Gas-phase Hydrogen Research Articles

Removal of gas-phase ammonia and hydrogen sulfide using photocatalysis, nonthermal plasma, and combined plasma and photocatalysis at pilot scale.

This study focuses on the removal of gas-phase ammonia (NH3) and hydrogen sulfide (H2S) in a continuous reactor. Photocatalysis and surface dielectric barrier discharge (SDBD) plasma are studied separately and combined. Though the removal of volatile organic compounds by coupling plasma and photocatalysis has been reported on a number of studies in laboratory scale, this is as far as we know the first time that it is used to remove inorganic malodorous pollutants. While each separate process is able to degrade ammonia and hydrogen sulfide, a synergetic effect appears when they are combined at a pilot scale, leading to removal capacity higher than the sum of each separate process. The removal capacity is higher when the gas circulates at a higher flow rate and when pollutant concentration is higher. The presence of water vapor in the gas is detrimental to the efficiency of the process. Operating conditions also influence the production of nitrogen oxides and ozone.

Generation of three-primary-color Raman comb in the continuous-wave regime

We demonstrate the generation of continuous-wave Stokes and anti-Stokes Raman sidebands including the three-primary-color (683, 532, and 436 nm) components. The Raman sidebands are generated through both stimulated and coherent anti-Stokes Raman scattering in a broadband high-finesse optical cavity filled with gas-phase hydrogen as a Raman-active medium and covering the entire visible spectral range (420–680 nm). The blue emission is considerably enhanced by matching the frequency with one of the longitudinal modes of the optical cavity, and high conversion efficiencies are observed when the coherent length corresponds to an integral multiple of the round-trip length of the optical cavity. This indicates that phase-matching plays a critical role in determining the efficiency of the Raman comb generation.

Spectroscopic and thermodynamic properties of molecular hydrogen dissolved in water at pressures up to 200 MPa.

We have measured the Raman Q-branch of hydrogen in a solution with water at a temperature of about 280 K and at pressures from 20 to 200 MPa. From a least-mean-square fitting analysis of the broad Raman Q-branch, we isolated the contributions from the four lowest individual roto-vibrational lines. The vibrational lines were narrower than the pure rotational Raman lines of hydrogen dissolved in water measured previously, but significantly larger than in the gas. The separations between these lines were found to be significantly smaller than in gaseous hydrogen and their widths were slightly increasing with pressure. The lines were narrowing with increasing rotational quantum number. The Raman frequencies of all roto-vibrational lines were approaching the values of gas phase hydrogen with increasing pressure. Additionally, from the comparison of the integrated intensity signal of Q-branch of hydrogen to the integrated Raman signal of the water bending mode, we have obtained the concentration of hydrogen in a solution with water along the 280 K isotherm. Hydrogen solubility increases slowly with pressure, and no deviation from a smooth behaviour was observed, even reaching thermodynamic conditions very close to the transition to the stable hydrogen hydrate. The analysis of the relative hydrogen concentration in solution on the basis of a simple thermodynamic model has allowed us to obtain the molar volume for the hydrogen gas/water solution. Interestingly, the volume relative to one hydrogen molecule in solution does not decrease with pressure and, at high pressure, is larger than the volume pertinent to one molecule of water. This is in favour of the theory of hydrophobic solvation, for which a larger and more stable structure of the water molecules is expected around a solute molecule.

Novel Options and Limitations of Methanol‐Based Production and Storage for Mobile Applications

AbstractMethanol is considered a promising liquid fuel in context with electrochemical energy conversion and storage for mobile applications. It is shown here that a direct methanol fuel cell can be used for spontaneous charging and discharging a supercapacitor (SC) for intermediate storage of chemical energy. Thereby, protons and electrons of the methanol‐derived hydrogen are stored separately in the electrical double layer of the SC electrode. The charging and discharging of this fuel cell–SC hybride device is investigated in experiments of spontaneous conditions (closed circuit) and also under externally enforced constant voltage sweep rate (cyclic voltammetry) and under constant current conditions. Alternatively, gas phase hydrogen is generated from methanol in an electro‐reforming process. When more efficient anode electrocatalysts become available this may become the method of choice for on‐board and on demand hydrogen production in mobile applications.

Novel insight into the hydrogen absorption mechanism at the Pd(110) surface

The microscopic mechanism of low-temperature (80 K < T < 160 K) hydrogen (H) ingress into the H2 (<2.66 × 10(-3) Pa) exposed Pd(110) surface is explored by H depth profiling with (15)N nuclear reaction analysis (NRA) and thermal desorption spectroscopy (TDS) with isotope (H, D) labeled surface hydrogen. NRA and TDS reveal two types of absorbed hydrogen states of distinctly different depth distributions. Between 80 K and ∼145 K a near-surface hydride phase evolving as the TDS α1 feature at 160 K forms, which initially extends only several nanometers into depth. On the other hand, a bulk-absorbed hydrogen state develops between 80 K and ∼160 K which gives rise to a characteristic α3 TDS feature above 190 K. These two absorbed states are populated at spatially separated surface entrance channels. The near-surface hydride is populated through rapid penetration at minority sites (presumably defects) while the bulk-absorbed state forms at regular terraces with much lower probability per site. In both cases, absorption of gas phase hydrogen transfers pre-adsorbed hydrogen atoms below the surface and replaces them at the chemisorption sites by post-dosed hydrogen in a process that requires much less activation energy (<100 meV) than monatomic diffusion of chemisorbed H atoms into subsurface sites. This small energy barrier suggests that the rate-determining step of the absorption process is either H2 dissociation on the H-saturated Pd surface or a concerted penetration mechanism, where excess H atoms weakly bound to energetically less favorable adsorption sites stabilize themselves in the chemisorption wells while pre-chemisorbed H atoms simultaneously transit into the subsurface. The peculiarity of absorption at regular Pd(110) terraces in comparison to Pd(111) and Pd(100) is discussed.

Formation of Self-Assembled Nanoplates via Hydrogenation of Epitaxial Pd Film

Understanding the relationship between the uptake of hydrogen gas and hydride phase formation and evolution in metal solids is a phenomenon of significant technological importance due to current development of hydrogen storage devices, sensors, and membranes. The performance of these devices is degraded by structural defect formation during incoherent metal-hydride phase transformation. In this work, atomic force and scanning electron microscopy reveal formation of nanoplates along the ⟨111⟩ directions in a (111) epitaxial Pd film. These nanostructures are observed after high temperature and high pressure gas phase hydrogenation and cooling in ambient temperature. Transmission electron microsocpy (TEM) analysis of a posthydrogenated film did not show considerable plastic deformation. The size of the nanoplates increased with increasing Pd film thickness. A formation mechanism of nanoplates is proposed: cooling the sample reactor in ambient temperature after hydrogen loading induced formation of coherent or partially coherent β-phase plates along {100} planes corresponding to minimum elastic energy of interaction between metal and hydride phases.

Gas phase hydrogen absorption and electrochemical performance of La2(Ni,Co,Mg,M)10 based alloys

The effect of M = In or Al on the hydrogenation behavior of the La2(Ni,Co,Mg,M)10 alloys at room temperature is presented. The ceramic like samples have been prepared by powder metallurgy route using pure Mg- and the La2Ni9−xMx alloy powder precursors. XRD analysis revealed predominantly the CaCu5-type structure for all final alloys. Partial substitution of Co by In in La2Ni8MgCo causes a slight decrease of hydrogen concentration whereas Al addition increases this parameter. The highest hydrogen concentration of 1.87 wt.% has been reached for La2(Ni8Co0.8Al0.2)Mg composition at hydrogen pressure of 10 bar. Indium addition dramatically decreases the middle-plateau hydrogen equilibrium pressure from peq = 0.37 bar (In-free alloy) to peq = 0.06 bar (1.7 at.% In). The electrochemical performance of the studied materials has been characterized using chronoamperometric and chronopotentiometric techniques. The galvanostatic hydrogenation experiments at 185 mA/g discharge rate revealed the largest discharge current capacity of 355 mAh/g for La2(Ni8Co0.8Al0.2)Mg alloy. The relative diffusivity factor of hydrogen (D¯H/a2) varies for the tested materials in the range of (2.0–5.4)·10−5 s−1.

Transient-state studies and neural modeling of the removal of a gas-phase pollutant mixture in a biotrickling filter

The removal efficiency (RE) of gas-phase hydrogen sulfide (H), methanol (M) and α-pinene (P) in a biotrickling filter (BTF) was modeled using artificial neural networks (ANNs). The inlet concentrations of H, M, P, unit flow and operation time were used as the model inputs, while the outputs were the RE of H, M and P, respectively. After testing and validating the results, an optimal network topology of 5-8-3 was obtained. The model predictions were analyzed using Casual index (CI) values. M removal in the BTF was influenced positively by the inlet concentration of M in mixture (CI=3.79), while the removal of P and H were influenced more by the time of BTF operation (CI=25.36, 15.62). The BTF was subjected to different types of short-term shock-loads: 5-h shock-load of HMP mixture simultaneously, and 2.5-h shock-load of either H, M, or P, individually. It was observed that, short-term shock-loads of individual pollutants (M or H) did not significantly affect their own removal, but the removal of P was affected by 50%. The results from this study also show the sensitiveness of the well-acclimated BTF to handle sudden load variations and also revival capability of the BTF when pre-shock conditions were restored.

On the encapsulation of halide anions by bambus[6]uril

The relative affinity of the recently synthesized receptor bambus[6]uril (BU[6]) towards halides in encapsulation processes was theoretically studied by means of M06-2X and B3LYP calculations. The gas-phase results do not follow the affinity experimentally observed in solution, as the largest encapsulation energy was obtained for fluoride, and the smallest one for iodide. Nevertheless, this finding is in agreement with the gas phase hydrogen bond energies determined for the CH4⋯X– complexes, X=F–, Cl–, Br–, I–. The structural changes experienced by the receptor when the halide is inside decrease as we move from fluoride to iodide. Thus, the relative affinity is due to a balance between the hydrogen-bond energies between the methine groups inside the cavity and the anions (CH⋯X–) and the deformation of the receptor induced by the anion. When solvents effects are considered, the affinity of BU[6] for halides is in line with experimental evidence. In effect, the difference between the ΔG298∘ computed for iodide and bromide is 1kcal/mol, just 0.5kcal/mol smaller than the experimental value. The effect of the counter ion was evaluated using Na+, but inclusion of the latter worsens the agreement with experiment. Finally, we discuss methodological problems observed for the BU[6]·X– complexes.

Quantitative relationship between rate constants and molecular structure descriptors for the gas phase hydrogen abstraction reactions

The abstraction of hydrogen by general radicals has a wide role in environmental and also in technological processes because it results in reactive free radicals that play a vital role in atmospheric chemistry and also in biochemical processes. In addition to experimental studies, the theoretical modelling of this elementary reaction has been important for understanding and predicting respective rate constants. In this paper, molecular descriptors in the context of a QSAR approach are used to codify the relationship between molecular structure and rate constants. Unique experimental data is collected from the literature for the reaction , where are diverse radicals. The four-parameter QSAR model (n = 34, r 2 = 0.81, = 0.74, = 0.12, s 2 = 0.19) is presented for the bimolecular rate constants, accompanied with model diagnostics and analysis of descriptors in the model.

Low Temperature Catalytic Decomposition of Hydrogen Sulfide into Hydrogen and Diatomic Gaseous Sulfur

A new catalytic reaction of hydrogen sulfide decomposition is discovered, the reaction occurs on metal catalysts in gas phase according to equation $$2{\text{H}}_{2} {\text{S}} \leftrightarrow 2{\text{H}}_{2} + {\text{S}}_{2}^{{({\text{gas}})}}$$ to produce hydrogen and gaseous diatomic sulfur, conversion of hydrogen sulfide at room temperature is close to 15 %. The thermodynamic driving force of the reaction is the formation of the chemical sulfur–sulfur bond between two hydrogen sulfide molecules adsorbed on two adjacent metal atoms in the key surface intermediate and elimination of hydrogen into gas phase. “Fingerprints” of diatomic sulfur adsorbed on the solid surfaces and dissolved in different solvents are studied. In closed vessels in adsorbed or dissolved states, this molecule is stable for a long period of time (weeks). A possible electronic structure of diatomic gaseous sulfur in the singlet state is considered. According to DFT/CASSCF calculations, energy of the singlet state of S2 molecule is over the triplet ground state energy for 10.4/14.4 kcal/mol. Some properties of gaseous diatomic sulfur are also investigated. Catalytic solid systems, both bulk and supported on porous carriers, are developed. When hydrogen sulfide is passing through the solid catalyst immersed in liquid solvent which is capable of dissolving sulfur generated, conversion of hydrogen sulfide at room temperature achieves 100 %, producing hydrogen in gas phase. This gives grounds to consider hydrogen sulfide as inexhaustible potential source of hydrogen—a very valuable chemical reagent and environmentally friendly energy product.

Indirect fuel cell based on a redox-flow battery with a new design to avoid crossover

A new design of a redox flow battery (RFB), which is composed of two subcells separated by a gas phase of hydrogen, is proposed to eliminate the crossover of ionic species between the anolyte and catholyte. This idea not only increases the possible combinations of the two electrolytes, but also opens up the prospect of a revival of the old idea of an indirect fuel cell, which is composed of an RFB and two chemical reactors to regenerate the electrolytes using a fuel and oxygen. This paper describes the operation of a subcell as a component of an indirect fuel cell system. In the cycling test, oxidation/reduction of the electroactive species in each electrolyte were repeated with a hydrogen electrode as the counter electrode. This result demonstrates the possibility of this newly proposed RFB without crossover. In the operation of the subcell with a chemical reactor, a molecular catalyst (a rhodium porphyrin) was dissolved in the anolyte, and then a fuel was bubbled in the anolyte reservoir. As the electroactive species was reduced by the fuel, a steady-state oxidation current was observed at the cell. This demonstrates the negative half of the newly proposed indirect fuel cell.

Ambient reaction kinetics of atmospheric oxygenated organics with the OH radical: a computational methodology study

The gas phase hydrogen abstraction reaction kinetics of short chained oxygenated hydrocarbons of atmospheric relevance has been studied using density functional theory, basis set extrapolation procedures, Møller-Plesset second order perturbation theory and Coupled-Cluster Singles Doubles. The rate constants for the reaction of the OH radical with nine different oxygenated compounds: CH3OH, CH3CH2OH, H2CO, CH3CHO, CH3COCH3, CH3OCH3, HCOOH, CH3COOH, HCOOCH3 with a total of 18 individual hydrogen abstraction reactions have been computationally determined and compared to experimental data. The performance of DFT in predicting the imaginary vibrational frequency of the nuclear motion at the transition state has been evaluated to assess tunnelling effects using Wigner, Bell and Eckart tunnelling corrections. Several different hybrid methodologies utilizing DFT/MP2 structures, vibrational frequencies and explicitly correlated Coupled Cluster single point energy corrections have been investigated to identify an approach for obtaining reliable reaction kinetics. Our investigation shows that CCSD(T)-F12a/VTZ-F12//BH&HLYP/aug-cc-pVTZ using a Bell or Eckart tunnelling correction yields rate constants within a factor of ~3 of experimental data and branching ratios within experimental uncertainty for the test set of short chained oxygenated compounds of atmospheric relevance.

Hydrogen spillover mechanism on covalent organic frameworks as investigated by ab initio density functional calculation

The hydrogen spillover mechanism, including the H chemisorption, diffusion, and H(2) associative desorption on the surface of COFs and H atoms migration from metal catalyst to COFs, have been studied via density functional theory (DFT) calculation. The results described herein show that each sp(2) C atom on COFs' surface can adsorb one H atom with the bond length d(C-H) between 1.11 and 1.14 Å, and the up-down arrangement of the adsorbed H atoms is the most stable configuration. By counting the chemisorption binding sites for these COFs, we can predict the saturation storage densities. High hydrogen storage densities show that the gravimetric uptakes of COFs are in the range of 5.13-6.06 wt%. The CI-NEB calculations reveal that one H atom diffusing along the C-C path on HHTP surface should overcome the 1.41-2.16 eV energy barrier. We chose tetrahedral Pt(4) cluster and HHTP as the representative catalyst and substrate, respectively, to study the H migration from metal cluster to COFs. At most, two H atoms can migrate from Pt(4) cluster to HHTP substrate. The migration reaction is an endothermic process, undergoing an activation barrier of 1.87 eV and 0.57 eV for the first and second H migration process, respectively. Three types of H(2) associative desorption from hydrogenated COFs were studied: (I) the two H adatoms recombining to one H(2) molecule with a recombination barrier of 4.28 eV, (II) the abstraction of adsorbed H atoms by gas-phase hydrogen atoms through ER type recombination reactions with a recombination barrier of 1.05 eV, (III) the H(2) desorption through the reverse spillover mechanism with an energy barrier of 2.90 eV.

Back Propagation Neural Network Model for Predicting the Performance of Immobilized Cell Biofilters Handling Gas-Phase Hydrogen Sulphide and Ammonia

Lab scale studies were conducted to evaluate the performance of two simultaneously operated immobilized cell biofilters (ICBs) for removing hydrogen sulphide (H2S) and ammonia (NH3) from gas phase. The removal efficiencies (REs) of the biofilter treating H2S varied from 50 to 100% at inlet loading rates (ILRs) varying up to 13 g H2S/m3 ·h, while the NH3 biofilter showed REs ranging from 60 to 100% at ILRs varying between 0.5 and 5.5 g NH3/m3 ·h. An application of the back propagation neural network (BPNN) to predict the performance parameter, namely, RE (%) using this experimental data is presented in this paper. The input parameters to the network were unit flow (per min) and inlet concentrations (ppmv), respectively. The accuracy of BPNN-based model predictions were evaluated by providing the trained network topology with a test dataset and also by calculating the regression coefficient (R 2) values. The results from this predictive modeling work showed that BPNNs were able to predict the RE of both the ICBs efficiently.

Electrochemical and Optical Properties of Magnesium-Alloy Hydrides Reviewed

As potential hydrogen storage media, magnesium based hydrides have been systematically studied in order to improve reversibility, storage capacity, kinetics and thermodynamics. The present article deals with the electrochemical and optical properties of Mg alloy hydrides. Electrochemical hydrogenation, compared to conventional gas phase hydrogen loading, provides precise control with only moderate reaction conditions. Interestingly, the alloy composition determines the crystallographic nature of the metal-hydride: a structural change is induced from rutile to fluorite at 80 at.% of Mg in Mg-TM alloy, with ensuing improved hydrogen mobility and storage capacity. So far, 6 wt.% (equivalent to 1600 mAh/g) of reversibly stored hydrogen in MgyTM(1-y)Hx (TM: Sc, Ti) has been reported. Thin film forms of these metal-hydrides reveal interesting electrochromic properties as a function of hydrogen content. Optical switching occurs during (de)hydrogenation between the reflective metal and the transparent metal hydride states. The chronological sequence of the optical improvements in optically active metal hydrides starts with the rare earth systems (YHx), followed by Mg rare earth alloy hydrides (MgyGd(1-y)Hx) and concludes with Mg transition metal hydrides (MgyTM(1-y)Hx). In-situ optical characterization of gradient thin films during (de)hydrogenation, denoted as hydrogenography, enables the monitoring of alloy composition gradients simultaneously.

Two-Dimensional Spin-Polarized Hydrogen at Zero Temperature

The ground-state properties of spin polarized hydrogen H↓ in two dimensions (2D) are obtained by means of diffusion Monte Carlo calculations. Using the most accurate to date ab initio H↓–H↓ interatomic potential we have studied hydrogen gas phase, from the very dilute regime until densities above its freezing point. For very low densities, the equation of state of the gas can be described in terms of the gas parameter na 2, where a is the s-wave scattering length in 2D. The solid phase in 2D has also been studied up to high pressures and the gas-solid phase transition determined using the double-tangent Maxwell construction.

Gas-phase hydrogen deuterium exchange behavior of lysine and its homologs

The gas-phase hydrogen/deuterium exchange behavior for protonated lysine and its three shorter homologs, ornithine (Orn), 2,4-diamino butanoic acid (Daba), and 2,3-diamino propanoic acid (Dapa) were studied in a modified LCQ-DECA ion trap mass spectrometer. The HDX behavior of protonated lysine has been studied previously by several groups. It undergoes five equivalent exchanges, corresponding to the hydrogen atoms attached to the protonated lysine side chain and amine terminus nitrogen, and one slower exchange corresponding to the COOH hydrogen. The shorter homologs also exchange all six labile hydrogen atoms but at different rates. Relative to protonated lysine, DapaH+ exchanges two times faster, DabaH+ exchanges slightly slower, and OrnH+ exchanges nearly 30 times more slowly. High-level hybrid density functional theory calculations attribute this difference to the increased barrier for the relay-type exchange mechanism in OrnH+, relative to the other homologs.

Investigation of H-bonding and halogen-bonding effects in dichloroacetic acid: DFT calculations of NQR parameters and QTAIM analysis

A theoretical study was performed to examine hydrogen and halogen bonds properties in gas phase and crystalline dichloroacetic acid (DCAA). The specific pattern of O-H∙∙∙O, C-H∙∙∙O, HCl, Cl∙∙∙O and Cl∙∙∙Cl interactions in DCAA dimers is described within the quantum theory of atoms in molecules (QTAIM) formalism. Based on QTAIM results, a partial covalent character is attributed to the O-H∙∙∙O hydrogen bonds in DCAA, whereas all the C-H∙∙∙O, Cl···O and Cl∙∙∙Cl intermolecular interactions are weak and basically electrostatic in nature. MP2/6-311++G** calculations indicate that the interaction energies for DCAA dimers lie in the range between -0.40 and -14.58kcalmol(-1). One of the most important results of this study is that, according to energy decomposition analyses, halogen bonds are largely dependent on both electrostatic and dispersion interactions. For those nuclei participating in the hydrogen-bonding and halogen-bonding interactions, nuclear quadrupole coupling constants exhibit significant changes on going from the isolated molecule model to the crystalline DCAA. Of course, the magnitude of these changes at each nucleus depends directly on its amount of contribution to the interactions.

Exploring the H-abstraction reactions of CHCl·−/CCl 2 ·− with CX3H (X = F, Cl, Br and I) using the density functional theory method

Gas-phase hydrogen abstraction reactions have been compared using the popular density functional theory (DFT) functional BHandHLYP/aug-cc-pVTZ/RECP level of theory, on the basis of the model reaction CHCl·-/CCl2·- + CX3H (X = F, Cl, Br and I). Our theoretical findings suggest the efficiency of the H-abstraction reactions induced by either CHCl·- or CCl2·- increases as the substrate is changed from CF3H to CI3H, and that CHCl·- has a higher activity in hydrogen abstraction than CCl2·- for a given substrate. The entropy effect at 298 K does not significantly change the trend in reactivity of the various reactions, which is in general controlled by the heights of activation energies D E ≠. Therefore, we have explored the origin of the energy barriers D E ≠ of the reactions using the activation strain model of chemical reactivity.