Pd-Cu alloy membrane deposited on alumina modified porous nickel support (PNS) for hydrogen separation at high pressure

This study reports on the hydrogen permeation properties of Pd-Cu alloy membranes at high pressures. A 7 μm thick Pd-Cu alloy membrane was prepared on an alumina-modified porous nickel support (PNS) by our developed magnetron sputtering and Cu-reflow method at 700 °C for 2 hours. The membrane was mounted in a stainless steel permeation cell with a gold-plated stainless steel O-ring. Helium leak testing confirmed that the membrane and membrane module were free of defects. Permeation tests were then conducted using hydrogen at temperatures in the range from 678 to 816 K with a transmembrane pressure difference of 1–20 bars, which showed that the membrane had a hydrogen permeation flux of 1.06 mol m⁻² s⁻¹ at a temperature of 816 K and a pressure difference of 20 bars. EDX analysis was carried out after hydrogen permeation test at 816 K and showed that there was no intermetallic diffusion between the Pd-Cu layer and PNS because the alumina layer inhibited it effectively.     

Silica-supported alloy catalysts for triglyceride hydrogenation: The preparation and properties of Pd–Ag and Pd–Ni systems

The binary metal systems Pd–Ag and Pd–Ni have been prepared on a silica support with a total metal loading of 2.5% (w/w). About a dozen catalysts were prepared in each series covering the range 0–100 at. % Pd. The catalysts were characterised by a number of techniques, principally temperature programmed reduction, differential scanning calorimetry and metal surface area measurement. The catalyst activity and selectivity were measured for the hydrogenation of soya bean oil in both stirred and shaken batch reactors at 1 atm H₂ pressure in the temperature range 100–160°C. The characterisation techniques provided strong evidence of alloying for both series of catalysts. The activity and selectivity measurements also provided supporting evidence of alloying, and the Pd–Ag system exhibited an activity maximum in the 90–100 at. % Pd range, while the Pd–Ni system maintained constant activity for alloys containing 0–60 at. % Ni. Trans-acid formation was suppressed by lower reduction temperature, and linolenate removal was improved at lower temperatures. However, it also appears that reaction rates were dominated largely by triglyceride diffusion effects.     

Adsorption of Heavy Metals from Aqueous Solutions onto Activated Carbon in Single Cu and Ni Systems and in Binary Cu–Ni,Cu–Cd and Cu–Zn Systems

Single copper and nickel adsorption from aqueous solutions onto a granular activated carbon is reported. Metal removals increase on raising pH and temperature, and decrease on raising the initial metal concentration at constant carbon dose. The adsorption processes are modelled using the surface complex formation (SCF) Triple Layer Model (TLM) with an overall surface bidentate species. A dependence of the SCF constant on pH, initial molar metal/carbon ratio and temperature is observed, and a correlation for log K_ads is determined. The SCF model successfully predicts copper and nickel removals in single metal solutions. Adsorption in the binary metal systems copper–nickel, copper–cadmium and copper–zinc is also reported, showing competitive adsorption effects. © 1997 SCI.     

A Cu–Pd–V System Filler Alloy for Silicon Nitride Ceramic Joining and the Interfacial Reactions

A Cu–Pd–V brazing alloy with the composition of Cu–(38.0~42.0)Pd–(7.0~10.0)V (in wt.%) was designed as a filler for joining Si₃N₄. Its wettability on Si₃N₄ ceramic was measured with the sessile drop method. It was shown that the Cu–Pd–V alloy gave a contact angle of 71° at 1473 K. The filler alloy was fabricated into foils with a thickness of 0.15 mm. The Si₃N₄–Si₃N₄ joints brazed at 1443 K for 10 min exhibit average three‐point bend strength of 263 MPa at room temperature, and the joint strengths at 973 K and 1073 K are 277 MPa and 218 MPa, respectively. The analysis results of SEM, XRD, and TEM for the brazed joint indicate the presence of V₂N at the surface of the Si₃N₄. The increase of the thickness of V₂N reaction layer obeyed parabolic law, and the parabolic rate constant (k) can be described as k = 2.8739 × 10^?9 exp(?162989.4/RT) m²/s. Pd₂Si and Cu₃Pd compounds as well as (Cu, Pd) solid solution were detected in the central part of the joints. The presence of (Cu, Pd) phases and especially refractory Pd₂Si compounds within the joints should contribute to the stable high‐temperature property. The interfacial reaction mechanisms were discussed.     

EXAFS study on Pd–Pt catalyst supported on USY zeolite

Local structure around Pd and Pt in the bimetallic Pd–Pt catalysts supported on ultra stable Y (USY) zeolite (SiO₂/Al₂O₃=680) was investigated by an extended X-ray absorption fine structure (EXAFS) method during oxidation, reduction, and sulfidation. The Pt L III-edge EXAFS spectra showed that a new bond that was significantly different from Pt–Pt to Pt–Pd metallic bonds was formed in the bimetallic Pd–Pt (4:1) reduced catalysts supported on USY zeolite. This new bond may reflect the ionic properties of Pt through the Pt–Pd interaction. Furthermore this new bond survived sulfidation indicating that the bond has a cationic property and sulfur-tolerance property. The Pt–Pd ionic interaction in these catalysts allows some of the Pd metal to survive as metallic phase. The existence of this metallic phase under sulfidation condition may result in high activity of Pd–Pt (4:1) catalyst supported on USY zeolite in the aromatics hydrogenation.     

Catalytic combustion of methane over bimetallic Pd–Pt catalysts: The influence of support materials

The effect of support material on the catalytic performance for methane combustion has been studied for bimetallic palladium–platinum catalysts and compared with a monometallic palladium catalyst on alumina. The catalytic activities of the various catalysts were measured in a tubular reactor, in which both the activity and stability of methane conversion were monitored. In addition, all catalysts were analysed by temperature-programmed oxidation and in situ XRD operating at high temperatures in order to study the oxidation/reduction properties.

The activity of the monometallic palladium catalyst decreases under steady-state conditions, even at a temperature as low as 470 °C. In situ XRD results showed that no decomposition of bulk PdO into metallic palladium occurred at temperatures below 800 °C. Hence, the reason for the drop in activity is probably not connected to the bulk PdO decomposition.

All Pd–Pt catalysts, independently of the support, have considerably more stable methane conversion than the monometallic palladium catalyst. However, dissimilarities in activity and ability to reoxidise PdO were observed for the various support materials. Pd–Pt supported on Al₂O₃ was the most active catalyst in the low-temperature region, Pd–Pt supported on ceria-stabilised ZrO₂ was the most active between 620 and 800 °C, whereas Pd–Pt supported on LaMnAl₁₁O₁₉ was superior for temperatures above 800 °C. The ability to reoxidise metallic Pd into PdO was observed to vary between the supports. The alumina sample showed a very slow reoxidation, whereas ceria-stabilised ZrO₂ was clearly faster.     

The preparation and properties of coprecipitated Cu–Zr–Y and Cu–Zr–La catalysts used for the steam reforming of methanol

Several samples of exhaust diesel soot are investigated by inverse gas chromatography and linear solvation energy relationship (LSER) modelling according to their soluble organic fraction content and their time of exposure in oxidative conditions. The results demonstrate the evolution of the adsorptive properties of the studied materials towards volatile compounds during the oxidation under NO₂.     

以TiAl金属间化合物为支撑体的多孔Ni膜的制备

为了克服传统有机膜与陶瓷膜的一些不足之处,以TiA l金属间化合物为支撑体,用悬浮粒子烧结法在孔径为10.6μm的片状支撑体上制备多孔金属N i膜。考察了浸浆时间、烧结温度等工艺参数对膜表面形貌和孔径大小、分布等膜性能的影响。结果表明,合适的制膜条件是:浸浆时间为60 s,烧结温度为500℃。得到了孔径分布比较窄而且表面比较平整的微滤膜,其平均孔径为0.83μm,膜厚约为30μm。     

ASAXS study of Au, Pd and Pd–Au catalysts supported on active carbon

Among the techniques commonly used, small angle X-ray scattering (SAXS) is, in principle, particularly suited for the analysis of nanostructured systems. However, catalysts supported on porous materials are three phase systems (support, voids and metal), so that the resulting spectrum contains more information than a single conventional SAXS measurement allows to extract. The use of synchrotron radiation source allows to circumvent this difficulty and to separate the scattering of the support from the one of metal by taking advantage of the so-called anomalous or resonant behavior of the atomic scattering amplitude of an element near its absorption edge. The results so far obtained on some Au, Pd and Pd–Au samples supported on active carbon are reported here.     

A reactor–separator incorporating porous and dense membrane systems

This study employs mathematical models to compare and assess the relative performance of various composite membranes incorporated in a high-temperature membrane reactor. Two categories (porous and dense) and five types of composite membrane systems (Pd/Ag, polyimide, silica, inert porous and Ru-dispersed porous) have been considered. Also included in the study is the special case of the Pd/Ag composite system having imperfections (pinholes and cracks). Ethylbenzene dehydrogenation over promoted iron oxide catalyst has been studied as the model reaction. Overall, the dense systems show higher performance levels at lower membrane thicknesses. However, the porous composite systems, especially those in which active metal particles have been incorporated within the micropores, can be very useful due to their significantly higher contact surface to volume ratio. The study has also confirmed that high hydrogen perm-selectivity is a key factor in determining reactor performance in terms of con-version enhancement. ©1997 SCI     

The kinetics of gasification of carbon deposited on nickel catalysts

The kinetics of gasification of carbon deposited on nickel foils and nickel-alumina catalysts by steam, carbon dioxide and hydrogen are reported for the temperature range 450–850°C. At atmospheric pressure steam is the most effective gasifying agent. In all cases, the kinetic data obtained at lower temperatures (below 600°C) is consistent with control of the process by the chemical reaction. As the temperature increases, the rates of gasification by steam and carbon dioxide are limited by mass transfer effects. The concentration of methane near reaction sites affects the rate of hydrogen gasification above 650°C.     

Compaction of porous silica – A photophysical study

Photophysical studies, utilizing pyrene, are used to investigate the compaction of porous silica. Conventional studies show that the volume of this material is markedly reduced (4×) on compression to 1 G Pa. The nature of the processes giving rise to this volume change vary with the logarithm of the applied pressure. Organic molecules in particular pyrene, indicate that the surface of the silica wrinkles and provides new adsorption sites that screen the adsorbate from other molecules such a O₂, NH₃, and CCl₄. At high pressures a portion of the adsorbate is completely trapped in silica, if loaded onto the material prior to compaction. Adsorbates with weak bonds, e.g., bromopyrene are chemically altered on compaction in silica. The data amplify earlier studies on the uncompacted system, and confirm the heterogeneous environment of SiO₂ at the sites where organic molecules are adsorbed.     

The nickel–niobia–silica interactions at low nickel contents

Nickel was impregnated in two Nb₂O₅/SiO₂ samples. The first one contained small crystallites of niobia dispersed over silica and the second one a niobia monolayer distributed quite uniformly over the silica substrate. These systems were submitted to different treatments (calcination and water vapor) in order to obtain different interactions between the nickel and niobia. A preferential interaction of the nickel with niobia was observed in both niobia–silica samples. The hydrogenation of benzene and dehydrogenation of cyclohexane were used to characterize the reduced surface nickel. Suppression in the catalytic activity was observed due to a strong metal-support interaction (SMSI) and nickel niobate formation. The extension of SMSI and nickel niobate formation depend on the niobia–silica interactions, which are a function of sample preparation and treatment.     

Dehalogenation of trihalomethanes in drinking water on Pd–Fe° bimetallic surface

Trihalomethanes (THMs), water disinfection‐byproducts, in potable water are of public health concern. Degradation of THMs by palladium‐treated iron granules (Pd–Fe° ) has been studied in a flow‐through column system. Laboratory‐scale columns of approximately 628 cm² were loaded with Torpedo and Silica sands plus anthracite mixed with Pd–Fe° at a 10 : 1 ratio (w/w). The column setup in regard to composition and flow rate was aimed at simulating real rapid‐sand filtration conditions. A single passage of THM samples with concentration range 50–200 ppb through the column resulted in greater than 90% disappearance of parent THMs with one or more bromine atoms (CHCl₂Br, CHClBr₂ CHBr₃), but the degradation of CHCl₃ occurred much more slowly. Only 4–11% of the degradation of THMs resulted in the formation of dihalogenated products, indicating that they are degraded to form products other than dihalomethanes. The dehalogenation of brominated THMs decreased by less than 6% when the column temperature was lowered from 23° to 4 °C. Within the pH range of 4.0–6.5, there was little change in the dehalogenation, however the substantial decrease in the degradation occurred at pH 10. The Pd–Fe° also contributed significantly to the degradation of other halogenated and some nonhalogenated volatile compounds. Dehalogenation efficiency of the column was decreased by about 38% following 3 weeks of daily operation but could be regenerated with simple acid washing. No measurable Pd and iron concentrations (<300 ppb) were detected in the column effluents over a period of 3–4 weeks, indicating that the Pd–Fe° is fairly stable in the column. Copyright © 2003 Society of Chemical Industry     

活性污泥对管式多孔α-Al_2O_3陶瓷膜支撑体性能影响的初步研究

以剩余活性污泥作为支撑体的成孔剂,采用滚压成型及熔膜芯法制备管状多孔α-Al2O3陶瓷膜支撑体,研究了粘结剂羧甲基纤维素(CMC)和活性污泥的加入量对氧化铝陶瓷膜支撑体品质的影响。结果表明,随着成孔剂和粘结剂的增多,支撑体孔隙率和渗透通量呈增大趋势,孔隙率最大可达43.07%,纯水通量在0.4~1.0 MPa压力下变化范围为12 786.67~37 617.84 L/(m2·h·MPa)。     

活性污泥对管式多孔α-Al_2O_3陶瓷膜支撑体性能影响的初步研究

以剩余活性污泥作为支撑体的成孔剂,采用滚压成型及熔膜芯法制备管状多孔α-Al2O3陶瓷膜支撑体,研究了粘结剂羧甲基纤维素（CMC）和活性污泥的加入量对氧化铝陶瓷膜支撑体品质的影响。结果表明,随着成孔剂和粘结剂的增多,支撑体孔隙率和渗透通量呈增大趋势,孔隙率最大可达43.07%,纯水通量在0.4~1.0 MPa压力下变化范围为12 786.67~37 617.84 L/（m2·h·MPa）。     

Highly dispersed Ni catalysts on carbon from thermal decomposition of cellulose-hydrous nickel gel membrane

Ultra fine particles were impregnated by using a finely porous cellulose gel membrane. The impregnated gel membrane is a green transparent one and looks like a solid solution. Highly dispersed Ni catalysts on carbon were obtained from thermal decomposition of these gel membranes. The particle size is in the range of several nm to a few ten nm. They show interesting catalytic properties for hydrogenation of olefins such as cyclooctadiene.