Particle Size and Crystal Phase Effects in Fischer-Tropsch Catalysts

Fischer-Tropsch synthesis （FTS） is an increasingly important approach for producing liquid fuels and chemicals via syngas-that is, synthesis gas, a mixture of carbon monoxide and hydrogen-generated from coal, natural gas, or biomass. In FTS, dispersed transition metal nanoparticles are used to catalyze the reactions underlying the formation of carbon-carbon bonds. Catalytic activity and selectivity are strongly correlated with the electronic and geometric structure of the nanoparticles, which depend on the particle size, morphology, and crystallographic phase of the nanoparticles. In this article, we review recent works dealing with the aspects of bulk and surface sensitivity of the FTS reaction. Understanding the different catalytic behavior in more detail as a function of these parameters may guide the design of more active, selective, and stable FTS catalysts.

The Structure and Size-effect of Calcium Modified Lead Titanate Nanocrystal,Pb_(0.85)Ca_(0.15)TiO_3

Calcium modified lead titanate nanocrystal material Pb0.85Ca0.15TiO3 was synthesized by means of a solgel method.The changes of crystal structure and grainsize of the samples were investigated under different conditions of heat treatment.the results show that the tetragonal symmetry is reduced and the ferroelectricparaelectric phase transformation temperature is decreased with the reduce of the grainsize of the sample.the critical grainsize for the ferroelectricparaelectric phase transformation at room temperature was calculated.The change regularities of the lattice constant and tetragonality with the grainsize are discussed.

The “Inverse Hall-Petch” effect on the impact response of single crystal copper

Based on the available experimental and compu- tational capabilities, a phenomenological approach has been proposed to formulate a hypersurface in both spatial and temporal domains to predict combined specimen size and load- ing rate effects on the material properties [ 1-2]. A systematic investigation is being performed to understand the combined size, rate and thermal effects on the properties and deformation patterns of representative materials with different nanos- tructures and under various types of loading conditions [3- 16]. The recent study on the single crystal copper response to impact loading has revealed the size-dependence of the Hugoniot curve. In this paper, the ＂inverse Hall-Petch＂ behavior as observed in the impact response of single crystal copper, which has not been reported in the open literature, is investigated by performing molecular dynamics simulations of the response of copper nanobeam targets subjected to impacts by copper nanobeam flyers with different impact velocities. It appears from the preliminary results that the ＂inverse Hall-Petch＂ behavior in single crystal copper is mainly due to the formation and evolution of disordered atoms and the interaction between ordered and disordered atoms, as compared with the physics behind the ＂inverse Hall-Petch＂behavior as observed in nanocrystalline materials

Bauschinger and size effects in thin-film plasticity due to defect-energy of geometrical necessary dislocations

The Bauschinger and size effects in the thinfilm plasticity theory arising from the defect-energy of geometrically necessary dislocations （GNDs） are analytically investigated in this paper. Firstly, this defect-energy is deduced based on the elastic interactions of coupling dislocations （or pile-ups） moving on the closed neighboring slip plane. This energy is a quadratic function of the GNDs density, and includes an elastic interaction coefficient and an energetic length scale L. By incorporating it into the work- conjugate strain gradient plasticity theory of Gurtin, an energetic stress associated with this defect energy is obtained, which just plays the role of back stress in the kinematic hardening model. Then this back-stress hardening model is used to investigate the Bauschinger and size effects in the tension problem of single crystal Al films with passivation layers. The tension stress in the film shows a reverse dependence on the film thickness h. By comparing it with discrete-dislocation simulation results, the length scale L is determined, which is just several slip plane spacing, and accords well with our physical interpretation for the defect- energy. The Bauschinger effect after unloading is analyzed by combining this back-stress hardening model with a friction model. The effects of film thickness and pre-strain on the reversed plastic strain after unloading are quantified and qualitatively compared with experiment results.

CRYSTAL STRUCTURE AND SHG EFFECT OF COMPLEX [Zn(POM)_2Br_2]

[Zn(POM)_2Br_2](POM is 3-Methyl-4-Nitropyridine-1-Oxide),C_(12)H_(12)Br_2N_4O_6Zn, Mr=533.44,triclinic,P1,a=11.450(3),b=13.027(2),c=6.605(1),α=101.25(1),β=96.96(2), γ=108.06(2)°,V=901.2(4)~3,Z=2,D_c=1.97g·cm^(-3),(MoK_α)=0.71069,F(000)=520, μ=58.21cm^(-1),final R=0.040 for 2192 observed reflections,T=296K.The compound is a mononuclear complex,containing a tetrahedrally coordinated zinc atom.

Steric Effect Modulating the Structures of Trinuclear Zinc Carboxylate Frameworks

By the reaction of different aromatic dicarboxylic acid with zinc nitrate, three metal-carboxylate frameworks, [Zn3（BDC）3（EtOH）2]（1）, [Zn3（BDC）3（py）2]·2DMF（2）, and [Zn3（NH2-BDC）3（H2O）2]·5DMF（3） which are constructed on the same linear trinuclear Zn3（RCOO）6 secondary building units, have been synthesized and characterized by X-ray diffraction analyses. Structural analyses showed that there are terephthalic acids as ligand linkers to form the hxl topological layer structures for 1 and 2. The introduction of the rigid aromatic ring pyridine in 2 as the terminal co-ligand of Zn3-SBU to instead of the flexible ethanol in 1, will form the layer-pillared supramolecular systems with 2-D crisscross channels, through its π-π stacking interactions. Owing to the steric hindrance of amino groups, 3 was assembled into a three-dimensional porous structure with pcu topology derived from the 2-amino-terephthalic acid as linkers to connect the Zn3-SBUs through a head-to-tail type.

SPECTRAL VARIATION AND CHARACTERISTICS OF LOW VALENCY RARE EARTH IONS IN COMPLEX OXIDESⅢ.EFFECT OF THE CRYSTAL ENVIRONMENT AND CHEMICAL FACTORS ON LUMINESCENCE PROPERTIES OF EUROPIUM (Ⅱ) ION

In this paper,the influence of crystal-field on the Luminescence properties of Eu^(2+) in complex oxides are studied theoretically by using purely electrostatic model,the dependence of the 4f^65d levels on Eu-O bond distance is given.Quantum chemistry calculation shows that the splitting extent of 4f^65d energy band in cubic or in octahedral fields will be inversely proportional to R^5,where R is the distance of Eu^(2+) to oxygen ligand.The value of R affects slightly the location of the centre of 4f^65d energy band.According to the exper- imental spectrum data,we have discussed the influence of the host chemical composition,the replaced sites of Eu^(2+) and degree of covalency of Eu-O bond on luminescence properties of Eu^(2+).Some regularity of fluorescence spectrum was observed. In alkali-alkaline earth-phosphates,the splitting extent of 4f^65d band (△E) becomes smaller as the Eu-O bond distance (R) increases.In Na_(3-x)(PO_4)_(1-x)(SO_4)_x and Na_(2-x)CaSi_(1-x)P_xO_4 hosts,d-d emission peak of Eu^(2+) will shift to shorter wavelength with the increase of x's value. The crystal structure data show that Eu^(2+) in K_2Mg_2(SO_4)_3 is affected more strongly by crystal-field and covalancy than in KMgF_3,so K_2Mg_2(SO_4)_3:Eu^(2+) emits blue light (E_(em)~m=400nm) and KMgF_3:Eu^(2+) produces ultraviolet fluorescence.

Kerr effect and Kerr constant enhancement in vertically aligned deformed helix ferroelectric liquid crystals

In this article,we review recently achieved Kerr effect progress in novel liquid crystal（LC） material：vertically aligned deformed helix ferroelectric liquid crystal（VADHFLC）.With an increasing applied electric field,the induced inplane birefringence of LCs shows quadratic nonlinearity.The theoretical calculations and experimental details are illustrated.With an enhanced Kerr constant to 130 nm/V2,this VADHFLC cell can achieve a 2π modulation by a small efficient electric field with a fast response around 100 μs and thus can be employed in both display and photonics devices.

Theoretical studies of CO oxidation with lattice oxygen on Co_3O_4 surfaces

Low-temperature CO oxidation has attracted extensive interest in heterogeneous catalysis because of the potential applications in fuel cells,air cleaning,and automotive emission reduction.In the present study,theoretical investigations have been performed using density functional theory to elucidate the crystal plane effect and structure sensitivity of Co3O4 nano-catalysts toward catalyzing CO oxidation.It is shown that the surface Co–O ion pairs are the active site for CO oxidation on the Co3O4 surface.Because of stronger CO adsorption and easier removal of lattice oxygen ions,the Co3O4（011）surface is shown to be more reactive for CO oxidation than the Co3O4（001）surface,which is consistent with previous experimental results.By comparing the reaction pathways at different sites on each surface,we have further elucidated the nature of the crystal plane effect on Co3O4 surfaces and attributed the reactivity to the surface reducibility.Our results suggest that CO oxidation catalyzed by Co3O4 nanocrystals has a strong crystal plane effect and structure sensitivity.Lowering the vacancy formation energy of the oxide surface is key for high CO oxidation reactivity.

Morphology-dependent structures and catalytic performances of Au nanostructures on Cu_2O nanocrystals synthesized by galvanic replacement reaction

Au nanostructures were prepared on uniform Cu2O octahedra and rhombic dodecahedra via the galvanic replacement reaction between HAuCl 4 and Cu2O. The compositions and structures were studied by Scanning Electron Microscope (SEM), Transmission Electron Microscope (TEM), High-Resolution Transmission Electron Microscope (HRTEM), X-Ray Diffraction (XRD), X-Ray Absorption Spectroscopy (XAS), X-ray Photoelectron Spectroscopy (XPS) and in-situ DRIFTS spectroscopy of CO adsorption. Different from the formation of Au-Cu alloys on Cu2O cubes by the galvanic replacement reaction (ChemNanoMat 2 (2016) 861-865), metallic Au particles and positively-charged Au clusters form on Cu2O octahedra and rhombic dodecahedra at very small Au loadings and only metallic Au particles form at large Au loadings. Metallic Au particles on Cu2O octahedra and rhombic dodecahedra are more active in catalyzing the liquid phase aerobic oxidation reaction of benzyl alcohol than positively-charged Au clusters. These results demonstrate an obvious morphology effect of Cu2O nanocrystals on the liquid-solid interfacial reactions and prove oxide morphology as an effective strategy to tune the surface reactivity and catalytic performance. (C) 2016 Science Press and Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. and Science Press. All rights reserved.

The influencing factors and mechanisms of the electromagnetic radiation during rock fracture

Based on the laboratory experiments this paper presented that the primary influence factors about the electromagnetic radiation during rock fracture are the rock mechanics characters and mineral components. The brittle samples and samples contained quartz, pyrite, chalopyrite produce electromagnetic radiation easily. There are three fracture radiation effects. The crystal fracture effect produces the high frequency electromagnetic signals, the piezoelectric effect produces low frequency signals and the natural semiconductor effect produces middle frequency signals possessed distinct wave shapes.

Optical simulation of in-plane-switching blue phase liquid crystal display using the finite-difference time-domain method

The finite-difference time-domain method is used to simulate the optical characteristics of an in-plane switching blue phase liquid crystal display.Compared with the matrix optic methods and the refractive method,the finite-difference timedomain method,which is used to directly solve Maxwell＇s equations,can consider the lateral variation of the refractive index and obtain an accurate convergence effect.The simulation results show that e-rays and o-rays bend in different directions when the in-plane switching blue phase liquid crystal display is driven by the operating voltage.The finitedifference time-domain method should be used when the distribution of the liquid crystal in the liquid crystal display has a large lateral change.

Low voltage transflective blue-phase liquid crystal display with a non-uniform etching substrate

A transflective polymer-stabilized blue-phase liquid crystal display（BP-LCD） with a non-uniform etching substrate is proposed.In-plane switching（IPS） electrodes on the bottom substrate are put on the different gaps,and the bottom substrate between the electrodes is etched into different depths in transmissive（T） and reflective（R） regions.This structure can balance the optical phase retardation in the two regions and is helpful to achieve well-matched voltag-dependent transmittance and reflectance curves.This transflective display has high optical efficiency,a wide viewing angle,and low operating voltage（approximately 6 V）.

Crystal Structures of Two Compounds from a Rapid and One-pot Synthesis Method

Compounds 1 （C17H22N2,Mr =254.37） and 2 （C13H16N2,Mr=200.28） have been synthesized and their crystal structures were determined by single-crystal X-ray diffraction.Crystal 1 belongs to triclinic,space group P（1） with a =6.524（2）,b =8.987（3）,c =12.746（5） A,α =95.220（7）,β =90.055（6）,γ =104.431（6）°,V =720.5（4） A^3,Z =2,Dc =1.173 g/cm^3,μ（MoKα） =0.069 mm1,F（000） =276,R =0.0578 and wR =0.1221 for 1487 observed reflections Ⅰ 〉 2o（Ⅰ）.Crystal 2 is of tetragonal system,space group Ⅰ41/a with a =20.763（10）,b =20.763（10）,c =11.427（6） A,V=4926（4） A3,Z =16,Dc =1.080 g/cm^3,μ（MoKα） =0.065 mm-1,F（000） =1728,R =0.0581 and wR =0.1288 for 1408 observed reflections with Ⅰ 〉 2σ（Ⅰ）.Although the two compounds are similar with the same pyrazole and benzene ring units,X-ray analysis reveals that their structures are completely different maybe caused by steric effects.

Asymmetric dynamic phase holographic grating in nematic liquid crystal

A new scheme for recording a dynamic phase grating with an asymmetric profile in C60-doped homeotropically aligned nematic liquid crystal（NLC） was presented.An oblique incidence beam was used to record the thin asymmetric dynamic phase holographic grating.The diffraction efficiency we achieved is more than 40%,exceeding the theoretical limit for symmetric profile gratings.Both facts can be explained by assuming that a grating with an asymmetric saw-tooth profile is formed in the NLC.Finally,physical mechanism and mathematical model for characterizing the asymmetric phase holographic grating were presented,based on the photo-refractive-like（PR-like） effect.

Parameter analysis of a photonic crystal fiber with raised-core index profile based on effective index method

Photonic crystal fibers （PCFs） with a stepped raised-core profile and one layer equally spaced holes in the cladding are analyzed. Using effective index method and considering a raised step refractive index difference between the index of the core and the effective index of the cladding, we improve the characteristic parameters such as numerical aperture and V-parameter, and reduce its bending loss to about one tenth of a conventional PCF. Implementing such a structure in PCFs may be one step forward to achieve low loss PCFs for communication applications.

Purcell effect of GaAs quantum dots by photonic crystal microcavities

We fabricate photonic crystal slab microcavities embedded with GaAs quantum dots by electron beam lithography and droplet epitaxy. The Purcell effect of exciton emission of the quantum dots is confirmed by the micro photoluminescence measurement. The resonance wavelengths, widths, and polarization are consistent with numerical simulation results.

EFFECT OF VACUUM ON THE CRYSTAL FORM AND MORPHOLOGY OF THE EVAPORATED FILM OF COPPER PHTHALOCYANINE

In a previous paper, we have reported the relationship between the crystallite orientation of the evaporated film of copper phthalacyanine （PcCu） （α-form） and the incident angle of molecular beam at 10-5 torr. In this paper, we shall show some research results about vacuum effects on the crystal forms and the morphology of the evaporat-

Shape-Controlled CuCl Crystallite Catalysts for Aniline Coupling

The catalytic activity of crystallites depends mainly upon the arrangement of surface atoms,the number of dangling bonds,and defect site distribution on different crystal planes.Here,we report the shape-controlled synthesis of CuCl crystallites,including tetrahedra,face-centered-etched tetrahedra,tripod dendrites,and tetrapods.These different morphologies of CuCl crystallites expose different proportions of{111}and{110}crystal planes,and materials with a preponderance of{111}crystal planes have better catalytic activity in aniline coupling than those with more{110}planes.