Presence Of Molecular Hydrogen Research Articles

Equation of State, Structure, and Transport Properties of Iron Hydride Melts at Planetary Interior Conditions

AbstractIron hydrides are a potentially dominant component of the metallic cores of planets, primarily because of hydrogen's ubiquity in the universe and affinity for iron. Using ab initio molecular dynamics, we examine iron hydrides with 0.1, 0.33, 0.5, and 0.6 mol fraction hydrogen up to 100 GPa between 3,000 and 5,000 K to describe how hydrogen content affects the melt structure, hydrogen speciation, equation of state (EOS), atomic diffusivity, and melt viscosity. We find that the addition of hydrogen decreases the average Fe–Fe coordination number and lengthens Fe–Fe bonds, while Fe–H coordination number increases. The pair distribution function of hydrogen at low pressure indicates the presence of molecular hydrogen. By tracking chemical speciation, we show that the amount of molecular hydrogen increases and the number of iron in Hx≥1Fey≥0 clusters decreases as the hydrogen concentration increases. We parameterize a pressure, volume, temperature, and composition EOS and show that the molar volume and Grüneisen parameter of the melts decrease while the compressibility and thermal expansivity increase as a function of hydrogen concentration. We find that hydrogen acts as a lubricant in the melts as the iron and hydrogen become more diffusive and the melts become more inviscid as the hydrogen concentration increases. We estimate 2.7 wt% hydrogen in the Martian core and 0.49–1.1 wt% hydrogen in Earth's outer core based on comparisons to seismic models, with the assumption that the cores are pure liquid iron‐hydrogen alloy, and we compare the small exoplanet population with mass‐radius curves of iron hydride planets.

Carbon Dioxide Utilization Using Plasma Reactor Packed with Magnesia-Ceria Catalysts with Various Morphology

A series of CeO2–MgO catalysts with different molar ratio was prepared for the plasma-activated CO2 decomposition to CO and O2. The catalysts were synthesized by the sol-gel method and characterized by physicochemical methods (XRD, SEM, XPS, low-temperature N2 adsorption, CO2-TPD). The highest CO2 conversion (31%) was achieved in the presence of the catalyst with the highest CeO2 content. The addition of H2 into a CO2 decomposition system was also studied. No CO2 methanation occurred in the presence of synthesized catalysts, though an increase in the CO2-to-CO conversion was observed due to an increase of a discharge power in the presence of molecular hydrogen.

Biowaste carbon supported manganese nanoparticles as an active catalyst for the selective hydrogenation of bio-based aldehydes

Hydrogenation of aldehydes with heterogeneous manganese catalysts is an appealing approach for producing alcohols. In this paper, we report a novel and robust MnO/PN-800 catalyst for the hydrogenation of versatile biomass-derived platform molecules in the presence of molecular hydrogen as a reductant. The effect of catalyst concentration, the operating hydrogen pressure, and the reaction temperature on the catalyst activity was investigated in detail. Under the mild reaction conditions, the full conversion of furfuraldehyde, 5-Methyl-2-furaldehyde, and 5-hydroxymethyl-2-furaldehyde (5-HMF) to their corresponding alcohols was achieved without any by-product formation. Additionally, other aromatic aldehydes bearing fluoro, chloro, and nitro moieties were also tolerated. The fresh and spent MnO/PN-800 catalyst was thoroughly characterized using XPS, powder-XRD, HR-TEM, N2 adsorption-desorption, and Raman spectroscopy. Noteworthy, the MnO/PN-800 catalyst can be recovered by centrifugation and then reused directly in the subsequent hydrogenation reactions. Importantly the synthetic utility of this protocol up to ∼5 g-scale is realized. Finally, our novel MnO/PN-800 nanocatalyst was successfully employed for the direct synthesis of furfuryl alcohol in high yields from raw sugarcane bagasse. We believe that these findings will help to advance the manganese-catalyzed hydrogenation reactions.

Molecularly Engineering Defective Basal Planes in Molybdenum Sulfide for the Direct Synthesis of Benzimidazoles by Reductive Coupling of Dinitroarenes with Aldehydes.

Developing more sustainable catalytic processes for preparing N-heterocyclic compounds in a less costly, compact, and greener manner from cheap and readily available reagents is highly desirable in modern synthetic chemistry. Herein, we report a straightforward synthesis of benzimidazoles by reductive coupling of o-dinitroarenes with aldehydes in the presence of molecular hydrogen. An innovative molecular cluster-based synthetic strategy that employs Mo3S4 complexes as precursors have been used to engineer a sulfur-deficient molybdenum disulfide (MoS2)-type material displaying structural defects on both the naturally occurring edge positions and along the typically inactive basal planes. By applying this catalyst, a broad range of functionalized 2-substituted benzimidazoles, including bioactive compounds, can be selectively synthesized by such a direct hydrogenative coupling protocol even in the presence of hydrogenation-sensitive functional groups, such as double and triple carbon–carbon bonds, nitrile and ester groups, and halogens as well as diverse types of heteroarenes.

Increasing reactivity of plasmonic hot holes by a trapping strategy

Plasmonic photocatalysis has emerged as a promising solution for global energy crisis and environment pollution by facilitating wide ranging chemical transformations using photons in a broad region of solar spectrum. Despite numerous successful examples on improvement of electron-driven photochemistry, effective utilization of plasmonic hot holes is a long-standing challenge due to their ultrafast relaxation and short lifetime. Herein, we report that the reactivity of plasmonic hot holes can be greatly enhanced by a novel hot hole trapping strategy. We demonstrate a new concept of a metal-adsorbate interfacial structure that can be in situ constructed on gold (Au) surface in the presence of molecular hydrogen (H2) under plasmonic excitation, where the key is to employ an electron-filled antibonding state hybridized by H1s and Au5d as a localized “trap” to improve utilization efficiency of plasmonic hot holes. This interfacial structure is evidenced by light-induced H2 spillover and d-band model analysis. The prolonged lifetime and preserved oxidation power of plasmonic hot holes was evidenced by superior photocatalytic activity for methylene blue (MB) degradation in the presence of H2 which was accelerated by over 5 times. In addition, FTIR coupled with CO molecular probe reveals that the physical location of hole trapping are low coordinated positions sites on Au nanoparticles. These findings could provide an innovative pathway to increase utilization efficiency of hot holes for visible-light-driven photocatalysis applications.

Reductive N-alkylation of primary amides using nickel-nanoparticles

Here we report Ni-nanoparticles as reusable catalysts for reductive N-alkylation of amides. These Ni-nanoparticles based catalysts have been prepared by the template synthesis of tartaric acid and 2-methyl imidazole ligated Ni-complex on SiO2 and subsequent pyrolysis under argon. Applying optimal Ni-nanostructured catalyst, N-alkylation of aromatic and heterocyclic primary amides with different aldehydes in presence of molecular hydrogen was performed to access structurally diverse N-alkylated amides in good to excellent yields. In addition, the applicability of this N-alkylation protocol has been demonstrated for the selective functionalization of primary amide group in Levetiracetam drug.

Enceladus as a Potential Niche for Methanogens and Estimation of Its Biomass.

Enceladus is a potential target for future astrobiological missions. NASA’s Cassini spacecraft demonstrated that the Saturnian moon harbors a salty ocean beneath its icy crust and the existence and analysis of the plume suggest water–rock reactions, consistent with the possible presence of hydrothermal vents. Particularly, the plume analysis revealed the presence of molecular hydrogen, which may be used as an energy source by microorganisms ( e.g., methanogens). This could support the possibility that populations of methanogens could establish in such environments if they exist on Enceladus. We took a macroscale approximation using ecological niche modeling to evaluate whether conditions suitable for methanogenic archaea on Earth are expected in Enceladus. In addition, we employed a new approach for computing the biomass using the Monod growth model. The response curves for the environmental variables performed well statistically, indicating that simple correlative models may be used to approximate large-scale distributions of these genera on Earth. We found that the potential hydrothermal conditions on Enceladus fit within the macroscale conditions identified as suitable for methanogens on Earth, and estimated a concentration of – cells/cm.

Reduction of 5-Hydroxymethylfurfural and 1,2-Dicarbonyl Compounds by Saccharomyces cerevisiae in Model Systems and Beer.

Glycation and caramelization reactions in malt lead to the formation of 1,2-dicarbonyl compounds, which come in contact with yeast during fermentation. In the present study, the metabolic fate of 5-hydroxymethylfurfural (HMF) and 1,2-dicarbonyl compounds (3-deoxyglucosone, 3-deoxygalactosone, 3-deoxypentosone, 3,4-dideoxyglucosone-3-ene) was assessed in the presence of Saccharomyces cerevisiae. HMF is degraded very fast by yeast with the formation of 2,5-bis(hydroxymethyl)furan (BHMF). By contrast, only 7-30% of 250 μM dicarbonyl compounds is degraded within 48 h. The respective deoxyketoses, 3-deoxyfructose (3-DF), 3-deoxytagatose, 3-deoxypentulose, and 3,4-dideoxyfructose, were identified as metabolites. While 17.8% of 3-deoxyglucosone was converted to 3-deoxyfructose, only about 0.1% of 3-deoxypentosone was converted to 3-deoxypentulose during 48 h. Starting with the parent dicarbonyl compounds, the synthesis of all deoxyketose metabolites was achieved by applying a metal-catalyzed reduction in the presence of molecular hydrogen. In a small set of commercial beer samples, BHMF and all deoxyketoses were qualitatively detected. 3-DF was quantitated in the four commercial beer samples at concentrations between 0.4 and 10.1 mg/L.

Greener Synthesis of Pristane by Flow Dehydrative Hydrogenation of Allylic Alcohol Using a Packed-Bed Reactor Charged by Pd/C as a Single Catalyst.

Our previous work established a continuous-flow synthesis of pristane, which is a saturated branched alkane obtained from a Basking Shark. The dehydration of an allylic alcohol that is the key to a tetraene was carried out using a packed-bed reactor charged by an acid–silica catalyst (HO-SAS) and flow hydrogenation using molecular hydrogen via a Pd/C catalyst followed. The present work relies on the additional propensity of Pd/C to serve as an acid catalyst, which allows us to perform a flow synthesis of pristane from the aforementioned key allylic alcohol in the presence of molecular hydrogen using Pd/C as a single catalyst, which is applied to both dehydration and hydrogenation. The present one-column-two-reaction-flow system could eliminate the use of an acid catalyst such as HO-SAS and lead to a significant simplification of the production process.

Molecular Hydrogen in Natural Mayenite

In the last 15 years, zeolite-like mayenite, Ca12Al14O33, has attracted significant attention in material science for its variety of potential applications and for its simple composition. Hydrogen plays a key role in processes of electride material synthesis from pristine mayenite: {Ca12Al14O32}2+(O2) → {Ca12Al14O32}2+(e−)2. A presence of molecular hydrogen in synthetic mayenite was not confirmed by the direct methods. Spectroscopy investigations of mayenite group mineral fluorkyuygenite, with empirical formula (Ca12.09Na0.03)∑12.12(Al13.67Si0.12Fe3+0.07Ti4+0.01)∑12.87O31.96 [F2.02Cl0.02(H2O)3.22(H2S)0.15□0.59]∑6.00, show the presence of an unusual band at 4038 cm−1, registered for the first time and related to molecular hydrogen, apart from usual bands responding to vibrations of mayenite framework. The band at 4038 cm−1 corresponding to stretching vibrations of H2 is at lower frequencies in comparison with positions of analogous bands of gaseous H2 (4156 cm−1) and H2 adsorbed at active cation sites of zeolites (4050–4100 cm−1). This points out relatively strong linking of molecular hydrogen with the fluorkyuygenite framework. An appearance of H2 in the fluorkyuyginite with ideal formula Ca12Al14O32[(H2O)4F2], which formed after fluormayenite, Ca12Al14O32[□4F2], is connected with its genesis. Fluorkyuygenite was detected in gehlenite fragments within brecciaed pyrometamorphic rock (Hatrurim Basin, Negev Desert, Israel), which contains reduced mineral assemblage of the Fe-P-C system (native iron, schreibersite, barringerite, murashkoite, and cohenite). The origin of phosphide-bearing associations is connected with the effect of highly reduced gases on earlier formed pyrometamorphic rocks.

Selective Oxidation of Methane over Fe-Zeolites by In Situ Generated H2O2

Liquid-phase selective oxidation of methane into methane oxygenates, including methanol and formic acid, with molecular oxygen was investigated using Fe-zeolites and Pd/activated carbon in the presence of molecular hydrogen as a reducing agent. Various Fe-zeolites such as Fe-ZSM-5, Fe-mordenite, Fe-β, Fe-Y, and Fe-ferrierite were prepared by ion-exchange and compared for this reaction. Among them, Fe-ZSM-5 was selected for further study because this catalyst showed high activity in the selective oxidation of methane with relatively less leaching. Further, the effect of reaction temperature, pH, and the amount of catalyst was examined, and detailed investigations revealed that the leached Fe species, which were facilitated in the presence of acid, were mainly responsible for methane oxidation under the given reaction conditions.

Chemoselective semihydrogenation of alkynes catalyzed by manganese(i)-PNP pincer complexes

A first homogeneous manganese catalyzed chemoselective semihydrogenation of alkynes to Z-olefins in the presence of molecular hydrogen is described.

Metabolic Potential of Sulfobacillus thermotolerans: Pathways for Assimilation of Nitrogen Compounds and the Possibility of Lithotrophic Growth in the Presence of Molecular Hydrogen

Sulfobacillus thermotolerans predominates in communities of acidophilic chemolithotrophic microorganisms and is of practical importance to biotechnologies for sulfide minerals processing. This is the first report on the presence of the genes encoding a quinone-binding [Fe-Ni] hydrogenase in S. thermotole-rans genome; this microorganism is therefore potentially capable of lithotrophic growth in the presence of molecular hydrogen. Components of the pathways for nitrogen compounds assimilation by S. thermotolerans probably include two assimilatory nitrate reductases, while NO dioxygenase and nitronate monooxygenases are probably involved in detoxication of nitric oxide and nitrocompounds. Research on the pathways of assimilation and detoxication of nitrogen compounds, as well as on alternative electron donors and acceptors in sulfobacilli will improve our understanding of the interactions within acidophilic chemolithotrophic communities in nature and industry.

Reusable Nickel Nanoparticles‐Catalyzed Reductive Amination for Selective Synthesis of Primary Amines

AbstractThe preparation of nickel nanoparticles as efficient reductive amination catalysts by pyrolysis of in situ generated Ni‐tartaric acid complex on silica is presented. The resulting stable and reusable Ni‐nanocatalyst enables the synthesis of functionalized and structurally diverse primary benzylic, heterocyclic and aliphatic amines starting from inexpensive and readily available carbonyl compounds and ammonia in presence of molecular hydrogen. Applying this Ni‐based amination protocol, ‐NH2 moiety can be introduced in structurally complex compounds, for example, steroid derivatives and pharmaceuticals.

Reusable Nickel Nanoparticles-Catalyzed Reductive Amination for Selective Synthesis of Primary Amines.

The preparation of nickel nanoparticles as efficient reductive amination catalysts by pyrolysis of in situ generated Ni-tartaric acid complex on silica is presented. The resulting stable and reusable Ni-nanocatalyst enables the synthesis of functionalized and structurally diverse primary benzylic, heterocyclic and aliphatic amines starting from inexpensive and readily available carbonyl compounds and ammonia in presence of molecular hydrogen. Applying this Ni-based amination protocol, -NH2 moiety can be introduced in structurally complex compounds, for example, steroid derivatives and pharmaceuticals.

The catalytic behavior of heterocenes activated by TIBA and MMAO under a low Al/Zr ratios in 1-octene polymerization

A series of SiMe2-bridged ansa-zirconocenes LZrCl2 derived from heterocyclic ligands such as cyclopenta[1,2-b:4,3-b']dithiophene, 5,6-dihydroindeno[2,1-b]indole and 5,10-dihydroindeno[1,2-b]indole, called "heterocenes", were synthesized and characterized by NMR spectroscopy and by X-ray diffraction analysis. These complexes were activated by triisobutylaluminium (TIBA) at AlTIBA/Zr ratio ∼75 and then by MMАO-12 at AlMAO/Zr ratio ∼10, and were studied in the polymerization of 1-octene in the absence or presence of molecular hydrogen. In the absence of molecular hydrogen, derivatives of cyclopenta[1,2-b:4,3-b']dithiophene and dihydroindeno[2,1-b]indole demonstrated high catalytic activity, while dihydroindeno[1,2-b]indole complexes catalyzed slow polymerization with the formation of ultrahigh molecular weight poly(1-octene)s. In the presence of molecular hydrogen, derivatives of dihydroindeno[1,2-b]indole showed an order of magnitude increase in the catalytic activity. β-Hydride elimination, β-hexyl elimination and Zr-Al transfer were detected as the main chain release mechanisms depending on the nature of the ligand used. A novel chain termination with selective formation of –C(Me)=CHCH2– unsaturations was detected. It was found that heterocenes maintained a high catalytic activity up to 120 °C. Due to their high thermal stability and good hydrogen response, heterocenes are promising catalysts for the oligomerization and hydrooligomerization of α-olefins in the production of high-quality motor oil base stocks.

Effects of Environment on the Wear Behavior of P/M Ti-47Al-2Cr-0.2Mo

The wear behavior of powder metallurgical Ti-47Al-2Cr-0.2Mo alloy prepared by pre-alloyed powders was investigated using pin-on-disk wear tests in different environments, viz, argon, 4% hydrogen in nitrogen, air and oxygen. The disk material was sinter-hot isostatically pressed, yttria-stabilized zirconia. Lower wear rates were found for the TiAl pins in oxygen-free environments, indicating that oxygen play a key role in the wear rate. In contrast, the presence of molecular hydrogen and moisture have nearly no effect. A combination of X-ray diffraction and energy dispersive X-ray spectroscopy indicated that the abrasive particles present mainly consisted of the zirconia. In addition, zirconia particles were embedded in the worn tips of the TiAl pins and mixed into the tribolayers. The high stress and high contact temperature at the wear surface made the zirconia disk undergo a phase transformation during the dry sliding wear, accompanied by grain pullout, surface uplifting and microcracking. The hard tribolayer with embedded zirconia particles provides some protection against further wear of the TiAl pin. The highly localized, repetitive shear stress during the wear tests may bring about amorphous TiAl in the wear debris. The main wear mechanisms were abrasive wear of two-body and three-body, some delamination and plastic deformation.

Evidence of molecular hydrogen trapped in two-dimensional layered titanium carbide-based MXene

Two-dimensional transition metal carbides and nitrides (MXenes) are one of the largest and fastest growing families of materials. The presence of molecular hydrogen at ambient conditions in a MXene ($\mathrm{T}{\mathrm{i}}_{3}{\mathrm{C}}_{2}{T}_{x}$, where ${T}_{x}$ represents a surface terminating species, including O, OH, and F) material is revealed here by inelastic and elastic neutron scatterings. The inelastic neutron-scattering spectrum measured at 5 K shows a peak at 14.6 meV, presenting a clear indication of the presence of parahydrogen in the MXene synthesized using $48%$ hydrofluoric acid and annealed at $110{\phantom{\rule{0.16em}{0ex}}}^{\ensuremath{\circ}}\mathrm{C}$ in vacuum prior to the measurement. An increase in the measurement temperature gradually reduces the peak intensity and increases the peak width due to the mobility of the molecular hydrogen in confinement. The presence of molecular hydrogen is confirmed further from the observed elastic intensity drop in a fixed energy-window scan of elastic intensity measurements in the temperature range of 10--35 K. Using milder etching conditions, ion intercalation, or an increase in the annealing temperature all result in the absence of the trapped hydrogen molecules in MXene. The results of this paper can guide the development of MXene materials with desired properties and improve our understanding of the behavior of MXenes in applications ranging from supercapacitors to hydrogen evolution reaction catalysis and hydrogen storage.

Diagnostics for the elemental composition of protostellar objects

The sensitivity of a number of aspects of the chemical evolution of a molecular cloud to its elemental composition is investigated. Four models are considered: one with high metallicity, for which the evolution proceeds exclusively in the gas phase, two with low metallicity, for which processes proceed both in the gas phase and on grain surfaces, and a model with low metallicity and an artificially reduced oxygen content. One of the low-metallicity models initially contains only neutral components, while some initial ionization of atoms of heavy elements is included in the other models. A network of chemical reactions, including a detailed description of the chemistry of deuterium compounds, is used to analyze this sensitivity. It is shown that the initial composition affects the chemical evolution of most components in some way, but this influence is sometimes negligible. The inclusion of certain chemical factors can be important, such as surface reactions and the loss of a substantial fraction of atoms of heavy elements that are in grains. However, some components are influenced by even small variations in the initial and elemental compositions. One such component is the DCO+ ion, whose evolution is sensitive to the initial degree of ionization of atoms of heavy elements, even if the set of reactions included and the elemental composition are the same in different cases. The possible use of HD and HF as indicators of the presence of molecular hydrogen is also considered. HF reliably traces H2 at times exceeding 105 years under the physical conditions considered. However,HD is not a reliable indicator of H2 at the densities characteristic for protostellar clouds.

Growth of aluminum oxide thin films with enhanced film density by the integration of in situ flash annealing into low-temperature atomic layer deposition

Aluminum oxide (Al2O3) thin films grown by atomic layer deposition (ALD) at low temperatures exhibit low film densities, and therefore, may not meet the requirements for demanding barrier applications. In this work, a novel approach is presented to obtain improved film densities by short-term thermal treatments while keeping the overall low thermal budget of the deposition process. For that purpose, millisecond flash lamp annealing (FLA) was directly integrated into the ALD process, enabling the thermal treatment of the growing films not only subsequent to the deposition process but already right during the stage of film growth. By applying this in situ FLA after every single ALD cycle, the density of Al2O3 films grown at a substrate temperature of 75°C could be increased from 2.8g/cm3 up to 3.1g/cm3. However, this 10% increase in film density was not related to an ordinary film densification. Instead, the studies reveal that in situ FLA promoted an enhanced and denser film growth, most probably by directly affecting the surface chemistry of the ALD process. The enhanced film growth was observed in terms of a 25% increase in the mass gain per cycle, reaching a level comparable to pure ALD at a deposition temperature of 250°C. Furthermore, the application of in situ FLA also resulted in an improved film composition, increased refractive indices, higher dielectric constants and reduced leakage currents. The presence of molecular hydrogen during the FLA treatments led to an even further improved mass gain per cycle, film composition and dielectric constant. Despite the FLA treatments the films remained amorphous. In addition, the film densities obtained by the application of in situ FLA were not achieved by conventional post deposition annealing with temperatures up to 600°C.