Dissociation Of H2S Research Articles

Insight into the adsorption and decomposition mechanism of H2S on clean and S-covered Au (1 0 0) surface: A theoretical study

Abstract Density functional theory (DFT) was employed to investigate the adsorption and decomposition of H2S on clean and S-covered Au (1 0 0) surface. Different kinds of possible modes of H2S, as well as HS, S and H adsorbed on both surfaces were considered. It was proposed that H2S prefers to adsorb on the top sites, HS and H adsorb preferentially on the bridge sites, while S atom is opt to occupy the hollow site. In addition, the optimum co-adsorption configurations for HS/H, H/S, H2S/S, HS/S, HS/HS and H/S/S were determined. It was revealed that the co-adsorbed species repel each other slightly on Au (1 0 0) surface and that co-adsorption tends to weaken the adsorbate–substrate interaction due to the presence of atomic sulfur. Finally, the pathways and transition states of H2S dissociation were also investigated. Through comparing the activation barrier on different surfaces, it was found that the presence of S atom can facilitate the first H S bond scission and go against the second dissociation of HS species. The distinct differences between Au (1 0 0) and Au (1 1 1) surface suggest that the decomposition of H2S over Au-based catalyst is a structure-sensitive reaction.

Decomposition of hydrogen sulfide (H2S) on Ni(100) and Ni3Al(100) surfaces from first-principles

Abstract Spin-polarized density functional theory studies of hydrogen sulfide (H2S) adsorption and decomposition on Ni(100) and Ni3Al(100) surfaces were conducted to understand the aluminum (Al) alloying effect on H2S dissociation. For such purpose, we first determined the near surface structure of fully ordered Ni3Al alloy along the [100] direction by calculating the Al segregation energy to the surface and then examined the adsorption energies of the adsorbates (H2S, HS, S, and H) and the activation barriers for the H2S and HS decomposition by using Climbing Image-Nudged Elastic Band method. We found that regardless of the way to terminate the surface, Al atom in bimetallic Ni3Al(100) tends to exist in the first surface layer, rather than in the second or third layer, and the Ni3Al(100) surface can substantially retard the H2S decomposition by reducing the adsorption energy of sulfur compounds compared to the pure Ni(100) case. Finally, we presented how the Al in Ni3Al modifies the activity of surface Ni atoms toward the sulfur compounds by calculating the local density of states and charge distribution in alloying components. This work hints the importance of knowing how to properly tailor the reactivity of Ni based materials to enhance the resistance for sulfur poisoning.

Thermodynamic Study of Hydrogen Sulfide Corrosion of Mild Steel

Expanding the basic knowledge required for improved understanding of hydrogen sulfide (H2S) corrosion of mild steel is needed. When it comes to even the most basic chemical descriptors of aqueous H2S systems such as H2S solubility, water chemistry, polymorphism of iron sulfide, the formation or dissolution of iron sulfide scale, and its protectiveness, many open questions persist and more investigation is required. Inconsistencies in prevailing expressions for H2S solubility constant (KH2S), the first dissociation constant (Ka,1), and the second dissociation constant (Ka,2) are reviewed here. By comparing with experimental data, the best prediction model for H2S solubility and dissociation in an H2S–H2O system was identified. Occurrence of iron sulfide polymorphs was experimentally investigated and it was found that, in short-term exposures, mackinawite formed at 25°C, while greigite and pyrite were detected at 60°C. The solubility limits for these iron sulfides were determined. Simplified Pourbaix diagra...

Effects of humidity, O2, and CO2 on H2S adsorption onto upgraded and KOH impregnated activated carbons

In the present work, low grade activated carbon was upgraded by steam activation to improve its surface properties and further impregnated with potassium hydroxide (KOH) to promote the H2S chemisorption for desulfurization applications. The H2S adsorption performance of these prepared samples was tested at ambient temperature under various operating conditions i.e. in the presence of isolated and integrated relative humidity (70%), O2 (2%), and CO2 (40%). It was found that the KOH impregnated activated carbons provide significantly higher H2S adsorption capacity and breakthrough time than the non-impregnated sample. Importantly, the presence of O2 in the gas stream greatly increases the breakthrough time of H2S adsorption, while the presence of humidity significantly increases the H2S adsorption capacity; these positive effects are related to the promotion of H2S oxidation to elemental sulfur and H2S dissociation. In contrast, the presence of CO2 strongly inhibited H2S adsorption due to competitive adsorption and reaction between CO2 and H2S, particularly for the KOH impregnated samples. Nevertheless, it was revealed from the study that the presence of O2 and humidity along with CO2 can efficiently minimize this negative effect; therefore, this highlights the importance of O2 and humidity addition for biogas purification.

Ab initio atomistic thermodynamics study on the sulfur tolerance mechanism of the oxygen-enriched yttria-stabilized zirconia surface

The first-principles method based on density functional theory (DFT) is used to investigate the reaction mechanism for the adsorption of H2S on the oxygen-enriched yttria-stabilized zirconia (YSZ+O) (111) surface. It is found that the H2S dissociation processes have low energy barriers (<0.5eV) and high exothermicities (2.5eV), and the dissociative S atoms may result in the poisoning of the YSZ+O surface by forming the SO and the hyposulfite (SO22−) species with very strong bonds to the surface. In addition, using the ab initio atomistic thermodynamics method, the surface regeneration or de-sulfurization process of a sulfur-poisoned (i.e. sulfur-covered) YSZ+O(111) surface is studied. According to the phase diagram, the adsorbed atomic sulfur can be oxidized to SO2 and removed from the YSZ+O surface by introducing oxidizing reagents, e.g. O2 and H2O.

Adsorption and dissociation of H2S on Mo(1 0 0) surface by first-principles study

Density-functional theory calculations had been used to investigate the adsorption and dissociation of H2S on Mo(100) surface. Adsorption mechanisms of H2S, HS, S and H on the Mo(100) surface were analyzed. H2S was found to be adsorbed at bridge, hollow and top sites with adsorption energies of −1.25, −1.03 and −0.92eV, respectively. HS was strongly chemically absorbed at hollow, bridge and top sites with adsorption energies of −4.51, −4.08 and −3.45eV, respectively, and sulfur and hydrogen preferred to be absorbed at hollow and bridge sites, respectively. In addition, potential energy profiles of H2S dissociation on Mo(100) had been constructed by a climbing image nudged elastic band method. Four possible dissociation pathways of the first H2S dehydrogenation were examined with reaction barriers of 0.28, 0.37, 0.075, and 0.21eV, respectively, while the energy barrier to break the SH bond of HS with or without hydrogen co-adsorption was almost the same low. This work showed that the decomposition of H2S on the molybdenum surface was kinetically and thermodynamically facile. Local densities of electronic states were further used to characterize the interaction between H2S and substrate.

Insight into the general rule for the activation of the X–H bonds (X = C, N, O, S) induced by chemisorbed oxygen atoms

Density functional theory calculations are presented for adsorption and dissociation of NH3, H2O, CH3OH, H2S and C2H4 on clean and oxygen atom pre-adsorbed metal surfaces (Cu, Ag, Au, Ni, Pd, Pt, Rh, Ru, Os and Ir). The calculation results indicated that the oxygen-promotion effect depends both on the metallic activity and the character of the X-H bond. On the one hand, for a given reaction on a series metals, a good linear correlation was found between the energy barrier difference of X-H bond breaking on clean and oxygen-covered metals and the binding strength of oxygen on metals, namely an oxygen-promotion effect was favorable to the less active metals but unfavorable to the more active metals. On the other hand, for a series of X-H bond breaking reactions on a given metal, it was found that the promotion effect follows the trend of O-H > N-H > C-H, that is, the O-H bond is most promoted by the oxygen atom. The possible reason is the O-H bond forms the strongest hydrogen bond in the transition state among the X-H bonds investigated in this work. Additionally, it was found that the oxygen coverage has little effect on the X-H bond scission.

The adsorption and dissociation of H2S on Cu(100) surface: A DTF study

Density functional theory was used to investigate the adsorption of H2S and H/HS, H/H/S on Cu(100). The pathways and transition states of H2S dissociation were also studied. Results show that H2S prefers the top site, while H, S and HS prefer the hollow site during the adsorption process. H2S, HS and S can chemisorb on Cu(100) through the SCu bond due to the hybridization of the s, p orbit of S and the d orbit of Cu. The order of the adsorption energy for three forms is as follows: H/H/S, H/HS and H2S. In addition, the dissociation of H2S molecule on Cu(100) is thought to be an exothermic process. The activation energy of the first and second SH bonds in H2S are low and similar (approximately 10.15kcal/mol). In the dissociation of H2S, Cu atoms attract electrons from HS bond which leads the bond-breaking.

Accurate prediction of H2S and CO2 containing sour gas hydrates formation conditions considering hydrolytic and hydrogen bonding association effects

An elegant thermodynamic model, considering the hydrogen bonding association effects in fluid phases by using cubic-plus-association equation of state (CPA EOS), electrostatic effects of hydrolytic dissociation of H2S and CO2 acidic gases according to the modified Pitzer–Debye–Hückle (PDH) model and an improved two step gas hydrate formation mechanism using Chen–Guo model is presented for accurate prediction of the pure and mixed sour gas hydrate formation conditions. The proposed CPA/Electrolyte/Chen–Guo model is quite reliable over wide ranges of temperatures, H2S and CO2 concentrations. The overall average absolute deviation between the predicted and measured sour gas hydrate equilibrium dissociation pressures regarding 149 data points comprising pure and multi-component sour gas mixtures, is about 3.32% which is considerably lower than the other thermodynamic models. The proposed model outperforms the other alternatives both in accuracy and generality and can be employed for accurate design of sour natural gas management and flow assurance systems and gas hydrate energy storage processes in oil and gas industries

Theoretical prediction of simultaneous removal efficiency of ZnO for H2S and Hg0 in coal gas

The simultaneous removal mechanisms of H2S and Hg0 on the perfect and oxygen-deficient ZnO (101¯0) surfaces are systematically investigated using periodic density functional theory (DFT) calculations. The most stable adsorption modes of Hg0 and HgS are located. It is determined that Hg0 is weakly adsorbed on the two ZnO (101¯0) surface, while HgS is strongly bound to the surface, which implies that the oxidized form of mercury is in favor of removing mercury from coal gas. For the reaction, the dissociation of H2S is occurred firstly, which is almost not affected by the adsorbed Hg atom on the ZnO (101¯0) surface comparing with that on the clean ZnO (101¯0) surface. The dissociated S easily captures Hg0 in gas or adsorbed on the perfect surface leading to the formation of HgS, which shows that the perfect ZnO (101¯0) surface is efficient to remove H2S and Hg0 in coal gas simultaneously and H2S is indispensable to remove Hg0. However, the activation energies of the formation of HgS on the oxygen-deficient ZnO (101¯0) surface are higher than that on the perfect surface. So the removal efficiency of Hg0 on the oxygen-deficient ZnO (101¯0) surface is lower than that on the perfect surface.

Can H2S poison the surface of yttria-stabilized zirconia?

The adsorption and dissociation of H2S on the yttria-stabilized zirconia (YSZ) (111) surface are studied using the first-principles methods. It is found that H2S and SH species are bound weakly on the YSZ(111) surface. Sulfur atom is essentially immobile both into the YSZ bulk and along the surface. Instead, it is stably anchored on the O atop of the YSZ surface with the formation of the SO2− fragment. The nudged elastic band (NEB) calculations show that the formation of SH from H2S (H2S → SH + H) is very easy, while the presence of a co-adsorbed H would inhibit the further dissociation of SH. In contrast, the hydrogenation of the adsorbed sulfur is rather easy. It is concluded that H could inhibit the formation of sulfur, thus the sulfur poisoning of the YSZ surface would be prevented by hydrogen.

Enhanced adsorption of hydrogen sulfide on mixed zinc/cobalt hydroxides: Effect of morphology and an increased number of surface hydroxyl groups

Mixed zinc and cobalt hydroxides were synthesized using a precipitation method and tested as adsorbents of hydrogen sulfide from either dry or moist air. The adsorption capacity increased with an increase in the content of cobalt in the structure of mixed hydroxides. The synergistic effect was demonstrated by a fourfold increase in the amount of hydrogen sulfide adsorbed on the surface of the best performing mixed hydroxide in comparison with the hypothetical mixture of the two hydroxides. The initial and exhausted materials were characterized by FTIR, thermal analysis, potentiometric titration, X-ray diffraction, SEM/EDX, and adsorption of nitrogen. The results obtained suggest that an increase in the content of cobalt results in an increase in amorphicity level and in an increase in the number of hydroxyl groups. These groups, besides providing higher basicity thereby increasing the extent of H2S dissociation in the presence of water, are the main active centers reacting with hydrogen sulfide. Defects in the structure and oxygen vacancies result in the oxidation of some H2S to sulfites and sulfates.

Kinetics of hydrogen sulfide decomposition in a DBD plasma reactor operated at high temperature

The present study investigates the kinetics of hydrogen sulfide (H2S) decomposition into hydrogen and sulfur carried out in a nonthermal plasma dielectric barrier discharge (NTP-DBD) reactor operated at ∼430 K for in situ removal of sulfur condensed inside the reactor walls. The dissociation of H2S was primarily initiated by the excitation of carrier gas (Ar) through electron collisions which appeared to be the rate determining step. The experiments were carried out with initial concentration of H2S varied between 5 and 25 vol% at 150 mL/min (at standard temperature and pressure) flow rate in the input power range of 0.5 to 2 W. The reaction rate model based on continuous stirred tank reactor (CSTR) model failed to explain the global kinetics of H2S decomposition, probably due to the multiple complex reactions involved in H2S decomposition, whereas Michaelis-Menten model was satisfactory. Typical results indicated that the reaction order approached zero with increasing inlet concentration.

ZnO Nanocluster as a Potential Catalyst for Dissociation of H2S Molecule

Adsorption of hydrogen sulfide (H2S) on the external and internal surface of Zn12O12 nanocluster was studied by using density functional calculations. The results indicate that the H2S molecule is physically adsorbed or chemically dissociated by the nanocluster. It was found that the H2S molecule can dissociate into –H and–SH fragments, suggesting that the nanocluster might be a potential catalyst for dissociation of the H2S molecule. Also, dissociation of H2S to S species in internal surface of the Zn12O12 nanocluster is energetically impossible. The HOMO–LUMO energy gap of H2S dissociation configuration is changed about 27.68 %, indicating that the electronic properties of the nanocluster by dissociation process have strongly changed.

Ag Supported Si-Doped Graphene for Hydrogen Sulphide Detection: A First-Principles Investigation

The adsorption of H2S molecule on Si-doped and Ag supported Si-doped graphene is studied by first-principles calculations. We find that the H2S floats on the Si-doped graphene sheet, indicating a weak physisorption. The calculated net charge transfer, charge density difference and density of states give evidence that the adsorption of H2S on Ag supported Si-doped graphene is by chemisorption. Moreover, the desorption and dissociation of H2S adsorbed on Ag supported Si-doped graphene occur at the external electric field of 1.4 and -0.8 V/Å, respectively. Therefore, the Ag supported Si-doped graphene can be expected to be a novel sensor for the detection of H2S gas.

Kinetics of the Decomposition of Hydrogen Sulfide in a Dielectric Barrier Discharge Reactor

AbstractKinetics of hydrogen sulfide (H2S) decomposition to hydrogen and sulfur was investigated in a nonthermal plasma dielectric barrier discharge (NTP‐DBD) reactor operated under ambient conditions. The reactions were carried out with a fixed flow rate and varying inlet concentration. The results indicated that the dissociation of H2S into H2 and S may be initiated by excitation of the carrier gas argon. A reaction rate model based on a Langmuir Hinshelwood/Michaelis‐Menten model was proposed. The formal reaction order approaches zero at high H2S concentrations. The parameters of the kinetic model were found to be dependent on the power input.

The adsorption and dissociation of H2S on the oxygen-deficient ZnO[formula omitted] surface: A density functional theory study

The adsorption and dissociation of H2S on the oxygen-deficient ZnO(101¯0) surface have been investigated by using the density functional theory (DFT) method with PW91 functional and DNP basis set. H2S is dissociatively adsorbed on the oxygen-deficient ZnO(101¯0) surface without an energy barrier, which is the first dehydrogenation step. The second dehydrogenation step takes place via H transferring from S in SH to the surface O atom forming OH group by overcoming an energy barrier of 22.69kJ·mol−1. Our results show that the adsorption of the dissociated S atom is more stable on the oxygen-deficient surface than on the perfect surface.

Influence of Step Defects on the H2S Splitting on Copper Surfaces from First-Principles Microkinetic Modeling

An atomic level insight into the chemistry of hydrogen sulfide (H2S) splitting by metallic copper (Cu) is a necessary prerequisite for understanding sulfur poisoning mechanism of Cu-based water–gas shift (WGS) catalysts. In the present work, we have combined periodic density functional theory predictions and a detailed microkinetic modeling of the H2S dissociation on the stepped-defect (211), (311), and regular (111) faces of Cu to define the effect of step defects upon the reaction. The results indicate that on each surface examined, the dissociative adsorption facilely leads to the formation of element sulfur (S) via a stepwise H–S bond cleavage mechanism, with the initial molecular adsorption of H2S preferred as the rate-limiting step. It has also been pointed out that the SH disproportionation reaction does not open an alternative path for surface atomic sulfur production under the studied reaction condition. These surfaces are all predicted to be significantly covered by the S species after sufficient exposure to a realistic environment containing only several ppm of H2S. Furthermore, it is confirmed that (i) the full decomposition process is structure sensitive, and (ii) the driving force behind the step-enhanced activity of Cu toward this reaction arises not from kinetic but from thermodynamic factors. More importantly, our calculations have demonstrated that the H2S tolerance of Cu steps (and other defects) for the WGS reaction is worsened by a factor of approximately 103 as compared to a perfectly regular surface. Because these deficient sites are known as the most active sites of Cu-based shift catalysts in the absence of sulfur-containing species, it appears to be impossible to improve their activity without a dramatic loss of sulfur resistance through simply tuning catalyst surface morphology.

DFT study on the sulfurization mechanism during the desulfurization of H2S on the ZnO desulfurizer

The sulfurization mechanism of H2S on the ZnO(101¯0) surface during the desulfurization of coal gas was investigated by using periodic density functional theory (DFT) calculations. The adsorption of H2S, SH, atomic S, and atomic H, as well as the coadsorption of SH and an H atom, and the coadsorption of S and two H atoms, were initially examined to identify energetically favorable intermediates. Potential energy profiles for three paths of H2S−ZnO(101¯0) interactions producing H2 and H2O were obtained, respectively. Our results show that H2S is preferred to dissociatively adsorb on the ZnO(101¯0) surface, followed by dehydrogenation process to form sulfur species. Molecular-level calculations demonstrate that H2O formation via the H2S−ZnO interaction is the most probable reaction pathway both kinetically and thermodynamically. ZnO has double functions during the desulfurization of H2S. One is as a catalyst to accelerate the dissociation of H2S, while the other is as the reactant participating in the reaction of H2S with ZnO to form H2O.

Density functional study of Hg adsorption mechanisms on α-Fe2O3 with H2S

First-principle calculations based on the density functional theory are performed to clarify the Hg0 adsorption reaction mechanism on an α-Fe2O3 surface with H2S in coal-utilizing facilities. Theoretical calculations based on the various adsorption mechanisms of H2S and Hg0 on α-Fe2O3 are performed to investigate a realistic reaction pathway. The results demonstrate that the Eley–Rideal mechanism with Hg0 adsorption on H2S/α-Fe2O3 surface is the most suitable reaction process, whereas the Mars–Maessen, Langmuir–Hinshelwood, and Eley–Rideal mechanisms with H2S adsorption on Hg0/α-Fe2O3 surface are not possible in real reaction mechanisms. In addition, the potential energy diagram of H2S dissociation on α-Fe2O3 surface is provided.