Combination Of Hydrogen Atoms Research Articles

Fluorinated carbon tubes as carriers for MgH2 with enhanced hydrogen storage performances

Heterogeneous elements doping in carbon materials has been an effective strategy to promote their chemical properties. In this work, fluorine atoms with strong electronegativity are doped on the surfaces of bamboo-shaped carbon nanotubes (FBCNTs) which serve as carriers for MgH2 nanoparticles (MgH2@FBCNTs) to improve the reversible hydrogen storage properties. Detailed experiments indicate that MgH2@FBCNTs begin to release hydrogen at 197.8 °C, and can release 5.36 wt% H2 at 275 °C within 30 min, and quickly absorb 3.48 wt% H2 at 100 °C under hydrogen pressure of 80 bar. In addition, cycling performance is significantly enhanced in the case of fluorinated Mg-based system. The mechanism of fluorine catalysis is mainly ascribed to the formation of C-F bonds, accelerating the dissociation or combination of hydrogen atoms, offering more active sites for the de/hydrogenation and preventing the growth and agglomeration during cycling. It is also important that fraction of F is consumed and form new phases MgF2/MgF2-xHx, which offers another pathway for H atoms.

Insights into the catalytic activity of trimetallic Al/Zn/Cu surfaces for the water gas shift reaction

In this study, we evaluated the performance of Al/Zn/Cu trimetallic catalysts for the water gas shift (WGS) reaction by Density Functional Theory (DFT) calculations. A previous DFT-based study comparing the activity of a large series of trimetallic surfaces towards the catalysis of water dissociation showed that the (AlZn)s@Cu(111) surface is likely the most active catalysts for the WGS reaction. Note that, the water dissociation is the rate-determining step of the WGS reaction on copper surfaces. Therefore, in this work we carried out a systematic study of all possible WGS reaction steps on such catalyst model surface. The most plausible WGS reaction mechanism on the trimetallic surface was inferred by comparing the activation energies, reaction energies and rate constants computed for its different reaction steps. The latter demonstrated that the WGS evolves on this trimetallic surface following an associative mechanism through the carboxyl intermediary, which is dehydrogenated on the surface, assisted by a hydroxyl, to produce CO2. The other WGS reaction product, this is H2, is obtained by the combination of hydrogen atoms from the water dissociation. The activation energy barriers obtained for the WGS reaction steps on that trimetallic surface are always lower than the adsorption energy of the correspondent reactants, indicating that desorption cannot compete with the catalytic process and also, that the trimetallic Al/Zn/Cu surface should be very reactive for the WGS reaction catalysis. Overall the results of this study allowed us to suggest that the active phase of commonly employed commercial catalyst based on Cu/ZnO/Al2O3 might embody a trimetallic alloy of Al/Zn/Cu.

極低炭素鋼の疲労強度

In order to study the effects of surface pickling in acid solution and test atmosphere on the fatigue strength of an ultra-low carbon steel (Interstitial free steel), the reversed bending fatigue tests were carried out under a bending stress range of 140-340MPa in air and Ar atmospheres.The results obtained were as follows.(1) The fatigue life for the test in air strongly depended on the time of pickling in the acid solution. The life increased as the pickling time increased, however it did not depend on the pickling time for a time span of less than 10minute. The fatigue life for a10minute pickling time increased with decrease in bending stress and a fatigue threshold existed at around120MPa.(2) The fatigue fracture surface showed that thecrack propagation process is dominated bx the formation of ductile fatigue striations and that the crack growth mechanism is a mixed mode of transgranular and intergranular.(3) However, the crack growth process was mostly intergranular in surface region and gradually changed to transgranular in the interior region.(4) The tendency of intergranular in the surface region was more distinguished in the longer pickling time and/or in air atmosphere.(5) The micromechanism of intergranular was believed to be related to a combination of hydrogen atoms dissolved during the pickling and, oxygen atoms penetrating from the test atmosphere at the crack front in the grain boundary region.

The Reaction of Hydrogen Atoms with Silyl Radicals; the Decomposition Pathways of Chemically Activated Silanes

Abstract The reactions of hydrogen atoms with silane and the methylated silanes - with the exception of tetramethylsilane -have been investigated in a fast flow reactor. Under our experimental conditions hydrogen abstraction from the Si-H bond is followed by combination of hydrogen atoms with the corresponding silyl radicals. The molecules formed in this way are activated by about 375 kJ/mol of vibrational energy. Two decomposition channels have been unequivocally identified, namely the elimination of molecular hydrogen and of methane, both with concomittant formation of the respective silylenes. In a subsequent step, silylene inserts into the substrate under formation of disilanes. With increasing degree of methylation. stabilization of the activated molecule competes with decomposition and dominates the kinetics in the case of trimethylsilane. With methyl -and dimethyl-silane, methyl radicals are observed as an additional reaction product. On the basis of RRKM calculations it is unlikely that they originate from a direct decomposition of the activated molecules. Absolute values for the room temperature rate constants of the abstraction reactions are given; for H+CH3SiH3, Arrhenius parameters have been determined.

Formation of Interstellar Molecular Hydrogen

Combination of hydrogen atoms on ice-coated grains can take place at temperatures above 20 K in the absence of enhanced binding sites.

Kinetics of the hydrogen-evolution reaction on palladium electrodes in molten potassium bisulphate

The kinetics of the electrochemical formation of hydrogen on differently prepared prepared palladium electrodes in the electrolysis of molten potassium bisulphate has been studied in the temperature range 240 to 330°C. Current/voltage curves fit two limiting Tafel lines having slopes of 2·3( RT/2 F) and 2·3(2 RT/ F) respectively. Semilogarithmic plots of decay curves exhibit a limiting region of slope 2·3( RT/2 F). At high temperature an interference due to permeation of hydrogen in the metal during the decay process is observed, particularly noticeable when bright palladium electrodes are used. The kinetics of the electrochemical process is interpreted, on the basis that the α-Pd-H system predominates, the rate-determining step being the combination of hydrogen atoms on the electrode surface, at least at low overvoltages. At higher ones the ion-plus-atom reaction can account for the experimental results.

Formation of ‘Molecular’ Hydrogen in the γ-Radiolysis of Water Vapour

In the Co/sup 60/ gamma radiolysis of water vapor in the presence of 0.054 mole % ammonia and >0.1 mole % oxygen (total pressure approximates 2 atm, temperature 120 deg C, dose rates 1.5 to 6 x 10/sup 17/ev g/sup -1/H/sub 2/O min/- 1), the production of molecular hydrogen was observed as a linear function of the dose. Under these conditions the rate of the reaction; H + O/sub 2/ yields HO/ sub 2/ precludes the formation of molecular hydrogen by the combination of hydrogen atoms or by hydrogen atom abstruction reaction with the ammonia, and the results are, therefore, strongly indicative of a process leading directly to inolecular hydrogen without hydrogen atom precurosors. This postulate was confirmed by measurements with oxygen-free water vapor containing 0.94, 3.8, and 4.7 mole % C/sub 6/D/sub 6/ (>95%) isotopic purity), under similar conditions of temperature, pressure, and dose rate. (P.C.H.)