Hydrogen Migration Processes Research Articles

Ferrocenyl conjugated oxazepines/quinolines: multiyne coupling and ring-expanding or rearrangement.

Ferrocenyl conjugated oxazepine/quinoline derivatives were presented through the reaction of hexadehydro-Diels-Alder (HDDA) generated arynes with ferrocenyl oxazolines under mild conditions via ring-expanding or rearrangement processes. Water molecule participated in this unexpected rearrangement process to produce quinoline skeletons, and DFT calculations supported a ring-expanding and intramolecular hydrogen migration process for the formation of oxazepine derivatives. Two variants of this chemistry, expanded the reactivity between ferrocenyl conjugated substances and arynes, further providing an innovative approach for the synthesis of ferrocene derivatives.

Enhanced formaldehyde oxidation over MnO2 and doped manganese-based catalysts: Experimental and theoretical Insights into mechanism and performance

Thermal catalytic degradation of formaldehyde (HCHO) over manganese-based catalysts is garnering significant attention. In this study, both theoretical simulations and experimental methods were employed to elucidate the primary reaction pathways of HCHO on the MnO2(110) surface. Specifically, the effects of doping MnO2 with elements such as Fe, Ce, Ni, Co, and Cu on the HCHO oxidation properties were evaluated. Advanced characterization techniques, including X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmett-Teller (BET), and X-ray photoelectron spectroscopy (XPS), were employed to discern the physical properties and chemical states of the active components on the catalyst surface. The comprehensive oxidation pathway of HCHO on the MnO2(110) surface includes O2 adsorption and dissociation, HCHO adsorption and dehydrogenation, CO2 desorption, H2O formation and desorption, oxygen vacancy supplementation, and other elementary reactions. The pivotal rate-determining step was identified as the hydrogen migration process, characterized by an energy barrier of 234.19 kJ mol−1. Notably, HCHOO and *CHOO emerged as crucial intermediates during the reaction. Among the doped catalysts, Fe-doped MnO2 outperformed its counterparts doped with Ce, Ni, Co, and Cu. The optimal degradation rate and selectivity were achieved at a molar ratio of Fe: Mn = 0.1. The superior performance of the Fe-doped MnO2 can be ascribed to its large specific surface area, conducive pore structure for HCHO molecular transport, rich surface-adsorbed oxygen species, and a significant presence of oxygen vacancies.

Adsorption and transfer behaviors of hydrogen on Fe1-xS catalysts for direct coal liquefaction

Direct coal liquefaction (DCL) is an important and effective method to convert coal into chemicals and fuel oil. Pyrite catalysts play an important role in improving the hydrogenation and liquefaction efficiency of coal. There have been many studies on its active component Fe1-xS in promoting pyrolysis of coal and producing active hydrogen, but studies about the hydrogen migration on Fe1-xS catalyst and the interaction between hydrogen and Fe1-xS catalyst were rarely reported. It is significant to study the hydrogen transfer behaviors on Fe1-xS in DCL and understand the influence of Fe1-xS on the hydrogen migration process. In this study, the chemical adsorption and desorption of hydrogen on Fe1-xS were firstly proved experimentally. After pre-sulfidation of Fe1-xS, the maximum amount of H chemically adsorbed in Fe1-xS is 8.20 mmol/g at 360 °C and 1.5 h. The dehydrogenation of Fe1-xS in an anthracene (ANT) system and re-hydrogenation of that in the hydrogen supply systems, such as H2 and 1,2,3,4-tetrahydronaphthalene (THN), were explored at different experiment conditions, which gave some quantitative results of hydrogen transfer. Particularly, the dehydrogenation of Fe1-xS in the ANT system was analyzed in thermodynamics. The enthalpy of dehydrogenation of Fe1-xS in the ANT system is 117.6 kJ mol−1. The results break the traditional view about Fe1-xS only as a medium for active hydrogen transfer and provides a new perspective for further understanding the hydrogen transfer process.

Understanding dehydrogenation sequence in fluorene+ by multiphoton ionisation-excitation processes

The dehydrogenation sequence in fluorene+ up to a loss of 3 hydrogen (H) atoms, is explored using a kinetic energy (KE) correlated time of flight mass spectrometer (ToFMS). Four dehydrogenation reactions are identified for the internal energy ranging between 8.5 and 9.0 eV. A dichotomy is observed in fluorene+ in the H-loss channel processed within the studied internal energy. This is explained with the help of a hydrogen migration process leading to post-ionisation isomerization, which is explored using DFT calculations. Presence of two modes of molecular hydrogen (H2) loss is also noted in the dehydrogenation sequence, including observation of direct elimination of H2 from fluorene+.

N‐nacnac stabilized tetrylenes: access to silicon hydride systems via migration processes

AbstractThe use of an amino‐functionalized β‐diketiminate (′N‐nacnac′) ligand in low‐valent silicon chemistry is investigated. In particular, the use of (LDipp)SiCl (LDipp=HC{(Me2N)CNDipp}2) to generate silicon‐containing products via metathesis chemistry is explored, in light of previously reported complications arising from heterocycle ring contraction. In the case of Na[C5H5], chloride metathesis is accompanied not by rearrangement of the N‐nacnac ligand, but by a C‐to‐Si hydrogen migration process, generating the hydridosilicon(IV) species (LDipp)Si(H)(C5H4), which features a silafulvene core. The potential intermediate arising from initial chloride/cyclopentadienide substitution can be modelled by the chemistry of the corresponding Ge(II) and Sn(II) systems, which generate (LDipp)E(η1−C5H5) (E=Ge, Sn) via straightforward metathesis chemistry. A Si(II) hydride species can be generated from (LDipp)SiCl via metathesis by making use of a d‐block reagent which can act as both hydride source and coordinative trap for (LDipp)SiH. Thus, the reaction of (LDipp)SiCl with K[(η5−C5H4Me)Mn(CO)2H] leads to the formation of (η5−C5H4Me)Mn(CO)2{Si(H)LDipp} – the first silylene complex containing this half‐sandwich manganese fragment.

THE FORMATION OF AN ELECTRICAL DOUBLE LAYER IN ACID AND NEUTRAL WATER SOLUTIONS ON THE 3-5 dm METALS

The rate-limiting steps of the electrolysis of water solution, taking into account hydrogen evolution overpotential were considered. A functional relationship between the electrical resistivity of 3–5 dm metals and their quantization energy of atomic electrons, as well as the coordination of metal atoms and hydrogen compounds, has been revealed. The rule of selecting effective metals for cathodes has been validated. Based on these rules, a reduction-relay mechanism of the hydrogen migration process in the electrical double layer in the electrochemical reduction of TiO2+ ions to Ti3+ and Fe3+ to Fe2+ in sulfuric acid process solutions for the production of pigment titanium dioxide was proposed. The method of the multistage electrochemical reduction of Fe3+ and [TiO2+ * nH2O] in process solutions for the production of titanium dioxide was design based on this study.

Theoretical and experimental studies on hydrogen migration in dissociative ionization of the methanol monocation to molecular ions H3 + and H2O.

The dissociative ionization processes of the methanol monocation CH3OH+ to H3+ + CHO and H2O+ + CH2 are studied by ab initio method, and hydrogen migration processes are confirmed in these two dissociation processes. Due to the positive charge assignment in dissociation processes, the fragmentation pathways of CH3OH+ to H3 + CHO+ and CH3OH+ to H2O + CH2+ are also calculated. The calculation results show that a neutral H2 moiety in the methanol monocation CH3OH+ is the origin of the formation of H3+, and the ejection of fragment ions H3+ and H2O+ is more difficult than CHO+ and CH2+ respectively. Experimentally, by using a dc-slice imaging technique under an 800 nm femtosecond laser field, the velocity distributions of fragment ions H3+, CHO+, CH2+, and H2O+ are calculated from their corresponding sliced images. The presence of low-velocity components of these four fragment ions confirms that the formation of these ions is not from the Coulomb explosion of the methanol dication. Hence, the four hydrogen migration pathways from the methanol monocation CH3OH+ to H3+ + CHO, CHO+ + H3, H2O+ + CH2, and CH2+ + H2O are securely confirmed. It can be observed in the time-of-flight mass spectrum of ionization and dissociation of methanol that the ion yields of fragment ions H3+ and H2O+ are lower than CHO+ and CH2+ respectively, which is consistent with the theoretical results according to which dissociation from the methanol monocation to H3+ and H2O+ is more difficult than CHO+ and CH2+ respectively.

The hydrogen migration in cryogenic tubes of superconductive accelerator with gas source

In superconductive linear accelerator, the performance and stability can be impacted by gas adsorbed on cryogenic surfaces adversely. The cryogenic devices usually work at 4.2 K or 1.9 K and are refrigerated by normal or super fluid liquid helium, respectively. The purpose of this paper is to study the character of gas migration in cryogenic tubes. Adsorption coefficient for hydrogen at 4.2 K is measured by experimental study. Then, a gas migration model is established based on the experimental results to depict the hydrogen migration process in cryogenic tubes. The experimental results and model analysis indicated that at cryogenic temperature (4.2 K), adsorption coefficient for hydrogen is very close to 1, which is several orders higher than the adsorption coefficient at room temperature, resulting in a unique pressure distribution pattern in cryogenic tubes when compared with the pressure distribution in room temperature tubes. At 4.2 K or 1.9 K, the gas migration process is obviously different from the process at room temperature and is significantly affected by the gas adsorption on the cryogenic surfaces. The model established in this article can be applied not only to hydrogen migration in cryogenic tubes but also to other gas migration in tubes with high adsorption coefficient.

Ultrafast Hydrogen Migration in Photoionized Glycine.

Hydrogen migration in the glycine cation has been investigated using a combination of a short train of attosecond extreme ultraviolet pulses with few-optical-cycle near-infrared pulses. The yield of the photofragments produced has been measured as a function of pump-probe delay. These time-dependent measurements reveal the presence of a hydrogen migration process occurring in 48 fs. Previous mass spectrometric experiments and theoretical calculations have allowed us to identify the conformations and cation states involved in the process induced by the broad band extreme ultraviolet radiation.

Hydrogen migration in Coulomb explosion of cyclohexane to C2H4+ and C4H8+: Theoretical and experimental studies

AbstractThe equilibrium structure of cyclohexane dication C6H122+ and singly charged ions C2H4+ and C4H8+ suggests that hydrogen migration can proceed in dissociation process of C6H122+ to C2H4+ and C4H8+. Using dc‐slice imaging technique, the fragmentation pathway C6H122+ → C2H4++C4H8+ is detected under an intense femtosecond laser field. Two‐body Coulomb explosion (CE) of C6H122+ to C2H4+ and C4H8+ is securely identified. The quasi‐isotropic distributions of ions indicate the precursor have a relatively long dissociation time. Then, B3LYP density functional theory calculations are performed on this dissociation process, the results show the precursor C6H122+ undergoes molecular rearrangement and 1, 2‐ and 6, 5‐ hydrogen migrations during the dissociation process. These molecular rearrangement and hydrogen migration processes can reduce the anisotropy distribution of fragment ions C2H4+ and C4H8+, which is consistent with the experimental results. The present work will be useful to understand hydrogen migration processes within the hydrocarbon molecules.

The influence of anionic heterovalent doping on transport properties and chemical stability of F-, Cl-doped brownmillerite Ba2In2O5

The novel Cl-doped compound based on brownmillerite Ba2In2O5 was synthesized by the solid state method and its structure, thermal properties, hydration behavior and electrical properties have been investigated. The thermogravimetry, mass spectrometry and impedance spectroscopy methods were used for the characterization of the materials. The conductivity was measured at T, pO2 and pH2O variation. The sample Ba1.95In2O4.9Cl0.1 was capable to water uptake, however in comparison with Ba2In2O5 and F-doped composition, the protonic conductivity was lower owing to the lower proton mobility. The changes in the chemical OH bonding due to introduction of halogen in oxygen sublattice play an important role in the hydrogen-migration process. It was found that anionic heterovalent doping (F, Cl) of brownmillerite Ba2In2O5 leads to an increase in oxygen-ion conductivity and chemical stability against carbon dioxide.

Synthesis of Polycyclic Benzo[b]indolo[3,2,1-de]acridines via Sequential Allenylation, Diels-Alder Cyclization, and Hydrogen Migration Reaction.

A novel methodology for stereoselective synthesis of benzo[b]indolo[3,2,1-de]acridines through the tandem reaction of propargylic compounds with organoboron is described, and only one diastereoisomer was obtained. The sequential procedure was triggered by Pd(0)-catalyzed allenylation of propargyl carbonate. Then, Diels-Alder cyclization and hydrogen migration processes proceeded successively to furnish the polycyclic target molecules. Control reactions suggested the base (Cs2CO3) was indispensable for the hydrogen migration.

How does a CC double bond cleave in the gas phase? Fragmentation of protonated ketotifen in mass spectrometry.

In the literature, it is reported that the protonated ketotifen mainly undergoes CC double bond cleavage in electrospray ionization tandem mass spectrometry (ESI-MS/MS); however, there is no explanation on the mechanism of this fragmentation reaction. Therefore, we carried out a combined experimental and theoretical study on this interesting fragmentation reaction. The fragmentation of protonated ketotifen (m/z 310) always generated a dominant fragment ion at m/z 96 in different electrospray ionization mass spectrometers (ion trap, triple quadrupole and linear trap quadrupole (LTQ)-orbitrap). The mechanism of the generation of this product ion (m/z 96) through the CC double bond cleavage was proposed to be a sequential hydrogen migration process (including proton transfer, continuous two-step 1,2-hydride transfer and ion-neutral complex-mediated hydride transfer). This mechanism was supported by density functional theory (DFT) calculations and a deuterium labeling experiment. DFT calculations also showed that the formation of the product ion m/z 96 was most favorable in terms of energy. This study provides a reasonable explanation for the fragmentation of protonated ketotifen in ESI-MS/MS, and the fragmentation mechanism is suitable to explain other CC double bond cleavage reactions in mass spectrometry. Copyright © 2016 John Wiley & Sons, Ltd.

Hydrogen diffusion in metal-hydrogen systems via NMR and DFT

Studies of interstitial hydrogen diffusion play a key role in understanding of fundamental properties of hydrogen storage materials since the activation energy required to jump from one interstitial site to another affects both the hydrogen sorption kinetics and the desorption temperature. Nuclear magnetic resonance is a very effective tool to study hydrogen diffusivity, jump frequency etc. but it cannot describe the microscopic hydrogen migration processes. From this perspective theoretical studies are very helpful and complement the experiment, however, the results depend on the quality of calculations. Here we provide a brief overview of our most recent results of both theoretical (DFT) and experimental (1H NMR) studies of hydrides of disordered Ti–V–Cr alloys and a theoretical study of hydrogen diffusion in magnesium.

Unusual hydrogen and hydroxyl migration in the fragmentation of excited doubly-positively-charged amino acids in the gas phase

SynopsisWe present a combined experimental and theoretical study of the fragmentation of doubly-positively- charged amino acids in the gas phase. The combination of ab initio molecular dynamics simulations with ion- molecule collisions followed by multiple-coincidence mass spectrometric techniques, allows us to obtain a complete picture of the fragmentation dynamics. In addition to the expected Coulomb explosion, we have found evidence of hydrogen and hydroxyl-group migration processes, which leads to unusual fragmentation products.

DFT calculations of hydrogen diffusion and phase transformations in magnesium

To describe microscopic hydrogen migration processes and steps of hydride formation we have carried out a theoretical study of the hydrogen diffusion in hexagonal closed packed (hcp), body-centered cubic (bcc), and face-centered cubic (fcc) Mg-lattices. To determine the preferable hydrogen diffusion pathways the activation energy Ea along the minimum energy path between two hydrogen positions were calculated. The hydrogen diffusion coefficient at 673K for hcp-Mg was found to be equal to 1.11×10−8m2/s that is in fair agreement with experiment data. The calculations of the hydrogen migration in Mg lattices have shown that bcc-Mg exhibits the lowest activation energy and, as the result, the highest diffusion coefficient. Taking into account that the bcc-Mg structure does not share the so-called blocking layer effect, we consider that this structure should promote fast hydrogen diffusion. On the bases of the present theoretical study, as well from previous calculations and experimental data we propose a scheme of structural hydrogen induced phase transformations in magnesium.

Hydrogen diffusion into three metallurgical microstructures of a C–Mn X65 and low alloy F22 sour service steel pipelines

This paper describes the process of hydrogen diffusion in API 5L X65 and ASTM A182 F22 steels with three different metallurgical microstructures (quenched and tempered, quenched and annealed) by an electrochemical technique which is a modified Devanathan and Stachurski's cell. The analysis of experimental results compares different measurement methods for hydrogen diffusion coefficients: 1) charge method; 2) partial charge and partial discharge method; 3) discharge method. For the steel, cathodically polarized in acidic medium (pH ≈ 4.2), the less dispersed and more meaningful results are obtained by partial charge and partial discharge method after about one hundred hours of polarization, i.e., when a stationary regime was reached. The discharge method, carried out after one hundred hours of polarization, provides analogous results by extrapolation of the experimental results obtained during the initial phase of hydrogen desorption. The hydrogen diffusion coefficients measured would appear dependent only on the hydrogen migration processes in the crystal lattice regular sites and corresponding values DL increase as follows: quenched < quenched and tempered < annealed.

Hydrogen migration in methanol studied under asymmetric fs laser irradiation

Hydrogen migration processes in deuterated methanol (CH3OD) under the irradiation of ultrashort (30fs) two color (400/800nm) laser field have been investigated by means of time-of-flight mass spectrometry. The utilization of an asymmetric ω/2ω laser field contributes to a better understanding of hydrogen migration processes. Based on the comparative study of the asymmetry dependence and the angular distributions of the H2D+, HOD+ and H2OD+ fragment ions, whose formation requires hydrogen migration, it was feasible to distinguish the most probable site of the molecular skeleton where the hydrogen migrates from.

ChemInform Abstract: Highly Selective β‐Hydride Elimination in Pd‐Catalyzed Decarboxylative Heck‐Type Reaction.

A variety of β-aryl ketones and aldehydes were facilely synthesized via a Pd(II)/Ag2CO3-mediated decarboxylative Heck type reaction between readily available benzoic acid derivatives and allylic alcohols under mild conditions. The control experiments indicated that this transformation may proceed via a hydrogen migration process.

Highly Selective β-Hydride Elimination in Pd-Catalyzed Decarboxylative Heck-Type Reaction

A variety of β-aryl ketones and aldehydes were facilely synthesized via a Pd(II)/Ag2CO3-mediated decarboxylative Heck type reaction between readily available benzoic acid derivatives and allylic alcohols under mild conditions. The control experiments indicated that this transformation may proceed via a hydrogen migration process.