Showing papers on "Oxide published in 1997"
TL;DR: In this article, the adsorption properties and reactivities of gold are summarized in terms of their size dependency from bulk to fine particles, clusters and atoms, and the catalytic performances of gold markedly depend on dispersion, supports, and preparation methods.
3,854 citations
TL;DR: A tin-based amorphous composite oxide (TCO) was synthesized in this paper to replace the carbon-based lithium intercalation materials currently in extensive use as the negative electrode (anode) of lithium-ion rechargeable batteries.
Abstract: A high-capacity lithium-storage material in metal-oxide form has been synthesized that can replace the carbon-based lithium intercalation materials currently in extensive use as the negative electrode (anode) of lithium-ion rechargeable batteries. This tin-based amorphous composite oxide (TCO) contains Sn(II)-O as the active center for lithium insertion and other glass-forming elements, which make up an oxide network. The TCO anode yields a specific capacity for reversible lithium adsorption more than 50 percent higher than those of the carbon families that persists after charge-discharge cycling when coupled with a lithium cobalt oxide cathode. Lithium-7 nuclear magnetic resonance measurements evidenced the high ionic state of lithium retained in the charged state, in which TCO accepted 8 moles of lithium ions per unit mole.
2,470 citations
TL;DR: In this paper, the structural, electronic and chemisorptive properties of ultrathin metal films on clean and well-defined oxide surfaces have been characterized using a variety of surface science techniques.
1,435 citations
TL;DR: CS and CS/PEO-PPO nanoparticles prepared by a very mild ionic crosslinking technique are novel and suitable systems for the entrapment and controlled release of proteins and vaccines.
Abstract: Purpose. The aim of this study was to investigate the interaction between the components of novel chitosan (CS) and CS/ethylene oxide-propylene oxide block copolymer (PEO-PPO) nanoparticles and to evaluate their potential for the association and controlled release of proteins and vaccines.
720 citations
TL;DR: In this article, a comparison of the molecular structure and reactivity information of supported vanadium oxide catalysts is presented, which provides new fundamental insights into the catalytic properties of surface vanadia species during hydrocarbon oxidation reactions.
Abstract: Supported vanadium oxide catalysts, containing surface vanadia species on oxide supports, are extensively employed as catalysts for many hydrocarbon oxidation reactions. This paper discusses the current fundamental information available about the structure and reactivity of surface vanadia species on oxide supports: monolayer surface coverage, stability of the surface vanadia monolayer, oxidation state of the surface vanadia species, molecular structures of the surface vanadia species (as a function of environment and catalyst composition), acidity of the surface vanadia species and reactivity of the surface vanadia species. Comparison of the molecular structure and reactivity information provides new fundamental insights into the catalytic properties of surface vanadia species during hydrocarbon oxidation reactions: (1) the role of terminal VO, bridging VOV and bridging VO-support bonds, (2) the number of surface vanadia sites required, (3) the influence of metal oxide additives, (4) the influence of surface acidic and basic sites, (5) the influence of preparation methods and (6) the influence of the specific oxide support phase. The unique physical and chemical characteristics of supported vanadia catalysts, compared to other supported metal oxide catalysts, for hydrocarbon oxidation reactions are also discussed.
644 citations
TL;DR: In this article, the main data appeared in the last years on the oxidative dehydrogenation (ODH) of short chain alkanes on supported vanadium oxide catalysts, and it was concluded that tetrahedral V5+-species are active and selective sites in the ODH of C2-C4 alkanes.
Abstract: This paper summarizes the main data appeared in the last years on the oxidative dehydrogenation (ODH) of short chain alkanes on supported vanadium oxide catalysts. The acid-base character of metal oxide support influences the dispersion of vanadium on the surface of the support, as well as the nature of the vanadium species. The reducibility and structure of surface vanadium oxide species and the acid-base character of catalysts, in addition to their catalytic properties in the ODH of C2–C4 alkanes, strongly depend on the metal oxide used as support and the vanadium loading. In this way, it appears that tetrahedral V5+-species are active and selective sites in the ODH of C2–C4 alkanes. The effect of the coordination number and aggregation state of surface vanadium oxide species, and the presence of acid/base sites on the catalytic behavior of supported vanadium oxide catalysts are discussed. It is concluded that these are important factors that must be considered to develop selective catalysts in ODH reactions.
627 citations
TL;DR: In this paper, high-resolution electron microscope (HREM) observations revealed that nanometer-sized cerium(IV) oxide ultrafine particles were formed using a reaction within reversed micelles, which was known as a microemulsion method.
Abstract: Cerium(IV) oxide ultrafine particles were prepared using a reaction within reversed micelles, which was known as a microemulsion method. The ultrafine particles, which were obtained by mixing the water-in-oil microemulsions containing cerium nitrate solution with those of ammonium hydroxide, were characterized by high-resolution electron microscope (HREM) observations. HREM micrographs revealed that nanometer-sized CeO2 particles were formed, and their shapes were uniform. Selected-area electron diffraction patterns of the particles were completely indexed as those of cerium(IV) oxide with the cubic fluorite structure, and the lattice constant calculated from radii of Debye−Sherrer rings was 0.541 nm. Most of the particles were distributed between 2 and 6 nm, and the mean particle size obtained in this method was between 2.6 and 4.1 nm. The size of 2.6 nm is the smallest among the values ever reported for CeO2 particles. Both direct and indirect optical energy gaps of the particles were independent of the...
461 citations
436 citations
TL;DR: In this article, the selectivity pattern and the formation rates of the reaction products are used to characterize both structural (dispersion) as well as chemical properties (acid base and redox) on supported oxide catalysts, especially for molybdenum-based systems supported on silica and vanadia on titanium oxide.
Abstract: The goal of this review is to present some aspects of the use of a test reaction, i.e., methanol oxidation, as a tool to characterize oxidation catalysts. The selectivity pattern and the formation rates of the reaction products are used to characterize both structural (dispersion) as well as chemical properties (acid-base and redox) on supported oxide catalysts, especially for molybdenum-based systems supported on silica and vanadia on titanium oxide. This highly sensitive technique which gives information on the catalytically active sites at the molecular level characterizes a catalyst at work and is particularly well-adapted to the study of supported catalysts.
428 citations
TL;DR: The thermoelectric properties of a mixed oxide were investigated in terms of materials for high-temperature thermal conversion in this paper, showing metallic behavior and the electrical conductivity of the oxide increases on Al-doping by more than three orders of magnitude up to ca.
Abstract: The thermoelectric properties of a mixed oxide
(Zn
1-x
Al
x
)O (x=0,
0.005, 0.01, 0.02, 0.05) are investigated in terms of materials for
high-temperature thermoelectric conversion. The electrical conductivity,
σ, of the oxide increases on Al-doping by more than three
orders of magnitude up to ca. 10
3
S
cm
-1
at room temperature, showing metallic behaviour. The
Seebeck coefficient, S, of
(Zn
1-x
Al
x
)O
(x>0) shows a general trend in which the absolute value
increases gradually from ca. -100 µV
K
-1
at room temperature to ca. -200 µV
K
-1
at 1000 °C. As a consequence, the power factor,
S
2
σ, reaches ca.
15×10
-4
W m
-1
K
-2
, the largest value of all reported oxide materials.
The thermal conductivity, κ, of the oxide decreases with
increasing temperature, owing to a decrease in the lattice thermal
conductivity which is revealed to be dominant in the overall
κ. In spite of the considerably large values of
κ, the figure of merit,
Z=S
2
σ/κ,
reaches 0.24×10
-3
K
-1
for
(Zn
0.98
Al
0.02
)O at 1000 °C. The extremely large
power factor of (Zn
1-x
Al
x
)O
compared to other metal oxides can be attributed to the high carrier
mobility revealed by the Hall measurements, presumably resulting from a
relatively covalent character of the Zn–O bond owing to a fairly
small difference of the electronegativities of Zn and O. The dimensionless
figure of merit,ZT, of 0.30 attained by
(Zn
0.98
Al
0.02
)O at 1000 °C demonstrates the
potential usefulness of the oxide.
420 citations
Journal Article•
TL;DR: In this article, the copolymer micellization in water as affected by cosolutes, and on the time-dependency of surface activity have also been reported, as well as the structural characterization of the morphologies using primarily small angle scattering techniques.
Abstract: Block copolymers consisting of poly(ethylene oxide) (PEO) and poly(propylene oxide) (PPO) can self-assemble in water and water/oil mixtures (where water is a selective solvent for PEO and oil a selective solvent for PPO) to form thermodynamically stable spherical micelles as well as an array of lyotropic liquid crystalline mesophases of varying morphology. Significant advances have been made over the past year on the identification of different morphologies, the delineation of the composition-temperature ranges where they occur, and the structural characterization of the morphologies using primarily small angle scattering techniques. Important new findings on the copolymer micellization in water as affected by cosolutes, and on the time-dependency of the surface activity have also been reported.
TL;DR: In this article, 4-NO2 and 4-Br benzenediazonium salts have been reduced on H-terminated Si(111) electrodes, showing that organic films are monolayer thick and that covalent ≡SiAr bonding occurs, with no oxide at the interface.
Abstract: 4-NO2 and 4-Br benzenediazonium salts have been electrochemically reduced on H-terminated Si(111) electrodes. Electrochemical measurements evidence that the reaction results in a robust modification of Si(111) surfaces. XPS shows that organic films are monolayer thick and that covalent ≡SiAr bonding occurs, with no oxide at the interface. In the case of the Br salt, quantitative RBS measurements suggest that layers are (2×1) close-packed and assess their stability against several rinsing procedures including exposure to 40% HF. A mechanism of grafting is discussed.
TL;DR: In this article, the chemistry, microstructure, and processing of buried oxides converted from AlGaAs layers using wet oxidation was reviewed and the influence of gas flow, gas composition, temperature, Al-content, and layer thickness on the oxidation rate was characterized.
Abstract: We review the chemistry, microstructure, and processing of buried oxides converted from AlGaAs layers using wet oxidation Hydrogen is shown to have a central role in the oxidation reaction as the oxidizing agent and to reduce the intermediate predict As/sub 2/O/sub 3/ to As The stable oxide is amorphous (Al/sub x/Ga/sub 1-x/)/sub 2/O/sub 3/ which has no defects along the oxide/semiconductor interfaces but can exhibit strain at the oxide terminus due to volume shrinkage The influence of gas flow, gas composition, temperature, Al-content, and layer thickness on the oxidation rate are characterized to establish a reproducible process Linear oxidation rates with Arrhenius activation energies which strongly depend upon AlAs mole fraction are found The latter produces strong oxidation selectivity between AlGaAs layers with slightly differing Al-content Oxidation selectivity to thickness is also shown for layer thickness <60 nm Differences between the properties of buried oxides converted from AlGaAs and AlAs layers and the impact on selectively oxidized vertical cavity laser lifetime are reported
TL;DR: In this paper, the authors demonstrate the versatility of fabricating a wide range of porous metal oxide films using this electrochemical route for use in capacitor applications, including porous cobalt oxide films.
Abstract: Porous nickel oxide films were prepared by electrochemically precipitating nickel hydroxide and heating the hydroxide in air at 300 C. The resulting nickel oxide films behave as an electrochemical capacitor with a specific capacitance of 59 F/g electrode material. These nickel oxide films maintain high utilization at high rates of discharge (i.e., high power density) and have excellent cycle life. Porous cobalt oxide films were also synthesized. Although the specific capacitances of these films are approximately one-fifth that of the nickel oxide films, the results demonstrate the versatility of fabricating a wide range of porous metal oxide films using this electrochemical route for use in capacitor applications. Electrochemical capacitors have generated wide interest in recent years for use in high power applications (e.g., in a hybrid electric vehicle, where they are expected to work in conjunction with a conventional battery).
TL;DR: In this article, the effect of chromia forming alloys on the performance of doped LaMnO3 air electrode has been studied at the current fuel cell operating temperatures in the vicinity of 900-1000 °C.
TL;DR: In this article, the surface chemical composition, the crystalline structure, and the oxidation state of Co and Ni in the bulk as well as on the surface were characterized by X-ray diffraction (XRD), infrared spectroscopy (IRS).
Abstract: Films of general composition CoxNi1-xOy with x = 0, 11.1, 22.2, 33.3, 44.4, 55.6, 66.7, 77.8, 88.9, and 100 mol %, prepared by thermal decomposition of 2-propanol solutions of Ni and Co nitrates on Ni supports, have been characterized by X-ray diffraction (XRD), infrared spectroscopy (IRS), and X-ray photoelectron spectroscopy (XPS). These techniques have provided the surface chemical composition, the crystalline structure, and the oxidation state of Co and Ni in the bulk as well as on the surface. The results have revealed, in addition to previous work where NiO and NixCo2-xO4 solid solutions were found to be the predominant crystalline phases, that Ni and Co hydroxides interact in the surface layer of nanosized crystallites of the oxide phase. The interaction in the hydroxylated surface has a redox character and results in two oxidation states (+2 and +3) for both Ni and Co ions. This work has shown that Co hydroxide fragments are localized in the periphery of Ni hydroxide domains. The redox interaction...
TL;DR: Magnesium oxide is an efficient catalyst for the cycloaddition of carbon dioxide to epoxides under mild conditions; the reaction of carbon======ウスdioxide with (R)-styrene oxide in the presence of magnesium oxide======ウスgives(R)-phenyl carbonate in 97% ee with retention of======¯¯¯¯stereochemistry as mentioned in this paper.
TL;DR: In this article, the authors present typical examples obtained in Japan of the low-temperature catalytic combustion, partial oxidation of hydrocarbons, hydrogenation of carbon oxides and unsaturated hydrocarbones, reduction of nitrogen oxides, and so forth.
Abstract: Gold exhibits a unique catalytic nature and action when it is deposited as nanoparticles on a variety of metal oxides. Most reactions are noticeably structure sensitive over such supported gold catalysts. Typical examples obtained in Japan of the low-temperature catalytic combustion, partial oxidation of hydrocarbons, hydrogenation of carbon oxides and unsaturated hydrocarbons, reduction of nitrogen oxides, and so forth, are presented. Another line of advance is also introduced in the thin films of gold metal oxide composites, which are applicable to electrical and optical gassensing.
TL;DR: In this article, a theoretical model describing the electrochemical oxidation of organics at oxide electrodes forming the higher oxide (MOx+1) is described, and the effect of concentration polarization in the electrolyte is also included in the theoretical model.
TL;DR: In this paper, a method for the quantitative analysis of the Fe(2p) and O(1s) core level XPS spectra which allows the determination of the intensity of specific shake-up features within the Fe 2p spectrum is presented.
TL;DR: In this paper, a planar thin-film solid oxide fuel cell has been fabricated with an inexpensive, scalable, technique involving colloidal deposition of yttria-stabilized zirconia (YSZ) films on porous NiO-YSZ substrates.
Abstract: A planar thin-film solid oxide fuel cell has been fabricated with an inexpensive, scalable, technique involving colloidal deposition of yttria-stabilized zirconia (YSZ) films on porous NiO-YSZ substrates, yielding solid oxide fuel cells capable of exceptional power density at operating temperatures of 700 to 800°C. The thickness of the YSZ film deposited onto the porous substrate is approximately 10 Rim after sintering, and is well bonded to the NiO/YSZ substrate. Ni-YSZ/YSZ/LSM cells built with this technique have exhibited theoretical open-circuit potentials (OCPs), high current densities, and exceptionally good power densities of over 1900 mW/cm 2 at 800°C. Electrochemical characterization of the cells indicates negligible losses across the Ni-YSZ/YSZ interface and minor polarization of the fuel electrode. Thinfilm cells have been tested for long periods of time (over 700 h) and have been thermally cycled from 650 to 800°C while demonstrating excellent stability over time.
TL;DR: In this article, the synthesis, characterization, and catalytic activity of titania−silica mixed oxides are described, and important structure/property relationships for these materials are emphasized.
Abstract: Titania−silica mixed oxides are intriguing catalysts and catalyst supports since their surface reactivities depend strongly on composition and homogeneity of mixing. In this review, the synthesis, characterization, and catalytic activity of titania−silica are described, and important structure/property relationships for these materials are emphasized.
TL;DR: In this paper, hollow nanotubes of SiO2, Al2O3, V2O5, and MoO3 have been prepared using carbon as templates using tetraethylorthosilicate, aluminum isopropoxide, or vanadium pentoxide gel.
Abstract: Hollow nanotubes of SiO2, Al2O3, V2O5, and MoO3 have been prepared using carbon nanotubes as templates. The procedure involves coating the carbon nanotubes with tetraethylorthosilicate, aluminum isopropoxide, or vanadium pentoxide gel, followed by calcination and heating at higher temperatures in air to oxidize the carbon. SiO2 nanotubes containing transition metal ions have been prepared by this procedure since such materials may be of use in catalysis.
TL;DR: The morphology and structure of oxide films formed naturally on pure magnesium by exposure to humid air and water have been investigated by use of ultramicrotomed cross sections and TEM as discussed by the authors.
TL;DR: In this paper, the binding energy of the anionic partner of the parent anion in Mg 2p has been investigated in the case of MgO samples with reference to specific lattice and surface properties of the oxide itself.
TL;DR: Amorphous and single-crystal α-SiC were exposed to various oxygen sources at room temperature and X-ray photoelectron spectroscopy was used to follow changes in the surface composition and to determine the local bonding environment of the Si atoms as discussed by the authors.
Abstract: Amorphous and single-crystal α-SiC were exposed to various oxygen sources at room temperature. The oxygen sources included the residual gas in an ultrahigh vacuum environment, ambient air, ozone, and oxygen plasma. X-ray photoelectron spectroscopy (XPS) was used to follow changes in the surface composition and to determine the local bonding environment of the Si atoms. It was found that silicon oxycarbide species are formed when these SiC materials are initially exposed to oxygen. With extended exposure to ambient air, a SiO2 layer is subsequently formed over the silicon oxycarbide. However, the native oxide on the single-crystal SiC consists mainly of silicon oxycarbide species. The thicknesses of these native oxides were calculated using the XPS data.
TL;DR: In this article, the results of nonrelativistic and relativistic gradient-corrected density functional calculations on the interaction of single transition metal atoms with the oxygen sites of the regular MgO(001) surface were reported.
Abstract: We report the results of nonrelativistic and relativistic gradient-corrected density functional calculations on the interaction of single transition metal atoms with the oxygen sites of the regular MgO(001) surface. The surface has been represented by stoichiometric clusters of ions embedded in large arrays of point charges. Two adsorption sites have been considered, the on-top adsorption on the oxide anion and the bridge adsorption over two adjacent oxide anions; on-top adsorption is found to be energetically preferred. The metal atoms considered are Cr, Mo, W; Ni, Pd, Pt; Cu, Ag, and Au. These adsorbates can be classified into two groups depending on the strength of the bond with the surface. Cu, Ag, Au, Cr, and Mo exhibit weak or very weak bonds of the order of one-third of an electronvolt; their interaction is due to polarization and dispersion with little mixing with the substrate orbitals. Ni, Pd, Pt, and W, on the other hand, form relatively strong bonds, of the order of 1 eV, with the oxide anions...
TL;DR: In this article, the photocatalytic reaction at 298 K by platinum-loaded titanium(IV) oxide (TiO2−Pt) particles suspended in deaerated aqueous solutions of 2-propanol or (S)-lysine (Lys) was investigated.
Abstract: Photocatalytic reaction at 298 K by platinum-loaded titanium(IV) oxide (TiO2−Pt) particles suspended in deaerated aqueous solutions of 2-propanol or (S)-lysine (Lys) was investigated. The TiO2 catalysts with various amounts of Pt loadings were prepared by impregnation from aqueous chloroplatinic acid solution onto a commercial TiO2 (Degussa P-25) followed by hydrogen reduction at 753 K. The physical properties of deposited Pt, e.g., particle size, surface area, and electronic state, were studied respectively by transmission electron microscopy, volumetric gas adsorption measurement, and X-ray photoelectron spectroscopy as well as infrared spectroscopy of adsorbed carbon monoxide. The increase in Pt amount mainly resulted in an increase of the number of Pt deposits, not of their size. The catalysts were suspended in the aqueous solutions and photoirradiated at a wavelength >300 nm under an argon (Ar) atmosphere. The overall rate of photocatalytic reactions for both 2-propanol and Lys, corresponding to the ...
TL;DR: In this paper, a range of different parameters (Gd doping level, temperature, oxygen activity and cell current) and for different geometrical configurations of an initially planar electrolyte membrane (self-supported or supported on a porous substrate) have been calculated for a variety of planar configurations.