共查询到19条相似文献,搜索用时 218 毫秒
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从过渡金属硫化物催化剂活性相理论出发,认为在加氢催化剂制备过程中保证活性组分的适度分散和金属-载体之间适度的相互作用能提高加氢催化剂的性能。本文针对加氢处理催化剂的制备技术,综述了添加有机助剂、平衡吸附法、浆液浸渍法等浸渍改进技术以及水热沉积法、原位晶化法、化学气相沉积法等新型的制备技术,并介绍了相关的国内外研究进展。分析指出有机助剂能与载体、金属作用,进而改变金属在载体表面的存在形态,有利于高活性CoMoS相的生成;水热沉积法和原位晶化法能够使活性组分在载体上均匀吸附沉积,从而实现活性组分在载体上的分散,并形成堆积程度更高的高活性Ⅱ型活性中心。 相似文献
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以大孔α-Al_2O_3陶瓷管(平均孔径为3μm)为载体,采用水热合成法在其表面形成一层纯硅沸石(Silicalite-1)修饰层,利用化学镀法在经过纯硅沸石修饰后的载体表面成功制备出致密钯复合膜,钯膜厚度约为5 μm.利用SEM对复合膜的结构和形貌进行了分析,并在350~500℃范围内对基于纯硅沸石修饰层的钯复合膜进行气体渗透测试表明,该沸石层修饰法制备的钯复合膜具有良好的氢渗透性.在500℃时,氧气渗透通量可达为0.12mol/(m~2·s),理想气体分离因子α(H_2/N_2)达到420.并对该钯膜与在载体表面直接制备的钯复合膜性能的差异进行了讨论. 相似文献
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Palladium membranes were prepared on large tubes (80 mm diameter and 150 mm length) of porous stainless steel supports (PSS) using a modified electroless plating technique. The morphology of the palladium layer was found to be depending on the container material of the coating apparatus. The use of PMMA resulted in compact palladium layers with smooth surfaces whereas PTFE led to inhomogeneous palladium coating with rough surface. Two different ceramic materials and coating methods were used to prepare an intermediate layer needed to prevent intermetallic diffusion between the palladium and the support at elevated temperatures. Wet powder spraying of TiO2 followed by sintering resulted in a smoother surface than atmospheric plasma spraying of YSZ, thus allowing for a thinner palladium coating. Pd/TiO2/PSS membranes showed about 4 times higher hydrogen permeances than Pd/YSZ/PSS membranes as a consequence of higher palladium thickness and lower porosity of the ceramic intermediate layer. The selectivity against nitrogen was comparable for both membranes. However, the YSZ intermediate layer showed better stability at elevated temperatures. Two membrane tubes were applied in the membrane reformer, which produced hydrogen successfully from a gas-to-liquid (GtL) fuel. 相似文献
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The increasing demand in compact hydrogen separators greatly stimulated the investigation and utilization of composite palladium membranes. Porous stainless steel (PSS) tubes were chosen as substrate material in this study, and a novel process of carbon-assisted solid-state sintering was introduced to modify the PSS surface with a TiO2 layer. A Pd/TiO2/PSS membrane with a Pd thickness of 6 µm was successfully fabricated via electroless plating. Scanning electron microscopy (SEM), metallographic microscopy, X-ray diffraction and pore-size analyses were performed for material characterizations. As measured by H2/N2 single-gas testing, the fabricated Pd/TiO2/PSS membrane is permeable and selective to hydrogen, and it was stable during a time-on-stream of 100 h under 450°C. 相似文献
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Thin palladium composite membranes were prepared by modified electroless plating method on a-alumina supports and a dense Pd/α-Al2O3 composite membrane with high hydrogen flux, good selectivity for hydrogen was obtained. It was tested in a single gas permeation system for hydrogen permeance and hydrogen selectivity over mtrogen. The hydrogen permeance of the corresponding membrane was ashigh as 2.45×10^-6mol·m^-2·s^-1.Pa^-1 and H2/N2 selectivityover700 at 623K and a pressure difference of 0.1MPa. The-main resistance of the composite membrane to H2 permeation lies in the aluminum ceramic support rather than the thin Pd layer. 相似文献
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《分离科学与技术》2012,47(14):2877-2889
Abstract Palladium acetate vapor was sublimed at a reduced pressure and was evacuated through the porous wall of an α-alumina support tube of 1.8 mm i.d. and 2.4 mm o.d. Due to chemical vapor deposition (CVD), a thin palladium membrane was formed in macropores of the support. The membrane part was about 50 mm in length and was used without any pretreatment. The palladium membrane, prepared at a maximum CVD temperature of 400°C, showed hydrogen permeance and selectivity to nitrogen higher than 10?6 mol·m?2·s?1·Pa?1 and 1000 at 300–500°C, respectively. Even after the permeation temperature was repeatedly varied between 100 and 300°C in a hydrogen atmosphere, the membrane exhibited no hydrogen embrittlement. The amount of palladium deposited in pores of the support tube was 22 g/m2 of the outer surface of the tube. The thickness of the palladium membrane calculated from this value was 4.4 μm. 相似文献
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奥氏体不锈钢焊件是高压氢系统中重要的承载结构,其长期服役在高压高纯氢气环境中会出现塑性损减、疲劳裂纹扩展速率加快等氢脆现象,导致高压氢系统存在安全隐患。因此,为保障高压氢系统的安全运行,研究高压氢环境奥氏体不锈钢焊件的氢脆具有重要意义。本文首先介绍奥氏体不锈钢焊件中氢的两种来源,随后讨论评价材料氢脆敏感性的静态实验方法和动态实验方法,其次概述当前主流的氢脆机理,然后着重分析内部因素及外部因素对奥氏体不锈钢焊件氢脆敏感性的影响,最后归纳并总结五种典型的奥氏体不锈钢焊接工艺对焊件微观组织的影响,并进一步探讨相应焊件的氢脆敏感性。基于上述分析,针对奥氏体不锈钢焊件氢脆性能研究现状及发展趋势提出了若干建议。 相似文献
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不锈钢是高压氢系统的常用材料,在氢能储输技术中发挥重要作用,但高压氢环境引起的塑性降低、疲劳裂纹扩展速率加快等不锈钢氢脆问题,严重阻碍了氢能的产业化发展,在不锈钢材料表面制备阻氢涂层是解决不锈钢氢损伤问题的重要手段之一。本文首先综合介绍了典型涂层材料的应用特点及阻氢性能,探讨了制备工艺对涂层阻氢性能的影响、不同涂层材料的阻氢机理,并分析了涂层阻氢性能影响因素,之后总结了涂层阻氢性能评价方法及各种评价方法的优势与不足,并根据各种评价方法的技术特点,指出每种方法的适用范围。最后,基于阻氢涂层研究进展,文章提出以开发新型涂层结构为研究重点,同时加快新型涂层材料的探索,并重点关注涂层氢环境原位性能评价方法的研究。 相似文献
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Fabrication of Palladium Membranes Supported on a Silicalite‐1 Zeolite‐Modified Alumina Tube for Hydrogen Separation
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Thin palladium membranes were fabricated on macroporous α‐Al2O3 tubes by electroless plating. The silicalite‐1 (Sil‐1) zeolite serving as intermediate and diffusion barrier layer was introduced to modify the surface roughness and pore size of the porous substrate and prevent the atomic interdiffusions of the metal elements between Pd layer and the support. The Pd composite membranes were studied by scanning electron microscopy (SEM), X‐ray diffraction (XRD), and electron probe microanalysis (EPMA), revealing that morphology and structure of the Sil‐1 layer significantly influence the Pd membrane preparation. Single‐gas permeation tests were carried out with gas H2 and N2 to determine the permeation performance of the membranes. The resulting membrane exhibited long‐term stability under hydrogen permeation. 相似文献
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Ting-Chia Huang Ming-Chi Wei Huey-Ing Chen 《Chemical Engineering Communications》2013,200(10):1340-1359
The permeation of hydrogen through palladium composite membranes was investigated at temperatures 523-669 K and hydrogen pressures 80-220 kPa. Two pieces of Pd/α-alumina composite membranes prepared by electroless deposition were used in this study. The permeation behavior of hydrogen through the palladium composite membranes was analyzed by a resistance model in order to obtain the permeation parameters of the support and palladium layer. The results demonstrated that the thickness of the Pd layer played an important role in the permeation properties of hydrogen. The hydrogen flux through a Pd/alumina composite membrane, with a palladium film of 7 μm thickness, deviated from Sievert's law. This was due to decreasing the thickness of the Pd film, resulting in a significant surface limiting process contribution. In addition, Sievert's law was in good agreement with the data obtained for thick Pd film (15 μm), and it provided accurate prediction of permeability coefficient, activation energy, and the values of Δ H H 0 and Δ S H 0 . These obtained parameters were in excellent agreement with the literature. 相似文献
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Palladium/Nafion composite membranes were synthesized by supercritical impregnation method to reduce methanol crossover in direct methanol fuel cells. The palladium complexes used in this study were palladium(II) acetylacetonate, palladium(II) hexafluoroacetylacetonate, and palladium (II) bis(2,2,6,6-tetramethyl-3,5-heptane-dionato). The palladium complexes with various loading amounts from 0.010 to 0.050 g in a high-pressure vessel were dissolved in supercritical CO2, and impregnated into Nafion membranes.The SEM images indicated that the palladium complexes were successfully deposited into Nafion membrane, and there were no problems such as cracking and pinhole. The EDX analysis showed that the palladium particles were distributed both at the membrane surface and also extended deeper into the membrane. The TEM images indicated that thin dense band of agglomerated Pd particles can be observed near the membrane surface, and a significant number of isolated Pd particles can be seen deeper into the membrane, when Pd(II) acetylacetonate was used as palladium complex. When palladium(II) hexafluoroacetylacetonate and palladium (II) bis(2,2,6,6-tetramethyl-3,5-heptane-dionato) were used, dense band of agglomerated Pd particles cannot be observed near the membrane surface, and small Pd particles were observed inside the membranes.The XRD analysis indicated that the crystalline peak of Nafion membrane at 2θ = 17° increased with the supercritical CO2 treatment. It means that the degree of crystallinity for Nafion membrane increased by supercritical CO2. The metal Pd peak at 2θ = 40° was observed for the Pd/Nafion membranes.The methanol crossover was reduced and the DMFC performance was improved for the Pd/Nafion membranes compared with Nafion membrane at 40 °C. The successful preparation of Pd/Nafion membranes by supercritical CO2 demonstrated an effective alternative way for modifying membranes and for depositing electrode catalytic nanoparticles onto electrolyte. 相似文献