The study of amorphous La@Mg catalyst for high efficiency hydrogen storage

Amorphous catalysts have a large number of catalytic active sites. Here, we report a magnesium composite trace lanthanum catalyst (La@Mg), in which La and Mg layers form amorphous Mg–La compound on the surface of layered Mg. The test shows this La@Mg has hydrogen storage capacity of about 7.6 wt% and hydrogen desorption of 7.2 wt%, higher than that of crystalline La@Mg and sole Mg, rapid absorption/desorption kinetic and stable reversible absorption/desorption cycles. La@Mg exhibits an optimistic hydrogen storage performance than Mg-based materials previously reported in the literature. Combined with theoretical calculations, it is shown that the amorphous Mg–La has an catalysis on hydrogen storage performance of La@Mg system, which contributing to the dispersion of Mg and providing channels for hydrogen diffusion, facilitating hydrogenation by accelerating H atoms diffuse between the subsurface and the surface. This work provides experiment and mechanism guidance for the development of efficient hydrogen storage materials.     

Effect of Al(H2PO4)3/Zn/B4C doped resin on properties and microstructure of unfired Al2O3–C slide plate materials

The unfired Al₂O₃–C slide plates have the advantages of energy saving, environment friendly, efficiency and relatively low-cost. However, the decomposition and oxidation of the phenol-formaldehyde (PF) resin at elevated temperatures deteriorate the properties and decrease service life of the unfired slide plates. In order to improve the property of resin, the doped PF resin is prepared by incorporating Al(H₂PO₄)₃, Zn and B₄C powders. The effects of the doped resin on medium-high temperature properties and microstructure of the unfired slide plate materials have been investigated. The results show that Zn and B₄C doped resin contributes to notable increasing the density and strength properties at medium temperature, because Zn and B₄C easily oxide and thus protect resin from oxidation, leading to form a dense structure. Zn and B₄C doped resin can significantly improve hot modulus of rupture of the materials at 1400 °C, which is due to Zn and B₄C react with oxidative gases leading to increase in concentration of C(g), CO and N₂, Al and Si would react with C(g), CO(g) and N₂(g) to form AlN and SiC whiskers creating strengthening effect. Specimens with Zn and B₄C doped resin addition have good oxidation resistance at 1500 °C, because Zn and B₄C in the surface of the material react with O₂ to form ZnAl₂O₄ or mullite containing dense glass film, which would retard O₂ diffusion into the inner of the specimens.     

Effect of annealing in argon atmosphere on the properties of zinc oxide nanoparticles doped with Mn(II) and Co(II) ions prepared in solvothermal synthesis

Methods of preparation and application of zinc oxide nanoparticles doped with Mn(II) and Co(II) ions are presented and discussed in the paper. Part one shows the results of the solvothermal synthesis of zinc oxide nanoparticles doped with Mn(II) and Co(II) ions. The effect of process parameters on the properties of doped nano zinc oxide has been identified. We also examined the impact of annealing in argon atmosphere of doped zinc oxide nanoparticles on physicochemical properties. Morphology analysis was performed using scanning microscopy and molecular analysis was performed using by inductively coupled plasma - optical emission spectrometry. The zeta potential was measured for samples annealed in argon atmosphere and for samples not annealed. Phase analysis was performed by x-ray diffraction. Based on this analysis, the lattice parameters were determined.     

Preparation of metal ion (Fe and Ni) doped TiO2 nanoparticles supported on ZSM-5 zeolite and investigation of its photocatalytic activity

Metal ion doped TiO₂ nanoparticles supported on ZSM-5 zeolite (M-TiO₂/ZSM-5 composites, M = Fe or Ni) were synthesized by hydrothermal method. The prepared composites were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV–vis diffuse reflectance spectra (DRS). The photocatalytic activities of composites were evaluated by degradation of yellow GX aqueous solution under ambient condition. Fe-TiO₂/ZSM-5 composite showed to be more efficient catalyst for degradation of dye molecules as compared with Ni-TiO₂/ZSM-5 and TiO₂/ZSM-5. Its higher photocatalytic activity is attributed to the effective separation of charge carriers that will be discussed in this paper in detail.     

Band-filling effect on the light emission spectra of InGaN/GaN quantum wells with highly doped barriers

We investigate spectra of InGaN/GaN quantum well (QW) light-emitting diode (LED) structures with heavily doped barriers at different excitation levels. We model the spectral shape and energy position in frames of dominating mechanism of free electron recombination accounting for the influence on the potential width of the QW of the random impurity potential penetrating from the doped barriers. The blue shift at high excitation is supposed to be due to the filling of the conduction band with degenerate 2D non-equilibrium electrons. A structure in the emission bands is observed and it is assumed to be a result from step-like 2D density of states in the QW. A good accordance is obtained between the calculated and experimental spectra assuming that the barriers are graded.     

杂质离子的微观状态与掺杂硅酸钙颜色特性的关系

本文利用固体谱学技术系统地研究了第四周期过渡金属离子在硅酸三钙(C_3S)和硅酸二钙(C_S)中的存在状态,及对硅酸钙颜色特性的影响。利用晶体场理论解释了掺杂硅酸钙的光学吸收光谱和电子顺磁共振谱,并由此半定量地计算了对装饰水泥的颜色特性有较大影响的五个过渡金属元素铬、锰、铁、钴、镍在硅酸钙中的晶体场参数,确定了它们的价态、配位状态和置换方式,提出了生产不同颜色的装饰水泥所应遵循的一些原则。本文还根据光学反射光谱数据,定量计算了掺杂硅酸钙水化前后,及经过人工气候老化后的色度学参数。探讨了掺杂离子种类、掺杂量和矿物种类对装饰水泥颜色特性的影响,探讨了硅酸盐彩色水泥退色的原因。并提出了彩色水泥发展的方向。     

锂离子电池正极材料LiMn2O4的电化学性能

锂掺杂到尖晶石型锂锰氧化物中时,锂掺杂量对材料的结构、初始容量及循环性能都有明显的影响.利用循环伏安法、恒电流充放电法研究了尖晶石型锂锰氧化物的电化学性质,并从结构化学的角度分析了充放电机理.结果表明,过量锂的锂锰氧化物具有两个氧化还原峰,放电容量大,可逆性好.当Li1+xMn2O4中的x=0.05时,其容量最高,稳定性最好.     

尖晶石型LiMn2O4的制备和性能研究

利用溶胶-凝胶法制备镧掺杂的锂离子电池正极材料尖晶石型LiLa0.005Mn1.995O4,利用X衍射、循环伏安、充放电测试、交流阻抗等手段对其进行了研究。结果表明样品呈良好的尖晶石结构，在0．3mA／cm^2和3．0～4．1V条件下恒流充放电，其首次放电容量大于110mAh／g，并具有较好的循环可逆性。活性物质在不同的电位下有不同的电化学特征，交流阻抗谱明显不同，并对其进行了合理的解释。     

Structure-activity relationship in water-gas shift reaction over gold catalysts supported on Y-doped ceria

The utilization of pure hydrogen as an energy source in fuel cells gave rise to renewed interest in developing active and stable water-gas shift catalysts. Gold catalysts have proven to be very efficient for water-gas shift reaction at low temperature. The aim of the present study was to investigate the effect of:(i) different preparation methods(impregnation and coprecipitation) to obtain a modified ceria support,and(ii) the amount of Y_2 O_3(1.0 wt%, 2.5 wt%, 5.0 wt% and 7.5 wt%) as dopant on the water-gas shift activity of Au/CeO_2 catalysts. An extended characterization by means of S_(BET), XRD, HRTEM/HAADF, FTIR,H_2-TPR and CO-TPR measurements in combination with careful evaluation of the catalyst behavior allowed to shed light on the parameters governing the water-gas shift activity. The catalysts show very high activity(90% CO conversion) in the temperature range 180-220 ℃,with a slightly better performance of the gold catalysts on supports prepared by impregnation. The decreased activity with increasing Y_2 O_3 concentration is related to the hindering of oxygen mobility due to ordering of surface oxygen vacancies in vicinity of segregated Y~(3+). The effect of catalyst pre-treatments and the stability of the best performing samples were examined as well.     

Kinetics and mass transfer effects in the oxidation of ferrous sulfate over doped active carbon catalysts

Ferric sulfate is used in water purification. The oxidation of ferrous sulfate, FeSO₄, to ferric sulfate in acidic aqueous solutions of H₂SO₄ over finely dispersed active carbon particles was studied in a vigorously stirred batch reactor. Molecular oxygen was used as the oxidation agent and two kinds of catalysts were utilized: active carbon, doped active carbon. Both active carbon and doped active carbon catalysts enhanced the oxidation rate considerably.

Systematic kinetic experiments were carried out at the temperature and pressure ranges of 60–100°C and 4–10 bar, respectively. The results revealed that both non-catalytic and catalytic oxidation of Fe²⁺ take place simultaneously. The experimental data were fitted to rate equations, which were based on a plausible reaction mechanism: adsorption of dissolved oxygen on active carbon, electron transfer from Fe²⁺ ions to adsorbed oxygen and formation of surface hydroxyls. A comparison of the Fe²⁺ concentrations predicted by the kinetic model with the experimentally observed concentrations indicated that the mechanistic rate equations were able to describe the intrinsic oxidation kinetics of Fe²⁺ over pure active carbon and doped active carbon catalysts.