Dissociation Of H2S Research Articles

Sulfur modified N-doped carbocatalysts promote the selectivity for H2S selective oxidation

Sulfur element is widely applied as a non-metallic dopant into carbon framework for the modulation of their chemical activities. An interesting question is whether the intrinsic catalytic performances for the H2S selective oxidation to sulfur can be manipulated by sulfur element introduction into carbocatalysts. In this study, we employ a simple solvent-free method to introduce S atoms into framework of N-doped carbocatalysts, resulting in a notable enhancement of the product S selectivity with negligible loss of H2S selective oxidation. The experimental results show that the as-synthesized N-S-C-2 catalyst exhibits a H2S conversion of 97.5 % and sulfur selectivity of >80 % at a high O2-to-H2S ratio (2.5) under continuous mode (over the dew point temperature of sulfur, c.a. 210 °C), while also demonstrating robust stability (> 100 h), anti-CO2 (up to 50 vol%) and anti-oxidation properties. Kinetic analysis and H2S/O2-TPD-MS results reveal that S introduction attenuates the adsorption and dissociation of H2S and O2 by the N-doped carbon catalyst. Furthermore, density functional theory calculations elucidate that S doping elevates the adsorption energies of H2S and O2 at the pyridinic N site, thereby moderately reducing the adsorption of H2S and O2, consequently preventing the over-oxidation of H2S to SO2 and enhancing S selectivity. The double doping promotion effect of carbon materials reported in this investigation offers an alternative insight for the development of highly selective carbon desulfurization catalysts.

Designing sulfide catalysts for H2S dissociation to H2 based on reaction descriptors and microkinetics

Molybdenum disulfide (MoS2) is a promising catalyst for the challenging transformation of hydrogen sulfide (H2S) into sulfur and hydrogen (H2). However, a detailed understanding of its structure-function correlation still needs to be provided. We used density functional theory calculations to extract relevant reaction indexes (binding energies and free energy barriers) over different MoS2 surfaces. We used these indexes as inspiration in developing new catalysts and a microkinetic model to compare the results, extracting insights into the reaction mechanisms and surface coverages. The turnover frequencies obtained experimentally and through microkinetic modeling are analogous, validating our approach. The findings pave the way for developing more efficient H2S decomposition catalysts and establish a descriptor-based design for other metal sulfide catalysts.

Modeling and simulation of a novel chemical process for clean hydrogen and power generation

The present work aims to develop a novel chemical process for clean hydrogen and power production and simulate it accordingly through a unique thermodynamic equilibrium model. This particular process is based on a partial oxidation of hydrogen sulfide (H2S) at superadiabatic conditions to study its respective chemical products. The simulation of superadiabatic partial oxidation of H2S is developed through the present model for the first time in the Aspen Plus. The process is further studied by varying different operating variables with an overall goal of optimizing the H2S conversion into hydrogen. The developed model predicts a satisfactory H2 production flow rate coupled with a low-sulfur dioxide (SO2) output within the superadiabatic partial oxidation regime at an operating pressure below 0.5 bar. The H2S conversion into H2 is then found to be 23.48 % at 0.25 bar. The overall energy and exergy efficiencies of the system are found to be 87.51 % and 70.08 % respectively. The dissociation of H2S in the presence of stoichiometric air results in elemental sulfur and hydrogen production rates of 0.0019 kg/s and 0.0012 kg/s, respectively.

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.

A density functional theory research on the interaction of H2X molecules with the Al2C nanosheet (X = O, S, Se, Te)

The potential application of the 2D material Al2C, as catalysts and as sensor of the hazardous molecules H2S, H2Se and H2Te, is studied using theoretical methods. Density functional theory (DFT) has been applied to study the interaction between the pristine Al2C nanosheet and small molecules, such as H2O, H2S, H2Se and H2Te. Results show the Al2C nanosheet is a promising material to dissociate the studied molecules as well as its potential use as sensor of these molecules in molecular or dissociated state. Molecular interactions are weak even considering the London dispersion forces. Partial dissociative adsorption is strongly preferred to molecular adsorption for all four molecules. Applying the climbing image NEB method, the activation energy for H2O dissociation to OH-H is calculated in ≈ 0.1 eV whereas it is just a few meV for H2S, H2Se and H2Te partial dissociation. The calculated energy gap for the clean Al2C nanosheet is 1.078 eV whereas it is increased to 1.371, 1.338, 1.379 and 1.416 eV for molecular adsorption and to 1.209, 1.363, 1.370 and 1.388 eV for partial dissociative adsorption.

Oxygen-containing functional groups of activated carbon fibers as efficient oxygen transfer channels for H2S catalytic oxidation at room temperature

Activated carbon fibers (ACFs) with different activation degrees were developed by KOH activation method. And then, series of Na2CO3 loaded ACF catalysts were prepared and tested for H2S catalytic oxidation at room temperature. Among them, Na/ACF-8 presented the highest saturation sulfur capacity (1.22 gH2S/g). Importantly, it was found that COOH, COC/COH and COOCO were the main active oxygen species, and acted as oxygen transfer channels during the reaction. The reaction process mainly involved the dissociation of H2S, the reaction of HS− with C-O bond containing groups to form C-S bonds and sulfur-containing products. Moreover, the oxygen-containing functional groups were just responsible for water generation and the superoxide radical (O2•−) was responsible for SS bond oxidation. The O2•− was activated by ring carbon defects for Na/ACF-6 and Na/ACF-8 catalysts. And the ring carbon defects and ultramicropores were jointly responsible for the activation of O2•− for Na/ACF-2 and Na/ACF-4 catalysts.

Ca-Cu/Al2O3 catalysts for H2S removal at near ambient temperature: Synthesis, characterization, DFT calculation, and mechanistic insights

A series of Ca-doped CuxO/Al2O3 catalysts were developed using the excessive impregnation method for H2S catalytic oxidation at near-ambient temperatures. Ca(NO3)-CuxO/Al2O3 catalyst with 2.5 wt% Ca exhibited optimal H2S desulfurization performance at 60 °C and RH 60%, achieving an H2S removal capacity of 401.34 mg/g. Experimental, characterization, and DFT calculation results demonstrate that during the catalytic oxidation of H2S, H2O can be catalytically convert into ·OH while simultaneously capturing and dissociating H2S. The ·OH and NO3- then catalyze the oxidation of HS-/S2- to elemental S. Moreover, the redundant OH adsorbed on the basic sites can buffer the pH and promote the dissociation of H2S. The above cyclic process could alleviate the deactivation of the Ca-Cu/Al2O3 catalyst. Therefore, a ·OH-induced desulfurization mechanism assisted with Ca2+ buffer the pH and NO3- cyclic oxidation of H2S has been proposed. This work contributes to the preparation of high-capacity mental-based catalysts for H2S oxidation.

Preparation of nitrogen-doped activated carbon used for catalytic oxidation removal of H2S

In this study, nitrogen-doped modified activated carbons were synthesized for H2S removal from Zhuxi activated carbon and 4,4′-bipyridine as raw material and nitrogen source, respectively. The synthesis strategy was hydrothermal treatment and subsequent NH3 annealing, and the formation and conversion patterns of the different N configurations were investigated. When the annealing temperatures were 500 °C and 600 °C, N-5 account for the majority. As the annealing temperature increased, the proportion of N-6 gradually increased. After the temperature increased to 1000 °C, N-5 and N-6 were converted to N-Q to a certain degree, while the amount of nitrogen doping decreased significantly. The sample H160-0.2-800 exhibited excellent H2S removal with a high sulfur capacity of up to 206.89 mg/g, significantly higher than that of the original activated carbon ZX1200 (67.56 mg/g). The reason for this is that the micropores (Vmic = 0.5155 cm3/g) and specific surface area (SBET = 1369.5 m2/g) of the modified activated carbon are more developed than those of the original activated carbon. A high nitrogen content (3.14 wt%) and N-6 configuration proportion (73.56 %) are significant reasons for the excellent adsorption properties. The mechanism of the catalytic oxidation was investigated. The introduction of surface nitrogen-containing functional groups alkalizes the activated carbon surface, enhancing the adsorption and dissociation of H2S and O2 and facilitating the formation of sulfur radicals and elemental sulfur.

First-principles study of H2S adsorption and dissociation on the Ni(111) and Cl-covered Ni(111) surfaces

This article is based on density functional theory to calculate and study the adsorption and dissociation of H2S on Ni(111) and Cl-covered Ni(111) surfaces. The calculation results show that H2S is stably adsorbed at the Top site on both surfaces. There is a certain repulsive effect between Cl and H2S, which leads to a decrease in the adsorption strength of H2S. The dissociation energy barriers of the first step for H2S are higher than those of the second step on both surfaces, indicating that the first step of dissociation is the rate-determining step. In the presence of Cl, the energy barrier for the first step of H2S dissociation decreases from 0.27 eV to 0.19 eV, while the energy barrier for the second step of H2S dissociation increases from 0.01 eV to 0.11 eV. This means that the presence of Cl accelerates the first step of H2S dissociation and hinders the second step. The increase energy barrier for the second step of H2S dissociation implies greater difficulty in breaking the SH bond during this step, so the presence of Cl can inhibit the breaking of the SH bond in the second step. Additionally, the decomposition of H2S on both Ni(111) and Cl-covered Ni(111) surfaces is an exothermic process and a spontaneous one.

Experimental study and DFT calculation of the role of Cu loaded on activated carbon in desulfurization under dry and moist atmospheres

The reactive adsorption of H2S under different atmospheres is of great significance to protect the staff on site from exposure risks of polluted gases. The Cu0-loaded activated carbon (AC@Cu0) adsorbent was synthesized and characterized, which was used to dynamic adsorption of H2S under ambient temperature and different relative humidity (RH). When RH was 60%, the highest adsorption capacity reached 77.7 mg/g. The desulfurization products comprised element sulfur, sulfide and sulfate by the catalytic oxidation and reactive adsorption of AC@Cu0. In addition to the chemical nature of AC@Cu0, the structural properties (surface area and pore volume) also play a crucial role in adsorption. DFT calculations were used to reveal the effect of Cu and H2O in the desulfurization process. The adsorption energy of H2S on activated carbon was improved, and the energy barrier of the dissociation of H2S was decreased when Cu was introduced under the moist atmosphere. Density of states and the interaction region indicator (IRI) analyses indicated that the strong attractive force was formed between Cu and S. According to the results of DFT calculations, the presence of Cu and H2O could promote the adsorption of H2S. Combined with the experimental and calculation results, possible desulfurization mechanisms were proposed, which provides novel insights for the efficient removal of H2S by adsorptive desulfurization, especially under moist conditions.

The effect of coordination states of cobalt on Co-Nx co-doped graphene for selective oxidation of H2S: A DFT study

The transition metal coordinated with nitrogen atoms doped carbon catalysts shows great potential on H2S selective oxidation into elemental sulfur. Herein, we conducted CoN3 and CoN4 co-doped graphene as model materials to elucidate the regulating effect of coordination environment of Co atom on the catalytic performance by Density Functional Theory (DFT) methods. The adsorption behavior, dissociation, oxidation by atomic O and O2 have been studied in detail. The CoN3 doped graphene (PG-Co-N3) exhibits stronger affinity towards both H2S and O2 molecules with adsorption energy of −0.774 eV and −2.385 eV than CoN4 doped graphene (PG-Co-N4) (−0.426 eV, −0.690 eV). Among three possible reaction routes, the oxidation by atomic O is the most favorable reaction pathway on both PG-Co-N3 and PG-Co-N4 surfaces. In other two routes, H2S dissociation with or without O2 assisting on PG-Co-N3 demonstrates lower reaction energy barrier of the rate determining steps than on PG-Co-N4. These results could provide a new strategy to design novel catalysts for H2S selective oxidation, and reveal the effect of coordination environment of transition metal and nitrogen co-doped graphene on the mechanism of oxidation process.

Towards highly exposed active sites via Edge-N-rich carbon nanosheet @ porous biochar for efficient H2S catalytic oxidation

In this study, Edge-N-rich carbon nanosheet @ porous biochar (NCN@PB) was synthesized successfully from waste biomass self-assembly in a simple and green approach. The accessible and efficient utilization of edge-N enriched on the surface, together with the hybrid structure of NCN@PB improved the H2S oxidation capacity up to 390.1 mg/g at room temperature, reflecting an 8-fold enhancement compared with the blank biochar. The Density functional theory calculation, in-situ DRIFTS, and the characterization results further uncovered the desulfurization mechanism of active sites. Edge-N species decreased the barriers in critical steps governing H2S catalytic oxidation, i.e., H2S dissociation and O2 activation, especially the pyrrolic N. This strategy is beneficial for the development of surface engineering on metal-free catalysts and provides a new idea for improving the catalytic combustion activity of N-doped biochar.

Enhancing the reactivity of clean, defect-free epitaxial graphene by the substrate—Experiment and theory

Experimental and theoretical evidence is presented that a sulfur compound dissociates on clean, defect-free epitaxial graphene (Gr) in ultrahigh vacuum (UHV). Together with density functional theory calculations (DFT), experimental kinetics and spectroscopic data suggest an auto-(/self)catalytic process. The results could open a pathway to a carbocatalyst. While adsorbing H2S in UHV at low temperatures on single-layer graphene/ruthenium (Gr/Ru), H2 desorbs and sulfur remains on the surface. Vacancy and grain boundary defects, respectively, can be excluded as active sites. DFT results indicate the importance of the Ru(0001) support in facilitating a reaction pathway with small activation energy for H2S dissociation. Gr becomes reactive due to a complex interplay of structural and electronic effects, including the corrugation of the graphene layer and the hybridization of ruthenium's d orbital with antibonding states of H2S.

Highly Dispersed FeAg-MCM41 Catalyst for Medium-Temperature Hydrogen Sulfide Oxidation in Coke Oven Gas.

The traditional hydrolysis-cooling-adsorption process for coke oven gas (COG) desulfurization urgently needs to be improved because of its complex nature and high energy consumption. One promising alternative for replacing the last two steps is selective catalytic oxidation. However, most catalysts used in selective catalytic oxidation require a high temperature to achieve effective desulfurization. Herein, a robust 30Fe-MCM41 catalyst is developed for direct desulfurization at medium temperatures after hydrolysis. This catalyst exhibits excellent stability for over 300 h and a high breakthrough sulfur capacity (2327.6 mgS gcat-1). Introducing Ag into the 30Fe-MCM41 (30Fe5Ag-MCM41) catalyst further enhances the H2S removal efficiency and sulfur selectivity at 120 °C. Its outstanding performance can be attributed to the synergistic effect of Fe-Ag clusters. During H2S selective oxidation, Fe serves as the active site for H2S adsorption and dissociation, while Ag functions as the catalyst promoter, increasing Fe dispersion, reducing the oxidation capacity of the catalyst, improving the desorption capacity of sulfur, and facilitating the reaction between active oxygen species and [HS]. This process provides a potential route for enhancing COG desulfurization.

Nickel-doped CuxO/Al2O3 catalyzes oxidation of H2S at near ambient temperature: Performance evaluation and mechanism exploration

A series of Ni-doped CuxO/Al2O3 catalysts were developed for catalytic oxidation of H2S, and catalytic conditions of Ni content, temperature and humidity were optimized by measuring H2S performance. The surface of the catalyst doped with Ni (2.5 wt%) exhibited three-dimensional (3D) nano-network structure, largest number of basic sites and oxygen vacancies (VOs). Ni-Cu synergistic effect improved desulfurization capacity of H2S by catalysts at near ambient temperature. 3D nano-network structure provided more sulfur storage space. Basic sites from NiO and VOs from CuxO effectively enhanced catalyst-H2S interaction by hydroxylating H2O, thus promoting dissociation and oxidation of H2S, eventually resulting in a high desulfurization capacity (334.3 mg/g). Desulfurization reaction product was mainly S (91.0%), and by-products were mainly sulfate and CuS. Additionally, our synthesized catalyst can realize sulfur recovery. Therefore, Ni-doped CuxO/Al2O3 is a promising H2S removal catalyst at low temperature.

Enriched oxygen vacancies of copper(I) oxide particles for enhanced removal of hydrogen sulfide at room temperature

In this work, the removal of hydrogen sulfide (H2S) by copper(I) oxide (Cu2O) and copper(II) oxide (CuO) particles synthesized by thermal decomposition (TD) and liquid reduction is investigated in a fixed-bed experiment at 25 °C and 1 atm. The surface oxygen vacancies (VOs) contents of the prepared Cu2O samples are more than twice that of the synthesized CuO particles, which are closely related to H2S removal performance. The H2S adsorption capacity of Cu2O prepared is 135.6 mg g−1, approximately 27 times that of CuO. A dense CuS layer formed on the CuO surface makes it significantly less reactive with H2S than Cu2O. Due to the crystal structure and abundant VOs on the Cu2O surface, the weak Cu–O bonds are broken during the sulfurization process, causing the rupture of the surface layer. And the sulfidation reaction gradually extends to the interior through the cracked surface layer, leading to the excellent sulfurization performance of Cu2O. The larger H2S adsorption capacity of Cu2O prepared by TD than that of Cu2O prepared by liquid reduction could be attributed to the presence of more numbers of VOs and Cu atoms on the surface. Moreover, H2O can enter VOs and promote the dissociation of H2S into S2−, thereby improving H2S adsorption capacity. This work demonstrates that Cu2O is a promising sorbent for H2S removal at room temperature.

One-step synthesis of flower-like MgO/Carbon materials for efficient H2S oxidation at room temperature

Regenerable materials with abundant basic sites and sulfur storage space are highly desirable for the removal of H2S. In this work, we synthesized a flower-like MgO/Carbon material by one-step carbonization of magnesium gluconate and applied it for H2S oxidation at room temperature. The results demonstrate that the high content of MgO and super-hydrophilic surface of the MgO/Carbon provide abundant basic sites for the adsorption and dissociation of H2S. Moreover, carbon defects and a well‐developed pore structure offer active sites for the desulfurization reaction and large space for storage of sulfur products. Consequently, the MgO/Carbon materials exhibit excellent H2S oxidation performance, which is far superior to that of commercial activated carbon. In addition, the MgO/Carbon materials show extraordinary regeneration capacity and maintain their high performance even after 5 cycles of desulfurization/regeneration. Furthermore, mechanisms for the H2S oxidation process, deactivation and regeneration are proposed based on the experimental and characterization results. Considering the simple preparation process, excellent desulfurization and regeneration performance of as-prepared MgO/Carbon material, our findings provide a new strategy for the design of efficient desulfurizers.

Solar Fuel Production from Hydrogen Sulfide: An Upstream Energy Perspective

Hydrogen sulfide is readily available in vast quantities in the subsurface as a byproduct of industrial processes. Hydrogen evolution from H2S can transform this highly toxic gas into a source of green fuel. Compared to water splitting, H2S dissociation is thermodynamically more favorable. However, feasible industrial‐scale catalytic technologies are not developed yet. The recovery of valuable chemicals using carbon‐neutral photocatalytic processes can capitalize on abundant solar irradiation and advanced semiconductors. The challenge is developing photocatalysts that can efficiently operate over the long term in the harsh environment of subsurface and industry, while utilizing as much of the light source spectrum as possible and providing optimum adsorption/desorption abilities of hydrogen and sulfur‐containing intermediates. Meeting these requirements demands improved kinematic models of photocatalytic H2S decomposition to assess the effect of high temperatures, pressures, mixtures of hydrocarbons, produced water, and other contaminants. Metal sulfides‐based catalysts may be the key to H2S decomposition in the subsurface (e.g., oil and gas reservoirs) and wellbores, but first they need to be upscaled as bulk, robust, and recyclable materials. This review presents a guide for the development of the upstream energy production technology via photocatalytic H2S conversion.

Sulfide (H2S) Corrosion Modeling of Cr-Doped Iron (Fe) Using a Molecular Modeling Approach.

This work presents the use of density functional theory to study the adsorption/dissociation mechanism of the H2S molecule at the Cr-doped iron (Fe(100)) surface. It is observed that H2S is weakly adsorbed on Cr-doped Fe; however, the dissociated products are strongly chemisorbed. The most feasible path for disassociation of HS is favorable at Fe compared to Cr-doped Fe. This study also shows that H2S dissociation is a kinetically facile process, and the hydrogen diffusion follows the tortuous path. This study helps better understand the sulfide corrosion mechanism and its impact, which would help design effective corrosion prevention coatings.

Experimental and theoretical insights into sulfur resistance of transition metal-doped Cu–Fe spinel during chemical looping combustion

A series of transition-metal doped Cu–Fe spinel oxygen carriers (M-CuFe2O4, M = Mn, Cr, Co and Ni) were synthesized and examined for their sulfur resistance by 500 ppm H2S in N2 atmosphere. The results showed that H2S vulcanized the M-CuFe2O4 surfaces and led to the generation of metal sulfide. The gaseous sulfur product was mainly SO2. The interaction between sulfur and CuFe2O4 was weakened when doping transition-metal into Fe site of CuFe2O4, especially Cr as dopant. The increase of temperature had an obvious impact on the reaction between H2S and the adsorbed oxygen species. Cr dopant reduced the enrichment of sulfur element on the surface, and it showed the weakest affinity towards sulfur because of the lowest orbital hybridization between S and Cr atom below the Fermi level. Moreover, the energies barriers of H2S dissociation over Cr–CuFe2O4 surface were obviously higher than those over CuFe2O4.