Papers by Keyword: Hydrogenation

Abstract: Mg/Al bilayer thin films were successfully deposited by using D.C. magnetron sputtering technique. To study the effect of hydrogenation on structural, optical and electrical properties of Mg/Al thin films, the hydrogenation of the annealed thin films was done under different hydrogen pressure (15, 30 & 30psi). The structural properties of the films were investigated by Raman spectroscopy and decrease in intensity of Raman peaks with increasing hydrogen pressure was observed; this typically confirms the existence of hydrogen in Mg/Al thin films. The thin film is of semiconducting nature and it was found that the electrical conductivity of the film decreases with increasing hydrogen pressure applied. In the hydriding kinetics of the films, it was seen that the resistivity increased along with hydrogen absorption time. Eventually, it attains the equilibrium stage indicating the hydrogen absorption in the thin films. The rate of absorption of hydrogen increases with the pressure of hydrogen over different time ranges and decreases with the absorption of hydrogen over time.

Abstract: This paper demonstrates the transport of electron and hole carriers in two distinct hydrogenated amorphous semiconductor materials at different temperatures. Compared to crystalline materials, the amorphous semiconductors differ structurally, optically and electrically, hence the nature of carrier transport through such amorphous materials differ. Materials like hydrogenated amorphous silicon and amorphous IGZO have been used for the study of temperature dependent carrier transport in this paper. Simulation results have been presented to show the variation of free electron and hole concentration, trapped electron and hole concentration with energy at 300K for both the materials. The change in mobility with a change in the Fermi level has been plotted for different temperatures. The effect of temperature on Brownian motion mobility of electrons and holes in hydrogenated amorphous silicon and amorphous IGZO has been demonstrated towards the end of this paper.

Abstract: This work is devoted to the study of the activity of 1% platinum catalysts containing rare earth element oxides (OREE) - Gd₂O₃, Ce₂O₃ and aluminum oxide as a carrier in the hydrogenation reactions of nitro compounds on the example of n-nitrotoluene. These catalytic systems in the conditions of liquid-phase hydrogenation provide high selectivity of the process and practically quantitative yield. The process was controlled by the potentiometric method, the reaction rate was judged by the amount of hydrogen absorbed per unit time. It is found that 20% and higher aqueous alcohol solutions can be used as a solvent during hydrogenation. It was found that the initial hydrogenation rate for 1% Pt/Gd₂O₃ is 3.2 times higher, and for 1% Pt/Ce₂O₃ Cerium it is 1.6 times higher relative to the 1% Pt/Al₂O₃ comparison catalyst.

Abstract: The paper studies the activity of 1 % palladium catalysts containing rare earth oxides (REOs) and alumina as a carrier in the hydrogenation of nitro compounds exemplified by nitrobenzene and o-nitro anisole. Under the liquid-phase hydrogenation conditions, these catalytic systems provide high selectivity of the process and a quantitative yield. It has been found that the partial replacement of Al₂O₃ with REO allows increasing the hydrogenation rate by 5–6 times, as compared with the reference catalyst and by 1.2–1.7 times as compared with the individual carrier. The oxide mixtures (REO and Al₂O₃) containing 20–40 % REO allow reaching the same hydrogenation rate with that over an REO-containing 1 % Pd catalyst.

Abstract: The paper presents a method for the production of 1% platinum catalysts containing oxides of rare-earth elements (REE); it also dwells upon the results of analyzing such catalysts by scanning electron microscopy (SEM), x-ray diffraction analysis (XDA), and thermal analysis (DTA-TGA).

Abstract: Hydrogen is expected to be a viable solution for green-energy investment in future. However, hydrogen storage is a big challenge for stationary and mobile applications. Severe Plastic Deformation (SPD) techniques are well-known to be effective in enhancement of hydrogenation in metals hydrides. This paper shows the effect of a novel SPD technique named “High Pressure Torsion Extrusion-HPTE” on the hydrogenation of metal hydrides and compare it with the conventional method of ECAP. Results of mechanical testing and X-ray diffraction patterns showed significant enhancement in hardness and microstructural refinement in materials after HPTE. Accordingly, hydrogenation kinetics improved dramatically. This achievement could be an initiative to implement HPTE in synthesis of metal hydrides for clean energy applications.

Abstract: Catalytic hydrogenation of CO₂ into fuels and chemicals is regarded as one of the most promising alternatives to reduce the concentration of CO₂ in the atmosphere. In this study, double-promoted Cu/ZnO catalysts were prepared on Al₂O₃ and CNTs supports via impregnation method. The physicochemical properties of the catalysts were characterized by XPS, TEM, N₂ adsorption, H₂-TPR and CO₂-TPD analyses. Introduction of Nb and Zr promoters into the Cu-based catalysts on CNTs support resulted in smaller Cu nanoparticles and improved reducibility compared to those of the Al₂O₃-supported catalyst. The catalyst activity was evaluated in a fixed-bed stainless steel reactor operated at 22.5 bar and 523K. Conversion of CO₂ higher than 20% was achieved and product distribution was influenced by the type of catalyst supports.

Abstract: The paper presents the results of a study the hydrogen effect on the structural-phase transformations and the superelasticity in binary ultrafine-grained (UFG) TiNi based alloy after diffusion redistribution hydrogen as a result of aging at room temperature. The redistribution of hydrogen in the process of long-term aging after electrolytic hydrogenation of UFG wire specimens the Ti_49,1Ni_50,9 (at.%) stabilizes the B2 structure. Superelasticity in samples aged at room temperature after hydrogenation is significantly deteriorated.

Abstract: CO₂ conversion into valuable chemicals is an attractive option to deal with the increasing CO₂ concentration in the atmosphere. In this study, Cu/ZnO catalyst was synthesized on multi-walled carbon nanotubes (MWCNTs) and Al₂O₃ supports via incipient wetness impregnation method. The physicochemical properties of the catalysts were investigated using TEM, XRD, N₂ adsorption-desorption analysis, H₂-TPR and XPS. The performance of the synthesized catalysts in a CO₂ hydrogenation reaction was evaluated in a fixed-bed reactor at 503 K, 22.5 bar and H₂:CO₂ ratio of 3:1. TEM images showed that Cu/ZnO nanoparticles were deposited inside the CNTs as well as on the exterior walls of the CNTs. The average CuO crystallite size on Al₂O₃ and CNTs supports was 15.7 and 11 nm, repectively. Results of H₂-TPR studies showed that the reducibility of the catalyst was improved on the CNTs support. XPS analysis confirmed the presence of Cu²⁺ in the samples, however, the binding energy of Cu 2p_3/2 peak on the Al₂O₃ support was shifted to higher value compared to that of CNTs support. Products obtained from the CO₂ hydrogenation reaction in the presence of these catalyts were methanol, ethanol, methyl formate and methane. The CO₂ conversion of around 23% was obtained using both types of catalysts, however, Cu/ZnO on CNTs resulted in higher yield of methyl formate compared to that of Al₂O₃-supported catalyst.

Abstract: The results of hydrogen sorption and desorption processes investigation at commercially pure titanium alloy during hydrogenation at gas atmosphere are shown in this article. Titanium alloy hydrogenation at temperatures 350, 450 и 550 °С leads to δ-hydrides formation in samples’ volume. Hydrogen sorption rates were calculated on the linear parts of sorption curves and equal to 0.15·10-4 wt%/s at 350 °C, 0.86·10-4 wt%/s at 450 °C, 1.55·10-4 wt%/s at 550 °C. Phase transition in titanium-hydrogen system during thermally stimulated hydrogen desorption investigation by the means of short-wave diffraction of synchrotron radiation shows hydrides dissociation until 520-530 °C. Then α→β transition takes place until 690-720 °C and at this temperatures the phase transformation ends and additional hydrogen desorption peak appears in thermally stimulated hydrogen desorption curve. Defect structure at different hydrogen concentration investigation by the means of electron-positron annihilation techniques shows that hydrogen penetration into titanium leads to crystal lattice expansion. It initiates vacancy-type defects formation which reacts with hydrogen and forms defect-hydrogen complexes.