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Desorption Measurements (desorption + measurement)

Distribution by Scientific Domains
Chemistry66%

Selected Abstracts

Structures of monolayers formed from different HS,(CH2)2,X thiols on gold, silver and copper: comparitive studies by surface-enhanced Raman scattering

JOURNAL OF RAMAN SPECTROSCOPY, Issue 11 2003
Andrzej Kudelski
Abstract Molecules of 2-aminoethanethiol (cysteamine, CYS), 2-mercaptoethanol (MET), 3-mercaptopropionic acid (MPA), sodium 2-mercaptoethanesulphonate (MES) and 1-propanethiol (PTH) were spontaneously chemisorbed on electrochemically activated silver, copper and gold surfaces. The structure of monolayers formed was studied with surface-enhanced Raman scattering (SERS). In CYS and MPA monolayers the relative surface concentration of gauche conformers was higher than in MET, PTH and MES monolayers. This is probably due to double bonding to the metal surface by a fraction of adsorbed MPA and CYS molecules (via the sulphur moiety and the terminal carboxylic or amino group). In CYS, MET, MPA and PTH monolayers the surface concentration of trans conformers is significantly higher on Ag than on Au or Cu. The structures of MES monolayers on Ag, Au and Cu are similar, with very high surface concentrations of trans conformers. Statistically, the wavenumbers of ,(C,S) bands of both gauche and trans conformers are the highest on Au, slightly lower on Ag and the lowest for Cu. However the positions of ,(C,S) bands are also sensitive to the other parameters (e.g. C,C,S,metal torsion angle, the overall ordering of the monolayer). Therefore, the wavenumbers of ,(C,S) bands are not good indicators of differences in the interaction between chemisorbed thiols and the metal substrates. Desorption measurements suggest that part of the adsorbed molecules is bonded significantly weaker than the rest. Thiolate monolayers on Cu decomposed relatively easily, forming a layer of copper sulphide. The strength of adsorbed MPA acid is similar on all substrates. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Palladium-Catalyzed Transformation of Renewable Oils into Diesel Components

ADVANCED SYNTHESIS & CATALYSIS (PREVIOUSLY: JOURNAL FUER PRAKTISCHE CHEMIE), Issue 11-12 2010
Junxing Han
Abstract A size-controlled palladium nanoparticle catalyst prepared by adsorption of colloidal palladium nanoparticles on barium sulfate is efficient and highly selective in transforming vegetable oils into diesel-like fuel. Preliminary kinetic investigations using model compounds indicated that decarboxylation of aliphatic esters on palladium in a hydrogen-rich atmosphere showed a zero-order rate. Hydrogen temperature-programmed desorption measurements revealed that the high-temperature desorption of hydrogen species might be the rate-determining step. [source]

Synthesis and Characterization of Silver Nanoparticles and Titanium Oxide Nanofibers: Toward Multifibrous Nanocomposites

JOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 9 2010
Fredrick O. Ochanda
A new method was investigated to produce new multiscale fibrous nanocomposites comprised of titanium oxide (TiO2) nanofibers and silver (Ag) nanoparticles (NPs). The process involved electrospinning TiO2 precursor solution containing colloidal solution of Ag NPs, and organic solvent (dimethyl- n,n -formamide) to fabricate a porous, nonwoven, free-standing nanofiber mesh. Postprocess heating of the electrospun nanofibers entailed calcination in air environment at 500°C for 3 h. Microemulsion processing was used to generate NPs of Ag in a monodispersed distribution throughout the colloidal solution. X-ray diffraction data were consistent with the anatase phase of TiO2, while transmission electron microscopy and hydrogen desorption measurements revealed a very porous microstructure. It was demonstrated that NP colloidal stability is solvent dependent. It is anticipated that incorporation of metal particles in nanofibers will lead to enhanced photocurrent generation, when used in functional devices. [source]

Structural and defect changes of hydrogenated SiGe films due to annealing up to 600°C

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3-4 2010
Petr Sládek
Abstract In order to better understand the effects of the hydrogen incorporation on the defects and the disorder in the undoped nano/microcrystalline SiGe:H, we performed a comparative study on samples deposited under different plasma conditions. With variation of the pressure, we were able to change the structure of SiGe:H films. We have used the combination of the infrared spectroscopy, CPM, PDS and thermal desorption measurements to study the thermal dependence of defect density, disorder, as well as hydrogen concentration. The film mechanical properties were tested by depth sensing indentation technique. The results showing a different hydrogen bonding with the change of deposition conditions are interpreted as a whole by terms of the specific local hydrogen bonding environment, related to different growth mechanism. (© 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Production of Hydrogen from Dimethyl Ether over Supported Rhodium Catalysts

CHEMCATCHEM, Issue 2 2009
Gyula Halasi
Abstract Infrared (IR) spectroscopy revealed that dimethyl ether (DME) undergoes partial dissociation on pure and rhodium-containing CeO2 at 300,K to yield methoxy and methyl species. This process is promoted by the presence of rhodium. By means of thermal desorption measurements (TPD), the adsorption of DME on Rh/CeO2 at 300,K and subsequent decomposition of DME (Tp,370,K), releasing H2, CO, CO2, and CH4, with Tp between 420 and 673,K, were ascertained. Rh/CeO2 is an effective catalyst for the decomposition of DME to give H2 (29,35,%), CO (27,30,%) and CH4 (32,38,%) as major products with complete conversion at 673,723,K. Adding water to DME changed the product distribution and increased the selectivity of H2 formation from 30,35,% to 58,% at 723,K. In,situ IR spectroscopy showed absorption bands of CO at 2034 and 1893,cm,1 during the reaction at 673,773,K. Deactivation of the catalyst did not occur at 773,K during the time measured (approximately 10 h). Rh deposited on carbon Norit also exhibited a high activity towards the decomposition of DME, but the selectivity towards hydrogen was lower. [source]

Solvate-Supported Proton Transport in Zeolites

CHEMPHYSCHEM, Issue 4 2004
Marion E. Franke Dr.
Abstract Solvate-supported proton transport in zeolite H-ZSM-5 was studied by means of complex impedance spectroscopy. The zeolite shows enhanced proton mobility in the presence of NH3and H2O that depends on the concentration of the solvate molecule, temperature (298,773 K), and the SiO2/Al2O3ratio of the zeolite (30,1000). In general, proton conductivity in H-ZSM-5 is most effectively supported in the presence of NH3and H2O at high concentrations, low temperatures, and low SiO2/Al2O3ratios (,80). For the aluminum-rich samples desorption measurements reflect different transport mechanisms that depend on the respective temperature range. Up to about 393 K a Grotthus-like proton transport mechanism is assumed, whereas at higher temperatures (393,473 K) vehiclelike transport seems to dominate. The activation energies for NH4+and H3O+vehicle conductivity depend on the SiO2/Al2O3ratio, and the values are in the range of 49,59 and 39,49 kJ,mol,1, respectively, and thus significantly lower than those for "pure" proton conduction in solvate-free samples. [source]