YMgGa as a hydrogen storage compound

The hydrogen absorption and desorption properties of the recently found ternary phase YMgGa have been studied. This compound absorbs 2.2 wt% hydrogen during the first cycle, but only 1.1 wt% can be stored reversibly for the following cycles under the applied pressure and temperature conditions. Hydrogen absorption and desorption properties were investigated by measuring the thermal desorption spectra and the pressure-composition isotherms while the crystal structure was determined using X-ray diffraction (XRD). The compound absorbs hydrogen at pressures above 0.2 MPa and 250 °C by decomposing into YH₃ and MgGa. This reaction is reversed when heating the hydride in a He atmosphere; hydrogen is released and the YMgGa phase is partially recovered together with YGa₂ and YH₂. The reformation of YMgGa occurs at temperatures below 450 °C on the expenses of hydrogen desorption from YH₂. This is not expected under these temperature conditions as YH₂ normally does not desorb hydrogen below 800 °C.     

Absorption-desorption of deuterium at Pd95%---RH5% alloy I: environment and temperature effects

The gas phase and electrolytic loading of Pd95%---Rh5% alloy with deuterium were investigated. Gas loading was carried out isochorically under 900 mbar D₂, by decreasing the temperature from 900 °C to 20 °C. Although some D₂ was absorbed from high temperatures downwards, most of the absorption was measured at 20 °C, at which the [D]/[Me] (deuterium to metal atom) ratio exceeded the value typical for pure Pd. When the alloy deuterides were heated from 20 °C to 900 °C, they where found to decompose for temperatures below 100 °C, but some deuterium was still absorbed at high temperatures. The electrolytic insertion of deuterium was carried out potentiostatically in alkaline D₂O electrolytes, the amount of deuterium loaded being determined by anodic extraction afterwards. The maximum [D]/[Me] ratios thus achieved at 25 °C, which exceeded those obtained by gas loading, were found to increase with the alkalinity of the electrolyte. With electrolytic insertion at 90 °C, alloy deuterides of large [D]/[Me] ratio could be obtained which, in the electrolytic environment, showed a thermal decomposition rate much slower than that tested in gas phase desorption experiments.     

Hydrogenation of arenes, alkenes and alkynes catalyzed by a sol–gel entrapped mixture of [Rh(cod)Cl]2 and Na[HRu3(CO)11]

A sol–gel entrapped 1:3 mixture of [Rh(cod)Cl]₂ and Na[HRu₃(CO)₁₁] catalyzes the hydrogenation of various unsaturated substrates by two distinguishable mechanisms. Under 13.8 bar H₂ and 20 °C methylated arenes react rapidly to give cycloalkane derivatives. XRD and TEM studies showed that under these conditions the hydrogenation proceeds without the generation of free metal particles. The hydrogenation of non-methylated arenes, as well as that of alkenes and alkynes, require a temperature of 80–120 °C at which the entrapped complexes form metallic nano-particles of 3–5 nm. Chloroarenes are also hydrodechlorinated at 120 °C, but require a hydrogen pressure of ≥25 bar. At both temperature ranges the catalysts are reusable at least four times. The high efficiency of the hydrogenation process at 20 °C is rationalized by a synergistic effect between the two different metal atoms of the combined catalyst. This may be related to a remote control model through a hydrogen spillover mechanism.     

Thermodynamic analysis of the copper production step in a copper–chlorine cycle for hydrogen production

The hybrid copper–chlorine (Cu–Cl) thermo/electrochemical cycle for decomposing water into its constituents is a novel method for hydrogen production. The process involves a series of closed-loop chemical reactions. The cycle is assumed driven in an environmentally benign manner using nuclear energy. The cycle involves five steps of which three are thermally driven chemical reactions and one has an electrochemical reaction. In the present study, the electrochemical reaction, copper (Cu) production step, is described with its operational and environmental conditions, and analyzed thermodynamically. Various parametric studies are carried out on energetic and exergetic aspects of the step, considering variable reaction and reference-environment temperatures. At a reaction temperature of 45 °C, the reaction heat of the Cu production step is 140,450 kJ/kmol H₂. At a constant reaction temperature of 45 °C, the exergy destruction of the step varies between 50 kJ/kmol H₂ and 7000 kJ/kmol H₂ when the reference-environment temperature increases from 0 °C to 30 °C. At a reaction temperature of 45 °C and a reference-environment temperature of 25 °C, the exergy efficiency of this step is 99% and decreases with increasing reference-environment and/or reaction temperatures.     

The influence of calcination on the size of nanocrystals, porous structure and acid–base properties of mesoporous anatase used as catalytic support

Mesoporous anatase was prepared following sol–gel and using urea as template. The influence of calcination temperature on the phase stability, nanocrystal/aggregate size, pore size distribution and specific surface area as well as on the acid–base behavior in aqueous solutions was studied using X-ray diffraction, laser-Raman and diffuse reflectance spectroscopies, scanning electron microscopy and laser scattering as well as N₂ adsorption–desorption isotherms and potentiometric mass titrations.The crystal structure was kept constant upon calcination over the whole temperature range, 200–500 °C. In this range anatase is constituted from primary nanocrystals. These are assembled into larger, rather spherical, clusters of about 30–40 nm and then into aggregates of various sizes (0.2–0.3 μm and 2–100 μm) with a distribution centered at about 12 μm. Increase of the calcination temperature caused an increase in the size of the primary nanocrystals from 8.1 nm at 200 °C to 17.1 nm at 500 °C, whereas calcination does not influence the morphology at micro-scale. Moreover, increase of the calcination temperature from 200 °C to 500 °C brings about a shift in the mean pore diameter from 47 nm to 91 nm accompanied by a decrease in the specific surface area and pore volume. The above effects were related with the aforementioned increase in the size of the primary nanocrystals. The value of pzc and the values of surface charge determined at various pH do not practically depend on the calcination temperature. The absence of pore space confinement effects was explained in terms of the structure and size of the interface development between the anatase surface and the electrolytic solution.     

Desorption related to adsorption of hydrogen via detailed balance on the Si(1 0 0) surfaces

Recent progress on desorption and adsorption dynamics of hydrogen (deuterium) on monohydride and dihydride Si(1 0 0) surfaces is reviewed and discussed. The dynamics experiments reveal that the desorption dynamics of hydrogen is well related to the adsorption dynamics via detailed balance. Dependence of time-of-flight (TOF) distributions of desorbed molecules on H(D) coverage is noticed to be important in understanding the kinetics mechanism of the adsorption/desorption reactions of hydrogen on the Si(1 0 0) surface. The desorption dynamics varies from the situation of strongly translational heating to the other situation of less translational heating with D coverage. This trend seems to be consistent with the 2H/3H/4H interdimer mechanism. However, despites by far the richest 4H configuration at high H coverage, the 2H desorption prevails over the 4H desorption already at 0.8 ML. To reconcile this unexpected desorption kinetics, a diffusion-promoted desorption mechanism is proposed. Height of the adsorption barriers for the 2H and 3H pathways could be reduced by the H-atom diffusion along the Si dimer rows, but that for the 4H pathway could not be the case because of no capability of diffusion on the H saturated surface. The desorption dynamics of hydrogen from the (3 × 1) dihydride surface is also reviewed and compared with the case on the monohydride surface. The sticking coefficients of hydrogen molecules onto the monohydride surfaces are evaluated from the TOF curves and found to be strongly activated by the kinetic energy. Not only the degrees of freedom of the molecules but also the vibrational degrees of freedom of substrate Si atoms determine the barrier height for adsorption. The desorption dynamics of hydrogen from the monohydride and dihydride surfaces appears to be quite similar, but the dynamics of substrate Si atoms is expected to be quite dissimilar between the two desorption pathways.     

Composition dependent structural modulations in transparent poly(vinyl alcohol) hydrogels

Transparent and stable Poly(vinyl alcohol) hydrogels were synthesized from polymer aqueous solution without resorting to a mixed solvent such as dimethyl sulfoxide and water. Contrary to the reported methods involving hydrogen bond induced physical crosslinking by repeated freeze–thawing at −20 °C, the present process demonstrates the gelation taking place at relatively higher temperature, i.e. 0 °C. While maintaining transparency in all the synthesized hydrogels, the present paper reports systematic structural and morphological variations in the hydrogels as a function of polymer concentration.     

Prediction of adsorption behavior of activated carbons

A study was made of the effect of temperature on predictive equations recently developed and applied to gas adsorption by beds of activated and impregnated carbons. Adsorption parameters, obtained for the adsorbate DMMP on small gram quantities of impregnated carbon at 25°C and applied to carbon bed breakthru times, were analyzed for changes resulting from direct temperature effects on gas diffusion, adsorption—desorption equilibria, volume expansion, relative pressure, and adsorbate—adsorbent interactions. Modifications in the adsorption parameters, calculated for bed temperatures ranging between 40.3 and 46.7°C, were used in the kinetic equations to predict breakthru times for M10 gas filters, each containing 13,847 g of carbon. The predicted values compared very well with those experimentally determined, the mean deviation in breakthru time being 5.82%, without regard to sign. A general analysis of a 10°C rise in temperature, from 25 to 35°C, for the M10 gas filter under the test conditions used, showed that the breakthru time would be lowered 20.0 min, 87% of this lowering due to a reduced adsorption rate constant, 9% due to a reduced adsorption capacity, and 4% due to volume expansion effects on concentration and flowrate.     

Preparation and properties of thermosensitive hydrogel microcapsules

Temperature-sensitive hydrophilic gel microcapsules have been newly prepared. That is, poly ( -lysineisopropylamide–terephthalic acid) microcapsules containing water have been obtained by an interfacial polymerization at a water/oil interface between -lysineisopropylamide and terephthaloyldichloride. The microcapsule changes its size between 33 and 35°C. Under 33°C, the microcapsules are fully spherical and can be redispersed in distilled water, while are aggregated above 35°C. The microcapsules, which are observed to show aggregation above 33°C, can be redispersed by decreasing temperature within a few second. The thermosensitive morphological changes of the microcapsules are thus reversible. Also, it has been shown that the permeability of sodium chloride through the microcapsule membrane changes remarkably between 33 and 35°C, while it is kept almost constant independent of temperature between 25 and 33°C or between 35 and 55°C. The permeability of solutes is higher under 33°C than that above 35°C. Such thermosensitive properties result from the fact that the polymer membrane has isopropylamide groups. That is, -lysineisopropylamide has a chemical structure similar to N-isopropylacrylamide, the polymer of which, poly (N-isopropylacrylamide), is a thermosensitive hydrogel having its phase transition temperature around 33°C.     

Rheological properties of reversible thermo-setting in situ gelling solutions with the methylcellulose–polyethylene glycol–citric acid ternary system (2): Effects of various water-soluble polymers and salts on the gelling temperature

The influences of various salts and water-soluble polymers on the phase transition temperature of thermo-setting gels prepared by combining methylcellulose (MC)–sodium citrate (SC)–polyethylene glycol (PEG) at appropriate ratios (the MC–SC–PEG system) were investigated. Concerning cations, comparison of the phase transition temperature between SC and tripotassium citrate (PC) showed a rapid increase in the viscosity of SC between 20 °C and 25 °C and an increase in the viscosity of PC between 30 °C and 35 °C. Concerning the valency of anions, comparisons among SC, disodium tartrate dihydrate (ST), disodium maleate hemihydrates (SM), and sodium sulfate (SS) showed a rapid increase in the viscosity of trivalent SC between 20 °C and 25 °C and changes in the viscosity of the three bivalent sodium salts (ST, SM, and SS) at ≥30 °C. Thus the phase transition temperature decreased with an increase in the valency of anions.Subsequently, the influences of various water-soluble polymers on the gelling temperature were compared. Using polyvinylpyrrolidone (PVP) instead of PEG, the gelling temperature decreased with an increase in the PVP concentration even without the addition of SC. Unlike PVP, the addition of xanthan gum as a viscosity-increasing polysaccharide did not reduce the gelling temperature irrespective of its concentration.Temperature-associated changes in viscosity were observed at a fixed SC concentration with changes in the concentration of PVP or PEG. The gel phase transition temperature increased from 46 °C to 50 °C in gels not containing PVP or PEG. The viscosity did not differ between the addition of PVP or PEG at a low concentration and its absence. However, the viscosity clearly changed after the addition of each agent at a high concentration.     

Nano-structured calcium silicate hydrate functionalised with iodine

Nano-structured calcium silicate hydrate can physisorb or chemisorb iodine, making it interesting for medical or materials science applications, where a slow, controlled release of iodine is desired. It was found that iodine can be sorbed and released by applying the elemental halogen in solution, either as a gas or as a solid. At ambient temperatures the sorption and desorption process is quantitative and physical, meaning that the same amount of iodine is taken up and released. At temperatures above 32.5 °C (305.7 K) iodine reacts with the calcium silicate hydrate forming a complex, which is stable above the sublimation temperature of iodine. The formation energy for the iodine calcium silicate hydrate complex was established to be 41.8 ± 0.8 kJ mol⁻¹ by calorimetry and the nature of the complex was investigated using X-ray photoelectron spectroscopy.     

Crystal and molecular structure, hydrogen bond and electrostatic interactions of bis(1-methylisonicotinate)hydrogen perchlorate studied by X-ray diffraction, DFT calculations, FT-IR, Raman and NMR spectroscopes

The crystal structure of bis(1-methylisonicotinate)hydrogen perchlorate, (MIN)₂H·ClO₄, has been studied by X-ray diffraction, DFT calculations, FT-IR, Raman, ¹H and ¹³C NMR spectra. The crystals are monoclinic, space group P2₁/n, with a pair of MIN molecules bridged by a short asymmetrical O·H·O hydrogen bond of 2.461(5) Å. The COO groups are twisted by 80.55° with respect to the plane of the pyridine ring. The anion interacts electrostatically with the positively charged nitrogen atoms of the neighbouring MIN molecules. The most stable conformer of isolated (MIN)₂H·ClO₄ and two homoconjugated cations, (MIN)₂H, have been analyzed by the B3LYP/6-31G(d,p) calculations in order to determine the influence of the anion on the hydrogen bonds in MIN·H·MIN unit. The FT-IR spectrum of the (MIN)₂H·ClO₄ shows a broad and intense absorption in the 1500–400 cm⁻¹ region, typical of short hydrogen bonds. The isotopic ratio, νOHO/νODO, is close to unity, indicating that the hydrogen bond is acentric (pseudo-type A).     

氢气在碳纳米管基材料上的吸附-脱附特性

利用高压容积法测定多壁碳纳米管(MWCNTs)及钾盐修饰的相应体系(K＋-MWCNTs)的储氢容量,并用程序升温脱附(TPD)方法表征研究氢气在MWCNTs基材料上的吸附-脱附特性.结果表明,在经纯化MWCNTs上,室温、9.0 MPa实验条件下氢的储量可达1.51％（质量分数）;K＋盐对MWCNTs的修饰对增加其储氢容量并无促进效应,但相应化学吸附氢物种的脱附温度有所升高;K＋的修饰也改变了MWCNTs表面原有的疏水性质.在低于723 K的温度下,H2/MWCNTs体系的脱附产物几乎全为氢气;773 K以上高温脱附产物不仅含H2,也含有CH4、C2H4、C2H2等C1/C2烃混合物;H2/K＋-MWCNTs储氢试样的脱附产物除占主体量的H2及少量C1/C2烃混合物外,还含水汽,其量与吸附质H2源水汽含量密切相关.H2在碳纳米管基材料上吸附兼具非解离 (即分子态) 和解离(即原子态)两种形式.     

A single-component liquid-phase hydrogen storage material

The current state-of-the-art for hydrogen storage is compressed H(2) at 700 bar. The development of a liquid-phase hydrogen storage material has the potential to take advantage of the existing liquid-based distribution infrastructure. We describe a liquid-phase hydrogen storage material that is a liquid under ambient conditions (i.e., at 20 °C and 1 atm pressure), air- and moisture-stable, and recyclable; releases H(2) controllably and cleanly at temperatures below or at the proton exchange membrane fuel cell waste-heat temperature of 80 °C; utilizes catalysts that are cheap and abundant for H(2) desorption; features reasonable gravimetric and volumetric storage capacity; and does not undergo a phase change upon H(2) desorption.     

贵金属铱对氨分解用镍基催化剂的促进作用研究

用湿式浸渍法制备了不同贵金属质量分数的镍-铱双金属催化剂,以氨分解为模型反应对其催化性能进行考察.结果表明,贵金属铱的添加提高了10%Ni/γ-Al2O3的低温活性.在铱的质量分数不高于1%时,氨分解反应活性随铱质量分数的增加出现最大值(相应的Ir质量分数为0.7%),对应的10%Ni-0.7%Ir/γ-Al2O3催化剂在400 ℃时,氨分解率为43.55%,较单组分的Ni催化剂高40.0%.用H2-TPR、H2-TPD 、BET和XRD表征方法对催化剂进行了表征.结果表明,Ir与活性组分Ni之间存在协同作用.铱的添加促进了活性组分的分散、减小了镍的晶粒尺寸,且增加了催化剂活性位的数量,从而提高了催化剂的氨分解性能.     

“Superpermeability” and “pumping” of atomic hydrogen through palladium membranes

Permeation of atomic as well as molecular hydrogen through palladium membranes has been investigated experimentally in the temperature range from room temperature to 200 °C and at a higher incident flux of hydrogen atoms on palladium surface than in previous studies. The results demonstrate that phenomena of ‘superpermeability’ and ‘pumping’ of atomic gases through metal membranes are of a common nature. A theoretical model based on chemical thermodynamics and diffusion theory adequately describes the quantitative relationships observed in experiments. It was found that permeability of atomic hydrogen depends strongly on the magnitude of surface incident flux and membrane temperature.     

Catalytic coprocessing of waste plastics and petroleum residue into liquid fuel oils

Waste plastics of different types were catalytically coprocessed with petroleum residue of light Arabian crude oil in the presence of a number of catalysts. The purpose of the study was to explore effects of various conditions such as catalyst type, amount of catalyst, reaction time, pressure and temperature on the product distribution. The waste plastic studied included low-density polyethylene (LDPE), high-density polyethylene (HDPE), polystyrene (PS) and polypropylene (PP). A series of single (waster plastic with catalyst) and binary (waste plastic and residue with catalyst) reactions were carried out in an autoclave reactor under variable reaction conditions. The reaction conditions used were 1, 3 and 5 wt.% catalysts, 30–120 min reaction time, 400–430 °C reaction temperature and 500–1200 psi hydrogen pressure. The product distribution achieved for residue/plastic/catalyst system showed higher yields of liquid fuels as compared to residue/plastic system. Hydrocarbon gases were formed as well along with heavy oils, insoluble gums and coke. At the reaction conditions of 3 wt.% NiMo catalyst, 90 min reaction time, 1200 psi hydrogen gas pressure, 430 °C temperature and residue to plastic feed ratio of 3:2 (wt.) afforded maximum conversion of the plastics into liquid fuel oils.     

Structural analysis of the microporous semiconductor K-SBC-1 during its reversible sorption of water

The reversible sorption of water molecules in the crystalline microporous semiconductor K-SBC-1 was investigated using temperature-resolved single-crystal XRD analysis. Three crystallographic sites of adsorbed water molecules, differing in adsorption strength, were discovered in the pores of K-SBC-1. The least tightly bound is located at the centre of the {Sb₁₂O₁₈} tube and begins to desorb around 50 °C. Above 200 °C the more strongly bound water molecules rearrange from their potassium-coordinating positions to the centre of the tube, thus obtaining the characteristics of the loosely bound water, and desorb thereafter. At 240 °C approximately 10% of the water has desorbed, leaving the host framework of K-SBC-1 intact. Upon re-adsorption of water at room temperature the molecules preferentially adsorb at sites in the centre of the {Sb₁₂O₁₈} tube. This shows that a heat treatment of 240–300 °C activates K-SBC-1 for sorption and explains the observed facile desorption of water from activated samples.     

Three steps in the anode reaction of the polymer electrolyte membrane fuel cell. Effect of CO

We studied the influence of CO poisoning of the anode in the polymer electrolyte membrane fuel cell (PEMFC) using electrochemical impedance spectroscopy (EIS). The anode impedance was found by first feeding neat hydrogen gas and next hydrogen with CO into one of the electrodes, keeping neat hydrogen gas on the other electrode as a reference. The electrodes were E-TEK Elat gas-diffusion electrodes with 0.5 mg Pt/cm², and the membrane was Nafion^® 117. The CO concentration was 103 ppm, and the total pressures were 1, 2.5 and 4 bar. Operating temperatures were kept constant, 30.0 °C or 50.0 ± 0.1 °C. Bias voltages of 0 and 0.05 V were used. Three steps were revealed in the reaction mechanism, the slow adsorption/diffusion step, the charge transfer step and the proton hydration step, confirming earlier results. Carbon monoxide affects the charge transfer step by blocking active sites and by affecting the surface polarisation. We further conclude that CO adsorbs to the porous carbon matrix, and reduces significantly the rate of surface diffusion of hydrogen to the surface.     

Kinetic models based in biomass components for the combustion and pyrolysis of sewage sludge and its compost

In the present work, pyrolysis and combustion of the sewage sludge (fresh and composted) have been simulated using five fractions: low stability organic compounds, hemicellulose, cellulose, lignin-plastic, and inorganic compounds. Thermal behavior and kinetic parameters (pre-exponential factor and apparent activation energy) of the main components of the sludge are similar to those reported for hemicellulose, cellulose, and lignin present in lignocellulosic biomass. Comparing non-isothermal thermogravimetric analysis data obtained from fresh and composted sewage sludge, it is possible to measure the efficiency of the composting process. Most of the biodegradable matter is volatized in a temperature range from 150 °C to 400 °C. Non-biodegradable organic matter volatilizes between 400 °C and 550 °C. In both, fresh and composted sludges, oxygen presence increases the mass loss rate at any temperature, but differences between pyrolysis and combustion are focused in two clearly defined ranges. At low temperature (200–350 °C), mass loss is related with a volatilization process. At higher temperature (350–550 °C), mass loss is due to slow char oxidation (oxidative pyrolysis).