga2O3 than on gamma-Al2O3. 相似文献
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COŞKUN DENIZ 《Pramana》2017,88(1):20
Common recipe for the lengthening pendulum (LP) involves some change of variables to give a relationship with the Bessel’s equation. In this work, conventional semiclassical JWKB solution (named after Jeffreys, Wentzel, Kramers and Brillouin) of the LP is being obtained by first transforming the related Bessel’s equation into the normal form ‘via the suggested change of independent variable’. JWKB approximation of the first-order Bessel functions (ν=1) of both types along with their zeros are being obtained analytically with a very good accuracy as a result of the appropriately chosen associated initial values and they are extended to the neighbouring orders (ν=0 and 2) by the recursion relations. The required initial values are also being studied and a quantization rule regarding the experimental LP parameters is being determined. Although common numerical methods given in the literature require adiabatic LP systems where the lengthening rate is slow, JWKB solution presented here can safely be used for higher lengthening rates and a criterion for its validity is determined by the JWKB applicability criterion given in the literature. As a result, the semiclassical JWKB method which is normally used for the quantum mechanical and optical waveguide systems is applied to the classical LP system successfully. 相似文献
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Onida B Bonelli B Flora L Geobaldo F Arean CO Garrone E 《Chemical communications (Cambridge, England)》2001,(21):2216-2217
Mesoporosu (MCM-41 type) silica containing surfactant-embedded Congo Red has been prepared and tested against gas phase HCl and ammonia, as well as solutions of ionic species; it is shown that the hybrid (organic-inorganic) material is permeable to both gases and ionic species, and can act as a pH indicator and as a selective chelating agent. 相似文献
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E. Escalona Platero C. Otero Arean J. B. Parra 《Research on Chemical Intermediates》1999,25(2):187-194
The mixed metal oxides CoAl2O4 and NiAl2O4 were prepared in a high surface area form by using a sol-gel method which involves hydrolysis of cobalt-aluminium and nickel-aluminium
isopropoxides. The resulting gels were calcined at 673 K to yield the corresponding spinel-type metal oxides. Powder X-ray
diffraction was used to confirm spinel formation. Nitrogen adsorption-desorption measurements have shown the materials obtained
to be highly porous. The BET surface area was found to be 240 m2g−1 for CoAl2O4 and 255 m2g−1 for NiAl2O4. Both materials showed a unimodal distribution of pore radii, where the most frequent pore radius is 5 nm for cobalt aluminate
and 3 nm for nickel aluminate. 相似文献
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Carlos O. Arean Elena Groppo Wei Liu Leticia F. Velasco Jose B. Parra 《Adsorption》2013,19(2-4):367-372
Porous copolymers of divinylbenzene (DVB) and acrylic acid (AA) having DVB:AA ratios of 6:4, 8:2 and 9:1 were prepared following a distillation-precipitation method, using toluene as the porogenic agent. The materials thus obtained, which showed specific surface area in the range of 380–600 m2 g?1 and pore volume in the range of 0.14–0.18 cm3 g?1, were investigated as possible adsorbents for CO2 capture from the flue gas of coal-fired power stations. For that purpose, the isosteric heat of adsorption (and CO2 adsorption capacity) was analysed from N2 and CO2 adsorption equilibrium isotherms obtained over a temperature range. For CO2, q st resulted to be in the range of 27–31 kJ mol?1 (the highest value corresponding to the 6:4 sample), while for N2 a value of q st ≈ 12 kJ mol?1 was obtained. Equilibrium adsorption capacity for CO2 (at ambient temperature and pressure) showed the value of about 1.35 mmol g?1. These results are discussed in the broader context of corresponding literature data for CO2 capture using protonic zeolites. 相似文献
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The nature of cationic adsorption sites in alkaline zeolites--single, dual and multiple cation sites
Nachtigall P Delgado MR Nachtigallova D Arean CO 《Physical chemistry chemical physics : PCCP》2012,14(5):1552-1569
Gas adsorption on zeolites constitutes the base of many technological applications of these versatile porous materials. Quite often, especially when dealing with small molecules, individual extra-framework (exchangeable) cations are considered to be the adsorption site on which molecules coming from a gas phase form the corresponding adsorption complex. Nonetheless, while that can be the case in some instances, recent research work that combines variable temperature infrared spectroscopy with periodic DFT calculations showed that some types of adsorption sites involve two or more cations, which constitute dual and multiple cation sites, respectively. Adsorption complexes formed on these cationic adsorption sites differ in both structure and stability from those formed on a single cation alone. Examples concerning CO, CO(2) and H(2) adsorption on alkali and alkaline-earth metal exchanged zeolites are reviewed, with the double purpose of clarifying concepts and highlighting their relevance to practical use of zeolites in such fields as gas separation and purification, gas storage and heterogeneous catalysis. 相似文献
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