H2 Reaction Research Articles

Stable α-MoO3 Electrode with a Widened Electrochemical Potential Window for Aqueous Electrochemical Capacitors

α-MoO3 is a promising electrode material for electrocapacitive energy storage. However, it has poor stability in aqueous electrolytes due to dissolution in water. Here, we demonstrate that an α-MoO3 electrode prepared using the electrochemical deposition method is stable over a wide potential window of 2.2 V in a neutral aqueous electrolyte. The improved stability of the α-MoO3 electrode in water is attributable to enhanced electron conductivity, which minimizes the polarization-induced structural collapse, and the dense microstructure of the α-MoO3 film electrode. The widened potential window is related to the electrocatalytic inactivity of the α-MoO3 toward water electrolysis and the high overpotentials of the neutral electrolyte toward H2 and O2 evolution reactions. A symmetric supercapacitor cell fabricated with the electrochemically deposited α-MoO3 electrode delivers a specific energy as high as ∼22 Wh/kg at a specific power of ∼301 W/kg. This work demonstrates that the electrochemical deposition method is a viable approach to fabricating α-MoO3 electrodes for aqueous electrochemical energy storage.

Signature of shape resonances on the differential cross sections of the S(1D)+H2 reaction.

Shape resonances appear when the system is trapped in an internuclear potential well after tunneling through a barrier. They manifest as peaks in the collision energy dependence of the cross section (excitation function), and in many cases, their presence can be observed experimentally. High-resolution crossed-beam experiments on the S(1D) + H2(j = 0) reaction in the 0.81-8.5 meV collision energy range reaction revealed non-monotonic behavior and the presence of oscillations in the reaction cross section as a function of the collision energy, as predicted by quantum mechanical (QM) calculations. In this work, we have analyzed the effect of shape resonances on the differential cross sections for this insertion reaction by performing additional QM calculations. We have found that, in some cases, the resonance gives rise to a large enhancement of extreme backward scattering for specific final states. Our results also show that, in order to yield a significant change in the state-resolved differential cross section, the resonance has to be associated with constructive interference between groups of partial waves, which requires not getting blurred by the participation of many product helicity states.

Interaction-Asymptotic Region Decomposition Method for a Triatomic Reactive Scattering with Symmetry Adoption.

For solving the "coordinate problem" in a product state-resolved calculation with the quantum wave packet method, an interaction-asymptotic region decomposition (IARD) method has been proposed for a general triatomic reactive scattering process. In the IARD method, the three asymptotic regions are represented by the corresponding Jacobi coordinates, but the hyperspherical coordinate is applied for representing the interaction region. For a triatomic reaction A + B2 with symmetry, explicit inclusion of all three channels in the calculations is unnecessary. Thus, numerical methods for exploring the symmetry of the A + B2 reaction need to be developed. Due to the symmetry of reactant B2, spherical harmonics with only even or odd number are required for representing the angular degree of freedom in the reactant channel and only one product channel needs to be considered. For representing the interaction region, the symmetry in the hyperspherical coordinate could also be explored to reduce the computational effort. The advantages of the IARD method with symmetry adoption were illustrated by calculating the product state-resolved reaction probabilities of the 16O + 36O2, 18O + 32O2, F + H2, and D+ + H2 reactions in the ultracold collision region. The numerical results calculated using the famous ABC code and the reactant coordinate-based method were provided for comparison.

Molybdenum-catalyzed hydrogenolysis of herbaceous biomass: A procedure integrated lignin fragmentation and components fractionation

In this work, a low-cost MoO2/C catalyst was prepared for the reductive catalytic fractionation (RCF) of various herbaceous biomass feedstocks (Miscanthus, Triarrhena, Floridulus, Sorghum stem and Corncob). Phenolic monomers from the hydrogenolysis of lignin component were obtained in up to 26.4 wt%, with high selectivity towards methyl coumarate (33%) and methyl ferulate (24%). The RCF left solid carbohydrate pulps with high retentions (up to 87%), which were suitable for enzymatic hydrolysis. The reaction conditions, including temperature, time, H2 pressure, and sawdust size were examined in terms of monophenols yield, selectivity, delignification and sugar retention. This study showed that MoO2/C could function as an excellent catalyst for lignin fragmentation as well as the fractionation of herbaceous biomass components.

The process of preparation of tellurium epitaxial films and layers with high structural perfection during vapor-deposition process in the pure hydrogen environment

The work is devoted to studying a new methodology for epitaxial films preparation on the mi-ca (muscovite) plates and based on carrying out the tellurium vapor-deposition process in the pure hydrogen environment. The formation of Н2Te molecules during reaction of H2 with sol-id Te in the hot zone, diffusion of Н2Te towards the cold surface with efficient thermalization due to high thermal conductivity of H2, Н2Te dissociative adsorption on the growth surface followed by H2 desorption and atomic Te accumulation are considered as key steps of crystal-line epitaxial films formation. Atomic Te assists the appearance and growth of directional liquid nucleuses at cold plate temperatures near Te melting point (about 450C). During coa-lescence of these liquid nucleuses the gradual formation of a liquid film is observed with a mosaic of voids of various size. After continuous liquid sheet formation, auto-epitaxial film growth begins also taking place according to vapor-liquid-crystal process described. The structural perfection of films formed is closed to three-dimensional monocrystalline samples. As a result, Te films with such characteristics may be put to use in various branches of micro-, opto-, acoustoelectronics.

Bottlenecks to interstellar sulfur chemistry

Hydride molecules lie at the base of interstellar chemistry, but the synthesis of sulfuretted hydrides is poorly understood and their abundances often crudely constrained. Motivated by new observations of the Orion Bar photodissociation region (PDR) – 1″ resolution ALMA images of SH+; IRAM 30 m detections of bright H232S, H234S, and H233S lines; H3S+ (upper limits); and SOFIA/GREAT observations of SH (upper limits) – we perform a systematic study of the chemistry of sulfur-bearing hydrides. We self-consistently determine their column densities using coupled excitation, radiative transfer as well as chemical formation and destruction models. We revise some of the key gas-phase reactions that lead to their chemical synthesis. This includes ab initio quantum calculations of the vibrational-state-dependent reactions SH+ + H2(v) ⇄ H2S+ + H and S + H2 (v) ⇄ SH + H. We find that reactions of UV-pumped H2(v ≥ 2) molecules with S+ ions explain the presence of SH+ in a high thermal-pressure gas component, Pth∕k ≈ 108 cm−3 K, close to the H2 dissociation front (at AV < 2 mag). These PDR layers are characterized by no or very little depletion of elemental sulfur from the gas. However, subsequent hydrogen abstraction reactions of SH+, H2S+, and S atoms with vibrationally excited H2, fail to form enough H2S+, H3S+, and SH to ultimately explain the observed H2S column density (~2.5 × 1014 cm−2, with an ortho-to-para ratio of 2.9 ± 0.3; consistent with the high-temperature statistical value). To overcome these bottlenecks, we build PDR models that include a simple network of grain surface reactions leading to the formation of solid H2S (s-H2S). The higher adsorption binding energies of S and SH suggested by recent studies imply that S atoms adsorb on grains (and form s-H2S) at warmer dust temperatures (Td < 50 K) and closer to the UV-illuminated edges of molecular clouds. We show that everywhere s-H2S mantles form(ed), gas-phase H2S emission lines will be detectable. Photodesorption and, to a lesser extent, chemical desorption, produce roughly the same H2S column density (a few 1014 cm−2) and abundance peak (a few 10−8) nearly independently of nH and G0. This agrees with the observed H2S column density in the Orion Bar as well as at the edges of dark clouds without invoking substantial depletion of elemental sulfur abundances.

Recent advances in vacancy engineering of metal‐organic frameworks and their derivatives for electrocatalysis

AbstractThe efficient electrocatalysis plays the key role in the development of electrochemical energy conversion technologies to alleviate energy crisis. Given their multiple active sites and large specific surface areas as electrocatalysts, metal‐organic frameworks (MOFs) and their derivatives have attracted considerable interests in recent years. Specially, exploring the roles of the enhanced active sites in MOFs and their derivatives is significant for understanding and developing new effective electrocatalysts. Recently, the vital role of vacancies has been proven to promote electrocatalytic processes (such as H2 or O2 evolution reactions, O2 reduction reactions, and N2 reduction reactions). In order to in‐depth exploring the effect of vacancies in electrocatalysts, the vacancies classification, synthetic strategy, and the recent development of various vacancies in MOFs and their derivatives for electrocatalysis are reviewed. Also, the perspectives on the challenges and opportunities of vacancies in MOFs and their derivatives for electrocatalysis are presented.

Interaction-Asymptotic Region Decomposition Method for an Insertion Reaction: Application to the S(1D) + H2 Reaction

With adjusting principal axes hyperspherical (APH) coordinate in the interaction region, and the Jacobi coordinates in the asymptotic regions, an efficient multidomain interaction-asymptotic region decomposition (IARD) method has been developed to solve the "coordinate problem" in a product-state-resolved reactive scattering calculation using the quantum wave packet method. Although the APH coordinate treats with all three channels equally, and is efficient for describing the interaction region for some direct reactions, it is inefficient for describing the insertion-type reaction due to the singularity problem, such as the S(1D) + H2 reaction. To deal with this issue, in this work, the channel-dependent Delves hyperspherical (DH) coordinate is proposed to describe the interaction region using the IARD method. The proposed DH-IARD method was applied to calculate the product-state-resolved reaction probabilities of the H + HD reaction, and the differential and integral cross sections of the typical insertion reaction S(1D) + H2. It is found that the new DH-IARD method is much more efficient than the previous APH-IARD method for dealing with insertion reactions. The partial wave resonance structures were observed in the integral cross section. It is found that at a low collision energy, the position of the initial wave packet has to be put far away. Otherwise, the partial wave resonance structures could not be correctly reproduced due to the reef well arising with a large total angular momentum J.

Numerical Simulation of the Effect of CH4/CO Concentration on Combustion Characteristics of Low Calorific Value Syngas.

The composition of low calorific value synthesis gas varies greatly depending on the raw material and processing technology, which makes the combustion extremely complicated. The three mechanisms of the GRI-Mech 3.0, Li-Model, and FFCM-Mech are used to numerically simulate CH4/CO/H2/N2 air premixed combustion by using ANSYS CHEMKIN-PRO. The numerical simulation is the calculation of laminar flame velocity and adiabatic flame temperature at an initial temperature of 298 K, an equivalence ratio of 0.6–1.4, and an initial pressure of 0.1–0.5 MPa, discussing through thermodynamics and chemical kinetics. The formation of NOX, H, and OH radicals by fuel composition was analyzed. The result shows that the concentrations of H, O, and OH radicals have a positive effect on laminar flame velocity. The combustion reaction of H2 is higher than that of CH4 and CO; with the increase of N2 content, the priority is higher. The thermal diffusivity of flame under different equivalence ratios is affected by inert gas, which affects adiabatic combustion temperature and laminar combustion velocity. In thermal kinetics and chemical kinetics, CH4 has more influence on combustion temperature than CO, while laminar flame velocity is relatively low. Under the change of initial pressure, the laminar combustion flux increases to the initial pressure and the laminar combustion velocity decreases to the increase in pressure. Reactions H + O2 = O + OH, HO2 + H = 2OH, and CH3 + HO2 = OH + CH3O are mainly due to change in the concentration of O, H, and OH radicals.

Sulfurization of MoO3 in the Chemical Vapor Deposition Synthesis of MoS2 Enhanced by an H2S/H2 Mixture.

The typical layered transition metal dichalcogenide (TMDC) material, MoS2, is considered a promising candidate for the next-generation electronic device due to its exceptional physical and chemical properties. In chemical vapor deposition synthesis, the sulfurization of MoO3 powders is an essential reaction step in which the MoO3 reactants are converted into MoS2 products. Recent studies have suggested using an H2S/H2 mixture to reduce MoO3 powders in an effective way. However, reaction mechanisms associated with the sulfurization of MoO3 by the H2S/H2 mixture are yet to be fully understood. Here, we perform quantum molecular dynamics (QMD) simulations to investigate the sulfurization of MoO3 flakes using two different gaseous environments: pure H2S precursors and a H2S/H2 mixture. Our QMD results reveal that the H2S/H2 mixture could effectively reduce and sulfurize the MoO3 reactants through additional reactions of H2 and MoO3, thereby providing valuable input for experimental synthesis of higher-quality TMDC materials.

Full-dimensional quantum dynamics study of isotope effects for the H2 + NH2/ND2/NHD and H2/D2/HD + NH2 reactions.

A full-dimensional quantum dynamical study for the bimolecular reactions of hydrogen molecules with amino radicals for different isotopologues is reported. The nonreactive amino radical is described by two Radau vectors that are very close to the valence bond coordinates. Potential-optimized discrete variable representation basis is used for the vibrational coordinates of the amino radical. Starting from the reaction H2 + NH2, we study the isotope effects for the two reagents separately, i.e., H2 + NH2/ND2/NHD and H2/D2/HD + NH2. The effects of different vibrational mode excitations of the reagents on the reactivities are studied. Physical explanations about the isotope effects are also provided thoroughly including the influence of vibrational energy differences between the different isotopologues and the impact of the tunneling effect.

Rate constants for the H+ + H2 reaction from 5 K to 3000 K with a statistical quantum method.

An exhaustive investigation of state-to-state H+ + H2(v, j) → H+ + H2(v', j') transitions for rovibrational levels of molecular hydrogen below 1.3 eV from the bottom of the H2 well is carried out by means of a statistical quantum method, which assumes the complex-forming nature of the process. Integral cross sections for transitions involving states H2(v = 0, j = 0-12), H2(v = 1, j = 0-8), and H2(v = 2, j = 0-3) are obtained for collision energies within a range of Emin = 10-5 eV and Emax = 2 eV. Rate constants are then calculated between T = 5 K and 3000 K, and they are compared, when possible, with previous values reported in the literature. As a first application, the cooling rate coefficient of H2 excited by protons is determined and compared with a recent estimate.

The sequential activation of H2 and N2 mediated by the gas-phase Sc3N+ clusters: Formation of amido unit.

The activation and hydrogenation of nitrogen are central in industry and in nature. Through a combination of mass spectrometry and quantum chemical calculations, this work reports an interesting result that scandium nitride cations Sc3N+ can activate sequentially H2 and N2, and an amido unit (NH2) is formed based on density functional theory calculations, which is one of the inevitable intermediates in the N2 reduction reactions. If the activation step is reversed, i.e., sequential activation of first N2 and then H2, the reactivity decreases dramatically. An association mechanism, prevalent in some homogeneous catalysis and enzymatic mechanisms, is adopted in these gas-phase H2 and N2 activation reactions mediated by Sc3N+ cations. The mechanistic insights are important to understand the mechanism of the conversion of H2 and N2 to NH3 synthesis under ambient conditions.

Discovery of the acetyl cation, CH3CO+, in space and in the laboratory.

Using the Yebes 40m and IRAM 30m radiotelescopes, we detected two series of harmonically related lines in space that can be fitted to a symmetric rotor. The lines have been seen towards the cold dense cores TMC-1, L483, L1527, and L1544. High level of theory ab initio calculations indicate that the best possible candidate is the acetyl cation, CH3CO+, which is the most stable product resulting from the protonation of ketene. We have produced this species in the laboratory and observed its rotational transitions Ju = 10 up to Ju = 27. Hence, we report the discovery of CH3CO+ in space based on our observations, theoretical calculations, and laboratory experiments. The derived rotational and distortion constants allow us to predict the spectrum of CH3CO+ with high accuracy up to 500 GHz. We derive an abundance ratio N(H2CCO)/N(CH3CO+)~44. The high abundance of the protonated form of H2CCO is due to the high proton affinity of the neutral species. The other isomer, H2CCOH+, is found to be 178.9 kJ mol-1 above CH3CO+. The observed intensity ratio between the K=0 and K=1 lines, ~2.2, strongly suggests that the A and E symmetry states have suffered interconversion processes due to collisions with H and/or H2, or during their formation through the reaction of with H2CCO.

Characteristics of solid oxide fuel cells in gasified gases from biomass

For an extremely efficient power generation using biomass, a renewable energy, we investigated characteristics of an autothermal downdraft gasifier and SOFCs. Cypress chips were converted into gasified gases with the efficiency of 90%. The gasification rate saturated as the air flow rate increased, because of the heat losses from char surfaces via radiation and convection. For the discharge of SOFCs, electrochemical H2 oxidation was more dominant than CO oxidation in a model gasified gas, due to water gas shift reaction and selective electrochemical H2 oxidation via H-spillover. Electrochemical H2O reduction was inhibited by strongly adsorbed CO on Ni in the model gasified gas with the reverse bias operation. The maximum polarization resistances of an anode-supported cell were more than two times larger than the charge transfer resistances in the model gasified gas. The power density in the model gasified gas attained 62% of that in humidified H2 at 0.8 V.

Structural Evolution of Ga-Cu Model Catalysts for CO2 Hydrogenation Reactions.

We studied the initial stages of Ga interaction with the Cu(001) surface and environment-induced surface transformations in an attempt to elucidate the surface chemistry of the Cu–Ga catalysts recently proposed for CO2 hydrogenation to methanol. The results show that Ga readily intermixes with Cu upon deposition in vacuum. However, even traces of oxygen in the gas ambient cause Ga oxidation and the formation of two-dimensional (“monolayer”) Ga oxide islands uniformly covering the Cu surface. The surface morphology and the oxidized state of Ga remain in H2 as well as in a CO2 + H2 reaction mixture at elevated pressures and temperatures (0.2 mbar, 700 K). The results indicate that the Ga-doped Cu surface under reaction conditions exposes a variety of structures including GaOx/Cu interfacial sites, which must be taken into account for elucidating the reaction mechanism.

Plasma-enhanced catalytic reduction of SO2: Decoupling plasma-induced surface reaction from plasma-phase reaction

Complex processes take place when coupling nonthermal plasma with heterogenous catalysis, obscuring mechanistic understanding of the plasma–catalysis synergy. Simultaneous homogenous plasma-phase reactions and heterogenous surface catalytic reactions occur in the system, which makes distinguishing the plasma’s contributions very challenging. In this work, we perform a careful and rigorous evaluation of surface reactions under plasma conditions. We use SO2 hydrogenation as a probe reaction to examine plasma-induced surface reactions, desorption, and dissociation of SO2 adsorbate. A temperature-programmed plasma-induced surface reaction approach is used to decouple plasma-induced surface reactions from plasma-phase reactions. The qualitative and quantitative analyses reveal a new Eley-Rideal reaction between plasma-generated atomic hydrogen in the gas-phase and strongly adsorbed SO2 over alumina, a reaction that is not thermally feasible. Furthermore, plasma causes partial desorption of weakly adsorbed SO2 species and enhances the strong chemisorption of SO2 over supported iron sulfide catalyst. Moreover, plasma facilitates H2 chemisorption and reaction with iron sulfide, producing sulfur vacancies. This work sheds light on the possible origin of plasma–catalysis synergy and offers fundamental insight about the underlying mechanisms of plasma-assisted SO2 hydrogenation reaction.

Perspectives for usage of adsorption semiconductor sensors based on Pd/SnO2 in environmental monitoring of carbon monoxide and methane emission

Nanosized semiconductor sensor materials based on SnO2 with different palladium contents were obtained via zol-gel technology with the use of ethylene glycol and hydrate of tin (VI) chloride as precursors. Morphology and phase composition of nanosized sensor materials were studied by X-ray diffraction and TEM methods. Catalytic activities of the Pd/SnO2 nanomaterials in the reaction of H2 and CO oxidation were investigated. Adsorption semiconductor sensors based on Pd/SnO2 nanomaterials were made by their calcination up to 620 0C in air and the sensors were found to be highly sensitive to presence of CO and CH4 in air ambient. Higher responses to CO of Pd-containing sensors in comparison with their responses to CH4 were confirmed by higher reaction activity of CO in catalytic oxidation reaction. Differences in sensitive properties of the sensors to methane and carbon monoxide were explained by features of the catalytic reactions of methane and carbon monoxide oxidation occurring on surfaces of the gas sensitive layers of the sensors.

Reactive Rate Constants for the C+ + H2(v = 0, 1) Reaction: An Accurate State-to-state Quantum Dynamical Study

Abstract The accurately calculated thermal rate constants of the C+ + H2(v = 0, 1) reaction are important for estimating the CH+ emission spectra in different astronomical environments. In this study, reactive quantum dynamics of the C+ + H2(v = 0, 1) reaction have been investigated with the time-dependent wave packet method on the high-quality potential energy surface recently developed by Guo et al. The simulated total cross sections are compared in detail with previous experimental measurements and dynamical results. The calculated total rate constants are found to be in good agreement with previous quasi-classical results by Herráez-Aguilar et al., except for the v = 0 reaction at low temperatures. The ro-vibrational state-resolved rate constants show that the CH+ product, obtained from both the v = 0 and v = 1 reactions, is significantly populated in the vibrational ground but rotational excited states. In particular, for the v = 0 reaction, the CH+ product is preferably formed at j′ = 4, 5 rotational levels, while the CH+ product for the v = 1 reaction prefers rotational excitation j′ = 6–8. This finding varies with previous J-shifting calculations by Zanchet et al., owing to the different potential energy surface and methodology employed in the calculations.

Ring polymer molecular dynamics of the C(1D)+H2 reaction on the most recent potential energy surfaces

Ring polymer molecular dynamics (RPMD) calculations for the C(1D)+H2 reaction are performed on the Zhang-Ma-Bian ab initio potential energy surfaces (PESs) recently constructed by our group, which are unique in very good descriptions of the regions around conical intersections and of van der Waals (vdW) interactions. The calculated reaction thermal rate coefficients are in very good agreement with the latest experimental results. The rate coefficients obtained from the ground ã1A′ ZMB-a PES are much larger than those from the previous RKHS PES, which can be attributed to that the vdW saddles on our PESs have very different dynamical effects from the vdW wells on the previous PESs, indicating that the RPMD approach is able to include dynamical effects of the topological structures caused by vdW interactions. The importance of the excited b̃1A″ ZMB-b PES and quantum effects in the title reaction is also underscored.