Hydrogen Decomposition Research Articles

Theoretical investigation of selective hydrogenation of 1,3-butadiene on Pt doping Cu nanoparticles

Recent results confirm that a single-atom Pt alloy effectively catalyzes hydrogenation of 1,3-butadiene. Here the C4H6 hydrogenation mechanisms on Pt doping Cu nanoparticles are studied using density functional theory simulations. The simulation results indicate that H2 dissociation on the surfaces of pure Cu is impossible at room temperature. However, the structure of Pt-doped Cu makes hydrogen decomposition process easier. The combination of H2 and C4H6 on the Pt single-atom site is possible since the corresponding reaction barrier values are less than 0.71 eV. The generated 1-C4H8 or 2-C4H8 molecule can not be co-adsorbed with H2 on the Pt single-atom site. Even if H2 is pre-decomposed as hydrogen atoms, they also can not react with C4H8 on the Pt single-atom site at room temperature since the corresponding reaction barrier values are more than 0.90 eV. The co-adsorption of H2 and C4H8 on Pt diatomic sites is probable, and the further saturated hydrogenation to generate C4H10 is promising due to a small reaction barrier (∼0.66 eV).

Heterogeneous Fenton oxidation of nitric oxide by magnetite: Kinetics and mechanism

Magnetite materials were used for catalytic decomposition of peroxide hydrogen since Fe2+ can react with peroxide hydrogen directly to generate OH rather than Fenton-like reaction. The purpose was to determine the NO oxidation under various working conditions. The features of fresh and used catalysts was analyzed according to XRD and XPS. In addition, the reaction conform to a pseudo-first order kinetics pattern on the basis of results. The rate constants was calculated by different results and the activation energy for the reaction was obtained as 32.07 kJ/mol.

A theoretical insight into a feasible strategy for the fabrication of borophane.

Borophane, hydrogenated borophene, is an ideal material for nanoelectronic applications because of its high stability and its excellent mechanical and electronic properties. However, the fabrication of borophane has not been realized. Through a comprehensive density functional theoretical study, we propose a novel and feasible strategy for the fabrication of borophane, which is accomplished through an electrochemical method by modulating the charge that the borophene carries to activate hydrogen molecule decomposition on it. Our computational results show that by modulating the charge state of borophene, the energy barrier of H2 dissociation on it can be dramatically reduced to 0.27 eV, and the reaction is exothermic by 2.08 eV. This study demonstrates that the reaction of hydrogen decomposition on charged borophene to produce borophane is kinetically and thermodynamically feasible. In addition, the modulation of the charge state of borophene is feasible and less energy consuming due to its metallic character.

First-Principles Study on the Mechanism of Hydrogen Decomposition and Spillover on Borophene

Borophane, a derivate of borophene, has been shown to eliminate the phonon imaginary frequency of borophene entirely with enhanced structural stability and be a 2D Dirac material with many appealing properties similar to its counterpart graphene. However, the mechanisms involved in borophene hydrogenation are still unclear, which are essential to borophane fabrication in experimental studies and which benefit our understanding of borophene functionalization. In this work, we investigate H2 adsorption and dissociation with (without) an external field and the subsequent spillover of H atoms on borophene based on density functional theory (DFT) to shed light on the procedure of borophene hydrogenation. We find that the incorporation of positive electric fields could facilitate the borophane formation with shallower energy barriers for H2 decomposition and H atoms present ultrahigh mobility on borophene under positive field. The origin of the field modulated energy barriers has been discussed. Our work provid...

XPS study of influence of exposure to air on thermal stability and kinetics of hydrogen decomposition of MgH2 films obtained by direct hydrogenation from gaseous phase of metallic Mg

Mechanism of influence of exposure to air on thermal stability of MgH2 obtained by direct hydrogenation from the gas phase, the nature of the hydride sensitivity to the negative impact of air and the role of its surface chemical state have not been studied enough. The present article presents data of X-ray photoelectron spectroscopy (XPS) measurements of the Mg 2s, O 1s, C 1s core-level spectra of surface of hydride MgH2 films derived by gas phase hydrogenation of model samples of metallic Mg, and the evolution of changes in the chemical state of the surface of the hydride films depending on the time of exposure to air and formation conditions (hydrogen pressure and hydrogenation regime). Based on results of XPS, X-ray diffraction (XRD), and thermodesorption spectroscopy (TDS), the existence of a relationship (correlation) between chemical surface condition of hydride MgH2 films obtained at different hydrogen pressures (3.0MPa and 11.5MPa) and their thermal stableness and temperature of the beginning of hydride decomposition has been established.

A suspected derivative morphology for pheophytin and the enhanced hydrogen decomposition it caused

A new class of unorthodox morphologies of pheophytin, called the semi- and fully-derivative forms, was suspected to have existed all along in the electron transfer pathway of photosystem-II (PS-II) in plants. More importantly, as likely a natural pre-form of the latter, the semi-derivative morphology was further conjectured to play a catalytic role in the hydrogen fuel cells owing to its particular structural features. In this research, the proposed new class of derivative morphologies was speculated to be energetically more favorable, than the orthodox one in textbooks, in supporting a proton current within its porphyrin ring and in interacting with hydrogen gas molecules. This supposition appeared to be viable according to the spectral comparison among results from 1st-principle quantum calculations, measurements and literatures, as well as to the need for a proton current to address existing NMR spectra of pheophytin. Then, indirect proof of existence of such derivative’s features was provided by our experimental effort that pheophytins could efficiently getter hydrogen gas. Lastly, processed pheophytin samples were experimentally shown to be capable of catalyzing the hydrogen decomposition in fuel cells.

Understanding Hydrogen Peroxide Decomposition Activity of Transition Metal Oxide Catalysts in Oxygen Reduction Reaction

Energy storage is essential for large-scale integration of renewable energy such as solar and wind into the electricity grid. Fuel cells and metal-air batteries are promising technologies for grid-scale energy storage owing to their high energy densities and environmental friendliness. However, it is well known that the slow kinetics of the oxygen reduction reaction (ORR) at the cathode limits the efficiency of these fuel cells and metal-air batteries. Among transition metal oxides, calcium-doped lanthanum cobalt oxide is one of the promising catalysts for ORR because of the ability of these materials to support both oxygen evolution and oxygen reduction reactions [1]. In previous work, we demonstrated that in transition metal oxide–carbon composites catalysts, carbon is the primary electrocatalyst for the two electron electro-reduction of oxygen to hydrogen peroxide and the transition metal oxide decomposes the hydroperoxide to generate additional oxygen [2]. Therefore, we have focused on understanding the role of mixed metal oxides on decomposition of hydrogen peroxide for designing more active carbon-based catalyst systems. Specifically, we have studied the effect of manganese substitution of cobalt in calcium-doped lanthanum cobalt oxide on the hydrogen decomposition rate of the catalysts. Manganese-substituted compounds of the formula La0.6Ca0.4Co1-xMnxO3 compound with x value = 0.0, 0.1, 0.3, 0.5, 0.7, 0.9 and 1 were synthesized by the sol-gel method using the Pechini process. As previously described [3], a two-step heat treatment was employed for the synthesis of these compounds. In the first step the material subjected to controlled combustion at 120-170 oC, then the material was collected, ground and heat-treated in a second step sintering process at 700oC for 2 hours. The decomposition characteristics of hydrogen peroxide on various transition metal oxides was measured by oxygen reduction studies on rotating-ring-disk (coated glassy carbon) electrode, and by steady state polarization studies of the oxidation and reduction of hydrogen peroxide. We have demonstrated that the mixed potential of the oxide electrode under open circuit conditions could be predicted from the kinetics of the conjugate reactions of peroxide oxidation and reduction. We also find that the higher rate of oxidation of hydroperoxide correlated directly with the improved oxygen reduction activity in the composite catalyst. The presentation will discuss these findings. Figure 1

Pouous TiO2 nanofibers decorated CdS nanoparticles by SILAR method for enhanced visible-light-driven photocatalytic activity

1D porous CdS nanoparticles/TiO2 nanofibers heterostructure has been fabricated via simple electrospinning and a successive ionic layer adsorption and reaction (SILAR) process. The morphology, composition, and optical properties of the resulting CdS/TiO2 heterostructures can be rationally tailored through changing the SILAR cycles. The photocatalytic hydrogen evolution and decomposition of rhodamine B (RhB) of the as-synthesized heterostructured photocatalysts were investigated under visible light irradiation. Compared to TiO2 nanofibers，the as-obtained CdS/TiO2 heterostructures exhibit enhanced photocatalytic activity for hydrogen production and decomposition of RhB under visible-light irradiation. The heterojunction system performs best with H2 generation rates of 678.61μmolh−1g−1 under visible light irradiation which benefits from the two effects: (a) the 1D porous nanofibrous morphology contributes to not only more active sites but also more efficient transfer of the photogenerated charges (b) the synergetic effect of heterojunction and photosensitization reducing the recombination of photogenerated electrons and holes.

Concept study of a hydrogen containment process during nuclear thermal engine ground testing

A new hydrogen containment process was proposed for ground testing of a nuclear thermal engine. It utilizes two thermophysical steps to contain the hydrogen exhaust. First, the decomposition of hydrogen through oxygen-rich combustion at higher temperature; second, the recombination of remaining hydrogen with radicals at low temperature. This is achieved with two unit operations: an oxygen-rich burner and a tubular heat exchanger. A computational fluid dynamics methodology was used to analyze the entire process on a three-dimensional domain. The computed flammability at the exit of the heat exchanger was less than the lower flammability limit, confirming the hydrogen containment capability of the proposed process.

Utilization of Low-grade Iron Ore in Ammonia Decomposition

Due to its cleanliness, fast energy cycle, and convenience of energy conversion, hydrogen has been regarded as the new energy source. Conventional process to produce hydrogen yield large amount of CO as byproduct. Moreover, the hydrogen storage and transportation have become the drawbacks in hydrogen economy. Thus, there has been increased interest in the hydrogen transportation medium as alternatives from the conventional process to produce and transport hydrogen. Ammonia has drawn worldwide attention as the most reliable hydrogen transportation medium. Through the decomposition of ammonia, hydrogen and nitrogen gas were produces as the byproduct without any CO or CO2 emission. In this experiment, the ore were introduced as the medium for ammonia decomposition. The ore were put into quartz tube reactor and were dehydrated at 400°C for 1 hour, then hydrogen reduced for 2hours before and undergone ammonia decomposition at 500-700°C for 3hours. The effects of temperature to the % conversion of ammonia decomposition were also studied. Ammonia decomposition at higher temperature gives higher conversion. As seen in the results, the NH3 conversion decreased with increasing time and the value after 3hours of reaction increased in the sequence of 500°C<600°C< 700°C. During ammonia decomposition, nitriding of iron occurred. The relation between temperature and the nitriding potential, KN is also investigated. The purpose of this study is to investigate the utilization of low-grade ore as medium for ammonia decomposition to produce hydrogen.

Hydrocarbons via CO2 Hydrogenation Over Iron Catalysts: The Effect of Potassium on Structure and Performance

We present a study in which the suitability of potassium promoted iron-based Fischer–Tropsch (FT) catalysts for the generation of synthetic natural gas additives via the hydrogenation of carbon dioxide through a combined reverse water gas shift (WGS) and FT reaction is studied. Using novel in situ instrumentation based on XRD and magnetometry techniques the reversible conversion of metallic iron to Hagg carbide under reaction conditions and its decomposition in hydrogen could be monitored. The facilitating effect of potassium in the formation of iron carbide could be exposed as function of time on stream. While the FT reaction was reduced in the presence of high potassium loadings the reverse WGS reaction seemed to be unperturbed. A faster activation of an iron phase obtained via the decomposition of iron carbide, compared to the initial activation of a pristine iron phase obtained via the reduction of iron oxide was witnessed.

Removal of SU-8 by two types of hot-wire atomic hydrogen sources—Dissection of contributions by atomic hydrogen and substrate heating

The removal of the permanent photoresist SU-8 by atomic hydrogen was studied using hot-wire reactors of the conventional open type and the remote type. The remote type hot wire reactor has a separate glass chamber for hydrogen decomposition via the hot wire, and can supply atomic hydrogen to a substrate without significant radiation from the hot wire. Therefore, the atomic hydrogen density and substrate temperature can be independently controlled. Using the remote type setup together with the conventional open type setup, the authors demonstrated that the presence of atomic hydrogen in combination with substrate heating was necessary to completely remove SU-8. At a substrate temperature below 150 °C, the SU-8 removal rate was impractically small. In addition, after the apparent removal of SU-8 a white powder-like residue was found on the sample, which was identified with x-ray photoelectron spectroscopy as silicon components that originated from the silane coupling agent in SU-8. At a substrate temperature above 250 °C, on the other hand, SU-8 was thermally decomposed in a reduced pressure hydrogen environment, but the final state of the sample was an apparently carbonized film, that is likely owing to the insufficient fragmentation of SU-8 molecules in the absence of atomic hydrogen.

Binding specificity of polypeptide substrates in NS2B/NS3pro serine protease of dengue virus type 2: A molecular dynamics Study

The pathogenic dengue virus (DV) is a growing global threat, particularly in South East Asia, for which there is no specific treatment available. The virus possesses a two-component (NS2B/NS3) serine protease that cleaves the viral precursor proteins. Here, we performed molecular dynamics simulations of the NS2B/NS3 protease complexes with six peptide substrates (capsid, intNS3, 2A/2B, 4B/5, 3/4A and 2B/3 containing the proteolytic site between P1 and P1′ subsites) of DV type 2 to compare the specificity of the protein-substrate binding recognition. Although all substrates were in the active conformation for cleavage reaction by NS2B/NS3 protease, their binding strength was somewhat different. The simulated results of intermolecular hydrogen bonds and decomposition energies suggested that among the ten substrate residues (P5–P5′) the P1 and P2 subsites play a major role in the binding with the focused protease. The arginine residue at these two subsites was found to be specific preferential binding at the active site with a stabilization energy of <−10kcalmol−1. Besides, the P3, P1′, P2′ and P4′ subsites showed a less contribution in binding interaction (<−2kcalmol−1). The catalytic water was detected nearby the carbonyl oxygen of the P1 reacting center of the capsid, intNS3, 2A/2B and 4B/5 peptides. These results led to the order of absolute binding free energy (ΔGbind) between these substrates and the NS2B/NS3 protease ranked as capsid>intNS3>2A/2B>4B/5>3/4A>2B/3 in a relative correspondence with previous experimentally derived values.

Binary complexes [Co(A)6][M(C2O4)3] (A = NH3, 1/2C2H8N2, M = Fe, Cr): Synthesis, properties, and thermal decomposition

Binary complexes [Co(A)6][M(C2O4)3] (A = NH3, 1/2C2H8N2, M = Fe, Cr) are synthesized, and their physicochemical properties and thermal decomposition in air, argon, and hydrogen are studied. The qualitative and quantitative analyses are carried out for the solid and gaseous thermolysis products. Similar regularities are revealed in the behavior of complexes [Co(NH3)6][Fe(C2O4)3] (I), [Co(En)3][Fe(C2O4)3] (II), [Co(NH3)6][Cr(C2O4)3] (III), and [Co(En)3][Cr(C2O4)3(IV). The solid thermolysis product for complexes I and III in argon at 225 and 300°C is Co(NH2)2M(C2O4)2, respectively; and that for complexes II and IV at 280 and 380°C is Co(En)2M(C2O4)2. The gaseous thermolysis products are CO and CO2, NH3, En partially isolated upon thermal destruction, other products of En destruction, and En itself. Complex III forms the most highly dispersed solid products in a range of 300–400°C.

A neutronic feasibility study on a small LEU fueled reactor for space applications

In this paper, a neutronic feasibility study on a small space reactor with LEU fuel is presented. The minimum critical reactor mass of a simple homogeneous core model was investigated for the variety of fuel types, moderator materials, and reflector materials. Lithium hydride (LiH) with 99.99% enriched 7Li showed a very good performance in terms of reactor mass. However, further study should be conducted to resolve the problems that could rise from the poor thermal properties of LiH such as a low melting point, low thermal conductivity, and high thermal expansion coefficient. The combination of uranium metal fuel and zirconium hydride (ZrH1.5) moderator with a Be reflector showed a good performance as well. Uranium hydride (UH3) is a very attractive fuel from a neutronic point of view. However, it requires hydrogen pressurization for high temperature operation due to its low hydrogen decomposition temperature. It was also shown that the core reactivity can be maximized or the critical reactor mass can be further reduced by adopting a heterogeneous core configuration through stacking fuel and moderator plates. Three small space reactors with a control rod system and NaK coolant pipes have been designed and the neutronic performance of these reactors during their life time as well as their safety behavior during various accident scenarios have also been investigated. All the three reactors showed similar neutronic performance during their life time, nevertheless, the smallest reactor mass was achieved in case of a reactor with heterogeneous core configuration. It was also found that a thick reflector is required to keep the reactor subcritical during launch accident scenarios involving a loss of the reflector and the control rods. In “the worst-case accident scenarios” in which the control rods are missing without any damage in the reflector, the reactors became supercritical even in cases when thick reflectors are used. Such situation is inevitable for any space reactor as long as a conventional control rod system or control drum system is adopted as the reactivity control system of the reactor. Efforts should be made to overcome this drawback of the conventional reactivity control systems.

Metal assessment for the catalytic reduction of bromate in water under hydrogen

The presence of bromate ion in water and wastewater is a known problem due to its carcinogenic potential, and other toxic effects on human health. The catalytic reduction under hydrogen is an attractive process for its removal by conversion into bromide ion.Different metals (Pd, Pt, Ir, Rh, Ru, Fe, Sn, Cu, Zu and Ni) supported on activated carbon were assessed for the catalytic reduction of bromate under hydrogen at room temperature and pressure. All these catalysts are active in the conversion of bromate into bromide. Ruthenium, palladium, platinum and rhodium were shown to be the most efficient metals. When the available metal surface for reaction was considered, platinum showed the best activity. The trend of activities was associated to (and discussed on the basis of) the dissociative chemisorption energy of hydrogen over the metals.A mechanism for the reduction of bromate was proposed, involving reactions in the liquid phase, on the surface of the activated carbon support, and on the surface of the supported metal particles. It is proposed that the reaction mechanism on the surface of the metal catalysts comprises the decomposition of hydrogen and subsequent reaction with bromate. This reaction leads to the release of bromide ion and water. The oxidized metal is then reduced by hydrogen, thus closing the catalytic cycle.

Pyrolysis characteristics of GFRP (Glass Fiber Reinforced Plastic) under non-isothermal conditions

The pyrolysis characteristics of GFRP (Glass Fiber Reinforced Plastic), which is a thermosetting plastic composed of glass fibers and polymer compounds, were determined under non-isothermal conditions while heating at 5–20°C/min from 500 to 900°C using a thermo-gravimetric analyzer (TGA) and a batch-type pyrolyzer. The kinetic parameters for the GFRP were derived from the Freedman method with resultant activation energy ranging from 41.4kJ/mol to 78.4kJ/mol. The main components of the product gases were carbon monoxide from the ether and carbonyl decomposition of polymer and hydrogen from the aromatic ring breakage. The structural variations in the GFRP char were determined using BET, SEM, and FT-IR techniques. The surface area of GFRP char exhibited its maximum value at 600°C, decreasing at higher temperatures with the collapsing macro-pore structure. The decomposed portion of the polymers attached to the glass fiber increased when increasing the temperature from SEM image. These data are useful for understanding the GFRP pyrolysis and gasification processes.

Decomposition of hydrogen sulfide (H2S) on Ni(100) and Ni3Al(100) surfaces from first-principles

Abstract Spin-polarized density functional theory studies of hydrogen sulfide (H2S) adsorption and decomposition on Ni(100) and Ni3Al(100) surfaces were conducted to understand the aluminum (Al) alloying effect on H2S dissociation. For such purpose, we first determined the near surface structure of fully ordered Ni3Al alloy along the [100] direction by calculating the Al segregation energy to the surface and then examined the adsorption energies of the adsorbates (H2S, HS, S, and H) and the activation barriers for the H2S and HS decomposition by using Climbing Image-Nudged Elastic Band method. We found that regardless of the way to terminate the surface, Al atom in bimetallic Ni3Al(100) tends to exist in the first surface layer, rather than in the second or third layer, and the Ni3Al(100) surface can substantially retard the H2S decomposition by reducing the adsorption energy of sulfur compounds compared to the pure Ni(100) case. Finally, we presented how the Al in Ni3Al modifies the activity of surface Ni atoms toward the sulfur compounds by calculating the local density of states and charge distribution in alloying components. This work hints the importance of knowing how to properly tailor the reactivity of Ni based materials to enhance the resistance for sulfur poisoning.

Clathrate hydrates for hydrogen storage: The impact of tetrahydrofuran, tetra-n-butylammonium bromide and cyclopentane as promoters on the macroscopic kinetics

Hydrogen hydrate formation and decomposition kinetics using tetrahydrofuran (THF), tetra-n-butylammonium bromide (TBAB) and cyclopentane (CP) as promoters under similar experimental conditions was studied. First set of experiments on hydrate formation were conducted at same promoter concentrations, experimental pressure and experimental temperature and the second set of experiments were conducted at same experimental pressure, same driving force and varying promoter concentrations. Hydrogen storage capacity of THF/Hydrogen hydrate was the highest amongst the three promoters under the experimental conditions studied. Hydrogen uptake of 0.0173 mole of gas/mole of water was obtained for the 3.5 mol% THF solution and it was about 2 times higher than hydrogen uptake obtained for 3.5 mol% TBAB solution under similar experimental conditions. With the same amount of heat supplied, TBAB/Hydrogen mixed semi-clathrates took longer time to dissociate compared to THF/Hydrogen hydrates under similar decomposition conditions. It was very difficult to form CP/Hydrogen hydrates even at a very high driving force.

Semi-transparent Si-rich SixC1−x p–i–n photovoltaic solar cell grown by hydrogen-free PECVD

A semi-transparent silicon-rich (Si-rich) silicon carbide (SixC1−x) based thin-film p–i–n junction photovoltaic solar cell is demonstrated, which is synthesized by hydrogen-free plasma enhanced chemical vapor deposition (PECVD) with the conversion efficiency optimized by detuning plasma power and intrinsic layer thickness. The hydrogen-free PECVD process effectively decelerates the decomposition of hydrogen from the Si-rich SixC1−x films so as to facilitate the passivation of surface dangling bonds. When synthesizing at a fluence ratio of R = [CH4]/[SiH4]+[CH4] = 60%, the optical bandgap of Si-rich SixC1−x film is greatly red-shifted to 1.54 eV due to the enhancement of Si content. By reducing the RF plasma power to 20 W, the Si-rich SixC1−x enlarges its above-bandgap (λ= 0.4–0.8 μm) optical absorption up to 104–105 cm−1, which is even one order of magnitude larger than that of bulk crystalline Si. The incomplete dissociation of CH4 and SiH4 under low-power PECVD growth also helps to suppress the defects and improve the electrical properties of Si-rich SixC1−x. By doping with the PH3 and B2H6 fluence ratios of 5.8% and 2.1%, the resistivities of n-type and p-type Si-rich SixC1−x films are decreased to 0.87 and 0.12 Ω cm, respectively. Thinning the intrinsic Si-rich SixC1−x layer to 25 nm further promotes the conversion efficiency of the Si-rich SixC1−x based p–i–n photovoltaic solar cell. After annealing at 650 °C, the open-circuit voltage (Voc) and short-circuit photocurrent density (Jsc) of the annealed Si-rich SixC1−x and amorphous Si based dual-junction thin-film photovoltaic solar cell are increased to 0.78 V and 19.1 mA cm−2, respectively, leading to a filling factor of 35% and a conversion efficiency of up to 5.24%.