H2 Source Research Articles

Hydrogen reaction analysis in aqueous solutions containing H2S/CO2 at different pressures

The hydrogen evolution reaction (HER) in H2S and H2S/CO2 solutions at different pressures was studied using platinum and stainless steel as working electrodes, with polarization curves and electrohydrodynamic impedance. When Pt was the working electrode, the polarization curves in H2S solutions without CO2 presentedonly one current plateau, while two plateaus were seen when a mixture of H2S/CO2 was used. However, when steel was the working electrode, two plateaus always existed even in the presence of H2S without CO2. HER was interpreted by another source of H2 coming from the H2S reaction coupled to the classical direct reduction of H+.

Subduction hides high-pressure sources of energy that may feed the\xa0deep subsurface biosphere

Geological sources of H2 and abiotic CH4 have had a critical role in the evolution of our planet and the development of life and sustainability of the deep subsurface biosphere. Yet the origins of these sources are largely unconstrained. Hydration of mantle rocks, or serpentinization, is widely recognized to produce H2 and favour the abiotic genesis of CH4 in shallow settings. However, deeper sources of H2 and abiotic CH4 are missing from current models, which mainly invoke more oxidized fluids at convergent margins. Here we combine data from exhumed subduction zone high-pressure rocks and thermodynamic modelling to show that deep serpentinization (40–80 km) generates significant amounts of H2 and abiotic CH4, as well as H2S and NH3. Our results suggest that subduction, worldwide, hosts large sources of deep H2 and abiotic CH4, potentially providing energy to the overlying subsurface biosphere in the forearc regions of convergent margins.

Alkaline thermal treatment of seaweed for high-purity hydrogen production with carbon capture and storage potential

Current thermochemical methods to generate H2 include gasification and steam reforming of coal and natural gas, in which anthropogenic CO2 emission is inevitable. If biomass is used as a source of H2, the process can be considered carbon-neutral. Seaweeds are among the less studied types of biomass with great potential because they do not require freshwater. Unfortunately, reaction pathways to thermochemically convert salty and wet biomass into H2 are limited. In this study, a catalytic alkaline thermal treatment of brown seaweed is investigated to produce high purity H2 with substantially suppressed CO2 formation making the overall biomass conversion not only carbon-neutral but also potentially carbon-negative. High-purity 69.69 mmol-H2/(dry-ash-free)g-brown seaweed is produced with a conversion as high as 71%. The hydroxide is involved in both H2 production and in situ CO2 capture, while the Ni/ZrO2 catalyst enhanced the secondary H2 formation via steam methane reforming and water-gas shift reactions.

Methane production by mechanochemical processing of MgH2-Li2CO3 as sources of H2 and CO2 at room temperature

The reutilization of CO2 to produce valuable chemical fuels is an attractive approach to reduce the greenhouse effect and global warming. In this work, the room temperature production of CH4/H2 fuel mixtures via mechanochemical activation of Li2CO3-MgH2 system was explored. The CH4/H2 fuel mixtures were obtained by a free-catalyst reaction, with high selectivity and using Li2CO3 and MgH2 as solid portable sources of CO2 and H2, respectively. The effect of processing parameters on both the evolution of the solid phases and the production of CH4/H2 fuel mixtures was studied using X-ray diffraction, spectroscopic techniques, electron scanning microscopy and gas chromatography. Thermodynamic calculations predict the complete CO2 reduction to CH4, with simultaneous formation of MgO and Li2O. Experimental evidence supports the progressive formation of MgO and the appearance of Li2O. The presence of H2 simultaneously with CH4 in the gas phase was due to kinetic restrictions. Based on experimental results and equilibrium composition calculations, the reaction mechanism was proposed. The kinetic analysis reveals that the rate limiting CH4 production is the nucleation of MgO/Li2O in the surroundings of Li2CO3, while the H2 release is controlled by the reaction interface between MgH2/Mg or MgH2/MgO.

Effective and selective direct aminoformylation of nitroarenes utilizing palladium nanoparticles assisted by fibrous-structured silica nanospheres

Palladium nanoparticles (~ 1–3 nm, 0.4 wt% Pd) were uniformly distributed over the surface of fibrous silica nanospheres (KCC-1) modified via aminopropyltriethoxysilane using a fast and cost-effective palladium (II) chloride reduction process. The Pd nanoparticles (Pd NPs) distribution over the ensuing catalyst Pd/KCC-1-NH2 showed much more uniform distribution, and smaller size compared with the tedious hydrothermal reduction method. The morphological, chemical, and size analyses of Pd/KCC-1-NH2 by BET, UV–Vis spectra, XRD, HR-TEM, EDS and XPS analysis revealed that the succeeding material consist of a distinct fibrous silica nanospheres support adorn with Pd NPs. The resultant nanocatalyst was tested for the one-step reductive aminoformylation of aromatic nitro compounds using formic acid. A wide range of substituted nitroarenes including electron withdrawing, releasing, sterically hindered and multifunctional groups have been converted to corresponding aryl formamide in quantitative yields (yields up to 98%) at moderate temperature (70 °C). Optimization study has proved that the 6 equivalent of formic acid is required and toluene was found to be the better solvent. The established practice is beneficial due to the use of formic acid as H2 source and formylating agent, easiness in handling of the catalyst and simple workup procedure with efficient catalyst reusability.

Ni Supported on Natural Clays as a Catalyst for the Transformation of Levulinic Acid into γ-Valerolactone without the Addition of Molecular Hydrogen

γ-Valerolactone (GVL) is a valuable chemical that can be used as a clean additive for automotive fuels. This compound can be produced from biomass-derived compounds. Levulinic acid (LA) is a compound that can be obtained easily from biomass and it can be transformed into GVL by dehydration and hydrogenation using metallic catalysts. In this work, catalysts of Ni (a non-noble metal) supported on a series of natural and low-cost clay-materials have been tested in the transformation of LA into GVL. Catalysts were prepared by a modified wet impregnation method using oxalic acid trying to facilitate a suitable metal dispersion. The supports employed are attapulgite and two sepiolites with different surface areas. Reaction tests have been undertaken using an aqueous medium at moderate reaction temperatures of 120 and 180 °C. Three types of experiments were undertaken: (i) without H2 source, (ii) using formic acid (FA) as hydrogen source and (iii) using Zn in order to transform water in hydrogen through the reaction Zn + H2O → ZnO + H2. The best results have been obtained combining Zn (which plays a double role as a reactant for hydrogen formation and as a catalyst) and Ni/attapulgite. Yields to GVL higher than 98% have been obtained at 180 °C in the best cases. The best catalytic performance has been related to the presence of tiny Ni particles as nickel crystallites larger than 4 nm were not present in the most efficient catalysts.

Balancing the hydrogen books.

Abiotic sources of H2 in the lithosphere outweigh the sinks, with the balance potentially being available to a large microbial community.

Abiotic hydrogen generation from biotite-rich granite: A case study of the Soultz-sous-Forêts geothermal site, France

Investigations on geochemical processes involved in H2 generation in natural reservoirs are important for the present energy transition from fossil fuels. Most studies related to native H2 focus on the serpentinisation of ultra-mafic rocks, in which the source of H2 is linked to oxidation of Fe2+-bearing minerals and a reduction of H2O. In this study, we investigate abiotic H2 generation from a biotite-rich granite using an approach based on a study case of the Soultz-sous-Forêts geothermal site in France. Using a geochemical and reactive transport model and an existing database, we simulated the hydrothermal alteration of the granite at 130–200 °C with a redox potential from −100 mV to −300 mV. The simulations show that generation of native H2 is possible in an open system by hydrothermal alteration of biotite as a source of Fe2+, which oxidises to Fe3+ leading to precipitation of Fe3+ minerals and reduction of H+. The amount of H2 produced depends on the type of Fe2+/3+ minerals which precipitate. The optimal conditions for H2 generation are related to magnetite precipitation as in the serpentinisation process. We assessed that the upper bound for H2 production for this site is 102 kt per km3 of granite. This is in case of complete oxidation of all the ferrous iron contained in the biotite of the geothermal reservoir. In practice, only part of this potential may be attained owing to the limited current exploitation methods which are unlikely to result in a complete disequilibrium of the whole biotite. Future research needs to focus on how to reach most of the H2 potential. Simulations with increasing CO2 pressures suggest that CO2 injection can stimulate the H2 production. This study has implications for possible coupling of heat extraction and future exploitation with H2 production.

Model Operational Matrix for the Betterment of Ruthenium As a Catalyst for the Electrochemical Nitrogen Reduction Reaction to Ammonia in Aqueous Electrolytes

Ammonia (NH3), as a green energy carrier, potential transportation fuel and chemical for fertilizer synthesis, plays an indispensable role in the agricultural, plastic, pharmaceutical and textile industries1. Industrially, NH3 manufacturing is dominated by the Haber–Bosch (HB) process, which consumes more than 2% of the global energy supply, and releases 1.87 tons of greenhouse gas, carbon dioxide (CO2), per 1 ton of NH3 2. This energy-intensive process is also inefficient and relatively low conversion ratio are achieved due to unfavorable chemical equilibrium 3. Hence, it is of great significance to develop alternative routes for more efficient N2 fixation under milder conditions. Recently, a worldwide gold rush has been triggered, and many pioneering methods are being investigated to convert N2 to NH3, including biological catalysis 4, photocatalysis 5,6and electrocatalysis 2,7. Particularly, electrochemical reduction of N2 to NH3 is thermodynamically predicted to be more energy efficient than the HB process by about 20% 7,8 . An electrochemical process could also provide the benefit of reducing greenhouse gas emission as the source of H2 is the electrolysis of water molecules instead of natural gas. With this scenario, ammonia would be synthesized in a carbon-neutral manner if renewable electrical energy is used.In the electrochemical N2 reduction reaction (NRR) system, though electrocatalysts are the paramount components, a rational cell design, synthesize and operation conditions are very vital 4. Most of recent studies have looked on a single parameter (or two) such as catalyst morphology, catalyst deposition and loading, nitrogen reduction potential or type, temperature, pressure and components of cell and electrolytes. However, the fact that NRR and catalyst deposition is a multistep process, sampled parameters study might not provide sufficient information about the actual electrocatalytic process. Therefore, our group tried to determine the best working conditions and ways of designing NRR experiments in order to draw conclusions on the process efficiency in terms of charge used and NH3 yield. In the present study, electrochemically deposited Ru metal catalysts have been investigated. It is found that in ambient reaction conditions and in highly concentrated electrolytes, a Faradic Efficiency as high as 1.2 % can be reached by optimizing the Ru deposition morphology and deposition time (loading), as well as the NRR potential, nature of cation/anion exchange membranes and size of the counter cations in the electrolyte. This is a 4-fold improvement compared to the maximum efficiency reported 4 with the same catalyst (< 0.3 %).

Transformation of a Norbornadiene Unit to Ethylenylcyclopentene Requiring Cooperation between Boron and Rhodium Centers

The synthesis of the lithium salt of a bis-substituted borohydride anion containing a phenyl substituent and a 2-mercaptopyridyl unit (mp) is reported herein. This salt has been used as a pro-ligand for the synthesis of rhodium(I) complex, [Rh{κ3-H,H,S-H2B(Ph)(mp)}(NBD)] (1) (where NBD = 2,5-norbornadiene). The new boron-based ligand coordinates to the rhodium center via the thione donor and the two B–H bonds of the BPhH2 unit, with a dihydroborate motif. Reaction of complex 1 with two equivalents of triphenylphosphine leads to an unprecedented rearrangement and transfer of the former norbornadiene ligand to the boron center. The transformation occurs via an initial hydride migration from boron to rhodium center followed by a hydroboration of one of the double bonds. Finally, a ring-opening process occurs involving both boron and rhodium centers leading to an unusual boron-bound ethylenylcyclopentene unit. The product of this reaction was confirmed as [Rh{η1-S,η2-B,C-B(Ph)(CHCH2(C5H7)(mp)}(PPh3)2] (2). The net result of these transformations is the incorporation of the two hydrogen atoms from the secondary borohydride ligand [BPhH2(mp)]− into the former norbornadiene unit. The end point positions of these hydrogen atoms were confirmed by deuterium labeling experiments. Complex 2 was further reacted with carbon monoxide to generate [Rh{η1-S,η2-B,C-B(Ph)(CHCH2(C5H7)(mp)}(CO)(PPh3)] (3) via ligand substitution. The new ligand and the three complexes, 1, 2, and 3, have been characterized by spectroscopic techniques as well as by X-ray crystallography. Detailed characterization of 2 and 3 revealed an unusual η2-B,C coordination mode within these complexes. Further studies have demonstrated that complexes 2 and 3 react with hydrogen gas (or dimethylamine borane as a source of H2) to generate the hydrogen addition products involving the unprecedented activation of the Rh−η2-B,C motif. Complexes 2 and 3 were further found to be active catalysts for the hydrogenation of olefins and the dehydrogenation of dimethylamine borane.

Unveiling the role of bisulfide in the photocatalytic splitting of H2S in aqueous solutions

Anaerobic photocatalytic conversion of aqueous H2S to H2 was tested on Pt-decorated N-doped TiO2 grown on graphene. The hydrogen production increased linearly (rate: 32.3 μmol/h/g, quantum yield: 1.4 × 10–4) with HS− concentration, until the critical value of 0.029 mol/dm3, after which it declined to negligible values. The latter was attributed to photon-blockage caused by sulfur-containing species formed on catalyst surface, which could be removed by simple washing of the catalyst leading to its regeneration, as highlighted by the characterization of fresh and used catalyst. Similar tests performed at constant HS− concentration and variable pH did not yield a correlation, thus suggesting HS− as the major source of H2, and not H+. A new kinetic model assessing the competitive adsorption mechanism reiterated the important role of sulfide ionic species in hydrogen production. A strong correlation between the latter and HS− concentration was established based on the reactivity results and proposed mechanism.

Thermally double coupled reactor coupling aqueous phase glycerol reforming and methanol synthesis

This study proposes a novel thermally double coupled reactor (TDCR) coupling endothermic aqueous phase glycerol reforming (APGR) with exothermic methanol synthesis (MS), utilizing heat transfer between both channels. Hydrogen (H2) source and availability are known as barriers to carbon dioxide conversion to methanol via MS reaction. Waste glycerol could be a source of H2 through APGR reaction. The steady state TDCR model consists of two concentric channels: 1) an inner tube to which CO₂ and H₂ are fed as reactants for exothermic MS and 2) an outer annulus channel through which glycerol and steam are supplied for endothermic APGR. The TDCR could operate without external heat supply when two reactions were coupled. A computational fluid dynamic (CFD) model was established to study this TDCR. APGR was assumed to be catalyzed by Pt/Al₂O₃ at 200−250 °C and 20−25 bar. MS was modeled with a Cu/ZnO/Al2O3 catalyst at 200−250 °C and 50−80 bar. Heat transfer from the exothermic channel to the endothermic channel helped increase glycerol conversion while methanol productivity is the same as conventional reactor. Cocurrent and countercurrent feed configurations were compared and it was found that the cocurrent configuration offered more uniform temperature distribution in the channel with a larger temperature difference between the two channels. On the other hand, hot spots and cold spots were observed in the countercurrent configuration. Effects of operating conditions of both channels: H2:CO2 and glycerol:steam ratios, inlet temperature, pressure, and total feed flow rate on reactor performance significantly affected the performance of TDCR.

Noble-Metal-Free Ni-W-O-Derived Catalysts for High-Capacity Hydrogen Production from Hydrazine Monohydrate.

Development of active and earth-abundant catalysts is pivotal to render hydrazine monohydrate (N2H4·H2O) viable as a hydrogen carrier. Herein, we report the synthesis of noble-metal-free Ni-W-O-derived catalysts using a hydrothermal method in combination with reductive annealing treatment. Interestingly, the thus-prepared Ni-based catalysts exhibit remarkably distinct catalytic properties toward N2H4·H2O decomposition depending upon the annealing temperature. From a systematic phase/microstructure/chemical state characterization and the first-principles calculations, we found that the variation of the apparent catalytic properties of these Ni-based catalysts should stem from the formation of different Ni-W alloys with distinct intrinsic activity, selectivity, and distribution state. The thereby chosen Ni-W alloy nanocomposite catalyst prepared under an optimized condition showed high activity, nearly 100% selectivity, and excellent stability toward N2H4·H2O decomposition for hydrogen production. Furthermore, this noble-metal-free catalyst enables rapid hydrogen production from commercially available N2H4·H2O solution with an intriguingly high hydrogen capacity of 6.28 wt % and a satisfactory dynamic response property. These results are inspiring and momentous for promoting the use of the N2H4·H2O-based H2 source systems.

Supercritical water gasification of phenol over Ni-Ru bimetallic catalyst: Intermediates and kinetics

Phenol is gasified in supercritical water at 400−500 °C under a pressure of 25 MPa over Ni-Ru bimetallic catalyst. Several liquid products including cyclohexanol, 2-methyl cyclopentanone, toluene, alkylphenol etc. are identified and possible reaction paths among them are proposed. Gaseous products consist of H2, CH4 and CO2. We develop a quantitative kinetic model based on a simplified reaction network in which intermediates are lumped. The model accurately captures the trends of concentration variation for phenol and gaseous products. Steam reforming of phenol to form CO is the main source of H2 and nearly all CH4 is formed from methanation of CO under 450 °C. Concentration of H2 is most sensitive to steam reforming to form CO2 while steam reforming to form CO strongly affects CH4 production at 450 °C. The model has predictive capacity when varying initial phenol loading while it lose some accuracy for a higher water density condition.

Deoxygenation of triolein to green diesel in the H2-free condition: Effect of transition metal oxide supported on zeolite Y

H2-free deoxygenation is a very important process in producing high-quality biofuel without the use of H2 gas supply. Considering the costly price of the noble metals, transition metal (TM) based catalysts are more affordable, and the performance is comparable to the noble metal-based catalyst. In this study, TMO supported on zeolite Y catalysts (Ni-, Cu-, Co-, Zn- and Mn-Y) are prepared via wet-impregnation for deoxygenation of triolein, a model compound of non-edible oil under H2-free condition. The deoxygenation activity of TMO supported on zeolite Y is following the order of Ni-Y > Co-Y > Cu-Y > Mn-Y > Zn-Y. The nickel oxide supported on zeolite-Y (Ni-Y) shows the highest conversion up to 76.21 % with 84.28 % hydrocarbon selectivity after reacted at 380 °C for 2 h. Besides, the selectivity toward diesel range hydrocarbon is 92.61 %. The superior deoxygenation activity of Ni-Y can be related to synergistic effect between the reduced B/L and high hydrogenolysis ability of Ni that promote the decarboxylation reaction, suppress the cracking and polymerization of heavy hydrocarbon. Therefore, Ni-Y is a potential catalyst to obtain high quality green diesel from non-edible oil through catalytic deoxygenation without addition of external H2 source.

Hydrogen and Abiotic Hydrocarbons: Molecules that Change the World

Molecular hydrogen (H2), methane, and hydrocarbons with an apparent abiotic origin have been observed in a variety of geologic settings, including serpentinized ultramafic rocks, hydrothermal fluids, and deep fractures within ancient cratons. Molecular hydrogen is also observed in vapor plumes emanating from the icy crust of Saturn’s moon Enceladus, and methane has been detected in the atmosphere of Mars. Geologic production of these compounds has been the subject of increasing scientific attention due to their use by chemosynthetic biological communities. These compounds are also of interest as possible energy resources. This issue summarizes the geological sources of abiotic H2 and hydrocarbons on Earth and elsewhere and examines their impact on microbial life and energy resources.

Abiotic Sources of Molecular Hydrogen on Earth

The capacity for molecular hydrogen (H2) to hydrogenate oxygen and carbon is critical to the origin of life and represents the basis for all known life-forms. Major sources of H2 that strictly involve nonbiological processes and inorganic reactants include (1) the reduction of water during the oxidation of iron in minerals, (2) water splitting due to radioactive decay, (3) degassing of magma at low pressures, and (4) the reaction of water with surface radicals during mechanical breaking of silicate rocks. None of these processes seem to significantly affect the current global atmospheric budget of H2, yet there is substantial H2 cycling in a wide range of Earth’s subsurface environments, with multifaceted implications for microbial ecosystems.

Selective Oxidation of H2 and CO by NiIr Catalyst in Aqueous Solution: A DFT Mechanistic Study.

One of the challenges in utilizing hydrogen gas (H2) as a sustainable fossil fuel alternative is the inhibition of H2 oxidation by carbon monoxide (CO), which is involved in the industrial production of H2 sources. To solve this problem, a catalyst that selectively oxidizes either CO or H2 or one that co-oxidizes H2 and CO is needed. Recently, a NiIr catalyst [NiIICl(X)IrIIICl(η5-C5Me5)], (X = N,N'-dimethyl-3,7-diazanonane-1,9-dithiolate), which efficiently and selectively oxidizes either H2 or CO depending on the pH, has been developed (Angew. Chem. Int. Ed. 2017, 56, 9723-9726). In the present work, density functional theory (DFT) calculations are employed to elucidate the pH-dependent reaction mechanisms of H2 and CO oxidation catalyzed by this NiIr catalyst. During H2 oxidation, our calculations suggest that dihydrogen binds to the Ir center and generates an Ir(III)-dihydrogen complex, followed by subsequent isomerization to an Ir(V)-dihydride species. Then, a proton is abstracted by a buffer base, CH3COO-, resulting in the formation of a hydride complex. The catalytic cycle completes with electron transfer from the hydride complex to a protonated 2,6-dichlorobenzeneindophenol (DCIP) and a proton transfer from the oxidized hydride complex to a buffer base. The CO oxidation mechanism involves three distinct steps, i.e., (1) formation of a metal carbonyl complex, (2) formation of a metallocarboxylic acid, and (3) conversion of the metallocarboxylic acid to a hydride complex. The formation of the metallocarboxylic acid involves nucleophilic attack of OH- to the carbonyl-C followed by a large structural change with concomitant cleavage of the Ir-S bond and rotation of the COOH group along the NiIr axis. During the conversion of the metallocarboxylic acid to the hydride complex, intramolecular proton transfer followed by removal of CO2 leads to the formation of the hydride complexes. In addition, the barrier heights for the binding of small molecules (H2, OH-, H2O, and CO) to Ir were calculated, and the results indicated that dissociation from Ir is a faster process than the binding of H2O and H2. These calculations indicate that H2 oxidation is inhibited by CO and OH- and thus prefers acidic conditions. In contrast, the CO oxidation reactions occur more favorably under basic conditions, as the formation of the metallocarboxylic acid involves OH- attack to a carbonyl-C and the binding of OH- to Ni largely stabilizes the triplet spin state of the complex. Taken together, these calculations provide a rationale for the experimentally observed pH-dependent, selective oxidations of H2 and CO.

Catalytic transfer hydrogenation of maleic acid with stoichiometric amounts of formic acid in aqueous phase: paving the way for more sustainable succinic acid production

The aqueous phase hydrogenation of maleic acid to succinic acid (SAc) is proved using an efficient and robust Pd/C catalysts and stoichiometric formic acid as source of H2. SAc can be separated from the reaction medium by precipitation.

Pentanoic acid from γ-valerolactone and formic acid using bifunctional catalysis

The production of pentanoic acid from γ-valerolactone and the one-pot route from levulinic acid both over bifunctional catalyst with formic acid as H2 source is an example for an integrated biorefinery in the direction to an industrial application.