共查询到20条相似文献,搜索用时 31 毫秒
1.
Investigation
of RuO2-IrO2-SnO2
thin film evolution 总被引:2,自引:0,他引:2
Elizabet Horváth J. Kristóf L. Vázquez-Gómez Á. Rédey V. Vágvölgyi 《Journal of Thermal Analysis and Calorimetry》2006,86(1):141-146
The thermal evolution process of RuO2–IrO2–SnO2
mixed oxide thin films of varying noble metal contents has been investigated
under in situ conditions by thermogravimetry-mass spectrometry (TG-MS), infrared
emission spectroscopy (IR) and cyclic voltammetry (CV). The gel-like films
prepared from aqueous solutions of the precursor compounds RuOHCl3,
H2IrCl6 and Sn(OH)2(CH3COO)2–xClx on titanium metal support were heated in an atmosphere
containing 20% O2 and 80% Ar up to 600°C. Chlorine
evolution takes place in a single step between 320 and 500°C accompanied
with the decomposition of the acetate ligand. The decomposition of surface
species formed like carbonyls, carboxylates and carbonates occurs in two stages
between 200 and 500°C. The temperature of chlorine evolution and that
of the final film formation increases with the increase of the iridium content
in the films. The anodic peak charge shows a maximum value at 18% iridium
content. 相似文献
2.
Lei Ge 《Journal of Sol-Gel Science and Technology》2007,44(3):263-268
Novel visible-light-activated In2O3–CaIn2O4 photocatalysts were developed in this paper through a sol–gel method. The photocatalytic activities of In2O3–CaIn2O4 composite photocatalysts were investigated based on the decomposition of methyl orange under visible light irradiation (λ > 400 nm).
The obtained samples were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive
spectrum (EDS), X-ray photoelectron spectroscopy (XPS) and UV–vis diffused reflectance spectroscopy (DRS). The results revealed
that the In2O3–CaIn2O4 composite samples with different In2O3 and CaIn2O4 content can be obtained by controlling the synthesis temperature, and the composite photocatalysts extended the light absorption
spectrum toward the visible region. The photocatalytic tests indicated that the composite samples demonstrated high visible-light
activity for decomposition of methyl orange. The significant enhancement in the In2O3–CaIn2O4 photo-activity under visible light irradiation can be ascribed to the efficient separation of photo-generated carriers in
the In2O3 and CaIn2O4 coupling semiconductors. 相似文献
3.
Jianxia Jiao Qun Xu Limin Li Takano Tsubasa Takaomi Kobayashi 《Colloid and polymer science》2008,286(13):1485-1491
Titania–silica composite have been prepared using polyethylene glycol (PEG) with different molecular weights (M
w), PEG20000, PEG10000, and PEG2000, as template in supercritical carbon dioxide (SC CO2). The composite precursors were dissolved in SC CO2 and impregnated into PEG templates using SC CO2 as swelling agent and carrier. After removing the template by calcination at suitable temperature, the titania–silica composite
were obtained. The composite were characterized by X-ray diffraction, Fourier transform infrared spectroscopy, and nitrogen
sorption–desorption experiment. Photocatalytic activity of the samples has been investigated by photodegradation of methyl
orange. Results indicate that there are many Si–O–Ti linkages in the TiO2/SiO2 composite; the PEG template has a significant influence on the structure of TiO2/SiO2. In addition, the TiO2/SiO2 prepared with PEG10000 exhibited high photocatalytic efficiency. So this work supplies a clue to control and obtain the TiO2/SiO2 composite with different photocatalytic reactivity with the aid of suitable PEG template in supercritical CO2. 相似文献
4.
Monika Ruszak Stefan Witkowski Zbigniew Sojka 《Research on Chemical Intermediates》2007,33(8):689-703
EPR and Raman spectroscopy jointed with temperature-programmed reduction (TPR) and oxidation (TPO) were used to elucidate
of the anionic redox processes occurring during the interaction of dioxygen, nitrous oxide and dihydrogen with nanoporous
12CaO·7Al2O3. The results showed that hydrogen and oxygen enter the mayenite cages following a dissociative pathway involving hydride,
hydroxyl and peroxide intermediates, respectively. Generation and annihilation of the cage O
2
−
and O− radicals upon oxidative and reductive treatments, confined to the near to the surface region, were found to be reversible.
The key intermediates of this process were identified and a detailed mechanism of the surface and cage reactions was proposed. 相似文献
5.
Julian R. Osman Joe A. Crayston Allin Pratt David T. Richens 《Journal of Sol-Gel Science and Technology》2007,44(3):219-225
Mixed IrO2–TiO2 oxides were prepared by the sol–gel method upon acid-catalysed hydrolysis of an iridium solution in ethanol mixed with titanium
tetraethoxide in ethanol. The iridium solution was obtained by reaction of the sodium hexachloroiridate(IV) precursor in the
presence of sodium ethoxide in ethanol. Gels were formed in all but the high-Ir samples. Analysis of the dried gels showed
minority-phase enrichment at the surface and the presence of Ir(III), while microscopy showed evidence for dispersed iridium-containing
nanoparticles (1–20 nm in diameter). XRD powder patterns of the calcined material showed peaks due to a small amount of crystalline
NaCl impurity which could be removed by washing. This left amorphous phases, except in the Ir:Ti 3:2 case, which showed evidence
for the presence of separate crystalline oxide phases: anatase, IrO2 and Ti
x
Ir1−x
O2. 相似文献
6.
The preparation of synthesis gas from carbon dioxide reforming of methane (CDR) has attracted increasing attention. The present
review mainly focuses on CDR to produce synthesis gas over Ni/MOx/Al2O3 (X = La, Mg, Ca) catalysts. From the examination of various supported nickel catalysts, the promotional effects of La2O3, MgO, and CaO have been found. The addition of promoters to Al2O3-supported nickel catalysts enhances the catalytic activity as well as stability. The catalytic performance is strongly dependent
on the loading amount of promoters. For example, the highest CH4 and CO2 conversion were obtained when the ratios of metal M to Al were in the range of 0.04–0.06. In the case of Ni/La2O3/Al2O3 catalyst, the highest CH4 conversion (96%) and CO2 conversion (97%) was achieved with the catalyst (La/Al = 0.05 (atom/atom)). For Ni/CaO/Al2O3 catalyst, the catalyst with Ca/Al = 0.04 (atom/atom) exhibited the highest CH4 conversion (91%) and CO2 conversion (92%) among the catalysts with various CaO content. Also, Ni/MgO/Al2O3 catalyst with Mg/Al = 0.06 (atom/atom) showed the highest CH4 conversion (89%) and CO2 conversion (90%) among the catalysts with various Mg/Al ratios. Thus it is most likely that the optimal ratios of M to Al
for the highest activities of the catalysts are related to the highly dispersed metal species. In addition, the improved catalytic
performance of Al2O3-supported nickel catalysts promoted with metal oxides is due to the strong interaction between Ni and metal oxide, the stabilization
of metal oxide on Al2O3 and the basic property of metal oxide to prevent carbon formation. 相似文献
7.
Photocatalytic Reduction of Greenhouse Gas CO2 to Fuel 总被引:1,自引:0,他引:1
Jeffrey C. S. Wu 《Catalysis Surveys from Asia》2009,13(1):30-40
Sun is the Earth’s ultimate and inexhaustible energy source. One of the best routes to remedy the CO2 problem is to convert it to valuable hydrocarbons using solar energy. In this study, CO2 was photocatalytically reduced to produce methanol, methane and ethylene in a steady-state optical-fiber reactor under artificial
light and real sunlight irradiation. The photocatalyst was dip-coated on the optical fibers that enable the light to transmit
and spread uniformly inside the reactor. The optical-fiber photoreactor, comprised of nearly 120 photocatalyst-coated fibers,
was designed and assembled. The XRD spectra indicated the anatase phase for all photocatalysts. It is found that the methanol
yield increased with UV light intensity. A maximum methanol yield of 4.12 μmole/g-cat h is obtained when 1.0 wt% Ag/TiO2 photocatalyst was used under a light intensity of 10 W/cm2. When mixed oxide, TiO2–SiO2, is doped with Cu and Fe metals, the resulting photocatalysts show substantial difference in hydrocarbon production as well
as product selectivity. Methane and ethylene were produced on Cu–Fe loaded TiO2–SiO2 photocatalyst. Since dye-sensitized Cu–Fe/P25 photocatalyst can fully harvest the light energy of 400–800 nm from sunlight,
its photoactivity was significantly enhanced. Finally, CO2 photoreduction was studied by in situ IR spectroscopy and possible mechanism for the photoreaction was proposed. 相似文献
8.
Li Chen Haixia Shen Zhen Lu Cang Feng Su Chen Yanru Wang 《Colloid and polymer science》2007,285(13):1515-1520
TiO2–SiO2 composite nanoparticles were prepared by a sol–gel process. To obtain the assembly of TiO2–SiO2 composite nanoparticles, different molar ratios of Ti/Si were investigated. Polyurethane (PU)/(TiO2–SiO2) hybrid films were synthesized using the “grafting from” technique by incorporation of modified TiO2–SiO2 composite nanoparticles building blocks into PU matrix. Firstly, 3-aminopropyltriethysilane was employed to encapsulate TiO2–SiO2 composite nanoparticles’ surface. Secondly, the PU shell was tethered to the TiO2–SiO2 core surface via surface functionalized reaction. The particle size of TiO2–SiO2 composite sol was performed on dynamic light scattering, and the microstructure was characterized by X-ray diffraction and
Fourier transform infrared. Thermogravimetric analysis and transmission electron microscopy (TEM) employed to study the hybrid
films. The average particle size of the TiO2–SiO2 composite particles is about 38 nm when the molar ratio of Ti/Si reaches to1:1. The TEM image indicates that TiO2–SiO2 composite nanoparticles are well dispersed in the PU matrix. 相似文献
9.
Fe3O4 nanorods and Fe2O3 nanowires have been synthesized through a simple thermal oxide reaction of Fe with C2H2O4 solution at 200–600°C for 1 h in the air. The morphology and structure of Fe3O4 nanorods and Fe2O3 nanowires were detected with powder X-ray diffraction, scanning electron microscopy and transmission electron microscopy.
The influence of temperature on the morphology development was experimentally investigated. The results show that the polycrystals
Fe3O4 nanorods with cubic structure and the average diameter of 0.5–0.8 μm grow after reaction at 200–500°C for 1 h in the air.
When the temperature was 600°C, the samples completely became Fe2O3 nanowires with hexagonal structure. It was found that C2H2O4 molecules had a significant effect on the formation of Fe3O4 nanorods. A possible mechanism was also proposed to account for the growth of these Fe3O4 nanorods.
Supported by the Fund of Weinan Teacher’s University (Grant No. 08YKZ008), the National Natural Science Foundation of China
(Grant No. 20573072) and the Doctoral Fund of Ministry of Education of China (Grant No. 20060718010) 相似文献
10.
11.
The electronic state of platinum supported on SO4/ZrO2, SO4/TiO2, SO4/Al2O3, and SO4/SiO2 systems and on systems unpromoted by sulfur was investigated by diffuse-reflectance IR spectroscopy using CO as the probe
molecule. The introduction of SO4
2− anions increases the electron deficit on platinum particles. This suppresses the formation of bridging CO complexes with
the metal, leads to the high-frequency shift of absorption maxima of CO adsorbed in the linear form, and stabilizes positively
charged metal species (Ptδ+ and Pt+) during the reduction process. The formation of the positively charged species includes the interaction between the acidic
protons and the metal particles yielding [Pt−H]δ+ adducts. The extent of the influence of the support on the electronic state of the metal increases in the series SO4/SiO2<SO4/Al2O3<SO4/TiO2<SO4/ZrO2 in parallel with an increase in the strength of the acid sites in the system.
Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1094–1099, June, 1998. 相似文献
12.
Bi2Al4O9 ceramics are difficult to sinter to greater than 80% theoretical density due to peritectic decomposition at 1,070 °C. A novel processing method is discussed where a high-bismuth oxide-based liquid is used as a sintering aid. After sintering, the high bismuth oxide phase is removed by leaching with 40% acetic acid. The resulting samples are phase pure and ∼91% dense. The grain size varies in a wide range with the average grain size of ∼1 μm. The electrical properties of these ceramics were measured as functions of temperature (550–850 °C) and oxygen partial pressure (6×10−6–1 atm). The total conductivity was separated into electronic and ionic contributions. The low ionic conductivity indicates that the material is not an ‘intrinsically defective fast ion conductor’. The ionic conductivity is due almost exclusively to compensating oxygen vacancies related to impurities. With increasing temperature and decreasing oxygen partial pressure, the electronic conduction dominates over the ionic conduction. 相似文献
13.
El-Shobaky G. A. Radwan N. R. E. Radwan F. M. 《Journal of Thermal Analysis and Calorimetry》2002,68(1):275-287
The results obtained showed that the addition of small amounts of LiNO3 to the reacting mixed solids, consisting of equimolar proportion of Fe2O3 and basic MgCO3 much enhanced the thermal decomposition of magnesium carbonate. The addition of 12 mol% LiNO3 (6 mol% Li2O) decreased the decomposition temperature of MgCO3 from 525.5 to362°C. MgO underwent solid–solid interaction with Fe2O3 at temperatures starting from800°C yielding MgFe2O4. The amount of ferrite produced increased by increasing the precalcination temperature of the mixed solids. However, the
completion of this reaction required prolonged heating at elevated temperature above 1100°C. Doping with Li2O much enhanced the solid–solid interaction between the mixed oxides leading to the formation of MgFe2O4 phase at temperatures starting from 700°C. The addition of 6 mol% Li2O to the mixed solids followed by precalcination at 1050°C for 4 h resulted in complete conversion of the reacting oxides
into magnesium ferrite. The heat treatment of pure and doped solids at 900–1050°C effected the disappearance of most of IR
transmission bands of the free oxides with subsequent appearance of new bands characteristic for MgFe2O4 structure. The promotion effect of Li2O towards the ferrite formation was attributed to an effective increase in the mobility
of the various reacting cations. The activation energy of formation (ΔE) of magnesium ferrite was determined for pure and variously doped solids and the values obtained were 203, 126, 95 and 61
kJ mol−1 for pure mixed solids and those treated with 1.5, 3.0 and 6.0 mol% Li2O, respectively.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
14.
Ab initio molecular orbital calculations have been performed to explore the reaction potential energy surfaces of silylenoid H2SiLiF with XH
n
hydrides, where XH
n
= CH4, NH3, H2O, HF, SiH4, PH3, H2S, and HCl. We have identified a previously unreported reaction pathway on each reaction surface, H2SiLiF + H-XH
n
−
1
→ H
n
XSiLiF + H2, which involves H2 elimination following the initial formation of an association complex via a four-membered ring transition state to form the substituted three-membered ring silylenoid H
n
XSiLiF and a H2 molecule. This theoretical calculations suggest that (i) for H2 eliminations there is a very clear trend toward lower activation barriers and more exothermic interactions on going from left to right along a given row in periodic table, and (ii) for the second-row hydrides, the H2 elimination reactions are less exothermic than for the first-row hydrides and the reaction barriers are lower for X–S and Cl. Compared to the insertions of H2SiLiF into XH
n
, the H2 elimination pathways should be unfavorable with higher barrier and lower exothermic. 相似文献
15.
Carbon dioxide reforming (CDR) of methane to synthesis gas over supported nickel catalysts has been reviewed. The present
review mainly focuses on the advantage of ceria based nickel catalysts for the CDR of methane. Nickel catalysts supported
on ceria–zirconia showed the highest activity for CDR than nickel supported on other oxides such as zirconia, ceria and alumina.
The addition of zirconia to ceria enhances the catalytic activity as well as the catalyst stability. The catalytic performance
also depends on the crystal structure of Ni–Ce–ZrO2. For example, nickel catalysts co-precipitated with Ce0.8Zr0.2O2 having cubic phase gave synthesis gas with CH4 conversion more than 97% at 800 °C and the activity was maintained for 100 h during the reaction. On the contrary, Ni–Ce–ZrO2 having tetragonal phase (Ce0.8Zr0.2O2) or mixed oxide phase (Ce0.5Zr0.5O2) deactivated during the reaction due to carbon formation. The enhanced catalytic performance of co-precipitated catalyst
is attributed to a combination effect of nano-crystalline nature of cubic Ce0.8Zr0.2O2 support and the finely dispersed nano size NiO
x
crystallites, resulting in the intimate contact between Ni and Ce0.8Zr0.2O2 particles. The Ni/Ce–ZrO2/θ–Al2O3 also exhibited high catalytic activity during CDR with a synthesis gas conversion more than 97% at 800 °C without significant
deactivation for more than 40 h. The high stability of the catalyst is mainly ascribed to the beneficial pre-coating of Ce–ZrO2 resulting in the existence of stable NiO
x
species, a strong interaction between Ni and the support, and an abundance of mobile oxygen species in itself. TPR results
further confirmed that NiO
x
formation was more favorable than NiO or NiAl2O4 formation and further results suggested the existence of strong metal-support interaction (SMSI) between Ni and the support.
Some of the important factors to optimize the CDR of methane such as reaction temperature, space velocity, feed CO2/CH4 ratio and H2O and/or O2 addition were also examined. 相似文献
16.
Miraç Ocak Hakan Alp Halit Kantekin Hülya Karadeniz Ümmühan Ocak 《Journal of inclusion phenomena and macrocyclic chemistry》2008,60(1-2):17-24
Three new macrocyclic crown ether ligands containing nitrogen–oxygen donor atoms were designed and synthesized from 1,4-bis(2′-formylphenyl)-1,4-dioxabutane
and 4-nitro-o-phenylenediamine. Ion-pair extraction of metal picrates such as Ag+, Hg2+, Cd2+, Zn2+, Cu2+, Ni2+, Mn2+, Co2+, and Pb2+ from aqueous phase to the organic phase was carried out using the novel ligands. The solvent effect over the metal picrate
extractions was investigated at 25 ± 0.1 °C by using UV–visible spectrometry. The extractability and the values of the extraction
constants (log Kex) were determined for the extracted complexes. 相似文献
17.
Tengborg Charlotte Stenberg Kerstin Galbe Mats Zacchi Guido Larsson Simona Palmqvist Eva Hahn-Hägerdal Bärbel 《Applied biochemistry and biotechnology》1998,(1):3-15
The pretreatment of softwood with sulfuric acid impregnation in the production of ethanol, based on enzymatic hydrolysis,
has been investigated. The parameters investigated were: H2SO4 concentration (0.5 – 4.4% w/w liquid), temperature (180 – 240°C), and residence time (1-20 minutes). The combined severity
(log Ro-pH) was used to combine the parameters into a single reaction ordinate. The highest yields of fermentable sugars,
i.e., glucose and mannose, were obtained at a combined severity of 3. At this severity, however, the fermentability declined
and the ethanol yield decreased. In a comparison with previous results, SO2 impregnation was found to be preferable, since it resulted in approximately the same sugar yields, but better fermentability. 相似文献
18.
Blue-light-emitting Sr2CeO4 phosphors were synthesized via a sol–gel process and the conventional solid-state method in this study. The developed sol–gel
process lowered the synthesis temperature of monophasic Sr2CeO4 to as low as 900 °C. In comparison with the solid-state derived powders, the sol–gel derived powders had more uniform morphology
and smaller particle sizes. In addition, sol–gel derived Sr2CeO4 displayed higher luminescent intensity than that prepared via the solid-state route under the same heating conditions. This
is attributed to the improved compositional homogeneity and crystallinity in the sol–gel process. During the heating processes,
Sr2CeO4 tended to thermally decompose at elevated temperatures. This decomposition reaction resulted in the formation of an impurity
phase- SrCeO3 and thereby a decrease in the luminescent intensity. For obtaining Sr2CeO4 phosphors with high luminescent intensity, the heating conditions in both processes need to be well modulated. 相似文献
19.
Two mixed oxide systems La2-xSrxCuO4±
λ (0.0⩽x⩽1. 0) and La2-xThxCuO4±
λ (O. O⩽x⩽ 0.4) with K2NiF4 structure were prepared by varyingx values. Their crystal structures were studied by means of XRD and IR spectra. The average valence of Cu ion at B site, nonstoichiometric
oxygen (λ) and the chemical composition in the bulk and on the surface of the catalysts were measured by means of chemical
analysis and XPS. The catalytic behavior in reaction CO+NO was investigated under the regular change of average valence of
Cu ion at B site and nonstoichiometric oxygen (λ). Meanwhile, the adsorption and activation of the small molecules NO and
the mixture of NO+CO over the mixed oxide catalysts were studied by means of MS-TPD. The catalytic mechanism of reaction NO+CO
over these oxide catalysts were proposed; and it has been found that, at lower temperatures the activation of NO is the rate
determining step and the catalytic activity is related to the lower valent metallic ion and its concentration, while at higher
temperatures the adsorption of NO is the rate determining step and the catalytic activity is related to the oxygen vacancy
and its concentration.
Project supported by the National Natural Science Foundation of China. 相似文献
20.
A single phase of monoclinic MnV2O6 nanoflakes was prepared by a hydrothermal process at 180°C for 18 h, using Mn (CH3COO)2·4H2O and NH4VO3 as starting materials and using acetic acid to adjust the pH value of the reaction solution. The as-prepared samples were
characterized by field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM). X-ray photoelectron
spectrum (XPS) measurements further confirm the component of MnV2O6. Results indicated that the products consisted of a large quantity of compact accumulated nanoflakes, with average width
of 0.85 μm, thickness of 100 nm and lengths up to 1.7 μm.
__________
Translated from Journal of Inorganic Materials, 2007, 22(6): 1139–1141 [译自: 无机材料学报] 相似文献