Construction of macromolecular model and analysis of oxygen absorption characteristics of Hongyang No. 2 coal mine

Understanding the molecular structure characteristics of coal from the molecular level is of great significance for realizing rational utilization and efficient transformation of coal. The molecular structure of coal samples from 1304 working face in No.13 coal seam of Hongyang No.2 Mine (HY) was studied by industrial analysis, elemental analysis, Nuclear magnetic resonance carbon spectroscopy (¹³C NMR) and Fourier transform infrared spectroscopy (FTIR). The results show that the aromatic compounds in coal samples of HY are mainly naphthalene ring structures. The aliphatic structure mainly consists of methyl, ethyl side chains and cycloalkanes. The ratio of aromatic bridge carbon to weekly carbon in molecular structure is 0.17. Oxygen atoms exist in the form of carbonyl, hydroxyl, and ether bonds, nitrogen atoms exist in the form of pyridine and pyrrole respectively, and sulfur atoms exist in the form of thiophene. Based on this, the planar structure model of coal macromolecule in HY is constructed, and its molecular formula is C₁₂₉H₈₈O₂₉N₂S, and its molecular weight is 2160. The structure optimization and annealing kinetics simulation of a single macromolecule model were carried out, and a stable three-dimensional coal model of HY was obtained. In addition, the oxygen absorption characteristics of coal samples in HY were studied by molecular dynamics and quantum chemistry. The results show that the adsorption capacity of the Wiser model is less than that of HY coal model. This is because, compared with the Wiser model, the content of oxygenated aliphatic hydrocarbons in the molecular structure of HY coal is higher, and the condensation degree of polycyclic aromatic hydrocarbons is lower. Due to the stronger physical adsorption capacity of hydroxyl, ether bond, and carbonyl on O₂, HY Mine has stronger physical adsorption capacity on O_2.     

均相催化剂催化氧气氧化生物质制备甲酸

甲酸是一种重要的化工原料,以可再生生物质为原料,通过催化氧气氧化制备甲酸具有重要意义。对于不溶于水的生物质原料的转化,采用可溶于水的均相催化剂体系证明是有效的。本文总结了均相催化剂体系(包括含钒杂多酸、含钒杂多酸+H₂SO₄、含钒杂多酸基离子液体、NaVO₃+H₂SO₄、VOSO₄、NaVO₃-FeCl₃+H₂SO₄、FeCl₃+H₂SO₄等)在催化氧气氧化生物质(包括生物质模型化合物、纤维素、木材、秸秆和玉米芯等)制备甲酸方面的研究,分析了其转化的过程和机理。最后,指出了目前催化氧化生物质制备甲酸存在的问题和挑战。     

微波热冲快速制备二维多孔La0.2Sr0.8CoO3钙钛矿用于高效电催化析氧反应

析氧反应(OER)被认为是电解水的关键限制步骤,已被广泛作为清洁能源方式用于解决能源和环境问题。钙钛矿氧化物(ABO₃)具有可调的电子结构、高灵活性的元素组成,能在OER中表现出良好的催化活性。然而,钙钛矿氧化物的合成通常需要经历长时间的高温,极易导致金属的聚集和影响材料的本征活性。气相微波技术可以显著缩短热处理时间,从而减少相关的碳排放。这项技术不仅解决了对碳中性过程日益增长的需求,而且还增加了对合成的控制,以避免产品的不良团聚。本文采用微波热冲法快速制备了二维(2D)多孔La_0.2Sr_0.8CoO₃钙钛矿。伴随微波过程的快速熵增可以有效地暴露La_0.2Sr_0.8CoO₃结构中丰富的活性位点。此外,高能微波冲击过程可以精准地将Sr²⁺引入到LaCoO₃的晶格中,通过增加Co的氧化态来增加氧空位量。这种锶元素取代镧引入的氧空位能极大提高催化剂的本征催化活性。对于碱性电解液中的OER应用,制备的La_0.2Sr_0.8CoO₃在10 mA∙cm⁻²下展现出了360 mV的过电位,Tafel斜率为76.6 mV∙dec⁻¹。且在经历30000秒的长时间循环测试后仍能维持初始电流密度的97%。这项研究为高活性二维钙钛矿的合成提供了一种简便、快速的策略。     

Experimental and modeling study of oxygen permeation modes for asymmetric mixed-conducting membranes

An asymmetric mixed-conducting membrane consists of a thin dense layer and a porous support, and its application has drawn considerable attention, because it is expected to have a more promising potential in the practical application compared with the symmetric membrane. However, with the introduction of support in the asymmetric membrane, two possible permeation modes are produced. One mode is that oxygen permeates from the support to the thin dense layer (designated as SD mode). The other is in the direction from the thin dense layer to the support (designated as DS mode). Thus, from the viewpoint of choosing an appropriate oxygen permeation mode to make better use of the membrane, it is necessary to study the oxygen flux in these two modes. In this paper, their effects on the oxygen flux of asymmetric membranes were investigated from the experiment and the model. The modeling results showed a good agreement with the experimental data. Our study demonstrates that when the asymmetric membrane adopts the SD mode, it is beneficial for the membrane to obtain higher oxygen permeation flux.     

Oxygen production at low temperature using dense perovskite hollow fiber membranes

A dense perovskite hollow fiber made of BaCo_xFe_yZr_zO_3−δ (BCFZ) was evaluated for the oxygen separation at low temperatures (400–500 °C). An oxygen permeation flux of 0.45 ml/min cm² was obtained at 500 °C, which is the first oxygen permeation data reported at such low temperature so far. A degradation of the oxygen permeation at 500 °C was observed, but the oxygen fluxes through the hollow fiber membrane can be regenerated by thermal treatment at 925 °C for 1 h in air. Energy-dispersive X-ray spectroscopy (EDXS) shows that a strong element segregation occurs in the membrane during operation at low temperature.     

Comparison between the electrocatalytic properties of different metal ion phthalocyanines and porphyrins towards the oxidation of hydroxide

This work reports on the electrocatalytic oxidation of hydroxide using different central metal ion phthalocyanines and porphyrins immobilized on gold electrodes. The apparent electrocatalytic activity of cobalt phthalocyanine or porphyrin modified electrodes was found to be the greatest among the present series of metal ion macrocycles investigated. Copper and unmetallated phthalocyanine or porphyrin modified electrodes show no electrocatalytic behaviour towards hydroxide, such as bare gold. A possible mechanism for the enhanced reactivity of cobalt ion macrocycles towards the oxygen evolution is given. It is also stated that the electrocatalytic activity towards an adsorbate involves several aspects, such as the coordination state of the central metal ion, the nature of the ligand, the stability of the complexes, the number of d electrons, the energy of orbitals and the strength of the bonding between the central metal ion and the axial ligand.     

First-principles study of O2 adsorption and dissociation on the CuCr2O4 (100) surface

The adsorption and dissociation of molecular oxygen on spinel CuCr₂O₄ (100) surface were carried out by first-principles calculations based on density functional theory (DFT). The calculated results indicate that the Cr site is most favorable for atomic oxygen adsorption, with an adsorption energy of 402.8 kJ/mol. For molecular oxygen adsorption, there are three types of favorable interaction modes: O₂ forms bonds with the Cu site or O₂ binds to two Cr sites or O₂ interacts with both Cu and Cr sites simultaneously. The lowest activation energy (E_a = 35.4 kJ/mol) was found through exploring possible reaction pathways for O₂ dissociation. The relationship between E_a and reaction enthalpy (ΔH) for O₂ dissociation adsorption reactions fits Brønsted-Evans-Polanyi (BEP) behavior.     

Conditions for superconductivity in the electron-doped copper-oxide system, (Nd1−xCex)2CuO4+δ

We report systematic studies on the relations among the Ce^IV-for-Nd^III substitution level (x), oxygen-partial pressure (P_O2), oxygen content (4+δ), lattice parameters (a, c) and superconductivity characteristics (T_c, volume fraction) in the (Nd_1−xCe_x)₂Cu_1−yO_4+δ system which includes electron-doped superconductors. Independent of the Ce-doping level x, samples synthesized in air are found oxygen deficient, i.e. δ<0. Nevertheless, reductive annealing is needed to induce superconductivity in the air-synthesized samples. At the same time, the amount of oxygen removed upon the annealing is found very small (e.g. 0.004 oxygen atoms per formula unit at x=0.075), and consequently the effect of the annealing on the valence of copper (and thereby also on the electron doping level) is insignificant. Rather, the main function of the reductive annealing is likely to repair the Cu vacancies believed to exist in tiny concentrations (y) in the air-synthesized samples.     

Structure and magnetic properties of Ca2Fe1−xMnxAlO5+δ

Ca₂Fe_1−xMn_xAlO₅ (0?x?1) compounds were prepared by a self-combustion method under air (x=0, 0.1, 0.2 and 0.3) and nitrogen (x=0.5, 0.7 and 1.0). The samples prepared under nitrogen were successfully oxidized after short annealing under air. Both X-ray powder diffraction (XRD) Rietveld analysis and electron diffraction revealed that all compounds adopt the brownmillerite-type structure. All samples present an overall antiferromagnetic behaviour and data from magnetic measurements and Mössbauer spectroscopy allowed to conclude that the transition temperature decreases as Mn content increases for x?0.3 and increases in the case of the x?0.5 compounds. Except for x=1, chemical disorder due to the occupancy of both octahedral and tetrahedral sites by different metals as well as the competition between different moments’ orientation induce a complex magnetic behaviour characterized by magnetic frustration and canted antiferromagnetism. Mössbauer spectroscopy and chemical titrations also allowed to conclude about the preferential oxidation of Mn³⁺ over Fe³⁺, obtained by thermal treatment under air of the x=0.5 and 0.7 compositions.     

Oxygen nonstoichiometry and defect structure analysis of B-site mixed perovskite-type oxide (La, Sr)(Cr, M)O3−δ (M=Ti, Mn and Fe)

The defect chemical relationships in various B-site mixed LaCrO₃-based ceramics were investigated by means of high-temperature gravimetry. The nonstoichiometric deviation, δ, in (La_0.7Sr_0.3)(Cr_1−yTi_y)O_3−δ (y=0.1, 0.2 and 0.3) (LSCT)_, (La_0.75Sr_0.25)(Cr_0.5Mn_0.5)O_3−δ (LSCM) and (La_0.75Sr_0.25)(Cr_0.5Fe_0.5)O_3−δ (LSCF) were measured as a function of oxygen partial pressure, P_O2, at temperatures between 973 and 1373 K.The effects of partial replacement of the donor on Cr-sites were examined in LSCT. In LSCM and LSCF, effects of the partial substitution of isovalent transition metals on Cr-sites are discussed. Oxygen nonstoichiometries of various B-site mixed LaCrO₃-based ceramics were compared with those of A-site substituted perovskite-type oxides, (La_1−xSr_x)MO_3−δ (where x=0-0.3, M=Cr, Mn and Fe). The partial substitution of the different elements on Cr-sites drastically changed the P_O2 and temperature dependence of oxygen vacancy formation in LaCrO₃-based ceramics. The defect equilibrium relationships of the localized electron well explained the oxygen vacancy formation in B-site mixed LaCrO₃-based ceramics. Oxygen vacancy formation in (La_0.7Sr_0.3)(Cr_1−yTi_y)O_3−δ (y=0.1 and 0.2) and (La_0.7Sr_0.3)(Cr_0.7Ti_0.3)O_3−δ was explained by redox reaction of Cr and Ti ions, respectively. The defect equilibrium relationships of LSCM and LSCF were interpreted by redox reaction of Mn ions and Fe ions, respectively. No significant change in valence state of Cr³⁺ ions in LSCM and LSCF was confirmed under the experimental conditions.