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1.
The activity of many water-splitting photocatalysts could be improved by the use of Rh III–Cr III mixed oxide (Rh 2−xCr xO 3) particles as cocatalysts. Although further improvement of water-splitting activity could be achieved if the size of the Rh 2−xCr xO 3 particles was decreased further, it is difficult to load ultrafine (<2 nm) Rh 2−xCr xO 3 particles onto a photocatalyst by using conventional loading methods. In this study, a new loading method was successfully established and was used to load Rh 2−xCr xO 3 particles with a size of approximately 1.3 nm and a narrow size distribution onto a BaLa 4Ti 4O 15 photocatalyst. The obtained photocatalyst exhibited an apparent quantum yield of 16 %, which is the highest achieved for BaLa 4Ti 4O 15 to date. Thus, the developed loading technique of Rh 2−xCr xO 3 particles is extremely effective at improving the activity of the water-splitting photocatalyst BaLa 4Ti 4O 15. This method is expected to be extended to other advanced water-splitting photocatalysts to achieve higher quantum yields. 相似文献
2.
The activity of many water‐splitting photocatalysts could be improved by the use of Rh III–Cr III mixed oxide (Rh 2?xCr xO 3) particles as cocatalysts. Although further improvement of water‐splitting activity could be achieved if the size of the Rh 2?xCr xO 3 particles was decreased further, it is difficult to load ultrafine (<2 nm) Rh 2?xCr xO 3 particles onto a photocatalyst by using conventional loading methods. In this study, a new loading method was successfully established and was used to load Rh 2?xCr xO 3 particles with a size of approximately 1.3 nm and a narrow size distribution onto a BaLa 4Ti 4O 15 photocatalyst. The obtained photocatalyst exhibited an apparent quantum yield of 16 %, which is the highest achieved for BaLa 4Ti 4O 15 to date. Thus, the developed loading technique of Rh 2?xCr xO 3 particles is extremely effective at improving the activity of the water‐splitting photocatalyst BaLa 4Ti 4O 15. This method is expected to be extended to other advanced water‐splitting photocatalysts to achieve higher quantum yields. 相似文献
3.
One of the main targets of studies on water splitting photocatalysts is to develop semiconductor materials with narrower bandgaps capable of overall water splitting for efficient harvesting of solar energy. A series of transition‐metal oxynitrides, LaMg xTa 1?xO 1+3xN 2?3x ( x≥1/3), with a complex perovskite structure was reported as the first example of overall water splitting operable at up to 600 nm. The photocatalytic behavior of LaMg 1/3Ta 2/3O 2N was investigated in detail in order to optimize photocatalyst preparation and water‐splitting activity. Various attempts exploring photocatalyst preparation steps, that is, cocatalyst selection, coating material and method, and synthesis method for the oxide precursor, revealed photocatalyst structures necessary for achieving overall water splitting. Careful examination of photocatalyst preparation procedures likely enhanced the quality of the produced photocatalyst, leading to a more homogeneous coating quality and semiconductor particles with fewer defects. Thus, the photocatalytic activity for water splitting on LaMg 1/3Ta 2/3O 2N was largely enhanced. 相似文献
4.
The effect of thermal treatment on the structural incorporation of Cr 2O 3 in xCr 2O 3·(100 – x)SiO 2 and 5R
n
O· xCr 2O 3·(95 – x)SiO 2 (where x=0.01–1 mol.% and R=Li, Na and Ca) gel glasses was studied by optical absorption spectrophotometry, DTA-TG, XRD and electron microscopy.Samples heat treated at 60°C have green color due to the presence of Cr 3+ in octahedral coordination. The optical transmission, and color (yellow, orange or ambar), of the samples heat treated between 200 and 700°C prove that Cr 3+ (octahedrally coordinated) and Cr 6+ (tetrahedrally coordinated) are both present. Segregation of Cr 2O 3 take place at temperatures above 800°C.In reducing conditions the gel glasses were green due to the presence of a high content of Cr 3+ ions. Samples containing Li or Na show crystalline phases at temperatures below 850°C. 相似文献
5.
DTA and XRD studies of the Fe 2V 4O 13–Cr 2V 4 O 13 system have shown that continuous solid solutions of a Fe 2–xCr xV 4O 13 type, bearing a Fe 2 V 4 O 13 structure, are formed in the system. With the increasing degree of the Cr3+ ion incorporation into the Fe 2 V 4 O 13 structure, a contraction of the solid solution crystal lattice develops. Solid solutions of a Fe 2–x Cr x V 4 O 13 type melt incongruently, their melting temperature increasing from 953 to 1003 K with increase in the degree of the Cr 3+ ion incorporation. The solid product of melting Fe 2–x Cr x V 4 O 13 solid solutions for 0.2< x >1.2 is the Fe 1–x Cr x VO 4 solution phase, and for x ≤0.2 and x ≥1.4 – the Fe 1–x Cr x VO 4 phase as well as FeVO 4 or CrVO 4 , respectively.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
Cr 1 – x
Ti
x
O 3+x/2, with x = 0.05,0.1 and 0.2, powders have been synthesised by an emulsion gelation route starting from aqueous chloride solutions. Gel particles were produced by de-anionisation of a water-in-oil emulsion using an immiscible organic amine solution. After calcination to produce the oxide, the powders were characterised in terms of particle size distribution, crystallinity, surface composition, particle shape, surface area, anion contamination and doping uniformity. By optimising the processing variables it has been possible to produce un-agglomerated, spherical, uniformly doped powders with a narrow particle size distribution. The mean particle size can be controlled within the range 0.3 to 3 microns and the particles are porous and nano-crystalline. The powders have been used to fabricate thick film sensor structures and show good response to combustible gases in air. 相似文献
7.
Al 2O 3 and Al 2−x
Cr
x
O 3 ( x = 0.01, 0.02 and 0.04) powders have been synthesized by the polymeric precursors method. A study of the structural evolution
of crystalline phases corresponding to the obtained powders was accomplished through X-Ray Diffraction and UV-vis spectroscopy
(reflectance spectra and CIEL *a *b * color data). The obtained results allow to identify the γ-Al 2O 3 to α-Al 2O 3 phase transition. The single-phase α-Al 2O 3 powder was obtained after heat treatment at 1050 °C for 2 h. The results show that the green to red color transition and
ruby luminescence lines observed for the powders of Al 2−x
Cr
x
O 3 are related to the γ to α-Al 2O 3 phase transition and the temperature and time range for such transition depends on the chromium content. 相似文献
8.
以Ga_2O_3、Y_2O_3、Cr(NO_3)_3·9H_2O为原料,柠檬酸为配位剂,通过溶胶-凝胶高温固相合成法制备出Ga_(2-2x)O_3∶2xCr~(3+)(Ga_2O_3∶xCr)与Y_3Ga_(5-5x)O_(12)∶5xCr~(3+)(YGG∶xCr)2种多晶粉体(x=0.01,0.03,0.05,0.07)。并采用X射线衍射(XRD)、红外光谱(IR)、扫描电镜(SEM)、荧光光谱(PL)对样品的结构、组成、形貌和荧光性能进行测试分析。XRD和IR分析结果显示在900℃煅烧后Ga_2O_3∶xCr和YGG∶xCr两种样品均成相。SEM照片显示Ga_2O_3∶xCr样品形貌为柱形多面体,YGG∶xCr为短棒状。PL结果显示Cr~(3+)在Ga_2O_3和YGG两种基质中的最强荧光发射峰分别位于742和740 nm,均属于Cr~(3+)的~2E-~4A_2跃迁,对比发现Cr~(3+)在YGG基质中的荧光发射强度更强,在远红光区的荧光性能更好,能满足温室照明中植物光合作用的需求。 相似文献
9.
An investigation was carried out to characterize the dissolution behavior of stabilized and unstabilized CrO 2 particles in water, used in magnetic recording. Special attention was paid to the measurement of Cr(VI) concentration in the contact solution and to the elucidation of the effects of the stabilizing treatment by x-ray photoelectron spectroscopy (XPS). The experimental results indicate that both stabilized and unstabilized CrO 2 particles predominantly release hexavalent chromium when in contact with water. The solubility of freshly stabilized CrO 2 is considerably smaller than that of unstabilized CrO 2, but the difference in solubility diminishes with aged particles. The XPS study indicated that stabilization of CrO 2 particles with a bisulfite solution results in the formation of Cr 2O 3 or a Cr 2O 3-like product on the particle. However, it appears that Cr(III) oxide coating does not uniformly form on all particles. 相似文献
10.
In situ photo-deposition of both Pt and CoO x cocatalysts on the facets of poly (triazine imide) (PTI) crystals has been developed for photocatalytic overall water splitting. However, the undesired backward reaction (i.e., water formation) on the noble Pt surface is a spontaneously down-hill process, which restricts their efficiency to run the overall water splitting reaction. Herein, we demonstrate that the efficiency for photocatalytic overall water splitting could be largely promoted by the decoration of Rh/Cr 2O 3 and CoO x as H 2 and O 2 evolution cocatalysts, respectively. Results reveal that the dual cocatalysts greatly extract charges from bulk to surface, while the Rh/Cr 2O 3 cocatalyst dramatically restrains the backward reaction, achieving an apparent quantum efficiency (AQE) of 20.2 % for the photocatalytic overall water splitting reaction. 相似文献
11.
The presence of SmCrO 4 is experimentally established. In Mg 2+-substituted SmCrO 3, single-phase perovskite Sm(Cr 1−xMg x)O 3, where x=0-0.23, are formed at ∼830°C by decomposition of Sm(Cr 1−xMg x)O 4 which crystallizes at 530-570°C from amorphous materials prepared by the hydrazine method. Sm(Cr 1−xMg x)O 3 solid solution powders consisting of submicrometer-size particles are sinterable; dense materials can be fabricated by sintering for 2 h at 1700°C in air. The relative densities, grain sizes, and electrical conductivities increase with increased Mg 2+ content. Sm(Cr 0.77Mg 0.23)O 3 materials exhibit an excellent direct current electrical conductivity of 2.2×10 3 S m −1 at 1000°C. 相似文献
12.
The fractions of clusters and single chromium atoms were calculated by the diluted solution and Heisenberg-Dirac-van-Vleck
models for a series of solid solutions containing chromium, strontium, and magnesium in the ratio 5:1:1, respectively. A principal
genetic relationship was revealed between La 1−0.2x
Sr 0.2x
·Cr
x
Ga 1−x
O 3−δ, La 1−0.5x
Sr 0.5x
Cr
x
Ga 1−x
O 3−δ, and La 1−0.2x
Sr 0.2x
Cr
x
Ga 1−1.2x
Mg 0.2x
O 3−δ systems. Deviations from Curie-Weiss law are observed for the systems with the ratio [Cr]:[Sr]:[Mg]=5:1:1, which point to
a noncompensated magnetic moment. 相似文献
13.
The compounds chosen to illustrate the interpretation of ligand field spectra of inorganic solids with A-B antiferromagnetic coupling between Fe 3+ tetrahedral and Fe 3+ or Cr 3+ octahedral cations belong to the Li 0.5Fe xGa 2.5-xO 4 and Li 0.5(FeCr) xGa 2.5-2xO 4 systems. New features, such as the interpretation of the iron(III) electronic spectrum in ferrimagnetic spinels, the influence of the nature of the superexchange interactions of the pair excitation processes, and the growth of an electronic transition assigned to Cr 3+ + Fe 3+ → Cr 4+ + Fe 2+ intervalence charge transfer at 1.8 eV are reported in this study. 相似文献
14.
Cr/MgO(x)–CeO2(100?x) nanocatalysts were synthesized by a coprecipitation method and characterized by X-ray diffraction (XRD) analysis, field-emission scanning electron microscopy (FESEM), energy-dispersive x-ray (EDX) spectroscopy, diffuse reflectance spectroscopy (DRS), and Brunauer–Emmett–Teller (BET) analysis. The effect of ceria addition on their physicochemical characteristics was investigated, and the results were correlated with their catalytic performance in oxidative dehydrogenation of ethane. A decrease in the size of the metal particles was found when adding a suitable content of ceria to the support. Crystalline Cr2O3 was not found in the calcined samples, indicating good dispersion of Cr species on the support. All samples showed nanosized particles with uniform morphology, with the best surface morphology for the Cr/MgO(50)–CeO2(50) sample, on which the particle distribution mainly lay in the range of 40–60 nm. Variation of the amount of Ce in the support led to an enhancement of the Cr6+/Cr3+ ratio, with the highest value for the Cr/MgO(50)–CeO2(50) sample. This catalyst effectively dehydrogenated ethane to ethylene with CO2 at 700 °C even after 5 h on-stream, giving 42.76 % ethylene yield. 相似文献
15.
A series of compounds with the general formula LiMn 2 - x - y
Cr
x
Ni
y
O 4, where x + y = 0.05, 0.5, or 1.0, is synthesized. It is shown that all these compounds are pure-phase spinels with parameter aequal to 0.8193-0.8236 nm. Doping a stoichiometric lithium-manganese spinel simultaneously with chromium and nickel makes the spinel structure stable. The initial specific capacity of a spinel depends on its doping degree. Doping LiMn 2O 4 with chromium and nickel simultaneously at an Mn : Cr : Ni ratio of 195 : 3 : 2 raises the spinel's specific capacity and reduces the cycling degradation. The change in the discharge capacity of LiMn 1.95Cr 0.03Ni 0.02O 4 electrodes cycled at 20, 0, and -14°C is determined. 相似文献
16.
The commercial high‐temperature water‐gas shift (HT‐WGS) catalyst consists of CuO‐Cr 2O 3‐Fe 2O 3, where Cu functions as a chemical promoter to increase the catalytic activity, but its promotion mechanism is poorly understood. In this work, a series of iron‐based model catalysts were investigated with in situ or pseudo in situ characterization, steady‐state WGS reaction, and density function theory (DFT) calculations. For the first time, a strong metal‐support interaction (SMSI) between Cu and FeO x was directly observed. During the WGS reaction, a thin FeO x overlayer migrates onto the metallic Cu particles, creating a hybrid surface structure with Cu‐FeO x interfaces. The synergistic interaction between Cu and FeO x not only stabilizes the Cu clusters, but also provides new catalytic active sites that facilitate CO adsorption, H 2O dissociation, and WGS reaction. These new fundamental insights can potentially guide the rational design of improved iron‐based HT‐WGS catalysts. 相似文献
17.
Summary Hydrated microcrystalline compound, V 1-xCr xO y·nH 2O, where x<0.063 and 4.4< n<8 and hydrated amorphous phases, CrVO 4·H 2O and Cr 2V 4O 13·4H 2O have been prepared using peroxo-polyacids of vanadium and chromium. The transformations of these hydrated phases upon heating
were studied by TG-DTA and XRD techniques and led to three crystalline anhydrous compounds: ( i) phase V 1-xCr xO y, which is closely related to the orthorhombic V 2O 5, ( ii) Cr 2V 4O 13 and ( iii) monoclinic CrVO 4-M. The ranges of coexistence of phases in equilibrium were also determined. 相似文献
18.
Zusammenfassung Aus Li 2CO 3 und (Al 1–x
Cr
x
) 2O 3 wurde durch Festkörperreaktionen die Mischkristallreihe LiAl 1–x
Cr
x
O 2 hergestellt. Die thermische Stabilität der mikrokristallinen Substanzen (-NaFeO 2-Typ, Raumgruppe R3m) wurde röntgenographisch verfolgt. Die diffusen Reflexionsspektren (12 bis 30 kK, 25°C) wurden mit dem Modell der erweiterten Kristallfeldtheorie ausgewertet. Die durch Multiphononen-Struktur charakterisierten spin-erlaubten Banden ergeben für kubische Mikrosymmetrie Dq- und Racah-B-Werte, die im Gegensatz zur Rubinreihe nur wenig von Cr-Gehalt abhängen. Dq beruht zum Teil auf dem Einfluß von zweitnächsten Li +-Nachbarn, wodurch die effektive Ladung der Sauerstoff-Liganden in der Bindung größer ist. Die breite spin-verbotene Bande bei 15 kK deutet auf eine Magnon-Satellitenstruktur durch antiferromagnetische Ordnung hin.
Optical studies and phase relations in the system Li2O–Al2O3–Cr2O3
The series LiAl1–x
Cr
x
O2 was prepared by solid state reactions with Li2CO3 and (Al1–x
Cr
x
)2O3. The thermal stability of the microcrystalline samples (-NaFeO2 type, space group R3m) was controlled by X-ray methods. The diffuse reflectance spectra at 25 °C in the region from 12 to 30 kK were analyzed by the extended crystal field theory. From the spin-allowed peaks characterized by a multiphonon structureDq-andRacah-B-values were obtained for cubic site symmetry (neglecting trigonal distortions and spin-orbit effects) that are only slightly dependent on the Cr-content, in contrast to the ruby series.Dq is partly due to the influence of the secondnearest Li+-neighbours leading to a greater effective charge of the oxygen ligands in the bond. The broad spin-forbidden peak at 15 kK points to a magnon satellite structure caused by antiferromagnetic ordering.
Mit 1 Abbildung 相似文献
19.
[M(NH 3) 4]A (M=Pt, Pd; A=CrO 4, Cr 2O 7) and [Pt(NH 3) 4(NO 2)(Cr 2O 7)]NO 3 complex salts were synthesized and characterized by a number of physicochemical methods of analysis (IR, single-crystal and powder XRD, and simultaneous thermogravimetry and differential scanning calorimetry with evolved gas analysis mass spectrometry). Thermolysis of the salts obtained in a hydrogen atmosphere proceeds with the partial reduction of chromium to a metallic state and the formation of M xCr 1−x (M=Pt, Pd) metal solid solution with a chromium content of up to 22 at % and chromium(III) oxide. The thermal decomposition of salts in an inert and oxidizing atmosphere passes through the formation stage of the MCrO 2 phase with the delafossite structure followed by its subsequent decomposition into chromium(III) oxide and noble metal. Nanosized Pt−Cr 2O 3 and Pd−Cr 2O 3 composites obtained by the thermolysis of precursor salts in air at 500 °C and being held at this temperature for 1 h showed a high catalytic activity in the CO total oxidation (TOX) and preferential oxidation in the excess of hydrogen (PROX) processes compared with that of monometallic Pt and Pd powders. 相似文献
20.
Magnetic Properties of Ti 3?xM xO 5 Phases (M = V 3+, Cr 3+, Nb 4+) The magnetic properties of Ti 3?xV xO 5, Ti 3?xCr xO 5, and Ti 3?xNb xO 5 phases are reported. In the case of V 3+ and Cr 3+ the magnetic leaping-temperature decreases, however Nb 4+ shift the phase-transition towards higher temperatures. All samples show a “memory-effect” in magnetic properties, i. e. the results of heating- and cooling-cycles are higher susceptibilities of the α-phase of Ti 3O 5. Endowed Ti 3O 5 phases show for the α- and β-Ti 3?xM xO 5 til the leap Curie-Weiss characteristic in 1/ X vs. temperature measurements. Exception is β-Ti 3?xNb xO 5, its susceptibility is independend of the temperature up to x ? 0.3. 相似文献
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