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The effect of addition of Ag to the catalytic properties of hollandite manganese oxide (HMO) was investigated for the oxidative acetalization of ethanol to diethoxyethane. Based on analysis with HR...

The selective catalytic reduction (SCR) of NOx with NH3 was studied over poorly-crystalline W Fe composite oxides (WaFeOx). The short-range order present within the W O Fe structure was found to be responsible for the excellent SCR activity, in which the strong atomic-level interaction between Fe and W atoms promoted the formation of both Lewis and Bronsted acidity. The W O Fe structure existed as amorphous overlayers, approximately 2 nm thick over the surface of crystalline particles after high-temperature aging as shown by high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM). After treatment at 800 °C for 5 h, the WaFeOx catalysts still showed almost 100% NO conversion in the range 300–450 °C with 100% N2 selectivity, despite the loss in surface area. This resistance to the impacts of high temperature ageing guarantees high activity of SCR catalysts which often suffer during high-temperature excursions as in the case of diesel exhaust due to diesel particulate filter (DPF) regeneration.

Identification of the catalytic active site is critical in the design and development of advanced heterogeneous catalysts. Many high-precision experimental techniques, as well as computational methods, have been developed to address this problem, but identifying the active site for composite oxide catalysts remains a challenging task because of their complexity and indiscernible microstructures. Herein, we provide a key new insight into the active site within a composite oxide catalyst by investigating an iron-based oxide catalyst with complex components. The dopant atoms with octahedral coordination located at substitution sites in the Fe2O3 lattice tune the electronic structure of the adjacent iron atoms, which act as the active sites that lead to enhanced catalytic activity. This atomic-scale doping is different from the emerging single-atom catalyst concept, in which the single atom on the support is the active site, and which provides an alternative methodology of improving the activity of heterogene...

Using high resolution transmission electron microscopy with image simulation and Fourier analysis, the Li1−xFePO4 (x

Ferromagnetic zinc ferrite nanocrystals at ambient temperature were synthesized via the thermal decomposition of metal−surfactant complexes. Characterization measurements including transmission electron microscopy and X-ray diffraction were performed for as-synthesized ZnFe2O4 particles. The sample has a relatively narrow size distribution with an average particle size of 9.8 ± 0.2 nm and standard deviation of 30%. The as-synthesized zinc ferrite nanocrystals are superparamagnetic at room temperature with a blocking temperature TB = 68 ± 2 K and a saturation magnetization MS = 65.4 emu·g-1 at T = 10 K, which are caused by the change in the inversion degree of the spinel structure. A coercive field of HC = 102 ± 5 Oe in the blocked state indicates small particle anisotropy, although evidence of surface spin canting was inferred from magnetization data in the as-synthesized ZnFe2O4 nanocrystals. Our results demonstrate that magnetic properties of magnetic particles can be largely modified by just changing p...

We report here a novel and simple method, without using any seeds or catalysts, to synthesize single-crystal germanium nanowires with tunable 10−115 nm diameters and of 10−20 μm length by the decomposition of a precursor [(CH3(CH2)7CHCH(CH2)7CH2NH2)4Ge]4+·(Cl-)4 (TOG) at 360 °C in trioctylamine. The diameter of Ge nanowires can be controlled by varying the concentration of TOG in solution.

A simple method was used to prepare monodispersed ZnO nanoparticles, which can be used as seeds for the synthesis of [0 0 0 1]oriented ZnO nanorods by refluxing. Based on the observation of shape and size of ZnO nanocrystals at different refluxing times and surface and attachment energies for various crystallographic planes calculated from the BFDH and HP models, a possible growth mechanism for ZnO nanorods was put forward to explain the experimental observations. The synthesized ZnO nanocrystals show green emission, which are correlated with the degree of oxygen vacancies in the samples. r 2007 Elsevier B.V. All rights reserved. PACS: 61.46.Df; 81.16.Be

The effects of laser radiation on soot in a vacuum were studied by Raman spectroscopy and transmission electron microscopy. It was found that defective carbon onions could be formed simply by irradiation of focused common diode lasers with intensity much lower (103–106 W/cm2) than those used in the previous work. A modified Melton model was introduced to analyze the formation of onions. The results show a threshold value of laser intensity (5.49 × 103 W/cm2), above which sublimation and rearrangement play a dominant role in the formation of onions. Such onions can also be formed with laser intensities below the threshold since neighboring graphene layers may merge and grow by capturing interstitial carbon atoms. The deposited soot is damage resistant to the diode laser radiation in air due to the rapid formation of carbon onions.

As an alternative to lead-bearing solder, isotropic conductive adhesives (ICA) have been utilized for many years in microelectronic packaging. ICAs filled with conductive particles generally show high initial contact resistance, unstable contact resistance, and inferior impact strength. In this study, silver nitrate (AgNO3) is used as a precursor, N, N-dimethylformamide (DMF) as a solvent and reducing agent for preparing silver (Ag) nanowires in the nanoporous templates formed by the controlled hydrolysis and condensation of butyl titanate (Ti(OC4H9)4). Fundamental material characterizations including X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy (SEM) are conducted on these Ag nanowires. A novel ICA is developed by using Ag nanowires as conductive fillers. Electrical and mechanical properties are investigated and compared with that of conventional ICA filled with micrometer-sized Ag particles or nanometer-sized Ag particles, the average diameter of these Ag particles is about 1 mm and 100 nm, respectively. It is found that at a lower filler content, the ICA filled with Ag nanowires exhibited lower bulk resistivity and higher shear strength than ICA filled with micrometer-sized Ag particles or nanometer-sized Ag particles. Possible conductive mechanism of the new ICA is analyzed.

Silver nanoparticles were prepared under mild conditions by exploiting poly(ethylene glycol) (PEG) in the absence of other chemicals. The chain length of PEG was discovered to play the key role in the formation of silver nanoparticles. Ethylene glycol, which was used as a reducing agent for the preparation of metal particles at high temperatures (>170 degrees C), was inactive for the reducing of Ag+ at 80 degrees C. Surprisingly, Ag+ can be smoothly reduced to silver nanoparticles at the same condition in PEG 2000. Further studies demonstrated that the reducing rate of Ag+ to nano-Ag was remarkably enhanced with the increase of polymer chain length of PEG. The particle size depended upon the reaction temperature and concentration of the precursor and an increase in temperature effected a shift of particle size range from ca. 10 to 80 nm. In addition, a noticeable change of sphere to polyprism nanosilver was observed when the reaction temperature was elevated to 120 degrees C.

Fused silica substrates were pretreated by ultrasonic vibration in diamond powder slurry. Under the appropriate pretreatment and growth conditions, the diamond nucleation density of higher than 1010 cm−2 was obtained. The average diamond grain size was ca. 150 nm, and continuous diamond thin films with smooth surfaces (average surface roughness ca. 6 nm) were synthesized by a four-step process using the hot filament chemical vapor deposition (HFCVD) technique. The optical transmittance of diamond thin films was 73–84% in the longer wave range (1–5 μm). The adhesion of diamond thin films grown 3 years ago is still good and the mechanism is briefly discussed.

Despite a few reports on the synthesis of ultrathin 2D nanosheets made of noble metals, it still remains a tremendous challenge to generate their ultrathin hollowed nanostructures, which are of particular interest in highly active catalysis due to their unique structural features. Here, the synthesis of ultrathin 2D Pd nanorings is reported with a hollow interior by selective epitaxial growth of Pd atoms on the periphery of the as-preformed Pd nanosheets in combination with oxidative etching. This approach can be extended to fabricate Pd-based bimetallic ultrathin nanorings such as Pd-Pt. The Pd nanorings exhibit substantially enhanced activity toward the hydrogenation of p-nitrophenol, which is 2.2 and 33.4 times higher than that of the Pd nanosheets and commercial Pd black, respectively. Significantly, the Pd nanorings are highly stable with only less than 11% loss in activity compared to 45.7% loss of the Pd nanosheets and 72.2% loss of the Pd black after ten cycles.

Using the sol–gel spin-coating method, La0.67Sr0.33MnO3 and La0.7Ca0.3MnO3 polycrystalline films have been prepared. The polycrystalline films show much lower resistivity peak temperature Tp than that of the corresponding epitaxial film, and Tp shifts to higher temperature when the annealing temperature increases. The magnetization measurement reveals that all of the polycrystalline films have the same magnetic transition temperature as the corresponding epitaxial films. These results are different from the previous works. We ascribe the difference to the grain size of our polycrystalline samples being much smaller, so the conduction through the grain boundaries predominates over the intragrain conduction. In this case, spin disorder and magnetocrystalline anisotropy should be taken into account in explaining the magnetotransport behavior.

Surface structures of the bare and AlPO 4 -coated LiNi 0.8 Co 0.2 O 2 particles in two electrolytes after 90 °C for 4 h storage were investigated using transmission electron microscope (TEM). The structure of bare LiNi 0.8 Co 0.2 O 2 particles in common electrolyte has been destructed from the layered structure with space group R-3m at interior region to a rock-salt phase (Fm-3m) at edge of the surface layer of the cycled particles, while AlPO 4 -coated LiNi 0.8 Co 0.2 O 2 particles in common electrolyte has been transformed into a spinel phase (Fd-3m) on the surfaces of the cycled particles. However, the surface structure of bare LiNi 0.8 Co 0.2 O 2 particles in functional electrolyte has not been changed. The results showed that functional electrolyte can more effectively improve thermal stability of LiNi 0.8 Co 0.2 O 2 cathode cells than the AlPO 4 coating.

We have grown large Sr-rich Pr(Sr,Ba) 2 Cu 3 O y single crystals using SrO-BaO-CuO mixture as the self-flux. The crystals were characterized by energy dispersive X-ray spectrometry, X-ray diffraction, temperature dependence of resistivity and susceptiblity, and thermal analysis. This high Sr content is probably due to Al incorporation from the Al 2 O 3 crucible. Our growth approach may provide an alternative to the preparation of twin-free 123 crystals.

Using high resolution transmission electron microscopy with image simulation and Fourier analysis, the Li1- x FePO4 (x 0.01), Li1- x FePO4 (x ∼ 0.5), and FePO4 particles, prepared by charging or discharging the 053048 electrochemical cells (thickness: 5 mm, width: 30 mm, height: 48 mm) and dismantled inside an Ar-filled dry box, were investigated. The high resolution images reveal: (1) the solid solution of Li1- x FePO4 (x 0.01) contains some missing Li ions leading PO4 group distorted around M1 tunnel of the unit cell; (2) the texture of the particles of Li1- x FePO4 (x ∼0.5) has homogeneously distributed compositional domains of LiFePO4 and FePO4 resulting from spinodal decomposition which promote Li ion easily getting into the particle due to uphill diffusion, (3) the particles of FePO4 formed in charging have heavily distorted lattice and contain some isolated LiFePO4 , (4) interface between LiFePO4 and FePO4 and between amorphous and crystal region provides the lattice distortion of small polarons.

Cu-Cr alloy is a kind of promising materials used as conductor due to its good strength and high conductivity.Heavy cold deformation could increase the strength effectively. Most of Cu and Cr phase are elongated into filaments during cold drawing.There exits plenty of Cu/Cr interface and the structure of Cu/Cr interface is thought to play an essential role in the properties of the Cu-Cr alloy.In this work,Cu-Cr wires were prepared by cold drawing method.The evolution of the microstructure and the structural change of phase interface during cold drawing have been investigated and the relationship between properties and microstructure also established.The microstructure consists of Cu matrix and Cr particles before cold drawing.As the drawing strain increases,both of Cu and Cr phases evolve into filamentary structure.Some residual Cr particles are still found in the alloy even at high drawing ratio.There is a relationship of(111)_(Cu)//(110)_(Cr) between Cu fibers and Cr fibers at high strain levels.The Cu/Cr interface is non-coherent before cold drawing and gradually evolves into the coherent interface at high drawing strains.The inter-solution ability of Cu and Cr elements across the Cu/Cr interface is enhanced with the increase in the drawing strain. The coherent Cu/Cr interface and the increasing of interface density should be responsible for the strength rising to an almost constant value and the increase in electrical resistivity of Cu-Cr alloys at high strain levels.