H2 Reaction Research Articles

Multifluid computational fluid dynamics simulation for sawdust gasification inside an industrial scale fluidized bed gasifier

Scarcity of fossil fuels, and to fulfill the energy demand of the increasing population, researchers need to shift their attention to the alternative of fossil fuels. It would be impractical and time-consuming to conduct extensive experiments on Fluidized Bed Gasifiers (FBG) of varying fuel types, sizes, geometries and operating conditions. The objective of the current research work is focused on numerical simulation of hydrodynamics behavior and sawdust gasification in an industrial scale FBG using the Eulerian-Eulerian multifluid model. For the accurate prediction of thermal and hydraulic performance (bed voidage, suspension density, pressure drop, heat transfer, and combustion kinetics), one should incorporate the correct parameters in the Computational Fluid Dynamics (CFD) simulation of a fluidized bed gasifier. It includes the multiphase gasification modeling using the Eulerian-Eulerian approach with an user defined heterogeneous reaction kinetics. The adopted CFD methodology is validated with experimental data and extended for the prediction of gasification characteristics of sawdust by incorporating eight heterogeneous (moisture release, volatile cracking, tar cracking, tar oxidation, char combustion, CO₂ gasification, steam gasification, methanation reaction) and five homogeneous oxidation of CO, CH₄, H₂, forward and backward water gas shift (WGS) reactions. In the result section, composition of gasification products is analyzed, along with the hydrodynamics of sawdust and sand phase, heat transfer between the gas, sand and sawdust, reaction rates of different homogeneous and heterogeneous reactions are being analyzed along the height of the domain.

Synthesis of Carboxylic Acids from Saccharides, CO2, and H2

Here we report a strategy to synthesize C7 carboxylic acids via the reaction of glucose, CO2 and H2. The reaction can be realized using Rh(acac)(CO)2 as catalyst and I2 as promoter in the binary solvent of acetic acid and water at 160 °C. The strategy also applies to other Cn saccharides, where the corresponding Cn+1 carboxylic acids could be obtained and the yield of the acids can reach 72% when glyceraldehyde was used. The reaction pathway was proposed based on a series of control experiments. This work utilized saccharide and CO2 simultaneously via C–C bond formation, which opens a promising way of biomass utilization and CO2 conversion.

Effects of B/C ratio on the structural and mechanical properties of TiBCN coating deposited by PACVD

TiBCN coating is known as a hard, self-lubricant and wear resistant coating which can be applied on industrial tools to increase their working life time under severe wear conditions. In this paper, TiBCN coatings with different B/C ratios were applied on H13 steel using plasma-assisted chemical vapor deposition from BBr3, TiCl4, CH4, N2 and H2 reactants at 500 °C. The results signified that the introduction of B and C elements to TiN changed its preferred crystalline orientation from (200) to (111) and decreased crystal size from 12 to 9 nm as a result of the formation of amorphous phases which constrain grain growth. The addition of B and C altered the coating's nucleation and growth mechanisms and generated a strong surface etching agent of HBr which significantly changed surface morphology and roughness. Increasing flow ratio of CH4 to BBr3 from 0.125 to 0.25 influenced the coating's mechanical properties and increased coating's hardness from 18.1 to 23.2 GPa and Young's modulus from 296 to 334.7 GPa. Rising coating's C content remarkably improved its nano-wear resistance and the coating with the highest C content exhibited a wear volume of 1*10−19 m3 which was about 63% lower than that of TiN coating.

Study of proton and deuteron pickup reactions (d,3He), (d,4He) with 8He and 10Be radioactive beams at ACCULINNA-2 fragment separator

The extremely neutron-rich systems 7H, 6H were studied in the 2H(8He, 3He)7H and 2H(8He, 4He)6H proton and deuteron pickup reactions with a 26 AMeV secondary 8He beam produced at the new ACCULINNA-2 fragment separator. In addition, the same proton and deuteron pickup reactions were generated using the 42 AMeV 10Be beam, and the population of low-lying 9Li and 8Li states was measured in reactions 2H(10Be,3He)9Li and 2H(10Be,4He)8Li, respectively. The latter were used as reference measurements in order to check the setup calibration over the excitation energy of 7,6H and to determine the real experimental energy resolution which was compared with Monte Carlo calculations. The corresponding results obtained for the superheavy hydrogen systems 7H, 6H are presented and discussed. Typical excitation spectra of the 9Li and 8Li nuclei are also shown.

Studying the Sulfur Poisoning Mechanism of Solid Oxide Fuel Cells by Means of Patterned Nickel/Yttrium-Stabilized Zirconia Electrodes

Sulfur causes Ni-based ceramic anode poisoning and thus shortens the life of the cell. Therefore, it is important to clarify the mechanism of sulfur poisoning to improve cell performance and lifetime. However, there is still some controversy about the mechanism of sulfur poisoning. In this work, Ni-patterned electrodes were used to investigate the mechanism of sulfur poisoning under different H2S concentrations and current densities. The electrochemical performance decreased with the H2S concentration increasing from 0 to 5 ppm due to the decrease of H2 reaction active sites. When further increasing the H2S concentration to 50 ppm, the performance showed a different trend and recovered to the initial performance without H2S due to the electrochemical oxidation of H2S. Increasing the current density was found to alleviate sulfur poisoning to some extent. The patterned electrode demonstrated a useful tool for the study of H2S poisoning mechanism.

Experimental study of the methane/hydrogen/ammonia and ethylene/ammonia oxidation: Multi-parameter measurements using a shock tube combined with laser absorption spectroscopy

Ammonia (NH3) is a promising hydrogen carrier and carbon-free fuel, which can be synthesized using renewable energy and has attracted increasing attention from both academic and industrial communities. This study selected six absorption lines and developed a laser absorption diagnostics system that can simultaneously measure the temperature, CO, CO2, H2O, NH3, and NO time-histories during the oxidation of CH4/H2/NH3 and C2H4/NH3 mixtures (equivalence ratio ϕ ≈ 1.2) behind reflected shock waves. Since the fuels were highly diluted to reduce the nonideal effects and heat release behind reflected shock waves, the maximum NO mole fraction was only ∼0.2% and led to a small absorption (< 2.0%). Therefore. the wavelength modulation spectroscopy (WMS-2f/1f) was used for the NO time-history measurements while the other species were measured using fixed-wavelength absorption spectroscopy. A total of thirteen kinetics models were used to interpret the measurements. The main differences between the model predictions and measured data lie in two aspects: the mixture reactivities and the NO production. Generally speaking, for both CH4/H2/NH3 and C2H4/NH3 mixtures, the Glarborg model performs the best in predicting the temperature and species time-histories but the differences still exist. The high-quality experimental data support further analyses and improvements. Detailed kinetics analyses based on the Glarborg 2018 model were performed. It indicates that H + O2 = O + OH is the most sensitive and promoting reaction for both mixtures, followed by the H-abstraction reactions of H2 and C2H4. Conversely, the H-abstraction reactions of CH4 and NH3 impede oxidation due to competition with promoting reactions for reactants (H, OH, or O). Moreover, subsequent reactions involving the produced CH3 or C2H3 radicals also have significant effects on oxidation. The reactions affecting the NO plateau were also selected as the basis to optimize the predicted NO plateau. Although updating the rate constants of some key reactions improved model performance for both mixtures, discrepancies still exist, particularly for the C2H4/NH3 mixture.

Free-Standing Dendritic Nanostructured Co/CNT/Carbon Nanofiber Composites for Efficient Water Splitting in Alkaline Media

Exploring highly efficient three-dimensional (3D) nanoarchitectures for H2 and O2 evolution reaction (HER and OER) has received tremendous interest. Here, a binder-free free-standing cobalt/bamboo-shaped carbon nanotube/carbon nanofiber (Co/CNT/CNF) film was prepared based on electrospinning, followed by thermal treatment. The synergistic effect between Co cores, CNT shells (5 nm), and CNF skeletons endows the as-prepared Co/CNT/CNF with a 3D porous dendritic nanostructure. Therefore, the unique Co/CNT/CNF film demonstrates prominent HER (overpotential = 129 mV) and OER (overpotential = 162 mV) catalysis behavior at 10 mA cm–2. Meanwhile, the as-prepared Co/CNT/CNF film displays excellent overall water splitting activity as well as durability (at least 40 h both under 10 and 40 mA cm–2). Moreover, the facile electrospinning followed by the thermal treatment approach is economically practical for flexible film production, which has great potential for industrial application in water splitting technology.

Copper nanoparticles encapsulated in a nanoporous carbon-based catalyst in the upgradation of γ-valerolactone to 1,4-pentanediol by selective hydrogenation

This research work introduces highly dispersed Cu nanoparticles encapsulated into a nanoporous carbon (Cu@C) structure as an efficient catalytic system in selective hydrogenation of γ-valerolactone (GVL) to 1,4-pentanediol. The nanoporous carbon support and the catalysts were synthesized by sequential novel methods and characterized extensively by using a combination of different analytical techniques to determine the phase, textural, morphology, nanoparticles size, and distribution analysis, and redox behavior. The designed Cu@C embedded catalysts show moderately high activity in GVL hydrogenation with different Cu loadings. The effect of copper loadings was found to be a significant parameter in gaining the best performance in GVL conversion. The copper nanoparticles were uniformly distributed over the nano-scaled carbon structure with active metallic Cu(111) sites with high dispersion and promote GVL hydrogenation, efficiently. Over a 5Cu@C catalyst exhibited the highest GVL conversion (∼91%) and 1,4-pentanediol selectivity (∼97%) at 200 °C for a 5 h reaction time under a 5 MPa H2 pressure. The dispersion of the active copper phase in combination with a smaller particle size and surface acidity is directly correlated with the catalytic performance activity. The effects of reaction parameters such as the reaction time, temperature, and H2 pressure were systematically investigated. Overall, Cu@C is a promising non-noble metal-based catalytic system for the upgradation of biomass-based platform molecules via selective hydrogenation.

Chemical Stability and Hydrogen Reaction Behavior of SmCo 2:17‐Type Permanent Magnets

Herein, the reaction behavior and chemical stability of two commercially available SmCo 2:17‐type sintered magnets with nominal composition of Sm23.75Co48.67FebalCu4.91Zr2.37 and Sm24.95Co48.80FebalCu4.46Zr2.68 (wt%) are investigated. The magnets are placed in a hydrogen atmosphere with systematically varied pressure, exposure time, and temperature ranging from 1–11 bar, 2–10 d, and 25–500 °C, respectively. Hydrogen content, magnetic properties, microstructure, and lattice constants are characterized in detail. It is found that for short exposure times like 2 d an activation temperature of 120 °C is necessary to initiate the reaction and to increase the amount of hydrogen in the Sm–Co material. Hydrogen absorption starts at lower temperatures with longer exposure times. An increase in exposure time, temperature, or pressure leads to a higher hydrogen content and a decrease in remanence Br, energy product (BH)max, and coercivity HcB. Lattice expansion, estimated by X‐ray diffraction analysis, correlates with the increasing amount of hydrogen in the Sm–Co magnets. With respect to all varied parameters under investigation, the exposure temperature has the highest impact on the observed property changes followed by reaction time and H2 pressure.

Support Nano‐Co/CeO2‐δ Catalyst for CO2 Hydromethanation

AbstractThe large‐scale use of fossil fuels had resulted in massive emission of CO2 and a series of serious environmental problems, which directly threatening human survival and sustainable development. CO2 is also the abundant carbon resource in C1 family. CO2 catalytic hydrogenation to CH4 is one of the effective ways to ultilize CO2 with low energy and high efficiency, which has been widely concerned in recent years. Suppoted nano‐Co/CeO2‐δ catalysts were prepared and evaluated their CO2 hydrogenation performances. XRD, H2‐TPR, H2‐TPD and CO2‐TPD had been conducted to study the physicochemical properties of the prepared Co/CeO2‐δ catalysts. The Co loading significantly affects the physicochemical properties and CO2 hydrogenation performances. The active metal Co species were highly diepersed on the CeO2 support surface. The number of active metal Co species, which formed by H2 reduction, increased with the increasing of Co loading. And the ability to adsorb and activate the reactant H2 and CO2 molecules was also enhanced, which effectively promoted the CO2 hydrogenation performances. Among of the studied Co/CeO2‐δ catalysts, the CoCe09 catalyst with Co loading of 9 % showed the best CO2 catalytic hydrogenation activity. In the reaction temperature of 240–400 °C, the CO2 conversion and CH4 selectivity follow the order: CoCe01&lt;CoCe03&lt;CoCe05&lt;CoCe11&lt;CoCe09. At 400 °C, the CO2 conversion increases from 30.1 % (CoCe01) to 59.2 % (CoCe09).

Scale-up analysis of hydrogen rich-stream production from biogas reforming in membrane reactors using numerical modeling

Biogas reforming in membrane reactors has been considered an alternative for hydrogen-rich stream production. Since this technology is not yet applied in industry, the performance of this process can only be evaluated by theoretical simulations. In this work, H2 production employing biogas as feedstock was simulated by Computational Fluid Dynamics in Pd membrane reactors, considering a two-dimensional and non-isothermal model on laboratory and industrial (20 times greater) scales. The most relevant operating parameters were external temperature and residence time (or inlet velocities). An optimal temperature range was proposed (823–948 K) to achieve a balance between reaction performance and H2 permeation rate. Significant thermal gradients were observed on the industrial scale, showing that non-isothermal modeling is crucial for designing a membrane reactor with larger dimensions. The better reaction performance was obtained at lower velocities (<0.046 m s−1), which is also an important information for the optimization and design of the membrane modules.

Design and assembly of TZCS/PO/Ni2P-MnOx composite with “homojunction + protection layer + cocatalyst” structure for photocatalytic overall water splitting

Herein, we synthesize a phosphate (PO) protection layer and various cocatalysts (Ni2P and MnOx) on the twinned Zn0.5Cd0.5S (TZCS) photocatalyst by a two-step photochemical synthesis method. The initial photocatalytic hydrogen production rate of TZCS/PO/Ni2P-MnOx composite with “homojunction + protection layer + cocatalyst” structure reaches 1.36 mmol h−1 g−1, which is about 1.72 and 2.56 times higher than WZCS/PO/Ni2P-MnOx and ZZCS/PO/Ni2P-MnOx photocatalysts (WZCS and ZZCS are abbreviations of wurtzite Zn0.5Cd0.5S and zinc-blende Zn0.5Cd0.5S solid solutions), respectively. The average photocatalytic hydrogen and oxygen production rate of TZCS/PO/Ni2P-MnOx are 1.21 mmol h−1 g−1 and 0.59 mmol h−1 g−1 within 12 h, which are close to the theoretical ratio of 2: 1. The excellent photocatalytic overall water splitting performance can be rationalized by the separation, transmission and application process of photogenerated electron-hole pairs, which can be efficiently separated and transported by the homojunction structure and further penetrate the PO protection layer, so that they have a greater chance of being captured by the Ni2P and MnOx cocatalysts, which can be used as the active catalytic site for the H2 and O2 production reaction, respectively.

Ir–Ru Electrocatalysts Embedded in N‐Doped Carbon Matrix for Proton Exchange Membrane Water Electrolysis

AbstractMore active electrocatalysts for H2 and O2 evolution reactions, efficient membranes, and robust porous transport layers (PTL) are required for designing advanced proton exchange membrane water electrolysis (PEMWE) systems. An N‐doped carbon matrix is introduced in this study to surpass the existing Ti PTLs. One‐step pyrolysis results in the carbonization of polyaniline films to the N‐doped carbon matrix, simultaneous formation of desiccation cracks and IrxRuy nanoparticles, and partial impregnation of the synthesized particles into the carbon matrix. The embedded IrxRuy nanoparticles are firmly bound to the surface of the carbon matrix, inhibiting the dissolution and detachment of the nanoparticles during the O2 evolution reaction (OER). The cracks in the carbon matrix allow the steady transport of the produced O2, comparable to conventional PTLs. After optimizing the Ir and Ru contents of the nanoparticles based on the electrocatalytic performance, Ir88Ru12 embedded in the N‐doped carbon matrix is found to be the most suitable catalyst for enhancing the OER performance of the PEMWE system with negligible degradation. These findings can potentially contribute to the industrial application of PEMWE. Relevant electrochemical systems with membrane electrode assemblies, such as fuel cells and CO2 reduction systems, can be modified using the suggested structure.

Zinc Speciation and Propane Dehydrogenation in Zn/H-ZSM-5 Catalysts

Zn/H-ZSM-5 catalysts have been frequently investigated for propane dehydrogenation (PDH); however, the active site remains unresolved due to the complexity of the system. We employed in situ FTIR spectroscopy and a kinetics method to correlate the Zn speciation and PDH activity in Zn/H-ZSM-5 with two Si/Al ratios (15 and 39) and a range of Zn/Al ratios (0–1.7). Incremental additions of zinc show that Zn2+ sites are preferentially formed on H-ZSM-5 over a fraction of paired Al sites followed by [Zn-O-Zn]2+ and [ZnOH]+ sites and then ZnOx clusters. The [Zn-OH]+ and [Zn-O-Zn]2+ sites in H-ZSM-5 are more active and selective than isolated Zn2+ for PDH. [Zn-OH]+ species sublimate over time on stream, leading to catalyst deactivation, while [Zn-O-Zn]2+ species are stable even after high-temperature reduction (750 °C for 60 min). Three distinct Zn sites ([Zn-O-Zn]2+, Zn2+, and [ZnOH]+) show a similar propane reaction order (close to 1) and H2 reaction order (close to 0). Combined with the lack of Zn hydride when propane flows over the catalyst at 550 °C, it is concluded that propane adsorption and dissociation is a rate-determining step and H2 desorption is fast. This work indicates that the preparation of H-ZSM-5 with abundant Al pairs may be a strategy to form stable and selective Zn/H-ZSM-5 catalysts for propane dehydrogenation. It is also highlighted that examining the effect of both metal/Al ratios and Al distribution of the zeolite is crucial in identifying the metal cations in metal–zeolite systems.

1ppm-detectable hydrogen gas sensors by using highly sensitive P+/N+ single-crystalline silicon thermopiles

Hydrogen (H2) is currently of strategic importance in the pursuit of a decarbonized, environmentally benign, sustainable global energy system; however, the explosive nature of H2 requires leakage monitoring to ensure safe application in industry. Therefore, H2 gas sensors with a high sensitivity and fast response across a wide concentration range are crucial yet technically challenging. In this work, we demonstrate a new type of MEMS differential thermopile gas sensor for the highly sensitive, rapid detection of trace H2 gas in air. Facilitated by a unique MIS fabrication technique, pairs of single-crystalline silicon thermopiles (i.e., sensing and reference thermopiles) are batch fabricated with high-density single-crystalline silicon thermocouples, yielding an outstanding temperature sensitivity at the sub-mK level. Such devices ensure the detection of miniscule temperature changes due to the catalytic reaction of H2 with a detection limit as low as ~1 ppm at an operating temperature of 120 °C. The MEMS differential thermopiles also exhibit a wide linear detection range (1 ppm-2%, more than four orders of magnitude) and fast response and recovery times of 1.9 s and 1.4 s, respectively, when detecting 0.1% H2 in air. Moreover, the sensors show good selectivity against common combustible gases and volatile organics, good repeatability, and long-term stability. The proposed MEMS thermopile H2 sensors hold promise for the trace detection and early warning of H2 leakage in a wide range of applications.

Revealing the Role of CO during CO2 Hydrogenation on Cu Surfaces with In Situ Soft X-Ray Spectroscopy.

The reactions of H2, CO2, and CO gas mixtures on the surface of Cu at 200 °C, relevant for industrial methanol synthesis, are investigated using a combination of ambient pressure X-ray photoelectron spectroscopy (AP-XPS) and atmospheric-pressure near edge X-ray absorption fine structure (AtmP-NEXAFS) spectroscopy bridging pressures from 0.1 mbar to 1 bar. We find that the order of gas dosing can critically affect the catalyst chemical state, with the Cu catalyst maintained in a metallic state when H2 is introduced prior to the addition of CO2. Only on increasing the CO2 partial pressure is CuO formation observed that coexists with metallic Cu. When only CO2 is present, the surface oxidizes to Cu2O and CuO, and the subsequent addition of H2 partially reduces the surface to Cu2O without recovering metallic Cu, consistent with a high kinetic barrier to H2 dissociation on Cu2O. The addition of CO to the gas mixture is found to play a key role in removing adsorbed oxygen that otherwise passivates the Cu surface, making metallic Cu surface sites available for CO2 activation and subsequent conversion to CH3OH. These findings are corroborated by mass spectrometry measurements, which show increased H2O formation when H2 is dosed before rather than after CO2. The importance of maintaining metallic Cu sites during the methanol synthesis reaction is thereby highlighted, with the inclusion of CO in the gas feed helping to achieve this even in the absence of ZnO as the catalyst support.

Organic-rich source rock/H2/brine interactions: Implications for underground hydrogen storage and methane production

There is increasing global interest in the attainment of a carbon dioxide-free global economy by replacement of carbon-based fossil fuels with clean hydrogen. But huge volume of hydrogen needs to be stored to address the imbalance between energy demand and supply due to low volumetric energy content of H2. Underground Hydrogen Storage (UHS) is an integral part of the hydrogen economy value chain and an appealing technology for the attainment of global decarbonization. The Jordan oil shale (Upper Cretaceous, organic-rich source rock sequence) has been proposed as a promising geological storage medium for hydrogen due to its exceptionally high organic content because methane can be produced from the reaction of trapped hydrogen with the kerogen. However, the extraction of methane from kerogen during hydrogen storage in organic-rich shale has not yet been reported. In this study, pressurized hydrogen was injected into high TOC shale samples for 80 days at 1500 psi and 75 °C to assess the extent of hydrogen-rock reaction and possible methane production. We also measured H2/brine and CH4/brine interfacial tensions (IFT), as well as the contact angles of H2/brine/shale and CH4/brine/shale systems at 75 °C and varying pressure (500–1500 psi) to understand the shale-fluid interaction at subsurface conditions. Results indicate some reaction of H2 with the shale after 80 days. No hydrogen sulfide was detected from gas chromatography analysis at the end of the experiment, but traces of methane (0.018 %) were detected. The reaction between hydrogen and organic matter of the shale yielded only a little methane under the conditions investigated in this research, possibly because the experimental temperature and reaction time was insufficient for copious methane generation. Furthermore, contact angle values of CH4/brine were found to be higher than of H2/brine. This means that under geo-storage conditions, the surface becomes fully CH4-wet condition (131o-149o) but remains only intermediate-wet in the presence of the H2/brine system (94o -106o) with increasing pressure, confirming that the interaction of methane with the shale surface is higher than hydrogen-shale surface interaction at similar conditions. The opposite trend was observed for IFT values. The hydrogen/brine IFT was 69.4 mN/m at 500 psi but decreased to 67.9 mN/m at 1500 psi. Likewise, the methane/brine IFT decreased from 69.7 mN/m to 58.3 mN/m with increasing pressure from 500 to 1500 psi. The findings of this study contribute to a better understanding of the adsorption trapping potential of organic-rich source rocks.

Effect of structure of Pd@Fe core–shell cubes on the enhancement of H2 conversion in direct reaction of H2 and O2

Structure engineering is an integrated strategy to regulate the performance of nanoparticles for various catalytic reactions, since the nanoparticle composition, shape, and interface affect the reaction activity and selectivity. Herein, we report a simple synthesis of clear core–shell structured Pd@Fe nanocubes with different shell thicknesses, which exhibit higher H2 conversion efficiency in direct hydrogen peroxide generation compared with ordinary Pd cubes. This result can be attributed to two main reasons: (i) the conformal growth of the Fe oxide shell consisting of loose structured Fe3O4 favors H2 penetration, and (ii) the capping agent (Br−) on the Pd–Fe3O4 interface that blocks the Pd active sites is removed during the shell formation. Therefore, the Fe oxide shell of the Pd@Fe nanoparticles not only helps maintaining the morphology of the nanoparticles but also increases the number of active sites on the inner core surface, confirming the advantage of the core–shell structure.

Carbon-Carbon Bond Formation from Carbon Monoxide and Hydride: The Role of Metal Formyl Intermediates.

Current examples of carbon chain production from metal formyl intermediates with homogeneous metal complexes are described in this Minireview. Mechanistic aspects of these reactions as well as the challenges and opportunities in using this understanding to develop new reactions of CO and H2 are also discussed.

Carbon‐Carbon Bond Formation from Carbon Monoxide and Hydride: The Role of Metal Formyl Intermediates**

AbstractCurrent examples of carbon chain production from metal formyl intermediates with homogeneous metal complexes are described in this Minireview. Mechanistic aspects of these reactions as well as the challenges and opportunities in using this understanding to develop new reactions of CO and H2 are also discussed.