Nanostructured catalysts for cathodes of oxygen-hydrogen fuel cells

Bimetallic catalysts platinum-cobalt, platinum-chromium, and platinum-tungsten, deposited onto highly dispersed carbon black from complex cluster-type compounds of corresponding metals with a 1: 1 atomic ratio of metals are developed. The catalysts are characterized by methods of x-ray diffraction analysis and energy dispersive analysis of x-rays. The procedure involving use of a thin-film rotating disk electrode is employed to probe kinetic parameters of the oxygen reduction reaction on the catalysts developed. The investigated binary catalysts exhibit specific electrochemical characteristics that are not inferior and, in some cases, are superior to the characteristics intrinsic to the commercial platinum catalyst E-TEK, when tested in the composition of a gas-diffusion electrode under conditions that are close to real conditions in which cathodes of oxygen-hydrogen fuel cells operate.     

SrTiO_3粉末在可见光照射下光氧化水产氧的研究

SrTiO_3粉末在FeCl_3水溶液里的悬浮体([Fe~(3+)]=1.0×10~(-3)mol/L,pH2.8,SrTiO_3含量1.25g/L)能在λ>400 nm的可见光照射下光氧化水产氧。在相同条件下SrTiO_3和WO_3粉末的混合悬浮体(SrTiO_3与WO_3含量均为1.25g/L)产氧的速率为两者单独存在时的速率之和。光声光谱实验显示SrTiO_3粉末在从溶液里吸附Fe~(3+)后对可见光的吸收大大增强,使它能在可见光下光氧化水产氧。     

纳米二氧化锆催化剂上一氧化碳加氢合成异丁烯

 考察了纳米ZrO2的制备方法及Al2O3和KOH助剂的添加对ZrO2催化\r\nCO加氢合成异丁烯反应的影响．纳米ZrO2的制备方法对ZrO2的物理性质\r\n和催化性能有较大的影响．用超临界流体干燥法干燥并在流动N2气氛中\r\n焙烧制得的ZrO2催化剂对异丁烯具有较高的选择性．Al2O3和KOH助剂表\r\n现出非常优良的助剂效应，在大幅度提高催化剂对i－C4烃选择性的同\r\n时保持了和ZrO2同样高的催化活性．催化剂的酸碱性表征结果表明，酸\r\n碱性对催化剂的催化性能影响很大，催化剂上适宜的酸碱数量和酸碱比\r\n例是影响其催化CO加氢合成异丁烯性能的非常重要的因素．     

Kinetic effect in the size-control of CdS nanoparticles

A new method of size control for CdS nanoparticles, called common cation coprecipitation, is reported. In the course of coprecipitation, both CdS and CdSt_2(cadmium stearate) formations are diffusion-controlled and their rates are quite different. The size of CdS nanoparticles depends on the ratio of initial concentrations of S~(2-) to St~- (stearate ion). Characterized by UV-Vis absorption, XRD, TEM, fluorescence and XPS, the results obtained show that the coprecipitate is a composite, i. e. CdS particle inserts in the CdSt_2 molecular layers to form a sandwich-like structure. The method reported for size control of CdS nanoparticles might be called kinetic self-assembling.     

Corrosion resistance in chloride solution of the AlSi10Mg alloy obtained by means of LPBF

The paper deals with the corrosion resistance in chloride solutions of an AlSi10Mg alloy obtained by laser powder bed fusion (LPBF) process. The potentiodynamic tests were carried out in solutions having different chloride contents. The results emphasize the role of chloride concentration on localized corrosion. The increase of concentration reduces pitting potential. In addition, the influence of the post-processing heat treatment temperature was recognized. Penetrating attacks occurred either on after low temperatures stress relieving or specimens without any treatment, promoted by selective dissolution of the α-Al phase stimulated by galvanic coupling with noble silicon precipitates at the border of the melt pool. Such penetrating morphology was not observed after heat treatments at high temperature.     

A TPD‐MS study of the interaction of coumarins and their heterocyclic derivatives with a surface of fumed silica and nanosized oxides CeO2/SiO2, TiO2/SiO2, Al2O3/SiO2

The interactions between coumarins and the surface of fumed SiO₂, CeO₂/SiO₂, TiO₂/SiO₂ and Al₂O₃/SiO₂ were assessed by means of temperature‐programed desorption mass spectrometry. The different stages of the thermolysis of coumarin were identified and an analysis of the underlying reactions was performed. The kinetic parameters of the involved reactions were thus obtained. The decomposition of thiazolyl‐substituted coumarins was found to proceed through a ‘thiazole–thiazine’ ring expansion in the adsorbed state. A linear correlation between the sigma constants (Σσ) of the coumarin substituents and the activation energy of CO₂ formation was obtained. Copyright © 2010 John Wiley & Sons, Ltd.     

Preparation of nanocrystalline lithium niobate powders at low temperature

A facile route to prepare lithium niobate (LiNbO₃) powders was proposed by an alternative solid‐state method. Stoichiometric Li₂C₂O₄ and ammonium niobium oxalate were mixed with small amounts of water and then dried at room temperature. It was demonstrated that Li[NbO(C₂O₄)₂]·n H₂O intermediate was produced by an ion‐exchange reaction. Pure LiNbO₃ powders were successfully synthesized by heating the intermediate at 500, 600 and 700 °C for 3 h. X‐ray diffraction (XRD), scanning electron microscopy (SEM), Fourier‐transform infrared (FTIR) spectroscopy, UV‐Vis diffuse reflectance (UV‐Vis) spectroscopy and thermogravimetric (TG) analysis were used to characterize the precursor compound and as‐prepared samples. XRD results reveal that all the products are identified as hexagonal structure with high relative crystallinity (>87%). The particle size is found to be about 40 nm for the mixture calcined at 500 °C according to XRD data, which is in good agreement with SEM data. The as‐prepared LiNbO₃ powders by this method are high quality according to FTIR spectra. (Li_0.996Nb_0.005)Nb_0.999O₃ phase was formed when the calcination temperature was raised to 800 °C. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Fe_2O_3/聚糠醛纳米复合材料的制备及光催化性能

以Fe(NO3)3·9H2O和糠醛(FD)为原料,通过聚合-热转化两步法制备了Fe2O3/聚糠醛(PFD)纳米复合材料,用TEM、XRD、XPS和UV-Vis等技术对其尺寸、结构及吸光特性等进行了表征。在自然光、室温条件下,以亚甲基蓝(MB)溶液的催化脱色降解为模型反应,考察了其光催化性能以及热转化温度对催化性能的影响。结果表明,利用该法可以得到纳米级的、相间以强相互相用结合的有机-无机复合材料Fe2O3/PFD,该纳米材料对紫外-可见区的全程光波有强的吸收;热转化条件对复合材料的结构、催化性能等有很大影响,在300℃下处理35min所得的纳米复合材料在自然光条件下具有最佳的催化性能,25min即可使MB溶液完全脱色,并且重复使用3次仍可使MB溶液的脱色率保持在75.0%以上。而在相同条件下,纳米Fe2O3仅能使MB的脱色率达到5.8%。     

Scaling-up the Production of Nanosized SiO2-particles in a Double Diffusion Flame Aerosol Reactor

Synthesis of nanophase silica (SiO₂) from hexamethyldisiloxane (HMDS) oxidation in a co-flow diffusion flame reactor at atmospheric pressure is investigated focusing on high production rates of powder. A new experimental set-up is introduced, including a diffusion burner which is operated with a ring-shape double diffusion flame. Significantly high HMDS concentrations are used resulting in SiO₂ production rates of up to 130g/h. Deposition of silica powder on the burner face is eliminated by the design of a special diffusion burner and higher collection rates are achieved using a baghouse filter. The specific surface area and the product powder composition are analyzed. Carbon black coated silica particles were produced at high production rates (130g/h) at low oxygen flow rates or using a mixture of nitrogen and oxygen as oxidant. The size of the product particles was controlled in the range of 15–170nm.     

Photoredox Chemistry of Polyoxometalates as a Photocatalyst

The photocatalytic action of polyoxometalates (PMs), which is initiated by the photoexcitation of the oxygen-to-metal charge-transfer (O M LMCT) bands of PM, is based on the electron–hole pair separation followed by reductive and oxidative reactions with surrounding molecules. It is shown that the O M LMCT triplet states are involved in the photoredox reactions in which the significance of the highly negative oxidation potential for the photoreduced PMs can be considered in connection with the photocatalytic H₂ formation from a great variety of organic substrates with their dehydrated oxidation. When the reaction of the photoreduced PMs with the electron acceptor hardly occurs kinetically or thermodynamically, they undergo self-assembled organization to nanosized supramolecules (as a result of photoencapsulation of small molecules and ring cluster formation). Some typical examples for the electron–hole pair separation and the photoredox reactions developed in our laboratory are discussed.