Efficient catalytic elimination of COS and H2S by developing ordered mesoporous carbons with versatile base N sites via a calcination induced self-assembly route

N-doped Porous Carbon Derived from the Pyrolysis of a Polydopamine-coated Hypercross-linked Polymer for Enhanced CO2 Adsorption

Porous carbon materials can simultaneously capture and convert carbon dioxide, helping to reduce greenhouse gas emissions and using carbon dioxide as a feedstock for the production of valuable chemicals or fuel. In this work, a series of N-doped porous carbons (PDA@HCP(x:y)-T) was prepared; the CO2 adsorption capacity of the prepared PDA@HCP(x:y)-T was enhanced by coating polydopamine (PDA) on a hypercross-linked polymer (HCP) and then adjusting the mass ratio of PDA to HCP and the carbonization temperature. The results showed that the prepared PDA@HCP(1 : 1)-850 exhibited a high CO2 adsorption capacity due to abundant micropores (0.6762 cm3/g), a high specific surface area (1220.8 m2/g), and moderate surface nitrogen content (2.75 %). Notably, PDA@HCP(1 : 1)-850 exhibited the highest CO2 uptake of 6.46 mmol/g at 0 °C and 101 kPa. Critically, these N-doped porous carbons can also be used as catalysts for the reaction of CO2 with epichlorohydrin to form chloropropylene carbonate, with chloropropylene carbonate yielding up to 64 % and selectivity of the reaction reaching 94 %. As a result, these N-doped porous carbons could serve as potential candidates for CO2 capture and conversion due to their high reactivity, excellent CO2 uptake, and good catalytic performance.

Sabatier Optimal of Mn-N4 Single Atom Catalysts for Selective Oxidative Desulfurization

Understanding the relationship of competitive adsorption between reactants is the prerequisite for high activity and selectivity in heterogeneous catalysis, especially the difference between the adsorption energies (Eads) of two reactive intermediates in Langmuir-Hinshelwood (L-H) models. Using oxidative dehydrogenation of hydrogen sulfide (H2S-ODH) as a probe, we develop various metal single atoms on nitrogen-doped carbon (M-NDC) catalysts for controlling Eads-H2S, Eads-O2 and investigating the difference in activity and selectivity. Combining theoretical and experimental results, a Sabatier relationship between the catalytic performance and Eads-O2/Eads-H2S emerges. Mn-NDC as the optimal catalyst shows excellent H2S conversion (>90 %) and sulfur selectivity (>90 %) in a wide range of O2 concentrations over 100 h. Such a high-efficiency performance is attributed to appropriate Eads-H2S and Eads-O2 on Mn-N4 sites, boosting redox cycle between Mn2+ and Mn3+, as well as preferential formation of sulfur. This work provides a fundamental guidance for designing Sabatier optimal catalysts in L-H models.

Deep Removal of COS and Hg0 by Carbon Aerogel in Natural Gas: Good Antipoisoning Properties as well as Synergy Effect at Low Temperatures on 0.9PPD-Cu/CA Adsorbent

A collaborative COS conversion of Hg0 in natural gas on the nitrogen-doped and copper oxide-supported carbon aerogel (0.9PPD-Cu/CA), which is synthesized by the p-phenylenediamine sources and carbon source of sodium alginate, was proposed to overcome the easy deactivation of the catalyst, high reaction temperature, and limited lifespan. At 40 °C, the 0.9PPD-Cu/CA presented a 100% COS conversion efficiency in the presence of H2O; meanwhile, the N doping realized the enhancement of basic density, leading to an improved COS conversion, and the intermediates H2S in the reaction were wholly adsorbed, implying that 0.9PPD-Cu/CA was a bifunctional carbon material. Furthermore, the Hg0 addition achieved a synergistic performance as well as higher COS yield and a significant lifetime period, in which the sulfur immediate could have a high reactive activity for Hg0 and the sulfate proportion would be alleviated as well. Subsequently, the catalyst poisoning would be alleviated after the protection of the collaborative process by strengthening the electron transfer, consuming the sulfur-based products, and accelerating the cleavage of the H-S bond. Finally, the synergetic mechanism on COS and Hg0 on 0.9PPD-Cu/CA was concluded according to the experimental results and sample analysis. Additionally, the effects of space velocity and the regeneration performance were explored.

Triple Templates Directed Synthesis of Nitrogen-Doped Hierarchically Porous Carbons from Pyridine Rich Monomer as Efficient and Reversible SO2 Adsorbents

Herein, a variety of 2,6-diaminopyridine (DAP) derived nitrogen-doped hierarchically porous carbon (DAP-NHPC-T) prepared from carbonization-induced structure transformation of DAP-Zn-SiO2-P123 nanocomposites are reported, which are facilely prepared from solvent-free co-assembly of block copolymer templates P123 with pyridine-rich monomer of DAP, Zn(NO3)2 and tetramethoxysilane. In the pyrolysis process, P123 and SiO2 templates promote the formation of mesoporous and supermicroporous structures in the DAP-NHPC-T, while high-temperature volatilization of Zn contributed to generation of micropores. The DAP-NHPC-T possess large BET surface areas (≈956-1126 m2 g-1), hierarchical porosity with micro-supermicro-mesoporous feature and high nitrogen contents (≈10.44-5.99 at%) with tunable density of pyridine-based nitrogen sites (≈5.99-3.32 at%), exhibiting good accessibility and reinforced interaction with SO2. Consequently, the DAP-NHPC-T show high SO2 capacity (14.7 mmol g-1, 25 °C and 1.0 bar) and SO2/CO2/N2 IAST selectivities, extraordinary dynamic breakthrough separation efficiency and cycling stability, far beyond any other reported nitrogen-doped metal-free carbon. As verified by in situ spectroscopy and theoretical calculations, the pyridine-based nitrogen sites of the DAP-NHPC-T boost SO2 adsorption via the unique charge transfer, the adsorption mechanism and reaction model have been finally clarified.

Preparation of red mud-modified sludge char through microwave-assisted one-step pyrolysis and steam activation and its adsorption properties for hydrogen sulfide

To improve the hydrogen sulfide (H2S) adsorption performance of sludge-derived char, a type of red mud-modified sludge char (RSC) was prepared through microwave-assisted one-step pyrolysis and steam activation of sludge and red mud (RM). The effects of pyrolysis temperature, RM mass percentage, and steam flow rate on the cumulative adsorption capacity of H2S were systematically investigated using response surface method. The results indicated that the sludge char showed a significant increase in cumulative adsorption capacity from 1.47 mg/g to 22.83 mg/g when it was modified with RM at a pyrolysis temperature of 625 °C, a mass percentage of RM of 20%, and a steam flow rate of 0.46 mmol/min. The XRD and XPS analysis results indicated that the RM doping generated abundant iron oxides on the surface of RSC, which is beneficial for the adsorption of H2S. Adsorption thermodynamics, isotherm fitting and thermodynamic calculations indicate that the adsorption mechanism of H2S on the RSC surface was attributed to the combined effects of physisorption and chemisorption. Additionally, the material exhibited reliable reusability, retaining more than 80% of its initial breakthrough capacity after three adsorption-regeneration cycles. Therefore, the RSC prepared in this study can be regarded as a promising adsorbent due to its low cost, effective adsorption capabilities, and reusability. The developed method is promising as it achieves environmental remediation through the utilization of waste sludge and RM.

Research progress on adsorption and separation of carbonyl sulfide in blast furnace gas

The iron and steel industry is one of the foundational industries in China. However, with the introduction of energy-saving and emission reduction policies, desulfurization of blast furnace gas (BFG) is also necessary for further sulfur control in the iron and steel industry. Carbonyl sulfide (COS) has become a significant and difficult issue in the BFG treatment due to its unique physical and chemical properties. The sources of COS in BFG are reviewed, and the commonly used removal methods for COS are summarized, including the types of adsorbents commonly used in adsorption methods and the adsorption mechanism of COS. The adsorption method is simple in operation, economical, and rich in types of adsorbents and has become a major focus of current research. At the same time, commonly used adsorbent materials such as activated carbon, molecular sieves, metal-organic frameworks (MOFs), and layered hydroxide adsorbents (LDHs) are introduced. The three mechanisms of adsorption including π-complexation, acid-base interaction, and metal-sulfur interaction provide useful information for the subsequent development of BFG desulfurization technology.

Carbonyl sulfur removal from blast furnace gas: Recent progress, application status and future development

Carbonyl sulfide (COS), a poisonous and harmful gas, is found in industrial gas products from various coal-firing processes. The emission of COS into the atmosphere contributes to aerosol particles that affect the global climate, posing a risk to climate change and population health. In recent years, the total amount of anthropogenic COS emissions has increased significantly, resulting in the prominent COS pollution problem and becoming a vital environmental issue. This review summarizes the research progress of removing COS from industrial gases. According to the characteristics of different industrial gas products, the COS removal mechanism and influence factors, as well as the advantages and disadvantages for various methods, are discussed, including oxidation, absorption/adsorption, hydrogenation, and hydrolysis. Although COS emission control technologies have attracted widespread attention, the progress of application in blast furnace gas purification has been extremely slow, insufficient and sporadic. To fill the gap, this work provides a timely review on blast furnace gas characteristics and application process of various methods for removing COS from blast furnace gas with varying compositions, and their challenges and future development. This work aims to provide guidance on how effective processes and techniques for removal of COS from blast furnace gas can be developed. This review emphasizes the desirability of direct COS removal from blast furnace gas compared to expensive terminal desulfurization technologies. Furthermore, the development of a new process for low-temperature COS removal from blast furnace gas based on a dual-functional catalyst of hydrolysis/adsorption is advocated.

Engineering of crystal phase over porous MnO2 with 3D morphology for highly efficient elimination of H2S

In the present work, we report a facile oxalate-derived hydrothermal method to fabricate α-, β- and δ-MnO₂ catalysts with hierarchically porous structure and study the phase-dependent behavior for selective oxidation of H₂S over MnO₂ catalysts. It was disclosed that the oxygen vacancy, reducibility and acid property of MnO₂ are essentially determined by the crystalline phase. Systematic experiments demonstrate that δ-MnO₂ is superior in active oxygen species, activation energy and H₂S adsorption capacity among the prepared catalysts. As a consequence, δ-MnO₂ nanosphere with a hierarchically porous structure shows high activity and stability with almost 100% H₂S conversion and sulfur selectivity at 210 °C, better than majority of reported Mn-based materials. Meanwhile, hierarchically porous structure of δ-MnO₂ nanosphere alleviates the generation of by-product SO₂ and sulfate, promoting the adoptability of Mn-based catalysts in industrial applications.

A regenerable N-rich hierarchical porous carbon synthesized from waste biomass for H2S removal at room temperature

In this study, N-rich hierarchical porous carbons (NPCs) were synthesized via one step strategy from cypress sawdust with carbon nitride (CN) loading and K₂CO₃ activation. NPCs exhibited excellent performance for H₂S removal with the sulfur capacity up to 426.2 mg/g at room temperature. It was much higher than 12.5 mg/g of porous carbon (PC) which was only activated by K₂CO₃. The NPCs with CN loading showed hierarchical porous structure with micropores and mesopores volume up to 0.434 and 0.597 cm³/g, respectively. Moreover, NPCs had high N contents (up to 12.37 wt%) and high relative contents of pyridinic N and pyrrolic N within 76.61-84.37%, which were identified as active sites for H₂S adsorption by density functional theory calculation, enhancing H₂S removal. The formation mechanism of NPCs was investigated by TG-FTIR, suggesting that CN pyrolysis result in hierarchical porous structure and rich N-containing functional groups by gradually releasing H₂O, CO₂ and NH₃. Moreover, the NPCs showed high regeneration ability, remaining 86.6% of the initial sulfur capacity after five regeneration cycles, and sulfur (S) was the main desulfurization product (H₂S + O₂ → S + H₂O). The results demonstrate that NPCs are promising catalysts to remove H₂S efficiently with low cost and high reusability.

N-doped honeycomb-like porous carbon derived from biomass as an efficient carbocatalyst for H2S selective oxidation

3D interconnected porous N-doped carbocatalyst derived from the waste air-laid paper plays as an efficient metal-free catalyst for H₂S removal in super-Claus reaction. The honeycomb-like porous nitrogen-doped carbons are fabricated through a facile impregnation of alkaline solution and NH₃ post-treatment method. The experiments prove that NH₃ post-treatment is an efficient way to improve the catalytic performance, which resulting in outstanding reactivity and stability with highest sulfur formation rate of 496.6 g_sulfurkg_cat.^-1 h^-1 and sulfur yield of 86.7 % in feed gas with high concentration (ca. 10,000 ppm) of H₂S for selective oxidation. Significantly, the optimized pyridinic-N content and defect degree endow the N-doped porous carbon (NPC700) with highest catalytic activity according to the Raman and XPS results. The high surface area and abundant porous structure also contribute to the high catalytic performance by increasing the exposure degree of active site and offering additional active surface. Based on the XPS, SEM, TEM and EDS mapping results, the N-doped porous carbon are proved to be stable catalysts since the morphology and surface chemical environment remain similar after the oxidative desulfurization process.

Doping strategy, properties and application of heteroatom-doped ordered mesoporous carbon

To date, tremendous achievements have been made to produce ordered mesoporous carbon (OMC) with well-designed and controllable porous structure for catalysis, energy storage and conversion. However, OMC as electrode material suffers from poor hydrophilicity and weak electrical conductivity. Numerous attempts and much research interest have been devoted to dope different heteroatoms in OMC as the structure defects to enhance its performance, such as nitrogen, phosphorus, sulphur, boron, and multi heteroatoms. Unfortunately, the "how-why-what" question for the heteroatom-doped OMC has not been summarized in any published reports. Therefore, this review focuses on the functionalization strategies of heteroatoms in OMC and the corresponding process characteristics, including in situ method, post treatment method, and chemical vapor deposition. The fundamentally influencing mechanisms of various heteroatoms in electrochemical property and porous structure are summarized in detail. Furthermore, this review provides an updated summary about the applications of different heteroatom-doped OMC in supercapacitor, electrocatalysis, and ion battery during the last decade. Finally, the future challenges and research strategies for heteroatom-doped OMC are also proposed.

Enhanced electrocatalytic H2S splitting on a multiwalled carbon nanotubes-graphene oxide nanocomposite

A non-precious graphene oxide (GO) based oxidized multiwalled carbon nanotubes (MWCNTs) metal-free electrocatalytic system was fabricated using a chemical method and further used for the electrocatalytic oxidation of hydrogen sulphide (H2S) to hydrogen.

A solid thermal and fast synthesis of MgAl-hydrotalcite nanosheets and their applications in the catalytic elimination of carbonyl sulfide and hydrogen sulfide

MgAl hydrotalcites with high exposed OH⁻ sites were designed, and showed superior performance for the catalytic elimination of COS and H₂S.

Highly Active and Sulfur-Resistant Fe-N4 Sites in Porous Carbon Nitride for the Oxidation of H2 S into Elemental Sulfur

Iron-based catalysts have been widely studied for the oxidation of H₂ S into elemental S. However, the prevention of iron sites from deactivation remains a big challenge. Herein, a facile copolymerization strategy is proposed for the construction of isolated Fe sites confined in polymeric carbon nitride (CN) (Fe-CNNχ). The as-prepared Fe-CNNχ catalysts possess unique 2D structure as well as electronic property, resulting in enlarged exposure of active sites and enhancement of redox performance. Combining systematic characterizations with density functional theory calculation, it is disclosed that the isolated Fe atoms prefer to occupy four-coordinate doping configurations (Fe-N₄ ). Such Fe-N₄ centers favor the adsorption and activation of O₂ and H₂ S. As a consequence, Fe-CNNχ exhibit excellent catalytic activity for the catalytic oxidation of H₂ S to S. More importantly, the Fe-CNNχ catalysts are resistant to water and sulfur poisoning, exhibiting outstanding catalytic stability (over 270 h of continuous operation), better than most of the reported catalysts.