Gas-phase Hydrogen Research Articles

Performance of a compost and biochar packed biofilter for gas-phase hydrogen sulfide removal

The main aim of this study was to evaluate the performance of an aerobic biofilter packed with compost for the removal of gas-phase hydrogen sulfide (H2S). After 52 d of operation, the biofilter was re-packed by replacing a certain portion (25%, v/v) of the existing compost with biochar and its performance was tested. The steady and transient performance of the biofilter was evaluated by varying the H2S concentrations from 0.1 to 2.9 g m−3 at an empty bed residence time (EBRT) of 119 and 80 s, respectively. The maximum elimination capacity (ECmax) of the compost and compost + biochar biofilter were ∼19 and 33 g m−3 h−1, respectively, with >99% removal efficiency at an EBRT of 119 s. The compost biofilter showed a quick response to shock loads and the critical load to the biofilter during the shock loading step was ∼81 g m−3 h−1.

Rapid Acceleration of Hydrogen Atom Abstraction Reactions of OH at Very Low Temperatures through Weakly Bound Complexes and Tunneling.

A generally accepted principle of chemical kinetics is that a reaction will be very slow at low temperatures if there is an activation barrier on the potential energy surface to form products. However, this Account shows that the reverse is true for gas-phase hydrogen abstraction reactions of the hydroxyl radical, OH, with organic molecules with which it can form a weakly bound (5-30 kJ mol-1) hydrogen-bonded complex. For hydrogen atom abstraction reactions of OH with volatile organic compounds (VOCs) containing alcohol, ether, carbonyl, and ester functional groups, the reaction accelerates rapidly at very low temperatures, with rate coefficients, k, that can be up to a 1000 times faster than those at room temperature, despite the barrier to products. The OH radical is a crucial intermediate in Earth's atmosphere, combustion processes, and the chemistry of the interstellar medium, where temperatures can reach as low as 10 K, so this behavior has very important implications for gas-phase chemistry in space. The key point is that at low temperatures the lifetime of the OH-VOC complex against re-dissociation back to reactants becomes much longer, and hence the probability of quantum mechanical tunneling under the reaction barrier to form products becomes much higher. These observations were made possible by using Laval nozzles to generate uniform supersonic flows at extremely low temperatures so that condensation of the reagents at reactor walls is avoided. In this Account, the use of laser flash-photolysis combined with laser-induced fluorescence spectroscopy within Laval flows is described to study the unusual kinetics of this type of reaction at temperatures down to 21 K and demonstrate the rapid upturn in the rate coefficient. For the reaction of OH with CH3OH, further evidence for the precomplex and tunneling mechanism comes from observation of the CH3O reaction product at very low temperatures, despite it being formed over the higher barrier to reaction. The experimental observations are supported by theoretical calculations using the MESMER master equation package to calculate k( T) and product yields as a function of temperature and which make use of potential energy surfaces determined using ab initio methods. The CH3O product is formed over a narrower barrier with a larger imaginary frequency and is calculated to be the sole product at very low temperatures. The kinetics of the OH reaction with CH3OH were measured to be independent of pressure, consistent with a tunneling mechanism rather than any collisional stabilization of the prereactive complex. In this Account, we collate available kinetic data and show that this newly discovered mechanism for H atom transfer reactions appears to be generally applicable for reactions of OH with organic molecules containing oxygenated functional groups, which have been observed in space by radio-astronomy. Rather than being ignored for a range of interstellar environments, these OH reactions are now being included in chemical networks in space and have been shown to significantly influence the abundance of OH, the organic molecules themselves, and reaction products and provide novel routes to forming even more complex functional groups, for example, precursors to prebiotic molecules.

Hydrogen storage and electrochemical properties of LaNi5-xCux hydride-forming alloys

LaNi5-type alloys are commercial materials for the negative electrode in Ni-MH rechargeable batteries. Partial substitution of La by mischmetal (Mm) and of Ni by elements like Co, Al, and Mn significantly improve the cycle stability and high-rate discharge capacity of the electrodes. The partial substitution of Ni by Cu was studied previously for several selected ternary alloys with a special focus on crystal structure change upon substitution and gas phase hydrogen absorption. We present in this paper the results of the study of the electrochemical activation, discharge kinetics, equilibrium charge/discharge, and cycle life of electrodes made from four different LaNi5-xCux (x = 0.1, 0.5, 0.9, 1) alloys in order to provide full insights into utilization of these alloys.

Hydrogen supersaturated layers in H/D plasma-loaded tungsten: A global model based on thermodynamics, kinetics and density functional theory data

In this work, we combine Density Functional Theory data with a Thermodynamic and a kinetic model to determine the total concentration of hydrogen implanted in the sub-surface of tungsten exposed to a hydrogen flux. The sub-surface hydrogen concentration is calculated given a flux of hydrogen, a temperature of implantation, and the energy of the incoming hydrogen ions as independent variables. This global model is built step by step; an equilibrium between atomic hydrogen within bulk tungsten and a molecular hydrogen gas phase is first considered, and the calculated solubility is compared with experimental results. Subsequently, a kinetic model is used to determine the chemical potential for hydrogen in the sub-surface of tungsten. Combining both these models, two regimes are established in which hydrogen is preferentially trapped at either interstitial sites or in vacancies. We deduce from our model that the existence of these two regimes is driven by the temperature of the implanted tungsten sample; above a threshold or transition temperature is the interstitial regime, below is the vacancy regime in which super-saturated layers form within tenths of angstrom below the surface. A simple analytical expression is derived for the coexistence of the two regimes depending on the implantation temperature, the incident energy and the flux of the hydrogen ions which we use to plot the corresponding phase diagram.

Structural Analysis of Phospholipid Using Hydrogen Abstraction Dissociation and Oxygen Attachment Dissociation in Tandem Mass Spectrometry.

Gas-phase hydrogen radicals were introduced into a quadrupole ion trap containing singly charged phospholipids to obtain structural fragmentation patterns in tandem mass spectrometry (MS/MS). Saturated and unsaturated phosphatidylcholines were used as a model phospholipid, whose chain-length ranges between 16 and 24. The MS/MS spectrum yielded a continuous series of fragment ions with a mass difference of 14 Da, representing the saturated fatty acyl chains. The fragment ions corresponding to the double-bond position within a single fatty acyl chain showed a characteristic mass difference of 12 Da. The detection of these diagnostic product ions enabled the structural analysis of double-bond isomers of phospholipids. To further investigate the potential of radical-induced dissociation for the isomeric analysis of phospholipids, gas-phase hydroxyl radicals, and triplet oxygen atoms were employed in tandem mass spectrometry. The methylene bridges adjacent to the double-bond positions were selectively dissociated, accompanied by oxidation of the double bonds. Tandem mass spectrometry incorporating multiple radical species facilitates the structural analysis of isomeric phospholipids.

Properties of planar structures based on Policluster films of diamond and AlN

AlN films doped with zinc were grown on Si substrates by RF magnetron reactive sputtering of a compound target. Policluster films of diamond doped with boron were formed on layered Si/AlN substrates from the gas phase hydrogen and methane, activated arc discharge. By electron microscopy, X-ray diffraction and Raman spectroscopy the composition and structure of synthetic policluster films of diamond and AlN films were studied. Photovoltaic devices based on the AlN/PFD layered structure are presented.

Full-dimensional analytical potential energy surface describing the gas-phase Cl + C2H6 reaction and kinetics study of rate constants and kinetic isotope effects.

Within the Born-Oppenheimer approximation a full-dimensional analytical potential energy surface, PES-2017, was developed for the gas-phase hydrogen abstraction reaction between the chlorine atom and ethane, which is a nine body system. This surface presents a valence-bond/molecular mechanics functional form dependent on 60 parameters and is fitted to high-level ab initio calculations. This reaction presents little exothermicity, -2.30 kcal mol-1, with a low height barrier, 2.44 kcal mol-1, and intermediate complexes in the entrance and exit channels. We found that the energetic description was strongly dependent on the ab initio level used and it presented a very flat topology in the entrance channel, which represents a theoretical challenge in the fitting process. In general, PES-2017 reproduces the ab initio information used as input, which is merely a test of self-consistency. As a first test of the quality of the PES-2017, a theoretical kinetics study was performed in the temperature range 200-1400 K using two approaches, i.e. the variational transition-state theory and quasi-classical trajectory calculations, with spin-orbit effects. The rate constants show reasonable agreement with experiments in the whole temperature range, with the largest differences at the lowest temperatures, and this behaviour agrees with previous theoretical studies, thus indicating the inherent difficulties in the theoretical simulation of the kinetics of the title reaction. Different sources of error were analysed, such as the limitations of the PES and theoretical methods, recrossing effects, and the tunnelling effect, which is negligible in this reaction, and the manner in which the spin-orbit effects were included in this non-relativistic study. We found that the variation of spin-orbit coupling along the reaction path, and the influence of the reactivity of the excited Cl(2P1/2) state, have relative importance, but do not explain the whole discrepancy. Finally, the activation energy and the kinetics isotope effects reproduce the experimental information.

PdII LMOF for the sensing of molecular hydrogen in gas phase

Pd^II LMOF for the sensing of molecular hydrogen in gas phase

Quantification of gas phase hydrogen peroxide and methyl peroxide in ambient air: Using atmospheric pressure chemical ionization mass spectrometry with O2−, and O2−(CO2) reagent ions

Instrumentation and ion chemistry are described for the measurement of hydrogen peroxide (H2O2) and methyl peroxide (CH3OOH) in ambient air by chemical ionization mass spectrometry (CIMS). A CIMS, designed and certified for aircraft deployment, was used in this work. The reagent gas was ultrapure air containing 400ppm CO2. The resultant reagent ions, O2− and O2−(CO2), form cluster ions with CH3OOH and H2O2, respectively, and are monitored at 80m/z [O2−(CH3OOH)] and 110m/z [O2− (CO2)(H2O2)]. The CIMS instrument was periodically calibrated using gas-phase standards generated from aqueous solutions. A Carulite-200® catalyst was used to remove peroxides from ambient air to blank the system to account for variations in the ambient air matrix. H2O2 also forms a stable cluster ion with O2− though its calibration behavior was more complex than that for O2−(CO2) in ambient air. The instrument was deployed on the National Center for Atmospheric Research Gulfstream-V aircraft. Representative measurements from the May-June 2012 Deep Convective Clouds and Chemistry experiment spanning altitudes between 0 and 13km over the south-central midwest and southeastern United States are shown. Laboratory experiments, airborne experiments and theoretical molecular modeling approaches were utilized to identify and select reagent ions and to understand the ion-molecule reactions for the formation of peroxide-ion clusters in the ambient air matrix under tropospheric conditions. The analytical viability of a particular ion-molecule adduct was supported by ab-initio molecular orbital calculations.

Continuous biohydrogen production from a food industry waste: Influence of operational parameters and microbial community analysis

The objective of this study was to assess the influence of the hydraulic retention time (HRT) and the pH on the fermentative hydrogen production from a food industry waste (FIW), in a continuous stirred tank bioreactor. Thus, hydrogen production was investigated for HRTs of 12, 8, 6 and 4 h and the results showed a long and stable reactor operation with high hydrogen content in the gas phase and high hydrogen production rates. The optimal HRT was found to be in the range between 6 and 12 h, corresponding to hydrogen yields of 96.27 ± 3.36 and 101.75 ± 3.71 L H2/kg FIW for 12 and 6 h, respectively. In the sequel, the effect of the pH (in the range 5–5.9) was investigated, by changing the buffer solution (BS) components, while the HRT value was maintained at 12 h. As anticipated, the results showed that the operating pH had a significant influence on hydrogen production rates and yields. Characterization of the microbial community was performed at various pH values, giving thus a deeper insight to the well-established hydrogen production process from FIW, since the possible biochemical pathways followed by the microbial consortium, under different operational conditions were elucidated.

Increase in the Surface Catalytic Ability by Addition of Palladium in C14 Metal Hydride Alloy

A combination of analytic tools and electrochemical testing was employed to study the contributions of Palladium (Pd) in a Zr-based AB2 metal hydride alloy (Ti12Zr22.8V10 Cr7.5Mn8.1Co7Ni32.2Al0.4). Pd enters the A-site of both the C14 and C15 Laves phases and shrinks the unit cell volumes, which results in a decrease of both gaseous phase and electrochemical hydrogen storage capacities. On the other hand, the addition of Pd benefits both the bulk transport of hydrogen and the surface electrochemical reaction. Improvements in high-rate dischargeability and low-temperature performances are solely due to an increase in surface catalytic ability. Addition of Pd also decreases the surface reactive area, but such properties can be mediated through incorporation of additional modifications with rare earth elements. A review of Pd-addition to other hydrogen storage materials is also included.

Anchoring Small Au Clusters on the Dehydroxylated and Hydroxylated SiO2 α-Quartz (001) Surface via Ti-Alloying

The adsorption of AuxTiy (x + y = 4, 5) bimetallic clusters on the hydroxyl-free and fully hydroxylated α-quartz (001) surfaces was investigated via density functional theory calculations including van der Waals (vdW) forces. The pure gold clusters adsorb only weakly on the silica surfaces via vdW forces. The interaction with the silica surfaces changes dramatically when Au atoms of the clusters are replaced by Ti. For y ≥ 2, the clusters react with the surface via oxygen spillover (on the hydroxyl-free surface) and hydrogen spillover (on the hydroxylated surface). These bimetallic clusters with more than one Ti atom exhibit very large adsorption energies in the range of −3 to −9 eV. The substitution of only one Au atom by Ti (y = 1) results in an intermediate effect on the adsorption strength. It may, however, be sufficient for the in situ formation of gas-phase hydrogen via reaction of the clusters with surface hydroxyl groups, resulting in strongly bound ≡Si–O–AuxTiy complexes.

On the effect of laser irradiation and heat treatment on the structure and field-emission properties of carbon nanowalls

The composition and structure of carbon nanowalls formed on silicon substrates from the gas phase of hydrogen and methane activated by a direct-current glow discharge are studied by methods of scanning electron microscopy, X-ray diffractometry, IR spectroscopy, and Raman spectroscopy. It is shown that nanowalls are comprised of a porous material consisting of curved lamellar (flaky) crystallites with a thickness of 3–10 nm. The effect of heat treatment and laser irradiation in air on the structure of the carbon nanowalls is studied, and the current–voltage characteristics of field-emission cathodes on their basis are obtained. The heating temperatures and laser-radiation power densities at which the morphology of the surface of carbon nanowalls changes and the characteristics of field-emission cathodes on their basis are determined.

Comprehensive Peptide Ion Structure Studies Using Ion Mobility Techniques: Part 1. An Advanced Protocol for Molecular Dynamics Simulations and Collision Cross-Section Calculation.

Collision cross-section (CCS) measurements with a linear drift tube have been utilized to study the gas-phase conformers of a model peptide (acetyl-PAAAAKAAAAKAAAAKAAAAK). Extensive molecular dynamics (MD) simulations have been conducted to derive an advanced protocol for the generation of a comprehensive pool of in-silico structures; both higher energy and more thermodynamically stable structures are included to provide an unbiased sampling of conformational space. MD simulations at 300K are applied to the in-silico structures to more accurately describe the gas-phase transport properties of the ion conformers including their dynamics. Different methods used previously for trajectory method (TM) CCS calculation employing the Mobcal software [1] are evaluated. A new method for accurate CCS calculation is proposed based on clustering and data mining techniques. CCS values are calculated for all in-silico structures, and those with matching CCS values are chosen as candidate structures. With this approach, more than 300 candidate structures with significant structural variation are produced; although no final gas-phase structure is proposed here, in a second installment of this work, gas-phase hydrogen deuterium exchange data will be utilized as a second criterion to select among these structures as well as to propose relative populations for these ion conformers. Here the need to increase conformer diversity and accurate CCS calculation is demonstrated and the advanced methods are discussed. Graphical Abstract ᅟ.

Kinetics study of the CN + CH4 hydrogen abstraction reaction based on a new ab initio analytical full-dimensional potential energy surface.

We have developed an analytical full-dimensional potential energy surface, named PES-2017, for the gas-phase hydrogen abstraction reaction between the cyano radical and methane. This surface is fitted using high-level ab initio information as input. Using the PES-2017 surface, a kinetics study was performed via two theoretical approaches: variational transition-state theory with multidimensional tunnelling (VTST-MT) and ring polymer molecular dynamics (RPMD). The results are compared with the experimental data. In the whole temperature range analysed, 300-1500 K, both theories agree within a factor of <2, reproducing the experimental behaviour taking into account the experimental uncertainties. At high temperatures, where the recrossing effects dominate and the RPMD theory is exact, both theories differ by a factor of about 20%; while at low temperatures this difference is larger, 45%. Note that in this temperature regime, the tunnelling effect is negligible. The CN + CH4/CD4 kinetic isotope effects are important, reproducing the scarce experimental evidence. The good agreement with the ab initio information used in the fitting process (self-consistency test) and with the kinetic behaviour in a wide temperature range gives confidence and strength to the new surface.

Combustion synthesis of CeO2 nanoparticles for aging and inhalation exposure studies

The continuous production of an aerosol of CeO2 nanoparticles is valuable for nanoparticle aging and inhalation exposure studies, compared with other synthesis processes that require subsequent handling and preparation of the aerosol which can alter nanoparticle properties. This paper describes a new method for producing CeO2 nanoparticles and a novel facility where a combustion synthesis system was integrated in-line with an atmospheric ultraviolet (UV) aging chamber and an inhalation exposure system. Poly-disperse CeO2 nanoparticles were continuously produced to demonstrate the capability of the integrated nanoparticle synthesis and delivery system. The CeO2 nanoparticles were products of combustion of cerium acetate hydrate, a solid-phase precursor, with gas-phase hydrogen, oxygen, and nitrogen reactants. Results for particle size, concentration, crystal structure, and morphology are presented for the CeO2 nanoparticles produced in this study with and without UV exposure in the aging chamber. The setup successfully demonstrated the capability to maintain a steady CeO2 particle number concentration throughout four hours of operation with ~90% of the particles less than 200nm in size, corresponding to a mass concentration of approximately 500μg/m3. The CeO2 nanoparticle morphology (including primary particle size and aggregate size) and crystalline phase showed minimal sensitivity to UV aging in the ambient urban environment used in the study. The results indicate other species co-produced in diesel fuel systems (where CeO2 nanoparticles are used as a fuel additive) or found in the urban atmosphere may be required to affect the aging of CeO2 nanoparticles observed in previous studies.

H2 hitting on graphene supported palladium cluster: molecular dynamics simulations

Dissociative adsorption of impinging gas-phase molecular hydrogen (H2) on a palladium cluster (Pd4) supported on defective graphene (C47) was studied by periodic density functional theory molecular dynamics simulations. The H2 on Pd4/C47 collision dynamics were investigated without any particular constraint, except for the Born–Oppenheimer approximation. The study, which had mostly method-testing aims, provided, anyway, valuable information about the collision kinetics of gas-phase molecular hydrogen. This was treated as an impacting projectile having different kinetic energy values. At lower kinetic energies, sticking was ruled by steering effects imputable to the Pd cluster that easily reoriented the incoming hydrogen molecule to the metallic surface sites, favoring fragmentation hence adsorption. Sticking decreased at higher kinetic energies for which the very fast corresponding projectile acquired a kind of elusiveness toward the metallic surface that for this was not able to steer and adsorb the gas-phase hydrogen molecule. Interestingly, altered steering effects, in this case, ruled by already adsorbed surface hydrogen, seemed to play a decisive role in refocusing both H2 hitting and sticking on the supported palladium surface, irrespective of the energy characterizing the impinging gas-phase molecules.

Molecular Simulations of Hydrogen Bond Cluster Size and Reorientation Dynamics in Liquid and Glassy Azole Systems.

We simulated the dynamics of azole groups (pyrazole, imidazole, 1,2,3-triazole, 1,2,4-triazole, and tetrazole) as neat liquids and tethered via linkers to aliphatic backbones to determine how tethering and varying functional groups affect hydrogen bond networks and reorientation dynamics, both factors which are thought to influence proton conduction. We used the DL_Poly_2 molecular dynamics code with the GAFF force field to simulate tethered systems over the temperature range 200-900 K and the corresponding neat liquids under liquid state temperatures at standard pressure. We computed hydrogen bond cluster sizes; orientational order parameters; orientational correlation functions associated with functional groups, linkers, and backbones; time scales; and activation energies associated with orientational randomization. All tethered systems exhibit a liquid to glassy-solid transition upon cooling from 600 to 500 K, as evidenced by orientational order parameters and correlation functions. Tethering the azoles was generally found to produce hydrogen bond cluster sizes similar to those in untethered liquids and hydrogen bond lifetimes longer than those in liquids. The simulated rates of functional group reorientation decreased dramatically upon tethering. The activation energies associated with orientational randomization agree well with NMR data for tethered imidazole systems at lower temperatures and for tethered 1,2,3-triazole systems at both low- and high-temperature ranges. Overall, our simulations corroborate the notion that tethering functional groups dramatically slows the process of reorientation. We found a linear correlation between gas-phase hydrogen bond energies and tethered functional group reorientation barriers for all azoles except for imidazole, which acts as an outlier because of both atomic charges and molecular structure.

Indirect Fuel Cell Based on a Redox-Flow Battery Toward the Reduction of Platinum Usage

An indirect fuel cell [1-3], which is composed of a redox-flow battery (RFB) and a chemical reactor to regenerate (oxidize) the catholyte by oxygen and another reactor to regenerate (reduce) the anolyte by a fuel, is constructed as an alternative to a PEFC. We have already proposed a new design for the RFB [4] for our indirect fuel cell, which has a gas phase of hydrogen to separate the catholyte and anolyte to eliminate the crossover of ionic species. In this work, to clarify the possibility to use an indirect fuel cell to reduce the usage of noble-metal catalysts, a non-noble-metal catalyst and a mixture of two molecular catalysts were used in the catholyte and anolyte regenerators, respectively. In the catholyte regenerator, a carbonized hemoglobin powder was used as a solid catalyst. This material has been proved to be effective as an electrocatalyst for oxygen reduction reaction (ORR) in a PEFC [5]. In this work, it was used after immobilization on a polymer sheet support. In the anolyte regenerator, a rhodium complex was used for hydrogen oxidation and another rhodium complex for carbon monoxide oxidation. Although these two complexes contain a noble metal, they are soluble in the electrolyte and used as homogeneous catalysts. Since the active site of such a complex molecular catalyst is a single metal atom, the usage of metal can be reduced compared with a metallic platinum catalyst. This work demonstrates a steady-state operation of the above-mentioned indirect fuel cell by feeding of oxygen and CO-containing hydrogen to the catholyte and anolyte regenerators, respectively. This work was supported by JSPS KAKENHI Grant Number 25289363. [1] A.M. Posner, Fuel, 34 (1955) 330. [2] S. Ashimura, Y. Miyake, Denki Kagaku, 31 (1963) 598. [3] D.-G. Oei, J. Appl. Electrochem. 12 (1982) 41. [4] Z. Siroma, S. Yamazaki, N. Fujiwara, M. Asahi, T. Nagai, T. Ioroi, J. Power Sources, 242 (2013) 106. [5] J. Maruyama, I. Abe, Chem. Mater., 18 (2006) 1303.

Identification of carbon-encapsulated iron nanoparticles as active species in non-precious metal oxygen reduction catalysts.

The widespread use of fuel cells is currently limited by the lack of efficient and cost-effective catalysts for the oxygen reduction reaction. Iron-based non-precious metal catalysts exhibit promising activity and stability, as an alternative to state-of-the-art platinum catalysts. However, the identity of the active species in non-precious metal catalysts remains elusive, impeding the development of new catalysts. Here we demonstrate the reversible deactivation and reactivation of an iron-based non-precious metal oxygen reduction catalyst achieved using high-temperature gas-phase chlorine and hydrogen treatments. In addition, we observe a decrease in catalyst heterogeneity following treatment with chlorine and hydrogen, using Mössbauer and X-ray absorption spectroscopy. Our study reveals that protected sites adjacent to iron nanoparticles are responsible for the observed activity and stability of the catalyst. These findings may allow for the design and synthesis of enhanced non-precious metal oxygen reduction catalysts with a higher density of active sites.