Structure and electrical properties of Y,Fe-based perovskite mixed conducting composites fabricated by a modified polymer precursor method

In this work, samples of Y_0.07Sr_0.93Ti_1-xFe_xO_3-δ with 20, 40, 60 and 80 mol% of iron amount were prepared by a low-temperature polymer precursor method. The SEM-EDS analysis proved that analyzed Y_0.07Sr_0.93Ti_1-xFe_xO_3-δ samples were composites of two Ti- and Fe-rich perovskite samples. This kind of composite consists of two phases in which one has a good ionic and the other electronic conductivity, which makes such a composite a potential mixed ionic and electronic conductors (MIECs) material. The total electrical conductivities of analyzed samples were measured in air atmosphere (cathode conditions in Solid Oxide Fuel Cell). The values changed from ∼10⁻³ to 10⁻¹ S cm⁻¹ and depended on the ratio between two observed perovskite phases. The 0.12 S cm⁻¹ conductivity value at 800 °C for sample with the highest amount of Fe-rich perovskite in the structure makes this composite material a candidate for air electrode in electrochemical devices.     

Revealing the unexpected promotion effect of EuOx on Pt/CeO2 catalysts for catalytic combustion of toluene

Pt/Eu₂O₃-CeO₂ materials with different Eu concentrations were prepared and applied to toluene destruction, and the remarkable promotion impact of EuO_x on Pt/CeO₂ can be observed. The characterization results reveal that the presence of EuO_x significantly enhances the redox property, lattice O concentration, and Ce³⁺ ratio of the Pt/CeO₂ material, which facilitates the dispersion and activity of Pt active sites and thus accelerates the decomposition process of toluene. Among all catalysts, a sample with an Eu content of 2.5 at.% (Pt/EC-2.5) possesses the best catalytic activity with 0.09 vol% of toluene completely destructed at 200 °C under a relatively high GHSV of 50000 h^?1. The possible reaction pathway and mechanism of toluene combustion over Pt/Eu₂O₃-CeO₂ samples are presented according to in-situ DRIFTS, which confirms that the toluene oxidation process obeys the Mars-van Krevelen mechanism with aldehydes and ketones as primary organic intermediates.     

Neutron and X-ray diffraction study on polymorphism in lithium orthotantalate,Li3TaO4

The structures of the low-and high-temperature modifications of lithium orthotantalate, Li₃TaO₄, have been determined by neutron and X-ray diffraction methods. The low-temperature, or β, phase has symmetry $\text{C2}\text{c}$ and lattice parameters a₁ = 8.500(3), b₁ = 8.500(3), c₁ = 9.344(3)Å, and β = 117.05(2)°. The high-temperature, or α, phase has symmetry P2 and lattice parameters a_h = 6.018(1), b_h = 5.995(1), c_h = 12.865(2)Å, and β_h = 103.53(2)°. Both structures are ordered. The β-phase has a rock salt-type structure with a 3 : 1 ordering of the Li⁺ and Ta⁵⁺ ions. Its structure can be generated from the low-temperature modification by means of a complex pattern of shifts of the Ta⁵⁺ ions.     

Heat of immersion of iron(III) oxides in water at 25°C

The heat of immersion in water was measured at 25°C for three iron(III) oxides using a twin-type microcalorimeter. One of the samples was commercial α-Fe₂O₃ (sample C) and the other two (samples M and F) were prepared by calcining magnetite and iron(III) hydroxide in air at various temperatures, T_p, from 300 to 700°C. The samples were evacuated at outgassing temperature, T_o, between room temperature and 500°C at a pressure of 1 × 10^?2?2.7 × 10^?2N m^?2 for 6 h. The heat of immersion, h_i(J m^?2), of samples C and M increased with an increase in T_o and showed the maximum h_i at T_o =400°C, while sample F did not show the maximum up to T_o =500°C. The systematic correlation was not observed between h_i and T_p of sample F. The heat of reproduction of the surface hydroxyl group on sample F was approximately estimated as 6.6 × 10⁴ J mole^?1 H₂O.     

纳米片聚结Co3O4微球催化甲苯燃烧

采用乙二胺辅助的水热法制备了纳米片聚结的Co₃O₄微球. 利用多种分析技术表征了其物化性质,并评价了其对甲苯燃烧的催化活性. 结果表明,由添加1.0 ml乙二胺经140 ℃水热处理12 h后制得的Co₃O₄样品呈纳米片聚结的微球状表面形貌. Co₃O₄微球样品的比表面积约为66 m² g^-1. 与体相Co₃O₄样品相比,Co₃O₄微球样品具有较高的氧吸附物种浓度和较好的低温还原性. 当空速为20000 ml g^-1 h^-1时,在Co₃O₄微球样品上甲苯转化率达到50%和90%时的反应温度分别为230和254 ℃. 这与该样品具有较大的比表面积、较高的氧吸附物种浓度和较好的低温还原性相关.     

Mercury forms and their transformation in pyrite under weathering

Pyrite is considered to be the major carrier of mercury in coal. Here, the chemical characteristics of two natural pyrite samples of different weathering degrees were characterized by time-of-flight secondary ion mass spectrometry (TOF-SIMS). Thermal stability of Hg was also analyzed via temperature programmed desorption experiment (TPD). Characteristic ions such as S⁻, Fe⁺, FeS⁻, and FeS₂⁻ were detected on the surface of fresh pyrite. The release temperature of Hg ranged between 180°C and 300°C, and the characteristic peak of black HgS was recorded. In addition, abundant Fe₂O₃⁻, FeSO⁻, SO₄⁻, and HSO₄⁻ were detected on the surface of weathered pyrite, and the release temperature of Hg therein was mainly distributed at 260°C to 380°C and 520°C to 600°C, corresponding to the characteristic peaks of red HgS and HgSO₄, respectively. The results show that pyrite is acidified during weathering and that Hg forms in pyrite are transformed from the original state (HgS) to HgSO₄.     

Na3GdCl6: Einkristalle der Tieftemperaturform bei der metallothermischen Reduktion von GdCl3 mit Na

Na₃GdCl₆: Single Crystals of the Low Temperature Form by Metallothermic Reduction of GdCl₃ with Na Single crystals of Na₃GdCl₆-I (low-temperature form, transition to form II at 205°C) are obtained by reaction of GdCl₃ with Na (tantalum tube, 700°C, 9 d). The crystal structure [a = 700.72(8), c = 1879.1(3) pm, c/a = 2,682, V_m = 160.40(3) cm³ mol^?1, trigonal, R3 (No. 148), Z = 3] may be derived from the LiSbF₆ type: Na2 ? Li Gd ? Sb, Cl: ¨AB¨ or h₆, with two Na 1 statistically distributed over four “octahedral” in terstices.     

Effect of Bismuth Oxide Particles Size on the Thermal Excitation and Combustion Properties of Thermite Systems

The influence of Bi₂O₃ particles size at the sub-micron scale on the thermal excitation threshold and combustion performance of nano-thermite systems was investigated. Three formulas were designed and prepared, Al(100 nm)/Bi₂O₃(170 nm), Al(100 nm)/Bi₂O₃(370 nm) and Al(100 nm)/Bi₂O₃(740 nm). The samples were characterized and tested by SEM, XRD, and DSC techniques. Electrical ignition and combustion experiments were performed. The results showed that with the increase of the particle size of Bi₂O₃, in the case of slow linear heating, the exothermic heat decreased (1051.2 J g⁻¹, 527.3 J g⁻¹ and 243.6 J g⁻¹) and the thermal excitation threshold temperature increased (564.52 °C, 658.1 °C and 810.9 °C). Simultaneously, the state of the thermite reaction correspondingly changed to solid-solid, liquid-solid and liquid-liquid thermite reaction. In the case of rapid heating , the increase in particle size increased the excitation current (0.561A, 0.710A and 0.837A). During the combustion process, the thermite system with the smallest Bi₂O₃ particle size showed the largest combustion rate, and that with the largest particle size had the longest combustion duration.     

Synthesis of two novel cobalt complexes and their crystal structures

Two new cobalt complexes were successfully synthesized from the reaction of binaphthyl Schiff base 2 with Co(OAc)₂ in the presence of sodium methoxide at 80 °C for 24 h and Co(acac)₃ in toluene under reflux. Their unique crystal structures are unambiguously disclosed by X‐ray analysis. Complex 3 is triclinic, space group P1 , unit cell dimensions a = 10.742(2) Å, b = 11.153(2) Å, c = 12.715 Å, α = 79.865(3) °, β = 76.053 °, γ = 72.532(4) °, volume 1401.3(5) ų, Z = 2. Complex 4 is triclinic, space group P1 , unit cell dimensions a = 10.801(2) Å, b = 12.554(3) Å, c = 15.219(3) Å, α = 105.672(4) °, β = 103.048 °, γ = 104.594(4) °, volume 1824.8(7) ų, Z = 2, calculated density 1.428 Mg m⁻³. Copyright © 2003 John Wiley & Sons, Ltd.     

Direct observation and stability of active species in cationic polymerization: A reexamination of the polymerization of styrene initiated by triflic acid

Polymerization of styrene initiated by triflic acid in CH₂Cl₂ solution was reexamined, using a new stopped-flow device working in high purity conditions over a wide temperature range. Monomer and styryl cation were followed simultaneously through their respective absorbances at 290 and 340 nm. Initiation is very rapid, and cations concentration reaches a plateau the duration of which is depending on temperature. In our conditions (I₀ = 0.5 − 9.10⁻³M, M₀/I₀ = 1 to 20), cations concentration is so low at room temperature that it is almost unmeasurable. At −65°C, it is 100 times higher, remains constant for several seconds and complete termination takes place within a minute or more. Such a profile of cation evolution agrees with an equilibrium situation between initiation and a much more temperature-dependent backward deprotonation. Apparent initial rate of initiation is first order with respect to monomer, but the order with respect to initiator was found very high and variable with temperature (from 4.5 at −65°C to 3 at −20°C). This supports the presence, even if they are in low concentration, of acid high agregates, the reactivity of which increases with size. A first order monomer consumption is observed during the plateau, which leads to k_p values ranging from 10³ at −65°C to 9.10⁴ M⁻¹.s⁻¹ at −10°C (Ep^# = 43 kJ.mol⁻¹). The disappearance of cations, which follows the plateau, slows down and becomes unimolecular when monomer consumption is complete, and k_t values range from 6.10⁻²s⁻¹ at −65°C to 1.2s⁻¹ at −23°C (E_t^# = 33 kJ.mol⁻¹).     

In Situ Preparation of CsPbBr3@CsPb2Br5 Composite Assisted with Water as a Highly Efficient and Stable Catalyst for Photothermal CO2 Hydrogenation

Lead halide perovskite has triggered a lot of research due to its superior optical properties. However, halide perovskite materials have poor environmental stabilities and are easily affected by external factors such as water and heat, resulting in structural decomposition and performance failure. Contrary to this commonplace concept, it is found that CsPbBr₃ (CPB) can convert to CsPb₂Br₅ (CP2B5) partially when meeting a small amount of water, and the CsPbBr₃@CsPb₂Br₅ (CPB@CP2B5) composite is synthesized by an in situ method accordingly. The CPB@CP2B5 composite shows an enhanced catalytic performance compared with pure CPB, as well as a dramatically synergistic effect of photo and thermal for catalytic CO₂ hydrogenation. The CO production rate of CPB@CP2B5 is determined as 69 μmol g⁻¹ h⁻¹ under light irradiation at 200 °C, which is 156.8 and 43.4 times higher than that under pure photo (0.44 μmol g⁻¹ h ⁻¹) and pure thermal (1.59 μmol g⁻¹ h ⁻¹) condition, respectively. Meanwhile, the CPB@CP2B5 sample is also stable, which shows no significant decline in the catalytic activity during 8 cycles of repeated experiments. The probable mechanism is explored by utilizing a series of in situ characterizations.     

Polyimide–Silica Gel Hybrids Containing Metal Salts: Preparation via the Sol–Gel Reaction

A facile preparation of polyimide–silica gel hybrids by the simultaneous in-situ formation of polyimides during the hydrolysis–condensation of tetramethoxysilane (TMOS) is reported here. The hydrolysis and condensation of TMOS was carried out in a solution of DMAc containing 5% LiCl, CaCl₂ or ZnCl₂ and the seven-membered cyclic polyimide intermediate. The seven-membered cyclic intermediates, precursors of polyimides, were derived from the low-temperature polycondensation of dianhydrides [benzophenonetetracarboxylic dianhydride (BTDA), pyromellitic dianhydride (PMDA), and 4,4-bis(hexafluoroisopropylidene)phthalic dianhydride (6FDA)] and di-isocyanates [isophorone di-isocyanate (IPDI), toluene di-isocyanate (TDI), hexamethylene di-isocyanate (HDI) and 4,4′-diphenylmethane di-isocyanate (MDI)]. These intermediates could readily be converted to the corresponding polyimides. Films were cast from the resulting mixtures and the solvent was gradually evaporated at 130 °C to result in the formation of clear, transparent, pale yellow or amber-colored hybrid films in which the salts were dispersed at the molecular level. Pyrolysis of polyimide–silica gel hybrids at 600 °C gave mesoporous silica. Silica gel obtained from hybrids HPI-8 (containing no salt) and HPI-11 (containing ZnCl₂) had a pore radius (BJH method) of 2.9 nm, while that from hybrid HPI-9 (containing LiCl) had a pore radius of 11.4 nm. The surface areas (BET method) obtained were 203 m² g⁻¹, 19 m² g⁻¹ and 285 m² g⁻¹, while the pore volumes were 0.373 cm³ g⁻¹, 0.158 cm³ g⁻¹ and 0.387 cm³ g⁻¹, respectively, for samples obtained from hybrids HPI-8, HPI-9 and HPI-11. © 1997 by John Wiley & Sons, Ltd.     

A Thermal And Structural Study on Lanthanum Hexacyanocobaltate(III) Pentahydrate. Part II

The thermal dehydration of La[Co(CN)₆]⋅5H₂O proceeded through at least three stages from the temperature range of30~230°C, and an abrupt mass loss occurred around 350°C and the perovskite type oxide,LaCoO₃ was obtained at 1000°C. After dehydration, the color of the anhydride changed from white to pale blue around 230°C and furthermore, the color changed to blue around 290°C. These color changes were discussed on the basis of the changes of coordination structures around Co ions. In La[Co(CN)₆]⋅5H₂O, Co³⁺ ions lie at the center of the O_h crystal field consisted of six CN^– ions. However, in the pale blue specimen, Co³⁺ ions were situated in the center of D_4h crystal field which was distorted the O_h one by lengthening of the trans CN^– ions along z-axis. In the blue specimen, Co³⁺ ions were reduced to Co²⁺ ions which were situated in the T_d crystal field formed by four CN^–ions as [Co(CN)₄]^2–. This revised version was published online in July 2006 with corrections to the Cover Date.     

Subnanometer Bimetallic Platinum–Zinc Clusters in Zeolites for Propane Dehydrogenation

Propane dehydrogenation (PDH) has great potential to meet the increasing global demand for propylene, but the widely used Pt-based catalysts usually suffer from short-term stability and unsatisfactory propylene selectivity. Herein, we develop a ligand-protected direct hydrogen reduction method for encapsulating subnanometer bimetallic Pt–Zn clusters inside silicalite-1 (S-1) zeolite. The introduction of Zn species significantly improved the stability of the Pt clusters and gave a superhigh propylene selectivity of 99.3 % with a weight hourly space velocity (WHSV) of 3.6–54 h⁻¹ and specific activity of propylene formation of 65.5 mol g_Pt⁻¹ h⁻¹ (WHSV=108 h⁻¹) at 550 °C. Moreover, no obvious deactivation was observed over PtZn4@S-1-H catalyst even after 13000 min on stream (WHSV=3.6 h⁻¹), affording an extremely low deactivation constant of 0.001 h⁻¹, which is 200 times lower than that of the PtZn4/Al₂O₃ counterpart under the same conditions. We also show that the introduction of Cs⁺ ions into the zeolite can improve the regeneration stability of catalysts, and the catalytic activity kept unchanged after four continuous cycles.     

Anionic polymerization of dodecamethyl-cyclohexasiloxane (D6) with lithium cryptate as a counterion

A kinetic study of the anionic polymerization of dodecamethylcyclohexasiloxane (D₆) has been carried out in toluene at 25°C with the cryptate Li⁺ + [211] as the counterion. The rate constants of propagation of D₆ and of the formation of cyclic oligomers have been determined. The results are in good agreement with those reported previously for the anionic polymerization of D₃ and D₄ under the same conditions. The rate constants of propagation and of formation of D₆ have been found to be equal to 1.1 l-mol⁻¹.h⁻¹ and 0.05 h⁻¹, respectively. In the case of the anionic polymerization of cyclosiloxanes with Li⁺ + [211] as the counterion, the order of reactivities of D_x as a function of × is as follows:      

NiMoW/P-Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Hydrotreating Catalysts: Influence of the Mo/W Ratio on the Hydrodesulfurization and Hydrogenation Activity

A series of NiMoW/P-Al₂O₃ catalysts with different Mo/W ratios (sample containing Mo only, Mo/W = 2: 1, Mo/W = 1: 1, Mo/W = 1: 2, and sample containing W only; P₂O₅ content of the support 2.0 wt %) were synthesized. The precursors of the active phase were the heteropoly acids H₃PMo₁₂O₄₀?nH₂O and H₃PW₁₂O₄₀?nH₂O, and also nickel citrate. The sulfide phase in the samples was studied by high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy; the catalytic activity of the samples in dibenzothiophene hydrodesulfurization and naphthalene hydrogenation was determined. For the dibenzothiophene hydrogenolysis in the presence of quinoline and naphthalene (content in the model mixture, wt %: dibenzothiophene 0.3, naphthalene 1.5, and quinoline 0.5), k_HDS for different samples is in the range 17.6–42.5 h^–1 at 275°C and 24.6–45.9 h^–1 at 300°C. For the naphthalene hydrogenation, k_HYD varies from 0.79 to 1.89 h^–1 at 275°C and from 0.91 to 3.78 h^–1 at 300°C. The sample based on molybdenum showed the highest activity in hydrogenation and hydrodesulfurization.     

Low Bandgap 2D Perovskite Single Crystal with Anomalous-large Charges/ions Collection Ratio for Ultra-sensitive and Stable X-ray Detectors

The low-dimensional halide perovskites have attracted increasing attention due to their improved moisture stability, reduced defects, and suppressed ions migration in many optoelectronic devices such as solar cells, light-emitting diodes, X-ray detectors, and so on. However, they are still limited by their large band gap and short charge carriers’ diffusion length. Here, we demonstrate that the introduction of metal ions into organic interlayers of two-dimensional (2D) perovskite by cross-linking the copper paddle-wheel cluster-based lead bromide ([Cu(O₂C−(CH₂)₃−NH₃)₂]PbBr₄) perovskite single crystals with coordination bonds can not only significantly reduce the perovskite band gap to 0.96 eV to boost the X-ray induced charge carriers, but can also selectively improve the charge carriers’ transport along the out-of-plane direction and blocking the ions motion paths. The [Cu(O₂C−(CH₂)₃−NH₃)₂]PbBr₄ single-crystal device can reach a record charges/ions collection ratio of 1.69×10¹⁸±4.7 % μGy_air⁻¹ s, and exhibit a large sensitivity of 1.14×10⁵±7% μC Gy_air⁻¹ cm⁻² with the lowest detectable dose rate of 56 nGy_air s⁻¹ under 120 keV X-rays irradiation. In addition, [Cu(O₂C−(CH₂)₃−NH₃)₂]PbBr₄ single-crystal detector exposed to the air without any encapsulation shows excellent X-ray imaging capability with long-term operational stability without any attenuation of 120 days.     

Catalytic toluene oxidation over the three-dimensionally ordered macroporous EuFeO3 catalysts fabricated by the sucrose-assisted polymethyl methacrylate-templating method

Three-dimensionally macroporous perovskite-type oxides EuFeO₃ (EFO-3DOM, EFO-sucrose-1, EFO-sucrose-2, and EFO-sucrose-3, respectively) have been prepared using the polymethyl methacrylate-templating method in the absence or presence of sucrose. Physicochemical properties of the materials were characterized by means of a number of analytical techniques, and their catalytic activities were evaluated for the total oxidation of toluene. It is shown that all of the EFO samples were of single-phase orthorhombic crystal structure with a 3DOM architecture. The sucrose addition during the preparation process had a great effect on the surface area and porous structure of the final product. A clear correlation of surface area, surface oxygen species concentration, and low-temperature reducibility with the catalytic performance was observed. The EFO-sucrose-1 catalyst performed the best, giving the T_50% and T_90% of 312 and 347 °C at space velocity = 20,000 mL/(g h), respectively. The apparent activation energies of the 3DOM-structured EFO samples were in the range of 82–97 kJ/mol. It is concluded that the higher surface area and oxygen adspecies concentration and better low-temperature reducibility account for the good catalytic activity of EFO-sucrose-1.     

A cobalt-free electrode material La0.5Sr0.5Fe0.8Cu0.2O3 − δ for symmetrical solid oxide fuel cells

Cobalt-free perovskite oxide La_0.5Sr_0.5Fe_0.8Cu_0.2O_3 − δ (LSFC) was applied as both anode and cathode for symmetrical solid oxide fuel cells (SSOFCs). The LSFC shows a reversible transition between a cubic perovskite phase in air and a mixture of SrFeLaO₄, a K₂NiF₄-type layered perovskite oxide, metallic Cu and LaFeO₃ in reducing atmosphere at elevated temperature. The average thermal expansion coefficient of LSFC in air is 17.7 × 10^− 6 K^− 1 at 25 °C to 900 °C. By adopting LSFC as initial electrodes to fabricate electrolyte supported SSOFCs, the cells generate maximum power output of 1054, 795 and 577 mW cm^− 2 with humidified H₂ fuel (~ 3% H₂O) and 895, 721 and 482 mW cm^− 2 with humidified syngas fuel (H₂:CO = 1:1) at 900, 850 and 800 °C, respectively. Moreover, the cell with humidified H₂ fuel demonstrates a reasonable stability at 800 °C under 0.7 V for 100 h.     

Molecular dimensions of polydipropylsiloxamer

The molecular dimensions of polydipropylsiloxamer were studied by intrinsic viscosity measurements in toluene and in 2-pentanone. The relationships between the molecualr weight and the intrinsic viscosity were found to be: [η]_25°C., toluene = 4.35 × 10^?4 M^0.58; [η]_θ(10°C.), toluene = 1.09 × 10^?3 M^0.5; [η]_θ(76°C.), 2-pentanone = 8.71 × 10^?4 M^0.5. This held reasonably well for molecular weights from 25,000 to 3000,000. The root-mean-square end-to-end length ratio, (r₀² /M)^1/2 as calculated from the constant K, exceeds the free rotation value by approximately 100%. The disparity is greater than that found with polydimethylsiloxamer, indicating a lower degree of flexibility for the polydipropylsiloxamer. This is largely due to the short range steric interaction between near neighboring units of the chain. Gel permeation chromatography was also employed to demonstrate the lower degree of flexibility for polydipropylsiloxamer as compared with polydimethylsiloxamer.