Kinetics of Synthesis of Ba1.0Co0.7Fe0.2Nb0.1O3-δ through Solid-Solid Reaction

The mechanism of solid-solid reaction between BaCO₃ and Co₃O₄/Fe₂O₃/Nb₂O₅ has been investigated by means of non-isothermal thermogravimetry and differential scanning calorimetry (DSC) under flowing air gas conditions at atmospheric pressure with a new solid-solid reaction model. The effects of high speed agitating mixing and ball-milling mixing processes on the synthesis kinetics were also studied. The synthesis kinetics of Ba_1.0Co_0.7Fe_0.2Nb_0.1O_3-δ from the BaCO₃ and Co₃O₄/Fe₂O₃/Nb₂O₅ particles was calculated by applying the modified model. The results indicated that the overall reaction process was considered involving two stages: addition reaction between BaCO₃ and Co₃O₄/Fe₂O₃/Nb₂O₅ particles in the first stage and solution reaction between BaCoO₃, BaFeO₃, and BaNbO₃ to form a homogeneous Ba_1.0Co_0.7Fe_0.2Nb_0.1O_3-δ phase in the second stage. The new model matched well with the experimental data. The apparent activation energy of addition reaction stage of the high speed agitating mixing sample was estimated to be 376.76 kJ·mol⁻¹, which was only 3/4 of that of the ball-milling mixing sample (494.76 kJ·mol⁻¹). These results indicated that the high-speed agitating process could enhance atomic diffusion and facilitate the subsequent reaction, thus it is believed as a more effective, energy saving, and environmentally benign mixing process.     

Crystal Structure of a New Form of Sodium Octoborate β-Na2B8O13

Single crystals of a new form of sodium octoborate, β-Na₂B₈O₁₃, were obtained fortuitously from a complex Na₂O-B₂O₃-P₂O₅ mixture, and studied. The compound is monoclinic, space group P2₁/c; the unit cell parameters are a=11.731(4) Å, b=7.880(3) Å, c=10.410(4) Å, β=99.883(3)°; Z=4. The crystal structure was solved from 1653 reflections until R₁=0.0444; it consists of two infinite, independent, and interleaved boron-oxygen networks containing a complex borate anion (B₈O₁₃)²⁻ formed by six BO₃ triangles (Δ) and two BO₄ tetrahedra (T), which can be viewed as a B₅O₁₀ group linked to a B₃O₇ group; this leads to a Fundamental Building Block (FBB) with the shorthand notation: 8: ∞³ [(5:4Δ+T)+(3:2Δ+T)]. This FBB is identical to that described in other octoborates such as α-Na₂B₈O₁₃ and Ag₂B₈O₁₃. However, some subtle differences exist in the interlinking of the octoborate anions found in these three compounds, which explains their different structure and unit cell parameters.     

Rotational Analysis of A2Πu-X2Σ+g System of 14N2+

The absorption spectrum of N₂⁺ has been studied using optical-heterodyne velocity mod-ulation spectroscopy in the near-infrared region. The observed spectral lines were assigned to the (3,1), (4,2), (5,3), (8,5) bands of the A²Π_u-X²Σ⁺_g system and the line lists were provided. The (5,3) band was studied for the first time. Fourteen rotational-resolved bands in literatures were fitted together with our observed bands and the molecular constants were obtained for υ_A=0-9 and υ_X=0-5.     

Reaction of tetrahydrofuran with H2S in the presence of Na+/γ-Al2O3

Modification of -Al₂O₃ by sodium hydroxide promotes the increase of surface basicity but does not exert a strong effect on catalytic activity in the reaction of thiolane production from tetrahydrofuran and H₂S. Introduction of NaOH to -Al₂O₃ in small concentration increases the number of Lewis acid centers but decreases their strength. The activity of Na/-Al₂O₃ referred to one Lewis acid center drops.     

Study of Dehydrocoupling Reactions of Diorganotin Dihydrides R1R2SnH2 with Biuret

phenylmethyltin dihydride (PhMeSnH₂), phenylethyltin dihydride (PhEtSnH₂), phenylbutyltin dihydride (PhBuSnH₂) and butylmethyltin dihydride (BuMeSnH₂) with biuret (H₂L) proceeds via SnH/NH dehydrocoupling to afford the corresponding tetra-coordinate cyclic products. The reactions in the molar ratios of 1∶1, 2∶1 and 1∶2 have been studied. The yellow derivatives so isolated were soluble in polar solvents and insoluble in nonpolar solvents. It was found that 1∶1 reaction went to completion while 2∶1 and 1∶2 did not go to completion. The derivatives had been characterized by elemental analysis and spectroscopic techniques viz. IR, ¹H NMR, ¹³C NMR, ¹¹⁹Sn NMR. DSC and TGA of the reaction products have also been studied. All the derivatives were thermally stable upto (190±10) ℃ and degradation occurred after that.     

Ab-initio structure determination of β-La2WO6

The structure of the low-temperature form of β-La₂WO₆ has been determined from laboratory X-ray, neutron time-of-flight and electron diffraction data. This tungstate crystallizes in the non-centrosymmetric orthorhombic space group (no. 19) P2₁2₁2₁, with Z=8, a=7.5196(1) Å, b=10.3476(1) Å, c=12.7944(2) Å, and a measured density 7.37(1) g cm⁻³. The structure consists of tungsten [WO₆] octahedra and tetrahedral [OLa₄]. Tungsten polyhedra are connected such that [W₂O₁₁]¹⁰⁻ units are formed.     

Refinement of α-CsB9O14 crystal structure

The structure of α-CsB₉O₁₄ was re-examined because the first determination corresponded to a poor reliability factor (12.9%). Single crystals were obtained by heating, melting and slow cooling a stoichiometric mixture (1:4) of β-Cs[B₅O₆(OH)₄]·2H₂O and H₃BO₃. This compound crystallizes in the non-centrosymmetric orthorhombic space group P222₁ (and not P4₁22) with the following parameters: a=8.732(2)Å, b=8.767(3)Å, c=15.736(4)Å, V=1204.6(6)ų, Z=4; after taking into consideration twinning, the structure was refined from 3188 reflections until R₁=0.0304. It consists of two infinite, interleaved three-dimensional boron-oxygen frameworks of the Fundamental Building Blocks formed by two B₃O₆ and one B₃O₇ groups; its shorthand notation is 9:∞³[(3:2Δ+T)+2(3:3Δ)] (Δ, triangle BO₃ and T, tetrahedron BO₄). Knowledge of the correct space group and the structure of α-CsB₉O₁₄ may help in the study of its physical properties, especially the non-linear optical ones.     

The effect of phase composition on the transport properties of composites La0.8Sr0.2Fe0.7Ni0.3O3 ? δ-Ce0.9Gd0.1O1.95

Full conductivity, diffusion and oxygen exchange processes in composites (100 − x)La_0.8Sr_0.2Fe_0.7Ni_0.3O_{3 − δ}−xCe_0.9Gd_0.1O_1.95 (x is the volume fraction, 0 ≤ x ≤ 71.1%) at 700°C over the oxygen partial pressure range from 0.2 to 3 × 10⁻³ atm are studied by the electrical conductivity relaxation method. The composites’ conductivity was shown to decrease monotonically with the increasing of Ce_0.9Gd_0.1O_1.95 fraction, while the oxygen chemical diffusion coefficient increased. The oxygen exchange constant is higher for the composites than for the individual phases of La_0.8Sr_0.2Fe_0.7Ni_0.3O_{3 − δ} and Ce_0.9Gd_0.1O_1.95. Possible reason of the dependence of the parameters D _chem and k _chem on the temperature, oxygen pressure, and the composite composition is the effect of the interface on the oxygen transfer processes. Most effective oxygen transfer occurs in the composites whose composition approaches La_0.8Sr_0.2Fe_0.7Ni_0.3O_{3 − δ}-Ce_0.9Gd_0.1O_1.95 (x = 71%).     

Impact of structural features on pigment properties of α-Fe2O3 haematite

Various α-Fe₂O₃ haematite samples were synthesized by precipitation routes (under standard or hydrothermal conditions) followed by thermal treatments under air. The trigonal distortion (C_3v point group) of the Fe³⁺ octahedral sites, which depends on the synthesis route and thermal treatment, was investigated by X-ray diffraction, Mössbauer spectroscopy and visible-near infrared (Vis-NIR) spectroscopy. The correlation between diffuse reflectance spectra and structural features of the haematite samples is reported and discussed herein. The slight increase of the average distortion of the Fe³⁺ octahedral sites, which depends on the annealing temperature of the precipitated sample, directly linked to the crystallite size, contrasts with the larger reduction of the sites distortion for the compound prepared by hydrothermal route due to the occurrence of hydroxyl groups substituted for O²⁻ anions as well as Fe³⁺ cationic vacancies. On a local point of view, as shown by Mössbauer spectroscopy, the Fe³⁺ octahedral sites distortion decreases from the centre towards the surface of the grains. Then the smaller the grain size, the lower the average site distortion. Finally, the reduction of the octahedral distortion was directly correlated to the two FeO charge transfer bands in the visible range and the colour of as-prepared haematites.     

Effects of surfactants on morphology in synthesis of α-Mn2O3 nanostructures

Cubic and chain-like structure of α-Mn₂O₃ with a high surface area was prepared by air oxidation of manganese chloride through sol process by adding hexamine and mercaptosuccinic acid as wetting agent, respectively. The as-synthesized products were characterized with X-ray powder diffraction (XRD), Energy Dispersive X-ray spectroscopy (EDX), transmission electron microscope (TEM), and selected area electron diffraction (SAED). The possible formation mechanism of α-Mn₂O₃ cubic and chain-like nanostructures has been proposed and discussed.     

Influence of electrospraying parameters on the microstructure of La0.6Sr0.4Co0.2F0.8O3−δ films for SOFCs

Ceramics can play a remarkable role in the engineering of intermediate temperature solid oxide fuel cells (IT-SOFCs) capable of meeting the ambitious targets of reduced cost and improved lifetime. While mixed ionic-electronic conductors such as La_xSr_1−xCo_yFe_1−yO_3−δ are being used as volumic cathodes to increase the catalytic performance of these components, adequate microstructures are also an important requirement for optimal performance, particularly at lower operating temperatures. This work is devoted to the fabrication of La_0.6Sr_0.4Co_0.2Fe_0.8O_3−δ films on Ce_0.9Gd_0.1O_2−δ substrates by electrostatic spray deposition (ESD) and to the characterization of the microstructural dependence on the deposition conditions. A wide variety of microstructures ranging from dense to porous, with particular features such as reticulation and micro-porosity, were obtained by varying the ESD deposition parameters: nozzle-to-substrate distance (15, 30, 43, 45, and 58 mm), solution flow rate (0.34 and 1.5 mL/h), and substrate temperature (300, 350, 400 and 450 °C). The correlation between deposition parameters and resulting microstructures was systematically studied and put into evidence.     

Influence of CO2 on Oxygen Surface Exchange Kinetics of Mixed-Conducting Ba0.5Sr0.5Co0.8Fe0.2O3?δ Oxide

The poisoning effect of CO₂ on the oxygen surface exchange kinetics of BSCF (Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3-δ) is investigated with a novel pulse isotopic exchange technique. The surface exchange rate of BSCF severely decreases after in situ exposure to CO₂, which is ascribed to carbonate formation on the material surface. The detrimental effect of CO₂ starts at a low temperature of 375 ^oC and concentration as low as 1%, and becomes more pronounced at higher temperatures. Degradation of the surface exchange kinetics is associated with a rapid loss of oxygen permeation performance of BSCF in CO₂.     

Effect of oxygen non-stoichiometry on the structural and magnetotransport properties of LaMn0.85Cr0.15O3+δ

Thermogravimetry, X-ray diffraction (XRD), d.c. magnetization, high-temperature susceptibility and electrical resistivity measurements were performed for LaMn_0.85Cr_0.15O_3+δ perovskites with accurate control of the oxygen content (0?δ?0.11). For 0?δ<0.09, three orthorhombic structures (Pnma) are found: for 0?δ<0.045, the O′ phase (b/√2<c<a), for 0.045?δ<0.06, the O″ (b/√2<a<c) and for 0.06?δ<0.09, the O^? (a<b/√2<c). For 0.09?δ?0.11, a rhombohedral symmetry coexists with O^? in a biphasic field. Magnetic measurements revealed the ferromagnetic interactions (FM) character of the Mn³⁺-O-Cr³⁺ interaction, but also the intricate magnetic phase diagram due to the presence of multiple interactions (Mn^3+,4+-O-Mn^3+,4+, Cr³⁺-O-Mn³⁺, etc.). The comparison of the results for LaMn_0.85Cr_0.15O_3+δ with those of LaMn_0.9Cr_0.1O_3+δ allows discuss the role of Cr³⁺ on the structural, magnetic and magnetotransport properties of the LaMn_1−xCr_xO_3+δ perovskites.     

Hydrodeoxygenation of Anisole over Ni/α-Al2O3 Catalyst

Ni-based catalysts supported on di erent supports (α-Al₂O₃,γ-Al₂O₃, SiO2, TiO₂, and ZrO₂) were prepared by impregnation. Effects of supports on catalytic performance were tested using hydrodeoxygenation reaction (HDO) of anisole as model reaction. Ni/α-Al₂O₃ was found to be the highest active catalyst for HDO of anisole. Under the optimal conditions, the anisole conversion is 93.25% and the hydrocarbon yield is 90.47%. Catalyst characteriza-tion using H₂-TPD method demonstrates that Ni/α-Al₂O₃ catalyst possesses more amount of active metal Ni than those of other investigated catalysts, which can enhance the cat-alytic activity for hydrogenation. Furthermore, it is found that the Ni/α-Al₂O₃ catalyst has excellent repeatability, and the carbon deposited on the surface of catalyst is negligible.     

Selective solution-phase synthesis of BiOCl, BiVO4 and δ-Bi2O3 nanocrystals in the reaction system of BiCl3-NH4VO3-NaOH

In this study, we demonstrate a straightforward solution-phase method for the selective synthesis of BiOCl, BiVO₄ and δ-Bi₂O₃ nanocrystals by simply manipulating the reaction temperature and the BiCl₃-to-NaOH mole ratio in the reaction system of BiCl₃-NH₄VO₃-NaOH. The experimental results revealed that BiOCl, as the sole product, was prepared when designating the reaction temperature ranging from room temperature to 100 °C, regardless of the BiCl₃-to-NaOH mole ratio; on the other hand, BiOCl, BiVO₄, and δ-Bi₂O₃ nanocrystals could be selectively prepared at 140-180 °C, depending on the BiCl₃-to-NaOH mole ratio in solution. Significantly, we first report on fabricating δ-Bi₂O₃ sample, the high-temperature cubic phase commonly stabilized at 730-824 °C, at the low reaction temperature of 140-180 °C under solution-phase synthetic conditions. In addition, the δ-Bi₂O₃ sample exhibits strong emission at room temperature.     

Conversion of alkylmercaptans in the presence of γ-Al2O3

In the presence of -Al₂O₃ at 200–500°C methylmercaptans quantitatively transform into dimethyl sulfides with almost equilibrium degrees of conversion. 100% selectivity towards diethyl sulfide is observed when ethylmercaptan conversion amounts to about 50% of its equilibrium value. In more severe conditions, dimethyl- and diethyl sulfides convert with eliminating hydrocarbons and H₂S. Selectivity towards diisopropylsulfide is as high as 30% with isopropylmercaptane conversion up to 25%; the reaction follows a parallel-consecutive scheme.

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-Al₂O₃ 200–500°C . 100% 50% . - H₂S. 30% 25%, - .

     

Dehydrogenation of Isobutane Over V2O5/γ-Al2O3 Catalyst

The effect of the type of the support and the amount of V₂O₅ loading on the activity of V₂O₅/γ-Al₂O₃ catalyst for the dehydrogenation of isobutane have been investigated. Based on the experimental results of TPR, XRD and ESR spectroscopy, it is suggested that there are strong interactions between vanadia and carrier and that the V⁴⁺ species on the surface is the active site of V₂O₅/γ-Al₂O₃ for this reaction. This revised version was published online in June 2006 with corrections to the Cover Date.