Dissociation Of Hydrogen Sulfide Research Articles

Direct solar-driven electrochemical dissociation of H2S to H2 with 12 % solar-to-hydrogen conversion efficiency in diaphragm electrolytic reactor

Solar-driven electrochemical dissociation of hydrogen sulfide (H2S) to hydrogen and sulfur products in photovoltaic-electrochemical (PV-EC) devices becomes an effective strategy for acid gas purification and energy-saving hydrogen production. However, available H2S splitting electrochemical devices suffer from inferior energy conversion efficiency and fussy multi-step sulfur recovery problems. Herein, we propose an integrated solar-driven PV-EC system with diaphragm electrolytic reactor to solve these challenges. The optimized system integrated commercial silicon solar delivers a high solar-to-hydrogen energy conversion efficiency of up to 12 %, with approximately 99 % H2 faradaic efficiency and demonstrates at least 50 hours of stability. More importantly, the S2-/HS- can be transformed into add-valued Na2S2O3 by one-step method in Na2SO3 media, which avoids complex sulfur recovery. This work presents an alternative method of low-energy consumption for producing H2 and high-value sulfur-related chemicals by H2S splitting through a PV-EC system.

Design of Sulfur Resistant Cobalt Catalysts by Boron Promotion: Atomic Scale Insights

The effect of boron promotion on atomic sulfur formation by hydrogen sulfide dissociation on Co(111), flat surfaces of cobalt nanoparticles, was investigated using Density Functional Theory calculations. The results show that on clean Co(111), hydrogen sulfide dissociation proceeds fast due to low activation barriers, yielding atomic sulfur on the cobalt surfaces. Boron promotion hinders the dissociation of hydrogen sulfide due to increased activation barriers. Furthermore, boron prevents the interaction of sulfur compounds with cobalt surface atoms, as these poisons bind on boron. The findings indicate that boron is an effective promoter that can be used to design sulfur resistant cobalt catalysts.

Investigation of the Adsorption of Hydrogen Sulfide on Faujasite Zeolites Focusing on the Influence of Cations.

During the conversion of natural gas to liquified natural gas, sulfur components are separated by adsorption on zeolites. New zeolite materials may improve this adsorption process. In this paper, the adsorption of hydrogen sulfide is studied on seven faujasite (FAU) zeolites, which differ only in the number of sodium and calcium cations. From a pure NaX zeolite (13X), which contains only sodium cations, the calcium cation content was gradually increased by ion exchange. In a fixed-bed adsorber, cumulative equilibrium loadings of H2S on these zeolites were determined at concentrations between 50 and 2000 ppm at 25 and 85 °C and 1.3 bar (abs). Adsorption isotherms were analyzed considering the influence of cation positioning in the FAU zeolites. The experimental data indicate a superposition of a chemisorptive and a physisorptive mechanism. At a small number of chemisorptive sites, we conclude a dissociation of hydrogen sulfide and covalent bonding of the proton and the hydrogen sulfide ion to the zeolite lattice. The contribution of chemisorption exhibits a very low temperature dependence, which is typical for nearly irreversible reactions with an equilibrium strongly shifted to one side. With an increase in the proportion of Ca2+ cations, only physisorptive adsorption by electrostatic interaction with the cations in the lattice was observed. A large number of physisorptive sites have a lower energetic value. The share of physisorption strongly depends on temperature, which is characteristic of reversible equilibrium reactions.

The adsorption and dissociation of hydrogen sulfide on transition metal atoms decorated graphdiyne: a first-principles calculation.

As a neurotoxic and corrosive gas pollutant, H2S is unhealthy for all creatures and limits the development of the industry. By first-principles calculation, the adsorption behaviors of H2S gas on the original graphdiyne (GDY), non-metallic atoms decorated GDY, and metal atoms decorated GDY were initially studied. The adsorption configuration, adsorption energy, and charge transfer between H2S and GDY were calculated in detail. The electron density and the partial density of states (PDOS) were also examined. The results show that there is only weak physical adsorption between the original GDY, non-metallic atoms decorated GDY, and H2S gas molecules, so GDY and non-metallic atoms decorated GDY cannot be directly used to adsorb H2S gas. The adsorption of H2S gas on GDY decorated with metal atoms (Cu, Ti, and V) was significantly enhanced, and the adsorption in this condition belongs to chemical adsorption. They can be used as H2S gas adsorbing materials. In addition, the dissociation of H2S on transition metal atoms decorated GDY was further investigated. The results show that H2S in one of the five configurations dissociates on V-decorated GDY directly. Cu- and Ti-decorated GDY can be used as substrates for the dissociation of H2S. The energy barriers in this process are 1.605eV and 0.360eV, respectively. It is hoped that the research results in this work can provide insights into the development of H2S gas adsorbing and dissociating materials based on transition metal atoms decorated GDY.

Study on the Physical Properties and Electric Dissociation of Hydrogen Sulfide under the Action of Strong Field

Study on the Physical Properties and Electric Dissociation of Hydrogen Sulfide under the Action of Strong Field

A theoretical study of H2S adsorption and dissociation mechanism on defected graphene doped with Pt

The adsorption and dissociation of hydrogen sulfide (H2S) molecule on Pt or Pt4 cluster doped graphene with different vacancy (VG), as well as their geometric and electronic structures have been investigated by density functional theory (DFT). It has found that H2S and H atom are weakly adsorbed on Pt/Pt4-VG, while HS and S atom are strongly chemisorbed on different surfaces. By using climbing nudged elastic band method (CI-NEB), three elementary processes have been studied: (I) H2S(gas)→H2S(ads); (II) H2S(ads)→HS(ads) + H(ads); (III) HS(ads) → H(ads)+ S(ads). The energy barriers to break the first H–S bond in H2S on four different surfaces (Pt-MVG, Pt-DVG, Pt4-MVG, Pt4-DVG) are 1.69, 0.52, 0.01 and 0.24 eV respectively. In contrast, the energy barriers to break the second H–S bond in HS are 2.34, 1.08, 0.81 and 1.12 eV respectively. It is suggested that the control step of the complete dissociation of H2S is the second H–S bond rupture process. The trend shown in this study reveals that single Pt atom doped defected graphene is favored for adsorption of H2S, but is disadvantage for dissociation. Pt cluster doped defected graphene with bigger vacancy can successfully adsorb and easily eliminate H2S molecule, which is expected to be the ideal material for the adsorption and dissociation.

A theoretical study of sulfur poisoning tolerance at the interface of Mo doped Ni/Yttria-Stabilized Zirconia

Sulfur poisoning is a crucial problem for solid oxide fuel cell (SOFC) anode leading to increasing research works on the development of the anode materials with high sulfur tolerance. By the first principle calculations of hydrogen sulfide dissociation and sulfur atoms diffusion at the interface between the Ni or Mo-doped-nickel and Yttria-Stabilized Zirconia (YSZ), we find that Mo-doped-Ni/YSZ anode not only increases the hydrogen sulfide dissociation barriers, but also increases the barriers of the sulfur diffusion to the oxygen vacancy at the interface of Ni and YSZ, especially for YSZ in oxygen enriched conditions. Here we offer a new theoretical study of Mo-doped-Ni/YSZ sulfur poisoning tolerance at the interface.

A revision of mechanistic modeling of mild steel corrosion in H2S environments

In this study, a predictive model for the corrosion rate and the polarization response of bare steel in aqueous hydrogen sulfide (H2S) environments based on H2S dissociation and its buffering effect was developed. In this model, the hydrogen ion reduction is the only cathodic reaction. The results confirmed that the increased limiting cathodic current densities and the characteristic “double wave” behavior in the cathodic current of this system could be explained by hydrogen sulfide dissociation in the vicinity of the metal surface. The effect of hydrogen sulfide on the rate of iron dissolution reaction was also taken into account by introducing a reaction sequence involving sulfide intermediates into the calculations, parallel to the acidic iron dissolution reaction. The developed model was shown to be able to reasonably represent the characteristic electrochemical behavior of this system. Furthermore, the predicted corrosion rates are shown to be in good agreement with the available experimental data in the literature over a wide range of conditions.

Impact of Na+ and Ca2+ Cations on the Adsorption of H2S on Binder-Free LTA Zeolites

Hydrogen sulfide is removed from natural gas via adsorption on zeolites. The process operates very effectively, but there is still potential for improvement. Therefore, in this article, the adsorption of hydrogen sulfide was investigated on eight LTA zeolites with different cation compositions. Starting with the zeolite NaA (4 A), which contains only Na+ cations, the Ca2+ cation content was gradually increased by ion exchange. Equilibrium isotherms from cumulative breakthrough curve experiments in a fixed-bed adsorber at 25°C and 85°C at 1.3 bar (abs.) were determined in the trace range up to a concentration of 2000 ppmmol. From a comparison of the isotherms of the different materials, a mechanistic proposal for the adsorption is developed, taking into account the specific positions of the cations in the zeolite lattice when the degree of exchange is increased. The shape of the isotherms indicates two energetically different types of adsorption sites. It is assumed that two mechanisms are superimposed: a chemisorptive mechanism with dissociation of hydrogen sulfide and covalent bonding of the proton and the hydrogen sulfide ion to the zeolite lattice and a physisorptive mechanism by electrostatic interaction with the cations in the lattice. As the degree of exchange increases, the proportion of chemisorption sites seems to decrease. Above an exchange degree of 50%, only evidence of physisorption can be found. It is shown that this finding points to the involvement of weakly bound sodium cations at cation position III in the chemisorption of hydrogen sulfide.

Superconductivity and structural studies of highly compressed hydrogen sulfide

Superconductivity exceeding 200 K was reported in the highly compressed hydrogen sulfide. The superconducting “material” was found to be synthesized by pressure above 90 GPa by the dissociation of hydrogen sulfide (H2S). We have investigated the superconducting properties after the discovery. Here, we report our recent investigations including confirmation the superconductivity and the crystal structure analysis using the synchrotron x-ray at room temperature and low temperature.

Hydrogen sulfide as a source of hydrogen production

Potentialities and perspectives of using the known processes of hydrogen sulfide decomposition (thermal, plasmochemical, electrochemical, and photochemical) to produce hydrogen are examined. The results of theoretical and experimental studies of hydrogen sulfide dissociation on the surface of single crystals are presented. The data on the low-temperature decomposition of H2S on the sulfide and metal catalysts are discussed. The electronic structure of diatomic sulfur and thermodynamics of its formation in the processes of H2S decomposition are considered. The decomposition of hydrogen sulfide on the heterogeneous catalysts placed under the solvent layer is shown to be promising. The mechanism of assimilation of hydrogen sulfide by colorless sulfur bacteria is proposed.

Adsorption and dissociation of H2S on nitrogen-doped TiO2 anatase nanoparticles: Insights from DFT computations

We have investigated the adsorption and dissociation of hydrogen sulfide (H2S) molecule on the pristine and nitrogen-doped TiO2 anatase nanoparticles using first-principles calculations in order to obtain insights into the adsorption behaviors of H2S molecules. We have investigated different adsorption geometries of H2S over the nanoparticles. We have found that the H2S adsorption is not energetically more favorable on the pristine nanoparticle surface, but H2S is preferentially adsorbed on the N-doped nanoparticles with a higher favorability in energy. H2S molecule adsorbs on the dangling oxygen, doped nitrogen and fivefold coordinated titanium sites of the TiO2 nanoparticle. The hydrogen atom in the H2S molecule forms a hydrogen bond with the surface oxygen or doped nitrogen atom of TiO2. We have reported the results of DFT calculations including the bond lengths/angles, adsorption energies, electronic density of states and molecular orbitals. Charge analysis based on Mulliken charges reveals a significant charge transfer from the molecule to the TiO2 anatase particle. The inclusion of the vdW interactions results in considerable enhancement of H2S–TiO2 interaction, thereby increasing the adsorption energies of the molecules. The N-doped nanoparticles have stronger adsorption ability than the undoped ones, indicating the higher sensing capability of N-doped nanoparticles for H2S detection. Our results suggest a great potential of N-doped TiO2 for application as a highly sensitive H2S sensor.

High conversion of hydrogen sulfide in gliding arc plasmatron

The experimental study discussed in this paper focused on increasing the hydrogen yield from direct dissociation of hydrogen sulfide in a gliding-arc discharge. The specific energy input to plasma in this study was noticeably higher than in previous studies involving H2S dissociation in gliding arc plasmatron (GAP) and gliding arc “tornado” (GAT) reactors. Several different techniques were used to increase the quenching rate of the reactor effluent mixture to prevent undesirable reverse reactions. The highest hydrogen yield obtained in this study was 65%, which was achieved at a specific energy input (SEI) of 1.52 eV/molecule and a corresponding specific energy requirement (SER) of 2.64 eV/molecule. Moreover, a detailed investigation of the dependence of SER on conversion degree was conducted over a wide range of SEI, which is necessary for process optimization from an economic standpoint.

Low-temperature catalytic decomposition of hydrogen sulfide into hydrogen and diatomic gaseous sulfur

The thermodynamics of three pathways of the hydrogen sulfide decomposition reaction is considered. In the thermal process, the gas-phase dissociation of hydrogen sulfide yields hydrogen and diatomic singlet sulfur. Over sulfide catalysts, the reaction proceeds via the formation of disulfane (H2S2) as the key surface intermediate. This intermediate then decomposes to release hydrogen into the gas phase, and adsorbed singlet sulfur recombines into cyclooctasulfur. Over metal catalysts, H2S decomposes via dissociation into surface atoms followed by the formation of gaseous hydrogen and gaseous triplet disulfur. The last two pathways are thermodynamically forbidden in the gas phase and can take place at room temperature only on the surface of a catalyst. An alternative mechanism is suggested for hydrogen sulfide assimilation in the chemosynthesis process involving sulfur bacteria. To shift the hydrogen sulfide decomposition equilibrium toward the target product (hydrogen), it is suggested that the reaction should be conducted at room temperature as a three-phase process over a solid catalyst under a layer of a solvent that can dissolve hydrogen sulfide and sulfur. In this case, it is possible to attain an H2S conversion close to 100%. Therefore, hydrogen sulfide can be considered as an inexhaustible source of hydrogen, a valuable chemical and an environmentally friendly energetic product.

The reaction thermodynamics of hydrogen sulfide decomposition into hydrogen and diatomic sulfur

To verify a hypothesis about the electronic state of diatomic gaseous sulfur formed during the low-temperature catalytic decomposition of hydrogen sulfide, we carried out some experiments to examine elemental sulfur dissociation. As shown, after heating at ∼1000 K, elemental sulfur sealed in quartz ampoules with metal catalysts followed by quenching at room temperature did not produce any visible changes on solid sulfur. However, conversion of solid sulfur into gaseous diatomic sulfur can be realized via intermediate interaction of melted sulfur with hydrogen in the presence of Pt followed by decomposition of H2S formed on the surface of the metal catalyst at room temperature. It is suggested that the conversion of the singlet sulfur atoms into the ground triplet state becomes feasible only on the surface of metal catalysts resulted from the dissociation of hydrogen sulfide into adsorbed atomic species.

DFT study on the adsorption and dissociation of hydrogen sulfide on MgO nanotube

The adsorption of a H2S molecule on the surface of an MgO nanotube was investigated using density functional theory. It was found that H2S molecule can be associatively adsorbed on the tube surface without any energy barrier or it can be dissociated into –H and –SH species overcoming energy barrier of 4.03–7.77 kcal/mol. The associative adsorption is site selective so that the molecule is oriented in such a way that the sulfur atom was linked to an Mg atom. The HOMO–LUMO energy gap of the tube has slightly changed upon associative adsorption, while they were significantly influenced by dissociation process. Especially, the highest occupied molecular orbital of the tube shifts to higher energies which can facilitate electron emission current from the tube surface. Also, energy gap of the tube dramatically decreased by about 0.93–1.05 eV which influences the electrical conductivity of the tube.

Utilization of Third-Stage Waste from a Rice Production for Removal of H2S, NO2 and SO2 from Air

Materials derived from rice husk fly ash were tested as adsorbents of hydrogen sulphide, sulphur dioxide and nitrogen dioxide. Breakthrough experiments were carried out at ambient temperature either in dry or moist air. The second-stage waste obtained in the extraction of silica from fly ash using sodium hydroxide exhibits the better adsorption capacity compared with that of caustic-modified activated carbons. The high performance is related to the presence of residual sodium hydroxide and other metals such as calcium, which react with acidic gases forming corresponding salts. Moreover, a high dispersion of the alkali and alkaline earth metal sites in the mesopores renders the pH of the solution basic, aiding in the dissociation of hydrogen sulphide, thereby facilitating its oxidation. The oxidation of species is also catalyzed by the carbonaceous surface. While in the case of hydrogen sulphide and sulphur dioxide, water helps in acid-base reactions, the opposite effect is found for NO2. Because its react...

Plasma assisted dissociation of hydrogen sulfide

Dissociation of hydrogen sulfide has been studied in four different discharges: AC corona, dielectric barrier, streamer, and contracted glow discharge. All experiments were done in a single geometry, close to a plug flow reactor, with the goal of fair comparison. The performance of corona discharge and DBD was studied in the initial gas temperature range of 300–1200 K. A specific energy requirement (SER) was calculated as function of energy input for each type of discharge and compared with earlier experimental results and modeling. The results showed that discharges with high E/n and low specific energy input (corona, DBD, and streamer) perform much worse than those with low E/n (contracted glow discharge) where specific energy input was high and gas temperature was elevated. The SER for non-thermal dissociation was 12–14 eV/molec. However, in the case of the contracted glow discharge, SER decreased to 2.4 eV/molec. This SER is close to the value predicted by thermodynamic equilibrium modeling. Further reduction of SER in a plug flow reactor does not seem possible.

Role of Microporosity and Nitrogen Functionality on the Surface of Activated Carbon in the Process of Desulfurization of Digester Gas

Microporous coconut-shell based activated carbon was modified by heating with urea or melamine at 450 and 950 °C. The materials were characterized using adsorption of nitrogen, thermal analysis, elemental analysis, and potentiometric titration to obtain detailed information about surface chemistry and texture. Then they were used as adsorbents of hydrogen sulfide from digester gas where CO2 and CH4 are present in predominant quantities. The experiments were run in dry conditions and with preadsorbed water on the surface. The results revealed the importance of water, which, by its adsorption in small pores, eliminated the adsorption of methane, and thus caused the accessibility of adsorption centers for H2S. That water also helps in H2S dissociation. The introduction of nitrogen groups, which provide basicity needed for hydrogen sulfide dissociation, enhanced significantly the removal process. Since oxygen is not supplied to the system and only that oxygen which is chemisorbed on the surface can be used, elemental sulfur is a predominant product of surface reaction. The importance of nitrogen is in providing basicity, which is not deactivated by the presence of CO2 in the challenge gas.

Density functional theory study of hydrogen sulfide dissociation on bi-metallic Ni–Mo catalysts

This work presents results on the dissociation of H 2S over Ni–Mo catalysts suggesting that the presence of surface Mo-atom(s) has a significant impact on both the energetics of the process and the reaction mechanism. The presence of one Mo atom provides an additional energetic advantage of 10.2 kcal/mol overall. While increasing the energetic advantage of the process, the presence of Mo atom also increases the activation barriers by at most 3 kcal/mol. The large exothermic nature of this process combined with the comparatively small activation barriers suggests that the H 2S dissociation process is a facile process on all of the surfaces studied here. Additionally, analysis was provided to explain the difference in catalytic behavior between a bi-metallic alloy and a bi-metallic sulfide. It was determined that the bi-metallic alloy binds sulfur strongly (>100 kcal/mol) which can be compared with the results of Sun and co-workers [M. Sun, A.E. Nelson, J. Adjaye, Catal. Today 105 (2005) 36] who predict that S adsorption on the metal sulfide phase is not energetically favorable. It is suggested that the sulfide surface does not bind S in an energetically favorable manner because the sulfide surface structure does not possess a binding site that can emulate the hollow site on a metal surface.