Initial Stage Of Hydrogenation Research Articles

The mechanistic role of Ti4Fe2O1-x phases in the activation of TiFe alloys for hydrogen storage

TiFe alloy is considered an excellent candidate for stationary hydrogen storage owing to its superior hydrogen storage properties. However, the requisite for activation at high temperatures has hindered the practical application of TiFe alloy for hydrogen storage. This work investigates the activation of TiFe alloys with different Ti/Fe ratios. Results show that the TiFe0.90 alloy can be activated at room temperature and moderate hydrogen pressure (80 bar) compared to the poor activation kinetics of equimolar TiFe alloy. Microstructural characterization and surface analysis indicate that a higher content of Ti4Fe2O1-x phase formed in the TiFe0.9 alloy than in the TiFe0.95 and TiFe alloys. The embedded Ti4Fe2O1-x phase in the TiFe matrix plays a critical role in the overall activation processes, which serves as a conduit for hydrogen to interact with TiFe when it cracks during the initial stage of hydrogenation. The activation behavior is described in the following steps: (1) hydrogen absorption by the Ti4Fe2O1-x oxide on the surfaces of the TiFe matrix; (2) the Ti4Fe2O1-x cracks; (3) cracks extend into the TiFe matrix; (4) TiFe absorbs hydrogen. Understanding the activation behavior is critical to designing TiFe-based alloys with improved hydrogen storage properties.

Hydrogen storage properties of Ti2FeV BCC solid solution

This paper deals with hydrogen storage properties of Ti-V based BCC solid solution incorporated with Fe. The alloy with composition Ti2FeV was prepared by arc melting method. X-ray diffraction (XRD) and energy dispersive X-ray analysis studies confirmed formation of solid solution phase with uniform composition and BCC structure. SEM studies revealed the formation of irregular shaped particles with size in the range of few microns up on hydrogenation of the parent alloy. The alloy shows maximum hydrogen storage capacity of 3.41 wt.% at 20 bar and 303 K and the thermodynamic parameters established near room temperature suitability of the alloy for solid state hydrogen storage applications. Hydrogenation kinetics is found to be quite fast and detailed kinetic analysis were done to underscore the hydrogenation mechanism. Activation energy during the initial stage of hydrogenation is found to be 30.8 kJ/mol. The value decreases to 14.4 kJ/mol for extended duration of hydrogenation, and this is explained based on difference in rate determining steps existing at different time scales. Extent of hydrogen absorption as a function of temperature and time for Ti2FeV alloy.

Effect of cold rolling on the structure and hydrogen properties of AZ91 and AM60D magnesium alloys processed by ECAP

This investigation was conducted to evaluate the effect of cold rolling on the structure and hydrogen properties of two magnesium alloys, AZ91 and AM60D, after processing by equal-channel angular pressing (ECAP). The results show that the use of cold rolling after ECAP significantly increases the preferential texture for hydrogenation and increases the potential for the use of these alloys as hydrogen storage materials. The ECAP was performed through two different numbers of passes in order to give different grain sizes and both materials were subsequently cold-rolled through the same numbers of passes for a comparison of the hydrogenation absorption. It is shown that the hydriding properties are enhanced by an (0001) texture which improves the kinetics primarily in the initial stages of hydrogenation. The results demonstrate that optimum sorption properties may be acquired through a combination of fine grains and appropriate texture.

In situ observation on hydrogenation of Mg-Ni films using environmental transmission electron microscope with aberration correction

In situ transmission electron microscopy (TEM) was performed to observe the hydrogenation of Mg-Ni films in a hydrogen atmosphere of 80–100 Pa. An aberration-corrected environmental TEM with a differential pumping system allows us to reveal the Angstrom-scale structure of the films in the initial stage of hydrogenation: first, nucleation and growth of Mg2NiH4 crystals with a lattice spacing of 0.22 nm in an Mg-rich amorphous matrix of the film occurs within 20 s after the start of the high-resolution observation, then crystallization of MgH2 with a smaller spacing of 0.15 nm happens after approximately 1 min. Our in situ TEM method is also applicable to the analysis of other hydrogen-related materials.

Correlation between hydrogen storage properties and textures induced in magnesium through ECAP and cold rolling

It is feasible to obtain a significant enhancement of the hydrogen storage capability in magnesium by selecting an appropriate sequence of mechanical processing. The Mg metal may be produced with different textures which will then give significant differences in the absorption/desorption kinetics and in the incubation times for hydrogenation. Using processing by equal-channel angular pressing (ECAP), different textures may be produced by changing both the numbers of passes through the ECAP die and the ram speed. Significant grain refinement is easily avoided by using commercial coarse-grained magnesium as the starting material. The use of cold rolling after ECAP further increases the preferential texture for hydrogenation. The results show that the hydriding properties are enhanced with a (002) texture where the improved kinetics lie mainly in the initial stages of hydrogenation. An incubation time is associated with the presence of a (101) texture and this is probably due to the magnesium oxide stability in this direction.

Measurement of thermodynamic properties of some hydrogen absorbing alloys

In this paper, the effect of hydrogen concentration on the reaction enthalpies of some metal hydride alloys during hydriding and dehydring is presented. Pressure–concentration–temperature characteristics of the metal hydride alloys are measured under nearly isothermal condition during both absorption and desorption. Reaction enthalpies and entropies of LaNi 5, LaNi 4.7Al 0.3, LmNi 4.91Sn 0.15, Ti 0.99Zr 0.01V 0.43Fe 0.09Cr 0.05Mn 1.5 and MmCo 0.72Al 0.87Fe 0.04Ni 3.91 are estimated by constructing van't Hoff plots at different hydrogen concentrations. It is observed that the effect of hydrogen concentration on reaction enthalpies is more significant for the alloys having larger plateau slopes. At the initial stage of hydrogenation, metal hydrides are found to have larger reaction enthalpies which decrease gradually by about 5–15% at the end of the hydrogen absorption. At any given temperature, desorption enthalpies of LaNi 5, LmNi 4.91Sn 0.15, MmCo 0.72Al 0.87Fe 0.04Ni 3.91, LaNi 4.7Al 0.3 and Ti 0.99Zr 0.01V 0.43Fe 0.09Cr 0.05Mn 1.5 are found to be higher by about 5, 8, 10, 28 and 32% than their respective absorption enthalpies. Reaction enthalpies of the selected metal hydride alloys are expressed as a function of hydrogen concentration by a fourth order polynomial equation obtained from fitting with the experimental data.

Effects of surface dynamic behavior on hydrogen storage properties of sputter-deposited MgNi films

We have studied experimentally the distribution profiles of accommodated oxygen and hydrogen atoms in Mg–Ni films after different stages of hydrogenation at 8 bar pressure in the range of temperatures 210–250 °C by Elastic Recoil Detection Analysis (ERDA) and Nuclear Reaction Analysis (NRA) techniques and performed X-ray diffraction (XRD) structural and surface topography analysis. In agreement with previous publications, it is shown that even small impurity levels of uncontrollable oxygen during hydrogenation result in the formation of the oxide barrier on the surface changing hydrogen permeation properties. It is registered that the quantity of stored hydrogen during the first 3 h of hydrogenation increases up to 40 at.%, decreases up to 20 at.% after 6 h and increases again up to 40 at.% after 72 h. The quantity of the released hydrogen after 3 h hydrogenation increases with the increase in hydrogenation temperature. The observed experimental results are explained assuming that properties of the surface barrier layer changes during hydrogenation and modify hydrogen transport mechanism. The growing hydride phase in the bulk generates stresses that induce cracks and holes in the oxide barrier formed during the initial stages of hydrogenation, and hydrogen release becomes possible. At steady state, the hydrogenation properties adjust to dynamic processes on the surface and in the bulk.

ADSORPTION OF HYDROGEN AND OXYGEN ON SINGLE AND DOUBLE LAYER STEPPED SI(100) SURFACES

We have investigated the electronic band structure of hydrogen and oxygen adsorbed single and double layer stepped Si(100) surfaces by Empirical Tight Binding (ETB) method. The total electronic energies of the H,O-SA, DA, DB type stepped Si(100) systems are calculated with limited number of hydrogen and oxygen atoms separately to find out the most probable adsorption sites of the adatoms in the initial stage of hydrogenation and oxidation.

Effects of Organometallic Complexes on Hydrogenation of Coal Tar Pitch for High Performance Carbon Fiber.

The effects of organometallic complexes (Fe3(CO)12, Mo(CO)6, Ru3(CO)12, and Ru(acac)3) on the hydrogenation of coal tar pitch for high performance carbon fiber were investigated, and their activities were compared with those of commercial molybdenum-based supported catalysts. The hydrogenation was carried out with tritium-labelled gaseous hydrogen using a 350ml autoclave. The catalysts derived from the organometallic complexes were found to be more active for the hydrogen transfer from the gas phase to pitch than the molybdenum-based supported catalysts. Especially, the ruthenium complexes were most active for hydrogen transfer, and could effectively catalyze the hydrogenation of not only low molecular weight aromatics but also high molecular weight polycondensed ones in pitch. The results from XPS analyses of the used organometallic complexes suggest that the fine metal particles with a reduced state formed at the initial stage of hydrogenation may be the active form for the activation of molecular hydrogen or pitch molecules.

石炭液化アスファルテンの水添特性

Reaction mechanism, hydrogen transfer and consumption of asphaltene hydrogenation were examined at 723K and 10.1MPa of nitrogen or hyd-rogen with or without solvent and catalyst. The asphaltene was prepared by hyd-rogenating Akabira coal at 723K and 10.1MPa of hydrogen. The oil products, i.e. the hexane solubles, were fractionated by gas chromatography into four oil compo-nents, O1 to O4, having different boiling-point temperature ranges and aromatic ring numbers.On the basis of the time profiles of the asphaltene conversion and the yields of oil fractions and gas, it was shown that the rate for formation of oil components from the heavier ones was negligibly small so that they could be assumed to be formed indepen-dently each other from asphaltene. Asphaltene was easily hydrogenated to oil compo-nents by tetralin. In the presence of Co-Mo-Al2O3, only the rate for formation of the heaviest oil component, O4, was accelerated by hydrogen transfer from the gas phase. The hydrogen consumption per unit mass of asphaltene was found to increase in prop-ortion to the asphaltene conversion, implying that reactivity of asphaltene was almost invariable during initial stage of hydrogenation.

ChemInform Abstract: HYDROGENATION AND HYDROGENOLYSIS. XVI. THE REACTIONS OF TWO ISOMERIC ENOL ETHERS OF 3‐METHYLCYCLOHEXANONE OVER PLATINUM GROUP METALS

AbstractDie Wirksamkeit der Pt‐Metalle als Hydrierungskatalysatoren nimmt in bezug auf den Enolether (I) im Sinne Pt>> Os > Rh > Ir > Pd > Ru und in bezug auf (II) im Sinne Pt >> Os > Rh > Ir > Ru > Pd ab.

Hydrogenation and Hydrogenolysis. XVI. The Reactions of Two Isomeric Enol Ethers of 3-Methylcyclohexanone over Platinum Group Metals

Abstract The two isomeric enol ethers of 3-methylcyclohexanone, 1-ethoxy-3-methyl-, and 1-ethoxy-5-methylcyclohexenes (5 and 6), have been hydrogenated in ethanol with six platinum group metals as catalysts. Palladium, rhodium, and platinum efficiently catalyzed the addition of ethanol to the enol ethers to give the corresponding acetal, while iridium and ruthenium catalyzed it only slightly. Osmium was moderately active for the acetal formation. Extensive isomerization between 5 and 6 occurred over all catalysts. In addition, isomerization to an allyl ether, 3-ethoxy-1-methylcyclohexene (9), was observed with 5 over the metals other than palladium. Hydrogenation of 5 and 6 with palladium gave the trans-ether predominantly. With the other metals, the cis-ether was formed in large excess from 5 and the trans-ether in slight excess from 6 at the initial stage of hydrogenation. Hydrogenolysis of the ethoxyl group occurred extensively over platinum but only slightly with palladium and ruthenium. These results are compared with those obtained with the corresponding dimethylcyclohexenes and allyl ether 9.

Variation in spin-lattice relaxation time with saturation of seed oil

The spin-lattice relaxation time and the iodine value of oil samples hydrogenated to different degrees were measured. Both these parameters are found to change in a similar way in the initial stages of hydrogenation when the seed oil is in liquid form. At the later stages of hydrogenation, while the iodine value still decreases, the spinlattice relaxation time becomes nearly constant.

Hydrogenation of Oils by the Continuous Process

V.T. Athavale and S. K. K. Jatkar have recently carried out a detailed study of hydrogenation of ethyl oleate using nickel-carbonate kieselguhr catalyst (J. Indian Inst. Soi., 21, A, Part 25, 1938) and show a definite advance on previously recorded results. Iodine values, refractive indices and dispersions were determined on a number of samples of hydrogenated ethyl oleate, and results are recorded graphically. Contrary to expectation, iodine values did not vary linearly with refractive index in the initial stages of hydrogenation, but only after the iodine value had fallen by about twenty-five per cent. Comparison of refractive index and dispersion values of samples hydrogenated at different temperatures and, with different rates of flow of ethyl oleate over the catalyst showed that dispersions of samples having almost identical refractive indices vary considerably. Similarly, it was found that samples having the same iodine value, had dissimilar dispersions, thus indicating the formation of oleic acid during the reaction. A study of the effect of temperature on the velocity of hydrogenation at a fixed rate of flow of ethyl oleate over the catalyst further revealed a marked difference in dispersion values of samples hydrogenated at low temperatures and the conclusion was, therefore, reached that the isomers of oleic acid are formed because of the low activity for hydrogenation of the catalyst at low temperatures.