Adsorption Behavior Of H2 Research Articles

Geo-storage of hydrogen in organic-rich shales: Multicomponent selectivity of organic nanopores

The gas adsorption capacity of kerogen is commonly obtained through experimental isothermal adsorption procedures. These experiments employ mathematical models called adsorption isotherms, which bridge the gap between empirical data and theoretical frameworks to offer a continuous representation of the underlying processes in the depleted shale formation with some fraction of resident adsorbed natural gas. However, an exploration of the adsorption behavior of H2, in the presence of CH4, C2H6, C3H8, and CO2 in organic-rich porous media of varying pore size remains an unaddressed area of study. Considering this, in this study, we conduct a molecular simulation of the adsorption and diffusion behavior of hydrogen (H2), methane (CH4), ethane (C2H6), propane (C3H8), and carbon dioxide (CO2) within a representative kerogen organic nanopore structure. In particular, we studied hydrogen adsorption behavior in organic-rich shale formations in varying nanopore size and multi-gas components. We also evaluate the suitability of different adsorption models (Langmuir, Langmuir-Freundlich, Toth) for depicting the adsorption characteristics of single species. For the multicomponent mixture (H2/CO2/CH4/C2H6/C3H8), we apply Langmuir ratio correlation model (LRC). The findings indicate C3H8 demonstrates the highest adsorption potential, while CH4 ranks lowest, followed by H2, CO2 and C2H6 exhibit intermediate potential. Furthermore, the adsorption of each species is hindered by organic nanopores of 1 nm, as opposed to 2 nm nanopores. For multicomponent adsorption, hydrogen exhibits minimal presence at equilibrium, which can be attributed to its higher diffusivity compared to other gases. Notably, the Langmuir, Toth, and Langmuir-Freundlich models exhibit ability to accurately depict the overall adsorption trends single-component. However, for the multicomponent mixture (H2/CO2/CH4/C2H6/C3H8), the LRC is found reasonable effective to capture the adsorption.

Molecular simulations of hydrogen adsorption on coal with different ranks: Implications for hydrogen geo-storage

Underground hydrogen storage is a promising solution for the safe and efficient storage of industrial-scale H2. In this study, the adsorption behaviors of H2 in coal with different ranks under various temperatures and pressures are investigated using molecular simulations. It is found that the H2 adsorption capacity is positively correlated with coal rank, which is mainly attributed to the combined effects of surface chemical property and pore structure. Moreover, the isosteric heat of adsorption of H2 increases with the reduction in pore size due to the overlap of potential energy. In addition, the absolute adsorption amount of H2 in moist coal generally decreases with the increase in moisture content because of the competitive adsorption between water and H2 and the spatial occupation of water clusters/bridges. As a result, the anthracite coal seam with abundant micropores and few hydrophilic groups is considered to have a high potential for H2 storage.

Adsorption behavior of H2 in quartz silt-pores at high temperature and pressure

To understand the storage and transport of H2 in the Earth’s interior, the adsorption behaviors of H2 in the slit-like pore of quartz under different conditions were calculated by the grand canonical Monte Carlo method. The Poisson distributions of interaction energy show unimodal, indicating that the adsorption behavior is mainly affected by van der Waals interaction between molecular H2 and quartz, the adsorption potential energy increases, and when the pressure increases, the temperature and pore size decrease. Isosteric heat of adsorption is in the range of −5.0 to −1.7 kJ/mol, which indicates that the adsorption behavior belongs to physical adsorption. The results of isosteric heat of adsorption show that strong energy exchange occurs in the H2-quartz system at the initial stage of adsorption, which may affect the stability of quartz. The average isosteric heat of adsorption linearly increases with temperature. However, the increasing rate of average isosteric heat of adsorption decreases with the increase in the pore size. Adsorption snapshots show most of the H2 distributed randomly and there is no obvious adsorption layer of H2 in the pores. Excess adsorption amount increases with the decrease in temperature and the increase in pressure and pore size. The change rate of excess adsorption amount with temperature increases with the increase in pressure. Similarly, with the increase in pressure, the change rate of excess adsorption amount with pore size decreases slowly at first, then increases rapidly, and finally decreases. The results are helpful to reveal the migration and formation of H2 reservoirs in the Earth’s interior.

Insights into Selective Mechanism of NiO-TiO2 Heterojunction to H2 and CO.

The construction of p-n heterojunctions has become a widely adopted strategy for achieving the selective detection of reducing gases, including H2 and CO. Nevertheless, the elucidation of the gas selectivity mechanism at the nanoscale remains elusive. First-principle calculations provide an attractive avenue for comprehending the influence of coordination structures on gas-sensitive selectivity, thereby unveiling the structure-activity relationship of p-n heterojunction sites. In this study, we investigate the selective adsorption behavior of H2 and CO on a NiO-TiO2 heterojunction using density functional theory. The results of d-band center analysis confirm that the NiO-TiO2 heterojunction with adsorbed oxygen significantly enhances the adsorption stability of reducing gases. Intriguingly, our calculations reveal that H2 has a higher affinity for adsorbed oxygen on the heterojunction surface compared to that of CO, corresponding to a lower H2 adsorption energy. Density of states (DOS) results indicate that the NiO-TiO2 heterojunction, with preadsorbed oxygen, exhibits ultrahigh selectivity with an n-type gas-sensitive response to H2, effectively eliminating the cross-sensitivity observed with CO, as confirmed by gas-sensitive characterization research. The sensing mechanism of the NiO-TiO2 heterojunction's selective detection of H2 without interference from CO can be visually explained by electron transfer and potential barrier changes, paving the way for future developments in novel, selective gas-sensitive materials.

Atomically Local Electric Field Induced Interface Water Reorientation for Alkaline Hydrogen Evolution Reaction.

The slow water dissociation process in alkaline electrolyte severely limits the kinetics of HER. The orientation of H2 O is well known to affect the dissociation process, but H2 O orientation is hard to control because of its random distribution. Herein, an atomically asymmetric local electric field was designed by IrRu dizygotic single-atom sites (IrRu DSACs) to tune the H2 O adsorption configuration and orientation, thus optimizing its dissociation process. The electric field intensity of IrRu DSACs is over 4.00×1010 N/C. The ab initio molecular dynamics simulations combined with in situ Raman spectroscopy analysis on the adsorption behavior of H2 O show that the M-H bond length (M=active site) is shortened at the interface due to the strong local electric field gradient and the optimized water orientation promotes the dissociation process of interfacial water. This work provides a new way to explore the role of single atomic sites in alkaline hydrogen evolution reaction.

Characteristics of Co–Ca catalyzed coal hydrogasification in a mixture of H2 and CO2 atmosphere

Coal catalytic hydrogasification (CCHG) is a promising approach for producing substituted natural gas by using pure hydrogen as a gasifying agent. If pure hydrogen could be replaced by cheaper crude gas from the coal gasifier, the economy of CCHG would be significantly improved. However, the composition of crude gas is complicated because in addition to H2, CO, CO2 and H2O are contained in it. To preliminarily investigate the influence of CO2 in the feed gas on CCHG, a mixture of H2 and CO2 with a CO2 concentration of 10% (denoted as H2 + CO2) was used for Co–Ca catalyzed coal hydrogasification at 850 °C and 3 MPa in a fluidized bed reactor. The results showed that the concurrence of coal hydrogasification with CO2 methanation produced CH4 efficiently. The CH4 yield (based on the carbon in coal) increased from 77.4% for pure H2 to 188% for H2 + CO2 within 120 min. More than 90% CO2 in situ conversion and 72.3% coal conversion were achieved. The catalytic effect of the Co–Ca loaded coal considerably improved the CH4 selectivity of CO2 methanation from 43.5% to 82.7%. The forms of Co and Ca in H2 + CO2 were consistent with those in pure hydrogen. The slow coal hydrogasification rate in H2 + CO2 was mainly attributed to the two-fold effects of CO2 methanation: the decrease in the partial hydrogen pressure and the competitive adsorption behavior of H2 and CO (a by-product of CO2 methanation) molecules on the cobalt active surface. This work provides a unique approach for simultaneously realizing the conversion of coal and the utilization of CO2.

Density functional study of PdaCubAuc (a + b + c = 7) clusters: Geometry, electronic and H2 physisorption properties

We report a systematic study of ternary PdaCubAuc clusters, with a + b + c = 7. The optimized geometries, binding energy per atom, excess binding energy, electrostatic potential surfaces and the physical adsorption behavior of H2 were analyzed by density function theory calculation with TPSSTPSS functional and SDD basis set. PdaCubAuc clusters with more Au atoms exhibit lower binding energy per atom. The average bond distance reduces with increasing Cu content. For PdaCubAuc-H2 clusters, the site precedence for the molecular H2 adsorption follows the order Pd > Cu > Au. The adsorption energy correlates linearly with the elongation of HH distance.

Strain-induced switch for hydrogen storage in cobalt-decorated nitrogen-doped graphene

As a feasibility study for hydrogen storage, the adsorption behavior of H2 on transition metal-decorated N-doped graphene is systematically investigated by density functional theory and the adsorption isotherm is used to predict to practical capacity at realistic condition by grand canonical partition function. The biaxial strain is proposed to be a reversible switch for hydrogen storage. Our computational results suggest that Co-decorated N-doped graphene is a highly promising material for hydrogen gas storage with good thermal stability and excellent gravimetric density. Additionally, the adsorption of H2 is sensitive to the biaxial tensile strain, and the transition point of chemisorption/physisorption occurs under 8% strain. By applying 10% strain for desorption, the storage capacity can be effectively improved to 6.00 wt% (i.e. 19% enhancement) at low pressure and room temperature. Our findings not only reveal the feasibility of a tunable material for hydrogen storage, but also provide a new strategy to control the performance for hydrogen storage by biaxial tensile strain.

Gas molecule adsorption on twisted nanographene C96H36 derivative: A theoretical study

Abstracts Twisted C96H36, a newly synthesized nanographene, may have distinct properties from those of planar graphene. The adsorption behaviors of H2, CO, NO, NH3, SO2, and HCHO on the surface of C96H36 derivative, which was labelled as C96, were systematically investigated by computational methods. The adsorption behaviors of 1–20 formaldehyde molecules on C96 were calculated to reveal potential uses of C96. The results indicate that these molecules could be physically absorbed on the surface of C96 with absorption energies in the range 0.5–5.5 kcal mol−1. The calculated HOMO-LUMO energy gap also showed that C96 could act as a potential gas sensor for O2 and SO2. When one formaldehyde molecule is absorbed, it prefers to locate at the edge of the distorted moiety of C96. A second formaldehyde also prefers to be absorbed at another edge position of the distorted moiety of C96. The results show that the absorption energies for the third to twelfth formaldehyde molecules are concentrated at 5 kcal mol−1, which indicates that more formaldehyde molecules could be absorbed onto C96, but a limit of 20 formaldehyde molecules was calculated.

First-principles study on the gas sensing property of the Ge, As, and Br doped PtSe2

Based on first-principles calculations, the adsorption behaviors of H2, O2, CO, CO2, NH3, NO, and NO2 molecules on the Ge-, As- and Br-doped PtSe2 monolayers are theoretically investigated. The results indicate that it is viable for the dopant atoms to be filled into the Se vacancies under Pt-rich conditions. Ge and As act as p-type dopants, while Br acts as n-type dopant. For the adsorption of molecules, the geometrical structures, adsorption energies, charge transfers and the electronic and magnetic properties of the most stable configurations are presented and discussed. It is found that the Ge-doped PtSe2 monolayers exhibit greatly enhanced sensitivity toward O2, CO, NH3, NO and NO2 molecules and the As-doped PtSe2 monolayers are more sensitive toward O2, NH3, NO and NO2 molecules than the pristine ones. This is evident from large adsorption energies, charge transfers, and obvious changes of the electronic states due to the molecule adsorption. However, Br doping cannot enhance the sensing sensitivity of the PtSe2 monolayer. The possible reason is that when substituting for the Se atom, the doped Br with more 4p electrons and less empty orbitals are already chemically saturated by the two of the three neighboring Pt atoms, and thus lose the ability of charge exchange with the adsorbed molecules. On the contrary, the Ge and As as p-type dopants have sizable empty 4p orbitals near the Fermi level to exchange the electrons with the adsorbed molecules, and thus form strong bonds with them.

Controlled Catalytic Properties of Platinum Clusters on Strained Graphene

We employed graphene under isotropic strain as the supporting material for Pt clusters (Ptx, x = 1, 4, or 6) and studied the site-resolved molecular adsorption behaviors of H2, CO, and OH on the clusters using ab initio calculations. It was shown that the applied strain enhances the binding of the Pt atom or clusters on the graphene, which lowers the average energy of the d electrons (d-band center). However, for the Pt4 and Pt6 clusters that form two Pt atomic layers on the graphene, only the d-band center of the bottommost Pt layer can be readily tuned by the external strain on graphene. However, the site-resolved calculations of molecular binding demonstrate that controlling the d-band center of the bottommost Pt atoms can be a substantial factor for all the catalytic activities of the Pt cluster. We also found that the stability of the Pt/graphene system was enhanced by applying strain to the graphene support.

H2 ADSORPTION ON LiB (001) SURFACE: A FIRST PRINCIPLES CALCULATION

The adsorption behavior of H2 on the LiB (001) surface was investigated with density functional theory (DFT) method. It was found that the site of H2 adsorbed on the Li-B bridge II was easier than the other four sites ( Li top, B top, hollow vertical and Li-B bridge I). H2 adsorbed on the Li-B bridge II site was a strong chemical adsorption. The adsorption energy was 2.190 eV, and the H , B atoms exhibited covalent characteristics, the H – H atoms have a little interaction, and the H2 was 0.331 Å below the surface of Li-B bridge II. The charge density, band structure, totals and partial density of states were calculated utilizing the first principle method. These calculations showed that the H interacted with the surface atoms, and partially saturated the dangling bonds with the surface atoms. The interaction between H and the surface atoms were mainly attributed to the H 1 s, B 2 s and B 2 p states. The calculated band gap was 0.075 eV and 0.199 eV before and after adsorption.

Microporous Cyanate Resins: Synthesis, Porous Structure, and Correlations with Gas and Vapor Adsorptions

Three silicon and nitrogen-centered cyanate monomers tetrakis(4-cyanatophenyl)silane, tetrakis(4-cyanatobiphenyl)silane, and tris(4-cyanatobiphenyl)amine were designedand synthesized, which were then polymerized via thermal cyclotrimerization reaction to create highly porous cyanate resin networks with systematically varied nodes and linking struts. The chemical structures of monomers and polymers were confirmed by 1H NMR, FTIR, solid-state 13C CP/MAS NMR spectra, and elemental analysis. The products are amorphous with 5% weight-loss temperatures over 428 °C. The results based on N2 and CO2 adsorption isotherms show that the pores in these polymers mainly locate in the microporous region, and the BET surface areas are up to 960 m2 g–1, which is the highest value for the porous cyanate resin reported to date. The nitrogen- and oxygen-rich characteristics of cyanate resins lead to the networks strong affinity for CO2 and thereby high CO2 adsorption capacity of 11.1 wt % at 273 K and 1.0 bar. The adsorption behaviors of H2, CO2, benzene, n-hexane, and water vapors were investigated by correlating with the chemical composition and porosity parameters of the networks as well as the physicochemical nature of adsorbates.

The effect of electric field on hydrogen storage for B/C/N sheets

Using first-principles calculations, we investigate the adsorption behaviors of H2 in B/C/N sheets (including BCN, BC2N, and BC3N) and discuss the effect of external electric fields on H2 adsorbed for BCN and BC2N sheets. For a single H2 adsorbed on BCN and BC2N sheets, the adsorption energy increases dramatically with the electric field intensity increasing, and the maximum adsorption energy can reach 0.55 eV in the electric field of F = 0.050 a.u. and one layer H2 can adsorb on BCN and BC2N sheets, corresponding to the maximum hydrogen storage capacity of 5.1 wt%. The average adsorption energy calculated larger than that of in the field-free case.

Potential energy surfaces for H2 dissociative adsorption on Pt(111) surface—effects of vacancies

AbstractIn this study, we determine the effects of having vacancies on the Pt(111) surface to the dissociative adsorption behavior of H2 on Pt(111). We study the potential energy behaviors along the reaction paths based on the potential energy surfaces (PESs) we calculated that are relevant to these systems. Partial results of our current calculations, based on the density functional theory, reveal that vacancies on the substrate can significantly lower the barrier for the dissociative adsorption of H2 on the Pt(111) surface. We attribute this behavior to the increased reactivity of the surface owing to the vacant sites. Of the substrate atoms, we find that those on the surface mainly influence the behavior of H2 adsorption on Pt(111). Copyright © 2008 John Wiley & Sons, Ltd.

STORAGE OF HYDROGEN ON CARBON MATERIALS: EXPERIMENTS AND ANALYSES

ABSTRACT Superactivated carbon and carbon nanotubes are both considered potential hydrogen carriers. Adsorption isotherms of H2 on activated carbon AX-21 and multi-wall carbon nanotubes were collected with a volumetric method for the temperature range of 77, 233–298 K and pressures up to 7 or 10 MPa. Based on the experimental data for 233–298 K, the limiting heats of adsorption of 7.6 and 1.8 kJ/mol were obtained for activated carbon and carbon nanotubes, respectively. The absolute adsorption was determined with a recently presented method, and the adsorption behavior of H2 on carbon nanotubes was thus reasonably explained. A comparison was given for the storage capacities of compression alone and of filling powder or pellets of the two materials. It was concluded that adsorption of H2 on carbon nanotubes is too weak to enhance storage, but activated carbon enhances storage capacity considerably. The weight percentage of hydrogen stored in carbon powder reaches 10.8% at 77 K and 6 MPa, including the quantity compressed in the void space, and 4.1 kg H2 was stored in a 100-liter container filled with carbon pellets for the same condition.

Multi-Component Adsorption Behavior of Hydrogen Isotopes on Zeolite 5A and 13X at 77.4 K

Equilibrium isotherms for the adsorption of H2, HD, HT, D2, DT and T2 on synthetic zeolite type 5A or 13X at 77.4 K are estimated by using a theoretical formula, where the isotopic difference in adsorption depends on the zero-point energy difference between hydrogen isotopes. The formula agrees with the experimental isotherms for H2 and D2 on the zeolites. Adsorption of H2-D2 and H2-HD-D2 mixtures on the same adsorbents is experimentally examined. The experiments are performed using a volumetric apparatus and a quadra-pole-type mass spectrograph. The experimental adsorption behavior of H2, D2 and HD shows agreement of separation factors with results calculated according to the ideal adsorbed solution theory describing multi-component behavior, where the equilibrium isotherms estimated for H2, HD and D2 are used. Based on the theoretical adsorption model, the multi-component behavior of HT, DT and T2 is predicted here.