Pd-Cu双金属催化剂上加氢反应的仲氢诱导超极化研究

本文通过多相催化-仲氢诱导超极化（HET-PHIP）核磁共振（NMR）技术研究了Pd-Cu/SiO₂双金属催化剂上丙炔选择性加氢反应.首先利用等体积浸渍法和连续浸渍法合成了一系列不同Pd/Cu比例和形貌的Pd-Cu/SiO₂双金属催化剂.通过ALTADENA（Adiabatic Longitudinal Transport After Dissociation Engenders Net Alignment）方法发现,催化剂的Pd/Cu比例和形貌均对PHIP的极化效率有较大影响.随着Pd-Cu双金属催化剂中Pd比例的增大,PHIP极化效率降低,同时反应活性增强.在同Pd/Cu比例下,相对于等体积浸渍法,连续浸渍法制备的层叠形貌催化剂具有较弱的极化效率以及较强的催化活性,这是由于催化剂表面暴露出的Pd数量增多,导致催化活性增强;同时单个Pd集簇表面积增大,使得氢原子移动范围扩大,从而造成极化效率降低.     

Pt/CeO2-ZrO2/Al2O3催化剂的光谱表征

利用拉曼光谱表征了不同方法添加ＣｅＯ２－ＺｒＯ２混合氧化物对Ｐｔ／Ａｌ２Ｏ３催化剂的影响,并采用了ＸＲＤ,Ｈ２化学吸附,ＢＥＴ表征了相应的分散度影响。结果表明：Ｃｅ、Ｚｒ、与金属Ｐｔ存在着强的相互作用,而ＣｅＯ２－ＺｒＯ２以盐的形式加入时,高度分散在Ａｌ２Ｏ３载体上,提高贵金属Ｐｔ的分散度,进而提高了反应的活性。     

Polarization effects in thin layers of SiO2 and Al2O3

For film metal-dielectric-metal and hybrid-metal-dielectric-semiconductor systems based on pyrolytic fully grown films of SiO₂ and Al₂O₃ the dependence of the remanent polarization coefficient on the magnitude of the field in the films and the short circuit time was investigated. The nature of relaxation processes related to remanent polarization effects was analyzed.The authors take the opportunity to express their gratitude to A. S. Bashakidze for help in carrying out the measurements.     

An XPS Study of the Effect of La2O3 Dopant on the Dispersion and Thermal Stability of Pt/Al2O3 Catalysts

The Pt(4d)/Al(2s) XPS intensity ratio for Pt/Al₂O₃ catalysts increases with the addition of La₂O₃ as a dopant. The Pt(311) line in the X-ray diffraction pattern also broadens with the addition of La₂O₃. These data imply that doping the Pt/Al₂O₃ catalyst with La₂O₃ increases the dispersion of the platinum which in turn would be expected to increase the activity and thermal stability of the catalyst.     

Structural and Magnetic Properties of the Al2O3/Ge-p/Al2O3/Co System

Technical Physics - The Al2O3/Ge-p/Al2O3/Co system with an Al2O3 buffer layer deposited by ion-plasma sputtering has been experimentally investigated. The dependences of the magnetic properties of...     

The desorption of CO from small Pt particles on Al2O3

The adsorption of CO on small Pt particles supported on alumina was studied using temperature programmed desorption (TPD). Samples were prepared by vapor deposition of Pt onto a flat substrate in ultra high vacuum. Metal coverages were reproducibly obtained using a film thickness monitor which was calibrated with Auger electron spectroscopy (AES). AES results indicated that Pt grew in a layer-by-layer manner on alumina at both 90 and 300 K and that these metal films aggregated into particles when heated above 650 K in vacuum. The average particle size could be estimated from the amount of CO desorbing in TPD and from the metal coverage and could be varied from 1.1 nm up to a continuous film. For the smallest particles, CO desorbed in a single state at 510 K. For larger particles, a second desorption state at 400 K was also observed. Since the desorption of CO occurs at similar temperatures on single crystals of Pt, these results indicate that the adsorption properties for CO on small particles of Pt on alumina are very similar to those for CO on bulk Pt. The change in the relative populations of the two desorption states with increasing particle size is interpreted as evidence for the formation of (111)-type facets on the larger particles.     

Thermal morphological evolution of platinum nano-particles in Pt–Al2O3 nano-composites

Temperature morphological evolution of nonpercolated granular nano-structures of platinum nano-particles embedded in an insulating alumina matrix was investigated by X-rays scattering in grazing angle reflection mode. In the investigated temperature range of 298–823 K, it was found that the annealing treatment tends to increase the Pt nano-particles' size and to produce a quasi-mono-disperse Pt nano-particles followed by a reduction of the barrier thickness between them. The percolation temperature is estimated to be of the order of 890 K. Using the rate constant governing the growth of the Pt nano-particles, the corresponding activation energy was determined to be about 90 kJ/mol.     

甲烷部分氧化制合成气Pt/Al_2O_3催化剂的表征及其反应性能评价

采用浸渍法制备了3种不同负载量的Pt/Al2O3催化剂,考察了催化剂的甲烷选择氧化性能,并用程序升温还原技术,程序升温脱附技术以及微型脉冲催化色谱技术对催化剂进行表征。结果表明,随着Pt的负载量升高,甲烷催化氧化的性能也越好,对CO与H2的选择性也越高。其中,在750℃原料气组成CH4/O2为2∶1,4%Pt负载量的催化剂,甲烷转化率达到98%以上。     

Interfacial characteristics of Al/Al2O3/ZnO/n-GaAs MOS capacitor

The interfacial characteristics of Al/Al2O3/ZnO/n-GaAs metal-oxide-semiconductor (MOS) capacitor are investigated. The results measured by X-ray photoelectron spectroscopy (XPS) and high-resolution transmission electron microscopy (HRTEM) show that the presence of ZnO can effectively suppress the formations of oxides at the interface between the GaAs and gate dielectric and gain smooth interface. The ZnO-passivated GaAs MOS capacitor exhibits a very small hysteresis and frequency dispersion. Using the Terman method, the interface trap density is extracted from C-V curves. It is found that the ZnO layer can effectively improve the interface quality.     

Au/Al2O3催化剂的UV-Vis谱研究

研究了十六烷基三甲基溴化铵 (CTAB) /正己醇 /水体系的W/O微乳体系中 ,几种主要实验参数对用NaBH4还原氯金酸溶液制得的金纳米粒子大小的影响。实验结果表明 :微乳体系中水与表面活性剂的摩尔比rw 在所研究的范围内对金粒子大小影响不大 ,而氯金酸溶液的浓度对金粒子大小影响较大。通过优化制备条件 ,用两种不同的方法制备了Au/Al2 O3 催化剂 ,并用紫外 可见光谱、透射电镜 (TEM)和X射线衍射(XRD)对其进行表征 ,初步考察了不同制备方法对催化剂中活性组分Au粒大小的影响     

NSR催化剂12CaO-7Al2O3/10%K中水对NO还原性能的影响

主要讨论在不同反应温度和不同水蒸汽浓度下,新型的NOx储存-还原催化剂12CaO·7Al2O3／10％K(简称C12A7／K)中水的存在对NO还原性能的影响．研究结果表明,当存在1．2％水蒸汽,并低于500℃时,NO转化率和N2的选择性均降低,水蒸汽的存在对催化剂低温区的活性起到较明显的抑制作用;而温度高于500℃时,此抑制作用则基本消失,说明此时C12A7／K催化剂的水热稳定性较好．FT-IR结果证明储存NOx后的C12A7／K样品小形成了NO3／NO2的反应中间物种,用H2还原则可消除中间物种,以N2等形式放出。     

CuO/Al2O3、CuO/CeO2-Al2O3和CuO/La2O3-Al2O3催化剂中CuO物种被CO氧化的比较

用浸渍法制备了CuO/Al2O3 (Cu/Al)、CuO/CeO2- Al2O3 (Cu/CeAl)和CuO/La2O3-Al2O3(Cu/LaAl)催化剂. 通过原位XRD、Raman和H2-TPR方法， 对催化剂中的CuO物种以及CuO-Al2O3的固-固相反应进行了表征. 结果表明，对于Cu/Al催化剂，CuAl2O4存在于CuO与Al2O3层之间，CuO以高分散和晶相两种相态存在于催化剂的表层；对于Cu/CeAl催化剂，除了少量高分散和晶相的CuO存在于表层外，大部分CuO迁移到了CeO2的内层，     

Hydrogen production over a commercial Pd/Al2O3 catalyst for fuel cell utilization

In order to produce a hydrogen stream for fuel cell utilization, the study of the ethanol steam reforming process over an alumina supported palladium commercial catalyst was carried out. The effect of the reaction temperature, the H₂O/C₂H₆O molar ratios and the contact time on catalytic activity and stability was studied. It was found that even at very low temperature values complete ethanol conversion was possible. Hydrogen selectivities up to 98% were obtained at temperature values close to 625 °C. It was also observed that for different reactant molar ratios carbon monoxide concentration exhibits a minimum at a temperature value close to 450 °C. Furthermore, carbon formation was found to be negligible even for H₂O/C₂H₆O molar ratios equal to the stoichiometric one. Paper presented at the 9th EuroConference on Ionics, Ixia, Rhodes, Greece, Sept. 15–21, 2002     

Study on ultrasound-assisted precipitation for preparing Ni/Al2O3 catalyst

With the rapid development of oil hydrogenation industry, the development of oil hydrogenation catalyst has also become a research hotspot. In this paper, ultrasound-assisted precipitation technique is used to prepare Ni/Al₂O₃ catalyst. The effect of ultrasonic output power on catalyst performance is investigated. The prepared catalyst is applied to the hydrogenation reaction of castor oil. It is found that the prepared catalyst shows the best hydrogenation performance when ultrasonic output power, frequency and ultrasonic treatment time are 80 W, 40 kHz and 600 min respectively. It also indicates that ultrasound-assisted precipitation technique can reduce the particle size and increase the specific surface area of Ni/Al₂O₃ catalyst so that its activity is improved. In addition, six important elements that should be considered in the development of industrial oil refining catalysts are discussed, and the effects of these factors on the catalyst performance are discussed. Finally, new way for improving catalyst performance is given, and the application of some new materials and methods in oil refining is introduced.     

NMR and Mössbauer Study of Al2O3–Eu2O3

Alumina–europia mixed oxides with 5 and 10 wt.% Eu₂O₃ were studied by Mössbauer spectroscopy, ²⁷Al MAS-NMR and X-ray diffraction (XRD). The samples were prepared by the sol–gel technique. The XRD patterns for the calcined samples show a broad peak around 2θ = 30° which is assigned to the Eu₂O₃; after treatment with hydrogen at 1073 K no reduction to Eu⁺² or Eu⁰ was observed. The NMR spectra show three peaks, which are assigned to the octahedral, pentahedral and tetrahedral aluminum sites; the intensity of each peak depends on the concentration of europium ions. The Mössbauer spectra of the calcined samples show a single peak near zero velocity which is attributed to the Eu⁺³; after H₂ treatment at 1073 K similar spectra were obtained, suggesting Eu⁺³ is not reducibly at this temperature.     

活性炭负载Pt/Fe3O4催化剂及其选择性转移加氢肉桂醛的催化性能

A variety of spherical and structured activated charcoal supported Pt/Fe₃O₄ composites with an average particle size of ～100 nm have been synthesized by a self-assembly method using the difference of reduction potential between Pt (IV) and Fe (Ⅱ) precursors as driving force. The formed Fe₃O₄ nanoparticles (NPs) effectively prevent the aggregation of Pt nanocrystallites and promote the dispersion of Pt NPs on the surface of catalyst, which will be favorable for the exposure of Pt active sites for high-efficient adsorption and contact of substrate and hydrogen donor. The electron-enrichment state of Pt NPs donated by Fe₃O₄ nanocrystallites is corroborated by XPS measurement, which is responsible for promoting and activating the terminal C=O bond of adsorbed substrate via a vertical configuration. The experimental results show that the activated charcoal supported Pt/Fe₃O₄ catalyst exhibits 94.8% selectivity towards cinnamyl alcohol by the transfer hydrogenation of cinnamaldehyde with Pt loading of 2.46% under the optimum conditions of 120℃ for 6 h, and 2-propanol as a hydrogen donor. Additionally, the present study demonstrates that a high-efficient and recyclable catalyst can be rapidly separated from the mixture due to its natural magnetism upon the application of magnetic field.     

Effective surface passivation of crystalline silicon using ultrathin Al2O3 films and Al2O3/SiNx stacks

We measure surface recombination velocities (SRVs) below 10 cm/s on p‐type crystalline silicon wafers passivated by atomic–layer–deposited (ALD) aluminium oxide (Al₂O₃) films of thickness ≥10 nm. For films thinner than 10 nm the SRV increases with decreasing Al₂O₃ thickness. For ultrathin Al₂O₃ layers of 3.6 nm we still attain a SRV < 22 cm/s on 1.5 Ω cm p‐Si and an exceptionally low SRV of 1.8 cm/s on high‐resistivity (200 Ω cm) p‐Si. Ultrathin Al₂O₃ films are particularly relevant for the implementation into solar cells, as the deposition rate of the ALD process is extremely low compared to the frequently used plasma‐enhanced chemical vapour deposition of silicon nitride (SiN_x). Our experiments on silicon wafers passivated with stacks composed of ultrathin Al₂O₃ and SiN_x show that a substantially improved thermal stability during high‐temperature firing at 830 °C is obtained for the Al₂O₃/SiN_x stacks compared to the single‐layer Al₂O₃ passivation. Al₂O₃/SiN_x stacks are hence ideally suited for the implementation into industrial‐type silicon solar cells where the metal contacts are made by screen‐printing and high‐temperature firing of metal pastes. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Al2O3绝缘层的AlGaN/GaN MOSHEMT器件研究

在研制AlGaN/GaN HEMT器件的基础上,采用ALD法制备了Al2O3 AlGaN/GaN MOSHEMT器件.通过X射线光电子能谱测试表明在AlGaN/GaN异质结材料上成功淀积了Al2O3薄膜.根据对HEMT和MOSHEMT器件肖特基电容、器件输出以及转移特性的测试进行分析发现:所制备的Al2O3,薄膜与AlGaN外延层间界面态密度较小,因而MOSHEMT器件呈现出较好的栅控性能;其次,该器件的栅压可以加至 3 V,此时的最大饱和电流达到800 mA/mm,远远高于肖特基栅HEMT器件的最大输出电流;而且栅漏反偏状态下的泄漏电流却减小了两个数量级,提高了器件的击穿电压,通过进一步分析认为泄漏电流主要来源于Fowler-Nordheim隧穿.