Introduction Of H2 Research Articles

Exploring the CO2 reduction reaction mechanism on Pt/TiO2 with the ambient-pressure X-ray photoelectron spectroscopy

Intensive efforts have been devoted to exploring the CO2 reduction reaction (CO2RR) mechanism to get valuable high-level hydrocarbons under mild reaction conditions. Herein, the investigation of thermocatalytic CO2RR on a metallic oxide-supported catalyst (Pt-TiO2) is conducted by utilizing the surface and chemical-state sensitive ambient pressure X-ray spectroscopy together with the mass spectroscopy. It is revealed that CO2 is first chemisorbed on surface in the form of CO2δ− by capturing electrons from Pt, while the introduction of H2 induces the formation of various intermediates species, such as HCOO, sp3 carbon, and CHxO. Subsequently, CO is discovered after the dissociation of the HCOO species from the reversed water–gas shift reaction, and CH4 is eventually formed after the further hydrogenation of CHxO. Importantly, increasing the concentration of H2 and the overall reactant pressure considerably improves the CO2 activation and the selectivity of CH4, while excessive H2 does not bring any more apparent enhancement of CO2RR on Pt-TiO2. Ultimately, the optimized concentration of H2 is proposed to be 1:2 in the reactant mixture, and the manipulation of methane product selectivity is also realized. Thus, our report might shed valuable insights on the fundamental understanding of CO2 conversion mechanism based on the metallic-oxide catalyst.

Synthesis of nanosized ultrathin MoS2 on montmorillonite nanosheets by CVD method

As an emerging material, exfoliated molybdenum disulfide (MoS2) has an excellent performance in catalysis, electronics and adsorption. However, the application performance of exfoliated MoS2 is limited by the strong adhesion between MoS2 layers and the low colloidal stability of MoS2 in water. In this study, for the first time, nanosized ultrathin MoS2 was successfully synthesized on exfoliated montmorillonite (MMT) by CVD method. Two reaction mechanisms were found when using flow gas with or without H2. The introduction of H2 promotes the growth of MoS2 crystals and reduces nucleation density. The MoS2/MMT showed excellent performance in dye degradation.

Covalent organic framework material as efficient adsorbent and H2-Accelerated catalytic Fenton catalyst for enhanced removal of sulfamethazine

A novel CHACF-JUC-505 system through the introduction of H2 and Pd/JUC-505 into the classic Fenton system under normal temperature and pressure was developed in this work. Through the experiment of quenching hydroxyl radical (·OH) by methanol, the analysis of degradation intermediates and total organic carbon, it was confirmed from the reverse that the target pollutant sulfamethazine (SMT) could be quickly adsorbed by JUC-505. The activated hydrogen generated from the adsorbed and activated H2 by Pd/JUC-505 accelerated the reduction of FeIII. It was confirmed that the continuous production of ·OH required only a trace amount of iron by the detection of para-hydroxybenzoic acid. The removal of SMT was further enhanced by the degradation of ·OH. The cleavage of SN bond was considered to be the major degradation pathway of SMT. The concentration of FeII in the CHACF-JUC-505 system could be at least 14.72 μM. And the removal efficiency of SMT was about 96.77 %. That was 3 and 4.6 times that of the Fenton system in the same reaction condition, respectively. The effects of the dosage of ferrous ion, H2O2 and Pd/JUC-505, initial concentration of SMT and pH, and the flow of H2 were investigated. The robustness and morphological changes in Pd/JUC-505 were also systematically analyzed.

Numerical Investigation of the Impact of H2 Enrichment on Lean Biogas/Air Flames: An Analytical Modelling Approach

The transition from natural gas to renewable gases such as biogas and hydrogen creates an interchangeability challenge. The laminar flame speed SL is a critical parameter in appliance design as it is a unique characteristic of the flame mixture. It is thus essential to evaluate the impact of renewable gases on SL. In this work, 1D simulations were conducted in Cantera with the USC-Mech 2.0 kinetic mechanism. The SL of three base biogas blends (BG100, BG90 and BG80) was computed for H2 enrichment up to 50% in volume, equivalence ratio 0.8≤ϕ≤1.0, p=1 atm and Tu=298 K. It was found that the effect of H2 enrichment is higher for base blends with higher CO2 content as the thermal-diffusive and dilution effects of carbon dioxide are mitigated by hydrogen. The introduction of H2 also increases the H radical pool, which is linked with the increase in SL. A new correlation to model the impact of H2 enrichment, SL(xH2)=ζ(ϕ)/SL′(xCO2)xH2exH2+SL′(xCO2), is proposed, which exhibits good agreement with the literature data and simulations. This equation can be directly used to estimate SL without the need for a priori adaptations of fit parameters as the contributions of CO2 and H2 are isolated in independent variables.

Coke Gasification in Blast Furnace Shaft Conditions with H2 and H2O Containing Atmospheres

Most of world steel in 2018 has been produced from virgin iron ore via the blast furnace (BF)—basic oxygen furnace route. Therewith the BF is one of the most important unit processes in worldwide steel making. Among others, energy efficiency of the BF is dependent on coke reactivity. Coke gasification occurs via solution‐loss reactions either with CO2 or H2O. Herein, the gasification of coke is studied in CO–CO2–H2–H2O–N2 atmosphere simulating the BF conditions. The simulated atmospheres are based on the measurements from an actual BF. This research studies the effect of the composition of the BF atmosphere representing conditions near the wall as well as at the center and influence of the H2O content on coke gasification under simulated BF conditions. It is found that the location plays a role in coke gasification: wall atmosphere yields higher coke gasification compared with center. Dynamic tests show that introduction of H2 and H2O in gas atmosphere fastens coke gasification by +119% at temperature range between 800 and 1200 °C in wall conditions. When H2O is present in gas atmosphere, the mass loss of coke is also greater in both wall and center conditions.

Probing the surface chemistry for reverse water gas shift reaction on Pt(1 1 1) using ambient pressure X-ray photoelectron spectroscopy

Using ambient pressure XPS (APXPS), we explored carbon dioxide (CO2) adsorption and CO2 hydrogenation on Pt(111) single crystal surface to observe the activation of CO2 and the subsequent reaction mechanism. In pure CO2, we observed CO adsorbates and adsorbed oxygen on Pt(111) derived from CO2 dissociation at room temperature. The introduction of H2 (at a pressure ratio of 1:1 (H2:CO2)) increased the production of CO across all temperatures by facilitating the removal of surface oxygen. As a consequence, the surface could expose sites that could then be utilized for producing CO. Under these conditions, the reverse water–gas shift (RWGS) reaction was observed starting at 300 oC. At higher H2 partial pressure (10:1 (H2:CO2)), the RWGS reaction initiated at a lower temperature of 200 oC and continued to enhance the conversion of CO2 with increasing temperatures. Our results revealed that CO2 was activated on a clean Pt(111) surface through the dissociation mechanism to form adsorbed CO and O at room temperature and at elevated temperatures. Introducing H2 facilitated the RWGS as adsorbed oxygen was consumed continuously to form H2O, and adsorbed CO desorbed from the surface at elevated temperatures. This work clearly provides direct experimental evidence for the surface chemistry of CO2 dissociation and demonstrates how hydrogen impacts the RWGS reaction on a platinum surface.

Improvement of transparent conductive properties of Cu films by introducing H2 into deposition atmosphere during RF magnetron sputtering

Abstract Different thicknesses (2–250 nm) of Cu films were deposited on glass substrate by RF magnetron sputtering in Ar and Ar + H2 atmospheres at room temperature. It is found that crystallinity and conductive properties of the films enhance but visible light transmittance (TVis) decreases with increase of film thickness. Compared with the Cu films deposited in Ar, those deposited in Ar + H2 have higher crystallinity and surface roughness, and they have better conductive properties and higher TVis at film thickness above 5 nm. Overall, the Cu films deposited in Ar and Ar + H2 can be achieved higher figure of merit (FOM) in a thickness range of 3~5 and 5~8.5 nm, respectively. Furthermore, the higher FOM values of Cu film deposited in Ar + H2 atmosphere are higher than those of Cu film deposited in Ar atmosphere. The correlation between the improvement of transparent conductive properties of Cu films and modification of film microstructure due to introduction of H2 into deposition atmosphere is discussed.

Self-assembly synthesis of lamellar molybdenum carbides with controllable phases for hydrodeoxygenation of diphenyl ether

The controllable synthesis of molybdenum carbides with different phases by a facile and environmentally friendly method and understanding their structure-performance relationship are still challenges. In this work, lamellar β-Mo2C and α-MoC1-x have been synthesized by a self-assembly synthetic route using Mo-dopamine as single source without any template and additive at a relatively low carburization temperature. The introduction of H2 fortifies the reducibility of the system and accelerates the carburization process and phase transformation. The structure-performance relationship was also investigated in the hydrodeoxygenation (HDO) of diphenyl ether. Thereinto, β-Mo2C exhibits 99.9% conversion and 95.2% selectivity to benzene, while α-MoC1-x shows only 74.6% conversion with 84.8% selectivity to benzene and 12.7% to O-containing product phenol at the same conditions. The superior HDO performance of β-Mo2C can be attributed to the more active sites in β-Mo2C than α-MoC1-x. β-Mo2C with stronger thermostability exhibits long-term stability during the HDO process. The results show that β-Mo2C is a promising catalyst for lignin valorization.

Facile synthesis of high-performance carbon nanosheet/Cu composites from copper formate

Recently, much research has been reported on the fabrication of carbon-nanofiller (e.g., carbon nanotube (CNT), carbon nanosheet (CNS), and graphene)-reinforced copper matrix composites due to their wide potential applications. However, the preparation processes are generally complicated and difficult for commercial applications. Here, we propose a facile method to fabricate CNS-reinforced copper matrix composites by directly pyrolyzing copper formate powder at high temperature and then consolidating by spark plasma sintering. Interestingly, a complex interface consisting of CNSs, Cu nanoparticles, and CuO nanoparticles is found in the composite. The as-sintered CNS/Cu composite containing 0.27 vol% CNSs has a tensile yield strength of 498 ± 2 MPa and an electrical conductivity of 80.8 ± 0.1% International Annealed Copper Standard. The analysis of strengthening mechanism indicates that 51% of the tensile yield strength is contributed by the complex interface. The introduction of H2 during the pyrolyzing copper formate process results in an increase on the elongation and conductivity of CNS/Cu composite. After rolling, the elongation of CNS/Cu composite is as high as 8.5% and the friction coefficient is 0.25. This work provides a new guideline to the facile fabrication and interfacial design of advanced carbon-nanofiller-reinforced metal matrix composites with high performance.

Creation of Well-Defined "Mid-Sized" Micropores in Carbon Molecular Sieve Membranes.

Carbon molecular sieve (CMS) membranes are candidates for the separation of organic molecules due to their stability, ability to be scaled at practical form factors, and the avoidance of expensive supports or complex multi-step fabrication processes. A critical challenge is the creation of "mid-range" (e.g., 5-9 Å) microstructures that allow for facile permeation of organic solvents and selection between similarly-sized guest molecules. Here, we create these microstructures via the pyrolysis of a microporous polymer (PIM-1) under low concentrations of hydrogen gas. The introduction of H2 inhibits aromatization of the decomposing polymer and ultimately results in the creation of a well-defined bimodal pore network that exhibits an ultramicropore size of 5.1 Å. The H2 assisted CMS dense membranes show a dramatic increase in p-xylene ideal permeability (≈15 times), with little loss in p-xylene/o-xylene selectivity (18.8 vs. 25.0) when compared to PIM-1 membranes pyrolyzed under a pure argon atmosphere. This approach is successfully extended to hollow fiber membranes operating in organic solvent reverse osmosis mode, highlighting the potential of this approach to be translated from the laboratory to the field.

Creation of Well‐Defined “Mid‐Sized” Micropores in Carbon Molecular Sieve Membranes

AbstractCarbon molecular sieve (CMS) membranes are candidates for the separation of organic molecules due to their stability, ability to be scaled at practical form factors, and the avoidance of expensive supports or complex multi‐step fabrication processes. A critical challenge is the creation of “mid‐range” (e.g., 5–9 Å) microstructures that allow for facile permeation of organic solvents and selection between similarly‐sized guest molecules. Here, we create these microstructures via the pyrolysis of a microporous polymer (PIM‐1) under low concentrations of hydrogen gas. The introduction of H2 inhibits aromatization of the decomposing polymer and ultimately results in the creation of a well‐defined bimodal pore network that exhibits an ultramicropore size of 5.1 Å. The H2 assisted CMS dense membranes show a dramatic increase in p‐xylene ideal permeability (≈15 times), with little loss in p‐xylene/o‐xylene selectivity (18.8 vs. 25.0) when compared to PIM‐1 membranes pyrolyzed under a pure argon atmosphere. This approach is successfully extended to hollow fiber membranes operating in organic solvent reverse osmosis mode, highlighting the potential of this approach to be translated from the laboratory to the field.

Correlation between the H2 response and its oxidation over TiO2 and N doped TiO2 under UV irradiation induced by Fermi level

In the previous work, we have ever found that the photocatalytic oxidation of a reactant gas over TiO2 would be somewhat dependent on the electron transfer behavior between the adsorbed gas and TiO2 under UV irradiation. To further confirm the viewpoint, in this work, a TiO2 (in-situ) sample was prepared by an in-situ method, and was tested its gas-sensing performance to H2 and its photocatalytic performance of oxidizing H2 as compared to a TiO2 (commercial) sample. It was found that TiO2 (in-situ) would increase the conductivity with the introduction of H2 under UV irradiation, but TiO2 (commercial) would decrease the conductivity in the same case. Based on the surface structural and electrochemical characteristics of samples, it was proposed that the existence of surface defects over TiO2 (in-situ) would decrease the Fermi level (EF), resulting in the electron transfer from the adsorbed H2 to TiO2, while the adsorbed H2 accepted electrons from TiO2 (commercial) due to its higher EF. Moreover, the adsorbed H2 on TiO2 (in-situ) could be oxidized under UV irradiation but that on TiO2 (commercial) could be hardly. This indicated that the photocatalytic oxidation of H2 over TiO2 would be dependent on the electron transfer direction between the adsorbed H2 and TiO2, i.e., the electron-donated H2 could be oxidized, while the electron-accepted H2 could be not. This above effect induced by the surface defects could be further demonstrated by a N-doped TiO2 (N-TiO2) sample. This N-TiO2 owned a lower EF than TiO2 (in-situ) due to the introduction of a more impurity defects, resulting in a more electron transfer from the adsorbed H2 to N-TiO2 and then the oxidation of more H2. This study also indicated that the adjustment of EF could improve the photocatalytic activity of oxidizing H2 by changing the adsorbed behavior of H2 over TiO2, which may be applicable for investigating other reactants’ oxidation behaviors over other semiconductor photocatalysts.

Effect of temperature and simulated coal gas composition on tar production during pyrolysis of a subbituminous coal

Simulated coal gas (SCG) was used as pyrolysis atmosphere to improve tar yield and quality of coal pyrolysis, and the effect of SCG compositions including H2, CH4, CO, CO2 on pyrolysis products was also investigated. The results show that tar yield of coal pyrolysis is obviously enhanced under SCG atmosphere compared with that under N2. The components in SCG apparently influence the distribution of pyrolysis products and play a different role in coal pyrolysis. The highest tar yield (16.3 wt%) is obtained under SCG atmosphere at 650 °C. H2 reduces the char yield by suppressing secondary reaction; coexistence of H2 and CO2 in pyrolysis atmosphere increases water yield significantly via reverse water gas shift reaction, but the addition of CO inhibits this reaction. The analysis of tar by simulated distillation and GC/MS showed that the addition of CH4 increases the contents of benzenes and phenols; the introduction of H2 mainly increases naphthalenes; while the introduction of CO inhibits the formation of phenols. Lower aromaticity of tar under SCG than that under N2 indicates that small molecular radicals (i.e. H, CHx radicals) generated from SCG participate in the stabilization of free radicals from coal pyrolysis, resulting in high tar yield and quality.

Hydrogen-assisted step-edge nucleation of MoSe2 monolayers on sapphire substrates.

The fabrication of large-area single crystalline monolayer transition metal dichalcogenides (TMDs) is essential for a range of electric and optoelectronic applications. Chemical vapor deposition (CVD) is a promising method to achieve this goal by employing orientation control or alignment along the crystalline lattice of the substrate such as sapphire. On the other hand, a fundamental understanding of the aligned-growth mechanism of TMDs is limited. In this report, we show that the controlled introduction of H2 during the CVD growth of MoSe2 plays a vital role in the step-edge aligned nucleation on a c-sapphire (0001) substrate. In particular, the MoSe2 domains nucleate along the [112[combining macron]0] step-edge orientation by flowing H2 subsequent to pure Ar. Systematic studies, including the H2 introduction time, flow rate, and substrate temperature, suggest that the step-edge aligned nucleation of MoSe2 can be controlled by the hydrogen concentration on the sapphire substrate. These results offer important insights into controlling the epitaxial growth of 2D materials on a crystalline substrate.

Effect of hydrogen additive on methane decomposition to hydrogen and carbon over activated carbon catalyst

The effect of H2 addition on CH4 decomposition over activated carbon (AC) catalyst was investigated. The results show that the addition of H2 to CH4 changes both methane conversion over AC and the properties of carbon deposits produced from methane decomposition. The initial methane conversion declines from 6.6% to 3.3% with the increasing H2 flowrate from 0 to 25 mL/min, while the methane conversion in steady stage increases first and then decreases with the flowrate of H2, and when the H2 flowrate is 10 mL/min, i.e. quarter flowrate of methane, the methane conversion over AC in steady stage is four times more than that without hydrogen addition. It seems that the activity and stability of catalyst are improved by the introduction of H2 to CH4 and the catalyst deactivation is restrained. Filamentous carbon is obtained when H2 is introduced into CH4 reaction gas compared with the agglomerate carbon without H2 addition. The formation of filamentous carbon on the surface of AC and slower decrease rate of surface area and pores volume may cause the stable activity of AC during methane decomposition.

Revealing the microscopic CVD growth mechanism of MoSe2 and the role of hydrogen gas during the growth procedure

Understanding the microscopic mechanisms for the nucleation and growth of two-dimensional molybdenum diselenide (2D MoSe2) via chemical vapor deposition (CVD) is crucial towards the precisely controlled growth of the 2D material. In this work, we employed a joint use of transmission electron microscopy and CVD, in which the 2D MoSe2 were directly grown on a graphene membrane based on grids, that enables the microstructural characterization of as-grown MoSe2 flakes. We further explore the role of hydrogen gas and find: in an argon ambient, the primary products are few-layer MoSe2 flakes, along with MoOx nanoparticles; while with the introduction of H2, single-layer MoSe2 became the dominant product during the CVD growth. Quantitative analysis of the effects of H2 flow rate on the flake sizes, and areal coverage was also given. Nevertheless, we further illuminated the evolution of shape morphology and edge structures of single-layer MoSe2, and proposed the associated growth routes during a typical CVD process.

Copolymerization Mechanisms of Propylene and Norbornadiene Catalyzed by Zirconocene Complexes: A Density Functional Theory Study

Copolymerization mechanisms of norbornadiene (NBD) and propylene, catalyzed by three zirconocene catalysts (namely, rac‐Me2Si(2‐Me‐4‐Ph‐Ind)2ZrCl2/MAO (catA), rac‐Me2Si(Ind)2ZrCl2/MAO (catB), and rac‐CH2CH2(Ind)2ZrCl2/MAO(catC)), have been studied, using density functional theory computations. It has been found that the barrier (28.5 kcal mol−1) for the insertion of propylene to the [Zr]A‐NBD‐PP1 (the NBD insertion product) is significantly higher than those to [Zr]B‐NBD‐PP1 (22.9 kcal mol−1) and [Zr]C‐NBD‐PP1 (20.5 kcal mol−1), rationalizing the experimental observation that addition of NBD deactivated catA system but only lowered the catalytic activity of catB and catC systems. However, [Zr]A‐NBD‐PP1 can react with H2 easily, which displaces NBD−PP1 chain and gives active [Zr]A−H species to continue copolymerization, which is why the introduction of H2 could recover the catalytic activity of catA system.

Biomethanation of blast furnace gas using anaerobic granular sludge via addition of hydrogen.

The high concentrations of CO (toxic) and CO2 (greenhouse gases) in blast furnace gas (a by-product of steelworks) reflect its low calorific value. In this study, anaerobic granular sludge was used to convert carbon from blast furnace gas to methane via exogenous hydrogen addition. The inhibition of methane production by CO partial pressure (PCO) was found to start from 0.4 atm. The intermediate metabolites from CO to methane including acetate, propionate, and H2 accumulated at higher CO concentrations in the presence of 2-bromoethanesulfonic acid. After the introduction of H2 and blast furnace gas, although the hydrogen partial pressure (PH2) up to 1.54 atm resulted in the maximum CH4 yield, the whole system was not stable due to the accumulation of a large amount of volatile fatty acids. The optimum PH2 on CH4 production from the simulated blast furnace gas, 5.32 mmol g−1 VSS, was determined at 0.88 atm in this study.

Steam reforming of α-methylnaphthalene as a model compound of biomass tar over Ni-based catalyst for hydrogen-rich gas

Tar is a barrier to limit the development of biomass gasification. Catalytic steam reforming experiments using α-methylnaphthalene (MNP) as a model tar compound were carried out in the two-stage reactor system (TSR). Based on response surface methodology, the effects of TSR temperatures and the molar ratio of steam to carbon (S/C) on MNP reforming performances were analyzed using the Li-modified Ni-based catalyst (NBC). The results show that the proper introduction of H2 is able to improve significantly the MNP conversion, specially at lower temperatures. Furthermore, it is more appropriate for the modified catalysts by Li and Mg to be loaded in the first reactor due to their significant promotion to hydrocracking reactions, and it is favorable to place the Ni/Al catalyst in the second reactor for H2-rich gas. Additionally, the carbon deposition resistance of the NBC modified by Li exhibits better than that of the NBC modified by Mg.

Working Principle of Hydrogen Sensor Based on Pentacene Thin-Film Transistor

A hydrogen sensor based on pentacene organic thin-film transistor (OTFT) with palladium (Pd) source and drain (S/D) electrodes is analyzed in detail. When exposed to H2 with different concentrations, the sensor shows a clear change in drain current due to three reasons: 1) work-function change of the source electrode induced by hydrogen absorption; 2) reduced carrier mobility; and 3) increased S/D series resistance both caused by the expansion of the S/D electrodes after absorbing hydrogen. Analysis of the data demonstrates that the first two are the dominant mechanisms. Without the need of heating, rapid, reversible, and concentration-dependent response of the OTFT is observed upon introduction and removal of H2 with concentration ranging from 200 to 17 000 ppm.