Surface acidic properties of alumina-supported niobia prepared by chemical vapour deposition and hydrolysis of niobium pentachloride

Niobia–aluminas were prepared by chemical vapour deposition at 150°C of niobium pentachloride on the surface of γ-aluminas calcined at different temperatures and with controlled degrees of hydration, followed by hydrolysis with water vapour at 150°C and a thermal treatment with steam at 440°C aimed at removing surface chloride contamination. The samples were characterised with respect to chemical composition, surface area, acidity by temperature-programmed desorption of ammonia, nature of acid sites by infrared spectroscopy of adsorbed pyridine and catalytic activity at 370°C in the dealkylation of cumene.

The results showed that, for each alumina calcination temperature, the catalysts with the lowest niobium content have a higher density of acid sites than the alumina support, but the acidity decreased, within each series with an increase in the niobium content. Comparatively to the TPD results, catalytic activity in cumene dealkylation was much more sensitive to the history and composition of the samples. The niobia-alumina samples were much less active than the alumina support, but this was most likely due to the severe hydrothermal treatment for chlorine removal, since their activity was close to that of an alumina submitted to the same treatment. A strong decrease in the acidic activity was observed with increase in the niobium content. A sample of pure niobium oxide had a much higher activity than the niobia-alumina samples. Brønsted acidic sites could only be observed by the IR spectra of adsorbed pyridine on the surface of the pure niobium oxide sample.     

Water Vapor Adsorption and Desorption on Materials Hydrothermally Solidified from Clay Minerals

Water vapor isotherms were examined and ¹H-magic-angle spinning nuclear magnetic resonance (¹H-MAS NMR) analysis was conducted to determine the amount of water vapor adsorbed and desorbed on hydrothermally solidified materials derived from clay minerals. The amount of water vapor adsorbed and desorbed decreased with increasing mesopore volume of the materials, which disagreed with the estimation obtained using the Kelvin equation. Water vapor was physisorbed on alumina-like sites in the materials. An increase in the binding energy between water vapor and the materials led to an improvement in the water vapor adsorption–desorption properties of materials.     

Investigations of the properties of water films on quartz surfaces

Isotherms of water adsorption on and desorption from quartz surfaces have been determined. Thermal analysis curves of water thermodesorption from quartz surfaces have also been determined. From the experimental data, the energetic changes accompanying the water adsorption and desorption processes were calculated. The mechanism of water adsorption has been proposed, and conclusions concerning the structure and other properties of water films on quartz surfaces have been drawn.     

Promoting effect of water vapor on catalytic oxidation of methane over cobalt/manganese mixed oxides

Methane oxidation was conducted in a fixed bed quartz tubular reactor on a series of mixed oxides of cobalt/manganese prepared by a sol–gel method. A unique promoting effect of water vapor on methane conversion was observed for the first time on these cobalt/manganese mixed oxides calcined at 450 or 600 °C. However, these mixed catalysts lost their catalytic activities after being calcined at 850 °C. The catalytic activity of methane oxidation was significantly improved by supporting the cobalt/manganese mixed species onto the high surface area SiO₂ or Al₂O₃–SiO₂ materials. It was noteworthy that the water enhancement effect was retained on these supported catalysts.     

Water adsorption and energetic properties of spark discharge soot: Specific features of hydrophilicity

Water adsorption was studied for spark discharge soot which is often used as a surrogate for atmospheric soot. Analysis by adsorption gravimetry and calorimetry showed that spark discharge soot exhibits specific features of hydrophilicity. Analysis of the isotherms and heats of water adsorption revealed the peculiarities of the mechanism of surface wetting related to significant changes in the soot microstructure. The first water adsorption/desorption cycle led to irreversible water adsorption and a decrease of the surface area available for water adsorption. Repeated water adsorption/desorption cycles demonstrated swelling phenomena related to the increase of the nitrogen surface area due to interparticle microporosity. The maximum effect of the transformation was observed under exposure to saturated water vapor following the microstructure stabilization. With decreasing temperature the amount of adsorbed water also decreased. Once emitted into the atmosphere the spark discharge soot particles will exhibit irreversible changes in surface area, porosity and hygroscopicity as a result of numerous humidity fluctuations until approaching a stable state of their microstructure due to long exposure to saturated water vapor.     

含气页岩中水分赋存与分布的研究进展

页岩气（主要组分为甲烷,CH₄）作为一种新兴的非常规天然气,对于优化我国现行能源消费结构、缓解能源消耗过程中的环境污染问题具有重要意义。研究表明,含气页岩储层中页岩气主要以吸附态形式存在。影响含气页岩吸附性能的因素包括页岩自身理化性质和外部储层条件。其中,页岩中的水分是影响页岩气吸附/解吸的重要因素。因此,本文结合国内外相关研究工作,分析了含气页岩中水分的赋存与分布特征,归纳了页岩储层中水分的分析方法,指出了水分赋存与分布的后续研究方向。分析表明：①页岩中水分主要赋存于孔隙结构中,且无机孔隙中的水分赋存量比有机孔隙多;②水分子主要通过氢键吸附于有机孔隙的亲水性位点,以及经由氢键和表面作用力结合于黏土颗粒或孔隙表面;③水分含量与页岩黏土矿物含量及总有机碳（TOC）含量有关;④探明页岩中水分赋存与分布的实验表征手段包括水蒸气等温吸附、低温差示扫描量热、低场核磁共振、红外热成像和等离子体低温灰化等。虽然页岩中水分的研究已经引起国内外学者的关注,但是相比煤中水分的研究仍显不足。因此,本文指出后续需开展以下工作：探明水分在页岩中的无机矿物质空间和有机质空间的含量分布和空间分布特征;明确水分对页岩吸附/解吸CH₄流体的作用规律;联用实验科学和理论模拟方法,探明水分对页岩吸附/解吸CH₄流体的作用机理。     

Adsorption and desorption properties of cationic polyethylene film gels to organic anions and their regeneration

An investigation was undertaken on the adsorption and desorption properties of 2‐(dimethylamino)ethyl methacrylate grafted polyethylene (PE‐g‐PDMAEMA) films to anionic dye anions with one to three sulfonic groups in response to pH and temperature changes. The amounts of dye anions adsorbed on the PE‐g‐PDMAEMA films passed through the maximum values at about pH 3 because of an increase in the protonation of dimethylamino groups caused by a decrease in the pH value. The amounts of adsorbed dye anions decreased below pH 3 because the ionic strength increased with the addition of HCl to adjust the initial pH values of the aqueous dye solutions. The amounts of adsorbed dye anions decreased with an increase in the number of sulfonic groups in the dye molecules at the same pH value because electrostatic repulsion was generated between free sulfonic groups of the dye anions adsorbed onto the PE‐g‐PDMAEMA films and free dye anions in the medium. A large number of dye anions adsorbed were desorbed from the PE‐g‐PDMAEMA film with initial pH values above 11.0. The cyclic processes of adsorption at pH 3.0 and desorption at pH 11.0 were repeated without considerable fatigue. The PE‐g‐PDMAEMA films showed practically regenerative adsorption and desorption behavior in response to the pH changes. In addition, when the dye‐anion‐adsorbed PE‐g‐PDMAEMA films were alternately immersed in water at two different temperatures, dye anions were desorbed in water at higher temperatures without any chemical agents because of the deprotonation of dimethylamino groups and thermosensitive contraction of grafted PDMAEMA chains. These results indicate that PE‐g‐PDMAEMA films can be applied as regenerative ion‐exchange membranes for adsorption and desorption processes of anionic compounds in response to the pH and temperature. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 99: 381–391, 2006     

Hydrogen absorption in palladium films sensed by changes in their resistivity

The resistance of pure palladium films of 11, 30 and 54 nm thickness was monitored during their exposure to H₂ at pressures ranging between 1 and 20 Torr. After completing a cycle of H₂ absorption/desorption, the resistivity changed in a ``saw tooth' fashion similar to the changes observed in surface adsorption of hydrogen by other transition metals. Large resistance changes are observed in these studies, confirming that bulk hydrogen absorption occurs in Pd while hydrogen surface adsorption becomes dominant over bulk absorption in other metals such as niobium. The resistance change curves carry the information of the kinetics of absorption. This revised version was published online in July 2006 with corrections to the Cover Date.     

石墨烯-13X/LiCl复合吸附剂开式吸附-解吸性能

利用不同质量分数的石墨烯（MLG）与13X/LiCl合成新型复合吸附剂。通过扫描电镜（SEM）和N₂吸附表征复合吸附剂的微观形貌和孔隙特性,测试了复合吸附剂开式环境下的水蒸气吸附及解吸性能,并探究复合吸附剂中石墨烯质量分数对吸附解吸性能的影响。通过80%相对湿度（RH）的高湿工况进一步筛选出盐的质量分数为18.4%的13X/LiCl为最佳盐含量的吸附剂（MZ）作为合成复合吸附剂的基质。实验结果表明：石墨烯增加了复合吸附剂的结构性参数（比表面积,孔体积及孔径）,其中比表面积由未添加石墨烯的MZ [(262±3)g/m²],最大可提升至12G-MZ [(304±4)g/m²];复合吸附剂表现出优异的水蒸气吸附性能,所有复合吸附剂的相对吸附量均高于MZ（0.554g/g）,3G-MZ吸附性能最佳,水蒸气吸附量高达0.587g/g,是13X的2.7倍;除12G-MZ外,随着吸附剂中石墨烯质量分数的增加,水蒸气解吸率随之增加,其中9G-MZ的解吸率接近90%,较MZ（81.8%）提升了9.7%。该研究可为复合吸附剂应用于吸附空气取水提供基础研究数据。     

乙醇在MIL-101上的吸附相平衡及其吸附机理

主要研究了MIL-101材料对乙醇的吸附性能和吸附机理。采用水热合成法制备了MIL-101(Cr),并分别应用N₂静态吸附、X射线粉末衍射(PXRD)、傅里叶红外光谱(FTIR)等分析手段对MIL-101晶形结构、孔隙结构参数进行分析表征。应用静态吸附法测定乙醇和水蒸气在不同温度下的吸附等温线,并讨论乙醇吸附在MIL-101(Cr) 4种吸附位的机理,根据吸附等温线估算出乙醇和水蒸气在MIL-101上的等量吸附热,并测试了乙醇在MIL-101上的吸附循环性能。研究表明,在298 K下,MIL-101的乙醇吸附容量为20.3 mmol·g^-1,远高于传统吸附材料。在低压下MIL-101对乙醇的吸附量高于水蒸气的吸附量,这是由于乙醇的偶极矩和分子动力学直径均比水大,使得乙醇分子在孔道中受到更大吸附力场作用;在低吸附量范围,乙醇在MIL-101上的等量吸附热要高于水蒸气的等量吸附热。在较高吸附压力条件下,主要发生多层吸附或孔填充,受吸附剂的孔容限制效应,尺寸越大的分子被吸附的物质的量会越少,由于乙醇的动力学直径(0.45 nm)大于水分子的动力学直径(0.268 nm),所以在较高吸附压力下乙醇在MIL-101上吸附量要小于水蒸气的吸附量。多次吸附脱附等温线测试显示MIL-101具有良好的乙醇吸附循环性能。     

Pollutant adsorption during activated carbon and steam regeneration in technical columns (experiments, modelling): Part 2. Influence of process parameters during steam regeneration of activated carbon beds on pollutant exit concentration

Experiments in activated carbon columns of technical scale with upstream adsorption and downstream steam regeneration showed that pollutant exit concentration of waste gas can be markedly decreased if the upper zone of the fixed bed is preheated to 120 °C before desorption and, additionally, if the bed is desorbed with superheated steam with a temperature 150 °C. With this improved steam regeneration technique a decrease in pollutant exit concentration is achieved: for example, from 20 to 3 mg m⁻³ toluene. An increase in adsorption time before pollutant breakthrough from 12 to 19 h is also noted.

During regeneration of a cold bed of activated carbon with saturated steam the particles will become wetted with condensate outside and adsorbed steam inside. These water condensation/adsorption effects are markedly reduced by preheating the particles to temperatures so far above that of steam condensation that steam adsorption is prevented too. Additionally the regeneration steam is superheated so that the temperature drop caused by heat of pollutant desorption is not so great that steam adsorption occurs.

The whole desorption-adsorption cycle in a technical scale bed, including the effects of Steam condensation/ adsorption, flux and suction of condensate, hetero-azeotropic pollutant distillation and evaporation of condensate was modelled.

Radial maldistribution effects (discussed in part 1 of this paper, Chem. Eng. Proc., 32 (1993) 359) have not been taken into account here.

The calculated flux rates of pollutant in the gas mixture leaving the bed during desorption and the pollutant breakthrough curves at the following adsorption step correlate quite well with experimental results.     

Glasses Resistant to Sodium Vapor at Temperatures to 700°C

Glasses resistant to attack by sodium vapor at temperatures up to 700°C were developed from the CaO-Al₂O₃-MgO-BaO-B₂O₃ system. The resistance of these glasses decreases sharply above the transformation temperature. The glasses have a high water content, have good wetting properties, and adhere well to materials such as aluminum oxide and niobium; thus they can be used as solder glasses and metalizing components. The surface layer formed on the glass during attack by sodium vapor has a specific electrical resistance which is lower by 2 to 3 orders of magnitude than that of glass not exposed to sodium vapor.     

Preparation of Porous Anatase Coating from Sol-Gel-Derived Titanium Dioxide and Titanium Dioxide-Silica by Water-Vapor Exposure

The effects of water vapor on the crystallization behavior of sol-gel-derived titanium dioxide (TiO₂) thin films that contained 0-50 mol% silica (SiO₂) were investigated. Anatase formed on exposure to water vapor at 60°-180°C, with a simultaneous decrease in the concentration of OH groups. An increase in the SiO₂ content of the exposed films led to an increase in the average crystalline size. Because crystallization of the exposed films of the films was not accompanied by shrinkage, porous anatase coatings were obtained via exposure at a relatively low temperature. Phase separation of the immiscible TiO₂-SiO₂ system was induced with water vapor, which resulted in acceleration of the crystallization of the sol-gel films.     

Adsorption kinetics and stability of poly(ethylene oxide)-block-polystyrene micelles on polystyrene surface

Herein, adsorption kinetics of poly(ethylene oxide)-block-polystyrene (PEO-b-PS) micelles from aqueous solution on PS thin films was investigated by quartz crystal microbalance with dissipation monitoring (QCM-D) and atomic force microscopy (AFM). The stability of adsorbed micelles against water washing was enhanced by the strong physical interaction between the substrate-identical core blocks of micelles and the PS substrate. The adsorption kinetics was investigated and analyzed by a model considering both the effects of diffusion and micelles reorganization on the PS surface. The micelles adsorption process was well captured by this model which demonstrated that the micelles reorganized on the surface after adsorption. The fitting results exhibited that the micelles with longer core blocks had less tendency to reorganize on the surface while reorganization took more part in the adsorption process of the micelles with shorter core blocks. In the stability studies, micelles with shorter PS blocks could partially desorb from the PS substrate while micelles with longer PS blocks were totally hindered from desorption. Desorption process of micelles was evaluated by the hydrodynamics-induced rolling model. The results indicated that hydrodynamic force-induced partial slip of the micelles on the PS surface might be responsible for micelle desorption. Because of the hydrophilicity of adsorbed micelle layer, adsorption amount of BSA on the modified surface was greatly reduced comparing with that of the bare PS surface.     

Modeling of coal swelling induced by water vapor adsorption

Gas adsorption-induced coal swelling is a well-know phenomenon. Coal swelling or shrinkage by adsorption or desorption of water vapor has not been well understood but has significant implications on gas drainage process for underground coal mining and for primary and enhanced coalbed methane production. Decreased matrix moisture content leads to coal shrinkage and thus the change of cleat porosity and permeability under reservoir conditions. Unlike gas adsorption in coal which usually forms a single layer of adsorbed molecules, water vapor adsorption in the coal micropores forms multilayer of adsorbed molecules. In this work, a model has been developed to describe the coal swelling strain with respect to the amount of moisture intake by the coal matrix. The model extended an energy balance approach for gas adsorption-induced coal swelling to water vapor adsorption-induced coal swelling, assuming that only the first layer of adsorbed molecules of the multilayer adsorption changes the surface energy, which thus causes coal to swell. The model is applied to describe the experimental swelling strain data measured on an Australian coal. The results show good agreement between the model and the experimental data.     

Effect of the substrate temperature on the physical characteristics of amorphous carbon films deposited by d.c. magnetron sputtering

The growth rate, composition, electrical resistivity, mass density, refractive index and microstructure of amorphous carbon (a-C) films prepared by direct current (d.c.) magnetron sputtering were investigated as functions of the substrate temperature (50–350°C). The hydrogen content determined by elastic recoil detection analysis (ERDA) and the electrical resistivity of films were found to be dependent on both the base pressure in the deposition chamber and substrate temperature. For films deposited below 200°C, the hydrogen content was less than 2 at.% and the substrate temperature was the only parameter which affected their electrical resistivity. The electrical resistivity decreased from 0.2 to 0.03 Ωcm as the substrate temperature increased from 50 to 200°C. The mass density of films evaluated from Rutherford backscattering (RBS) data and film thickness decreased from 2.2 to 1.4 g cm⁻³ with increasing substrate temperature. A linear relationship between the refractive index and the mass density of a-C films was clearly established. From the optical measurements, the decrease in mass density was correlated to an increase in porosity of films with increasing substrate temperature. The decrease in electrical resistivity with increasing substrate temperature was attributed to a graphitization of a-C films. This modification of the microstructure of a-C films as the deposition temperature was varied from 50 to 350°C was observed by examination of the cross-section of samples by transmission electron microscopy and Raman spectroscopic analyses of a-C films.     

Investigation into adsorption equilibrium and thermodynamics for water vapor on montmorillonite clay

The isothermal adsorption curves for water vapor on montmorillonite were measured by a gravimetric adsorption system. Dent's model was employed to estimate the adsorption behaviors of water vapor on primary adsorption sites and secondary adsorption sites. The thermodynamics analysis of water vapor adsorption was performed. At low vapor pressure region, primary adsorption predominates, and with increasing vapor pressure, secondary adsorption becomes notable. Primary adsorption sites have an evidently stronger adsorption affinity than secondary adsorption sites. With increasing vapor pressure, Gibbs free energy variation rapidly increases and then reduces slowly. Although increasing vapor pressure raises adsorption spontaneity on primary adsorption sites, the enhancement in vapor pressure decreases the spontaneity of water vapor adsorption on secondary adsorption sites. As adsorbed loading increases, isosteric heat of adsorption and entropy loss decrease first and then increase quickly. The gradually growing water clusters are responsible for the increase of entropy loss at late stage.     

多级孔硅铝酸盐的结构特性及其除湿性能

采用水热法制备出具有深度除湿功能（RH<20%）、高饱和吸附量和中低温快速脱附性能（<100℃）的除湿轮用多级孔硅铝酸盐吸附剂。采用N₂-吸附脱附、XRD、透射电镜、FT-IR和NMR等技术表征吸附剂的微观结构;采用动态水汽吸附分析仪（DVS）测试其吸附-脱附性能。结果发现,通过控制制备前体的微晶温度,可调控吸附剂在中低湿度工况下的除湿性能：微晶温度是通过影响吸附剂微观结构中有序介孔和类微孔结构的比例,来影响吸附剂的深度除湿功能;升高微晶温度会提高吸附剂中类微孔和骨架Al比例从而强化其深度除湿能力,但会显著降低介孔有序度及总孔容,削弱其饱和吸附量及脱附性能;过高的类微孔和骨架Al比例会提高吸附剂的脱附再生温度,增大除湿能耗。     

Monitoring of formation and redox transformations of poly(Methylene blue) films using an electrochemical quartz crystal microbalance

An electrochemical quartz crystal microbalance and cyclic voltammetry have been used to monitor the growth of poly(methylene blue) films on gold during potential cycling between −0.6V and 1.0V vs. sce in sodium phosphate buffer (pH 8.2) and Na₂SO₄ solutions. Both the adsorption/desorption of monomer methylene blue and the formation of poly(methylene blue) film can be followed by microgravimetry. The response of the polymer films is significantly separated from that of the monomer species in solution. It has been proved that anion sorption/desorption occur during the redox transformation of the polymer, while cations play no role. Preliminary results on the complex protonation/deprotonation equilibria are also discussed.     

ZIFs椭圆形孔窗的精细调控及糠醛/5-羟甲基糠醛吸附分离性能研究

在生物质催化炼制呋喃化合物的过程中,通常得到的是低浓度糠醛（Fur）和5-羟甲基糠醛（5-HMF）的混合物。基于Fur和5-HMF都是椭圆形分子,因此通过设计构筑和调控椭圆形孔窗的吸附剂可以实现Fur和5-HMF的筛分分离。选用二价钴盐和三种烷基取代基团逐渐增大的咪唑配体（2-乙基咪唑/2-eIm、2-丙基咪唑/2-pIm和2-丁基咪唑/2-bIm）合成了三种椭圆形孔窗尺寸逐渐减小的ANA拓扑ZIFs材料：ANA-[Co(eIm)₂]、ANA-[Co(pIm)₂]和ANA-[Co(bIm)₂]。首先解析了这三种ZIFs材料的晶体结构,并对其进行了PXRD、水蒸气吸附、N₂吸脱附和SEM等基本表征,然后采用静态吸附和动态柱吸附研究了这三种材料对Fur和5-HMF的吸附分离性能。静态吸附、单组分动态柱吸附以及综合速率模型模拟计算结果显示：ANA-[Co(pIm)₂]狭窄的椭圆形孔窗与Fur分子尺寸接近,但小于5-HMF,使得Fur分子可以吸附进入椭圆形孔窗,而5-HMF分子几乎不能通过。进一步在双组分Fur/5-HMF（5%/5%,质量分数）动态柱吸附中,ANA-[Co(pIm)₂]对Fur的吸附量为91.7 mg·g^-1,不吸附5-HMF。因此,通过改变咪唑配体取代基团精细调控ZIFs椭圆形孔窗尺寸,并利用ZIFs椭圆形孔窗的位阻效应实现了Fur和5-HMF的筛分分离。