Sensitivity of styrene oxidation reaction to the catalyst structure of silver nanoparticles

This study shows how different morphologies of silver nanoparticles affect the selective oxidation of styrene in the gas phase using oxygen as oxidant. Silver nanoparticles (nanowires and nanopolyhedra), prepared using the polyol process, were supported on α-Al₂O₃. For comparison, a conventional catalyst obtained by wet impregnation was also prepared. Phenylacetaldehyde (Phe) and styrene oxide (SO) were the main products for nanoparticles catalysts. The promotion effect on the catalytic activity of potassium and cesium on the silver nanowires catalysts was also studied. At 573 K, the styrene conversion and selectivity to styrene oxide with the silver nanowires catalyst were 57.6 and 42.5%, respectively. Silver nanopolyhedra catalyst showed 57.5% conversion and 30.8% selectivity to styrene oxide. The promotion by cesium played an important role in improving the epoxidation of styrene. The samples were structurally characterized using X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-vis), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR) were applied to characterize the oxygen species detected (O_β, O_γ) on the silver surface.     

Radiative recombination in iridium-doped silver bromide single crystals

The infrared emission spectrum of iridium-doped silver bromide results from a process that is competitive with the visible emission due to iodide centers in pure AgBr crystals. The emitting species is Ir³⁺, and experiments are described which help elucidate the nature of the radiative processes involved.     

Morphology of silver single crystals obtained by electrodeposition

The morphology of silver single crystals obtained by electrodeposition with varying parameters—such as the electrolyte composition, substrate material, current density, and deposition time—is discussed, and respective experimental data are presented.     

Ethane hydrogenolysis over single crystals of nickel: Direct detection of structure sensitivity

Single crystal catalysts have been used to investigate ethane hydrogenolysis. The apparatus used in these studies allows for catalyst preparation and surface characterization in ultrahigh vacuum (UHV) with an in vacuo transfer to a second UHV chamber designed for high pressure kinetic studies. Kinetic measurements on single crystals of nickel show the hydrogenolysis of ethane to be “structure sensitive”. Absolute rate and activation energy differences are observed over different facets of nickel. The (100) surface is observed to be significantly more active for this reaction than the (111) surface.     

Vortex structure in FeTeSe single crystals

Vortex structure in FeTe_0.66Se_0.44 and FeTe_0.6Se_0.4 single crystals with T _c ∼ 11.7 and 14.5 K, respectively, has been studied using the decoration technique. It has been found that in single crystals with the simplest crystalline structure of 11-family iron-containing superconductors (without interlayers), no regular vortex lattice is observed, similar to the case of the previously studied 122 and 1111 families. Using transmission electron microscopy, the dislocation structure with a density of ∼10⁹ cm⁻² has been observed. The problem of pinning in iron-containing superconductor single crystals is discussed.     

Sputtering experiments with silver single crystals and the channeling phenomena

Sputtering yields of monocrystalline silver under irradiation with 7-30 keV Ar⁺, Kr⁺ and Xe⁺ ions, not reported earlier, have been determined. The yield has been found to depend strongly on the orientation of the crystal and mass of the impinging ion. Onderdelinden's model based on Lindhard's theory of Channeling is found to describe satisfactorily, the observed orientation and ion-mass dependence of the yields for the ions of energy ～10 keV or above. The role of the barrier potential approximated in the model in predicting the experimental results is discussed.     

Electrical properties of CdSb single crystals doped with silver

A study is made of the electrical and thermoelectrical properties of CdSb single crystals weakly and heavily doped with silver. The electrical conductivity, the Hall effect and the thermoelectric force in intrinsic conduction are studied on samples of CdSb oriented in the direction of the crystal-lographic axisb. The activation energy of the acceptors is determined as well as the density of states effective mass and their dependence on the temperature and concentration, and the mobility of holes is studied.     

The bordoni peak in silver single crystals at megahertz frequencies

Summary The dislocation relaxation maximum has been investigated at frequencies of 5, 10 and 30 MHz. The three (very high-purity) silver crystals of crystallographic orientation 〈111〉, 〈110〉 and 〈100〉 which are given a resolved shear stress of 20 MPa were found to produce dislocation relaxation maximum at 107 K in all the three samples. The maximum shifts to 117 K when measurement is carried out at 10 MHz and to 127 K at 30 MHz. The results reveal that the maximum is orientation independent. The activation energy and the attempt frequency were calculated and found to be equal to 0.105 eV and 2·10⁹ Hz, respectively. Meanwhile the larger magnitude of the maximum was found on the 〈111〉 crystal and the least was on the 〈100〉 crystal. Finally, it was clearly shown that the dislocation relaxation strength decreases as the frequency increases.     

Diffusion of silver in TiSe2 single crystals

Diffusion of deposited silver through the surface of TiSe₂ single crystals has been investigated. It is found that diffusion occurs only near lattice defects. The X-ray photoelectron spectra of TiSe₂ single crystals with in situ deposited silver have been studied. It is found that, upon annealing in the spectrometer chamber, silver does not form chemical bonds with the host lattice. Original Russian Text ? A.I. Merentsov, E.A. Titova, P.E. Panfilov, S.N. Shamin, A.M. Ionov, A.N. Chaika, 2009, published in Izvestiya Rossiiskoi Akademii Nauk. Seriya Fizicheskaya, 2009, Vol. 73, No. 4, pp. 566–568. The paper was reported at the International Simposium.     

Wavelength modulation spectra of single crystals of silver and gold

The logarithmic derivative of the reflectivity is measured for Ag and Au for 2.0 ⪕ħω⪕ 6.0 eV at T = 5, 80 and 300K. The results are compared with a calculated spectrum.     

Influence of surface oxidation on the photoelectron diffraction intensities from InP single crystals

The Monte Carlo method was used to calculate the influence of amorphous overlayers on the angle-dependent intensity distribution due to photoelectron diffraction (XPD) in monocrystalline substrates. The influences of the overlayer thickness, the elastic and inelastic mean free paths in the amorphous overlayer, the shape of the initial intensity distribution, as well as the overlayer chemical composition, on XPD is discussed and some trends are formulated. The simulated P 2p intensities of oxidized InP agree with the experimental data. The effect of elastic scattering on the intensity minimum around the detection angle 18° is stronger than that of inelastic scattering. A new method for the thickness determination of thin overlayers on single ecrystals is discussed.     

Domain structure of silicon iron single crystals

The model of a new domain structure arising after the magnetization of silicon iron single crystals in planes of the (110) type at an angle of 0°<Θ<-55° to the axis of easy magnetization is considered. Using this model the angular dependence of the domain-structure characteristics is established; it agrees closely with direct observations. On magnetizing a single crystal in the angular range 55° <Θ≤ 90° to the easy axis, layers with a uniform resultant magnetization parallel to the [001] direction are formed.     

Electronic structure of CsCdCl3 single crystals

Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 53, No. 6, pp. 988–991, December, 1990.     

The influence of oxygen partial pressure on recovery creep in magnetite single crystals

Creep tests of magnetite single crystals have been performed in compression at high temperatures (between 1000 and 1340°C). The main goal was two-fold: First of all, the determination of the dependence of steady state creep rate as a function of the oxygen partial pressure in the external atmosphere. Secondly, the comparison of this dependence with that of oxygen self-diffusion coefficient with the partial oxygen pressure. This second one had been reported in literature previously. Both are quantitatively very similar. This fact has allowed us to discuss some aspects of the minority point defects in the oxygen sub-lattice of this oxide.     

Surface structure of large germanium single crystals

The dependence between structural-defect generation and the growth kinetics of germanium single crystals pulled from melts is investigated via selective chemical etching and the optical, atomic-force and scanning electron microscopy techniques. It is ascertained that the surface microrelief of germanium crystals grown from melts by means of directional crystallization contains protrusions and cavities with spatial periodicities of 5 and 50 μm. The values of the kinetic coefficients are estimated. It is demonstrated that the main part of the crystals is formed according to the normal mechanism with the kinetic coefficients β_k = 2 × 10^?5 m s^?1 K^?1.     

Vortex structure in superconducting iron pnictide single crystals

The vortex structure in the iron pnictide single crystals Ba_1?x K _x Fe₂As₂ and Sr_1?x K _x Fe₂As₂ of the 122 type and SmFeAsO_1?x F _x of the 1111 type has been investigated using the decoration method. In all of the crystals under investigation, no regular vortex lattice has been revealed in the magnetic field range up to 200 Oe. The disordered vortex structure is discussed in view of the vortex pinning in single crystals.     

Defect structure in EuS single crystals grown from the melt

The defect structure in EuS single crystals grown form the melt is studied by etch pitting, scanning and high-voltage electron microscopy. Circular and square etch pits and a second phase in the shape of thin hexagonal platelets are observed by etching. Microprobe analysis indicates the platelets to consist of Eu metal. In the transmission electron microscope, smoothly curved dislocations and helical dislocations, small dislocation loops and inclusions associated with dislocations are observed. The possible origin of the detected dislocation structure is considered with reference to climb and glide processes occurring during cooling down the grown crystals. The results corroborate the glide geometry of the NaCl lattice for EuS. On leave from Institute of Physics, Academic Sinica, Peking, VR China     

Strong,large distance impurity dipole interaction in KNbO3 single crystals

It is found that the unrelaxed impurity dipoles can arrange themselves linearly in the structure joining each other end-to-end in pseudocubic [110] direction at the tetragonal to the orthorhombic phase transition. It is shown that this alignment precedes the domain formation at the phase transition, which implies quick movements of the dipoles in the structure, and a strong dipolar interaction. The experiments with the application of dc fields to the crystals showed that the dipolar interaction becomes stronger with the field. The dipoles can see each other across the existing domain walls implying the large distance nature of the interaction. The observation of impurity clusters arranged in pseudocubic [110] direction confirmed the large distance nature of the interaction. It is concluded that this strong, large distance interaction is very interesting in as much as such an interaction of dipoles forms the basis of ferroelectricity.