A critical review towards the causes of the iron-based catalysts deactivation mechanisms in the selective oxidation of hydrogen sulfide to elemental sulfur from biogas

Hydrogen sulfide(H_(2)S) not only presents significant environmental concerns but also induces severe corrosion in industrial equipment,even at low concentrations.Among various technologies,the selective oxidation of hydrogen sulfide(SOH_(2)S) to elemental sulfur(S) has emerged as a sustainable and environmentally friendly solution.Due to its unique properties,iron oxide has been extensively investigated as a catalyst for SOH_(2)S;however,rapid deactivation has remained a significant drawback.The causes of iron oxide-based catalysts deactivation mechanisms in SOH_(2)S,including sulfur or sulfate deposition,the transformation of iron species,sintering and excessive oxygen vacancy formation,and active site loss,are thoroughly examined in this review.By focusing on the deactivation mechanisms,this review aims to provide valuable insights into enhancing the stability and efficiency of iron-based catalysts for SOH_(2)S.

Review of Iron-Based Catalysts for Carbon Dioxide Fischer-Tropsch Synthesis

Capturing and utilizing CO_(2)from the production process is the key to solving the excessive CO_(2)emission problem. CO_(2)hydrogenation with green hydrogen to produce olefins is an effective and promising way to utilize CO_(2)and produce valuable chemicals. The olefins can be produced by CO_(2)hydrogenation through two routes, i.e., CO_(2)-FTS (carbon dioxide Fischer- Tropsch synthesis) and MeOH (methanol-mediated), among which CO_(2)-FTS has significant advantages over MeOH in practical applications due to its relatively high CO_(2)conversion and low energy consumption potentials. However, the CO_(2)-FTS faces challenges of difficult CO_(2)activation and low olefins selectivity. Iron-based catalysts are promising for CO_(2)-FTS due to their dual functionality of catalyzing RWGS and CO-FTS reactions. This review summarizes the recent progress on iron-based catalysts for CO_(2)hydrogenation via the FTS route and analyzes the catalyst optimization from the perspectives of additives, active sites, and reaction mechanisms. Furthermore, we also outline principles and challenges for rational design of high-performance CO_(2)-FTS catalysts.

Effect of Al_2O_3 Binder on the Precipitated Iron-Based Catalysts for Fischer-Tropsch Synthesis

A series of iron-based Fischer-Tropsch synthesis （FTS） catalysts incorporated with Al2O3 binder were prepared by the combination of co-precipitation and spray drying technology. The catalyst samples were characterized by using N2 physical adsorption, temperature-programmed reduction/desorption （TPR/TPD） and MSssbauer effect spectroscopy （MES） methods. The characterization results indicated that the BET surface area increases with increasing Al2O3 content and passes through a maximum at the Al2O3/Fe ratio of 10/100 （weight basis）. After the point, it decreases with further increase in Al2O3 content. The incorporation of Al2O3 binder was found to weaken the surface basicity and suppress the reduction and carburization of iron-based catalysts probably due to the strong K-Al2O3 and Fe-Al2O3 interactions. Furthermore, the H2 adsorption ability of the catalysts is enhanced with increasing Al2O3 content. The FTS performances of the catalysts were tested in a slurry-phase continuously stirred tank reactor （CSTR） under the reaction conditions of 260 ℃, 1.5 MPa, 1000 h^-1 and molar ratio of H2/CO 0.67 for 200 h. The results showed that the addition of small amounts of Al2O3 affects the activity of iron-based catalysts to a little extent. However, with further increase of Al2O3 content, the FTS activity and water gas shift reaction （WGS） activity are decreased severely. The addition of appropriate Al2O3 do not affect the product selectivity, but the catalysts incorporated with large amounts of Al2O3 have higher selectivity for light hydrocarbons and lower selectivity for heavy hydrocarbons.

Effect of Manganese Incorporation Manner on an Iron-Based Catalyst for Fischer-Tropsch Synthesis

A systematic study was undertaken to investigate the effects of the manganese incorporation manner on the textural properties, bulk and surface phase compositions, reduction/carburization behaviors, and surface basicity of an iron-based Fischer-Tropsch synthesis （FTS） catalyst. The catalyst samples were characterized by N2 physisorption, X-ray photoelectron spectroscopy （XPS）, H2 （or CO） temperature-programmed reduction （TPR）, CO2 temperature-programmed desorption （TPD）, and M5ssbauer spectroscopy. The FTS performance of the catalysts was studied in a slurry-phase continuously stirred tank reactor （CSTR）. The characterization results indicated that the manganese promoter incorporated by using the coprecipitation method could improve the dispersion of iron oxide, and decrease the size of the iron oxide crystallite. The manganese incorporated with the impregnation method is enriched on the catalyst＇s surface. The manganese promoter added with the impregnation method suppresses the reduction and carburization of the catalyst in H2, CO, and syngas because of the excessive enrichment of manganese on the catalyst surface. The catalyst added manganese using the coprecipitation method has the highest CO conversion （51.9%） and the lowest selectivity for heavy hydrocarbons （C12＋）.

Promoter effect on the CO_2-H_2O formation during Fischer-Tropsch synthesis on iron-based catalysts

The effects of Mg,La and Ca promoters on primary and secondary CO2 and H2O formation pathways during Fischer-Tropsch synthesis on precipitated Fe/Cu/SiO2 catalysts are investigated.The chemisorbed oxygen atoms in the primary pathway formed in the CO dissociation steps reacted with co-adsorbed hydrogen or carbon monoxide to produce H2O and CO2,respectively.The secondary pathway was the water-gas shift reaction.The results indicated that the CO2 production led to an increase in both primary and secondary pathways,and H2O production decreased when surface basicity of the catalyst increased in the order Ca 〉 Mg 〉 La.

Effect of Addition Sequence during Neutralization and Precipitation on Iron-based Catalysts for High Temperature Shift Reaction

The preparation of the iron-based catalysts promoted by cobalt with a small amount of copper and aluminum for the high temperature shift reaction （HTS） with different sequences of adding catalyst raw materials during neutralization and precipitation was investigated. XRD, BET and particle size distribution （PSD） were used to characterize the prepared catalysts. It was found that the catalyst crystals were all γ-Fe2O3, and the intermediate of the catalyst after aging was Fe3O4. The crystallographic form of the catalyst and its intermediate was not affected by the addition sequence in the neutralization and precipitation process. The results showed that the specific surface area and the particle size of the catalysts depended on the addition sequence to the mother liquor. Cobalt with a small amount of copper and aluminum could increase the specific surface area and decrease the particle size of catalysts.

Study of Manganese Promoter on a Precipitated Iron-Based Catalyst for Fischer-Tropsch Synthesis

The effects of Manganese （Mn） incorporation on a precipitated iron-based Fischer-Tropsch synthesis （FTS） catalyst were investigated using N2 physical adsorption, air differential thermal analysis （DTA）, H2 temperature-programmed reduction （TPR）, and Mǒssbauer spectroscopy. The FTS performances of the catalysts were tested in a slurry phase reactor. The characterization results indicated that Mn increased the surface area of the catalyst, and improved the dispersion of （α-Fe2O3 and reduced its crystallite size as a result of the high dispersion effect of Mn and the Fe-Mn interaction. The Fe-Mn interaction also suppressed the reduction of （α-Fe2O3 to Fe3O4, stabilized the FeO phase, and （or） decreased the carburization degree of the catalysts in the H2 and syngas reduction processes. In addition, incorporated Mn decreased the initial catalyst activity, but improved the catalyst stability because Mn restrained the reoxidation of iron carbides to Fe3O4, and improved further carburization of the catalysts. Manganese suppressed the formation of CH4 and increased the selectivity to light olefins （C2-4^=）, but it had little effect on the selectivities to heavy （C5＋） hydrocarbons. All these results indicated that the strong Fe-Mn interaction suppressed the chemisorptive effect of the Mn as an electronic promoter, to some extent, in the precipitated iron-manganese catalyst system.

Activation pressure studies with an iron-based catalyst for slurry Fischer-Tropsch synthesis

Fischer-Tropsch synthesis （FTS） was carried out with an industrial iron-based catalyst （100Fe/5Cu/6K/16SiO2, by weight） under the baseline conditions in a stirred tank slurry reactor （STSR）. The effects of activation pressure on the catalyst activity and selectivity were investigated. It was found that iron phase compositions, textural properties, and FTS performances of the catalysts were strongly dependent on activation pressure. The high activation pressure retards the carburization. MФssbauer effect spectroscopy （MES） results indicated that the contents of the iron carbides clearly decrease with the increase of activation pressure, especially for the activation pressure increasing from 1.0 MPa to 1.5 MPa, and the reverse trend is observed for superparamagnetic Fe^3＋ （spm）. The higher content of Fe^3＋ （spm） results in the higher amount of CO2 in tail gas when the catalyst is reduced at higher pressure. The catalyst activity decreases with the increase of activation pressure. The high quantity of iron carbides is necessary to obtain high FTS activity. However, the activity of the catalyst activated in syngas can not be predicted solely from the fraction of the carbides. It is concluded that activation with syngas at the lower pressure would be the most desirable for the better activity and stability on the iron-based catalyst.

Iron-based catalysts encapsulated by nitrogen-doped graphitic carbon for selective synthesis of liquid fuels through the Fischer-Tropsch process

Fischer‐Tropsch synthesis(FTS)has the potential to be a powerful strategy for producing liquid fuels from syngas if highly selective catalysts can be developed.Herein,a series of iron nanoparticle catalysts encapsulated by nitrogen‐doped graphitic carbon were prepared by a one‐step pyrolysis of a ferric L‐glutamic acid complex.The FeC‐800 catalyst pyrolyzed at 800°C showed excellent catalytic activity(239.4μmolCO gFe–1 s–1),high C5–C11 selectivity(49%),and good stability in FTS.The high dispersion of ferric species combined with a well‐encapsulated structure can effectively inhibit the migration of iron nanoparticles during the reaction process,which is beneficial for high activity and good stability.The nitrogen‐doped graphitic carbon shell can act as an electron donor to the iron particles,thus promoting CO activation and expediting the formation of Fe5C2,which is the key factor for obtaining high C5–C11 selectivity.

KINETICS OF IRON-BASED CATALYST IN TEMPERATURE-PROGRAMMED REDUCTION

In this work, Temperature-Programmed Reduction Processes of iron oxide and 12 other kinds of promoted iron oxides were investigated. It is suggested that the reduction activation energy can be expressed as a normal distribution. The distribution parameters were obtained by kinetic data fitting, which depends on the chemical and geometric characteristics of both the iron oxide and the promoter.

THE BEHAVIOR OF HOMOGENEOUS IRON-BASED CATALYSTS BEARING PYRIDINE DIIMINE LIGANDS FOR ETHYLENE POLYMERIZATION

The polymerization of ethylene by two iron-based catalysts, {[2,6-ArN=C(Me)(2)C5H3N]FeCl2} (Ar = 2,6-C6H3-Me-2 I; 2,6-C6H3 (i-Pr)(2) II) has been investigated. Catalyst II produces higher molecular weight polyethylene (PE) and broadened polydispersities relative to catalyst I under analogous conditions and all polymers are linear. The kinetic profiles with iron catalysts showed a smooth pattern during both rate build-up and rate lowering, which are different from the metallocene catalysts. The polymerization activity increases with Al/Fe value and an optimum temperature range at 40 similar to 45 degreesC was observed. The molecular weight of PE decreases with the increase of Al/Fe ratio and rise of polymerization temperature.

Role of iron-based catalysts in reducing NO_(x) emissions from coal combustion

Nitrogen oxide(NO_(x))pollutants emitted from coal combustion are attracting growing public concern.While the traditional technologies of reducing NO_(x) were mainly focused on terminal treatment,and the research on source treatment is limited.This paper proposes a new coal combustion strategy that significantly reduces NO_(x) emissions during coal combustion.This strategy has two important advantages in reducing NO_(x) emissions.First,by introducing iron-based catalyst at the source,which will catalyze the conversion of coke nitrogen to volatile nitrogen during the pyrolysis process,thereby greatly reducing the coke nitrogen content.The second is de-NO_(x) process by a redox reaction between NO_(x) and reducing agents(coke,HCN,NH_(3),etc.)that occurred during coke combustion.Compared to direct combustion of coal,coke prepared by adding iron-based catalyst has 46.1% reduction in NO_(x) emissions.To determine the effect of iron-based additives on de-NO_(x) performance,demineralized coal(de-coal)was prepared to eliminate the effect of iron-based minerals in coal ash.The effects of iron compounds,additive dosages,and combustion temperatures on de-NO_(x) efficiency are systematically studied.The results revealed that the NO_(x) emission of the coke generated by pyrolysis of de-coal loaded with 3%(mass)Fe_(2)O_(3) decreases to 27.3% at combustion temperature of 900℃.Two main reasons for lower NO_(x) emissions were deduced:(1)During the catalytic coal pyrolysis stage,the nitrogen content in the coke decreases with the release of volatile nitrogen.(2)Part of the NO_(x) emitted during the coke combustion was converted into N_(2) for the catalytic effect of the Fe-based catalysts.It is of great practical value and scientific significance to the comprehensive treatment and the clean utilization process of coal.

Study on Catalytic Behavior of Iron-based Catalyst with IITP as Electron Donor in the Polymerization of Butadiene

In this study,a novel iron-based catalyst system,Fe(acac)3/(isocyanoimino)triptenylphosphorane(IITP)/AlR3,was employed for the synthesis of syndiotactic 1,2-polybutadiene in hexane.This catalyst system exhibits remarkably high catalytic activity,achieving a polymerization activity of 762 kgpolymer·molcatalyst^(-1)·h^(-1)at 50℃with a[BD]/[Fe]molar ratio of 20000.Furthermore,living polymerization characteristic were observed during the investigation of the polymerization kinetics of 1,3-butadiene polymerization.These characteristics were well demonstrated by a narrow molecular weight distribution(PDI≈2.0)of the resulting polybutadiene and a linear relationship between-ln(1-c)and polymerization time as well as number average molecular weight and polymer yield.The resultant polymer showed a 1,2-selectivity of approximately 76%and stereoregularity ranging from 62%to 73%(rrrr).Additionally,through kinetic studies on polymerization reaction,an apparent activation energy Ea value of this catalytic system was calculated to be 84.98 kJ·mol^(-1),which suggests that high polymerization temperature favors efficient polymerization.

Iron-based Fischer–Tropsch synthesis of lower olefins: The nature of χ-Fe_5C_2 catalyst and why and how to introduce promoters

As a sustainable and short-flow process, iron-catalyzed direct conversion of CO-rich syngas to lower olefins without intermediate steps, i.e., Fischer–Tropsch-to-Olefins (FTO), has received increasing attention. However, its fundamental understanding is usually limited by the complex crystal phase composition in addition to the interferences of the promoter effects and inevitable catalyst deactivation. Until recently, the combination of multiple in-situ/ex-situ characterizations and theoretical studies has evidenced Hägg iron carbide (χ-Fe5C2) as the dominant active phase of iron-based Fischer–Tropsch catalysts. This perspective attempts to review and discuss some recent progresses on the nature of χ-Fe5C2catalyst and the crucial effects of promoters on the FTO performance from theoretical and experimental viewpoints, aiming to provide new insights into the rational design of iron-based FTO catalysts. © 2016 Science Press

Research progress of alkaline earth metal iron-based oxides as anodes for lithium-ion batteries

Anode materials are an essential part of lithium-ion batteries(LIBs),which determine the performance and safety of LIBs.Currently,graphite,as the anode material of commercial LIBs,is limited by its low theoretical capacity of 372 mA·h·g^(−1),thus hindering further development toward high-capacity and large-scale applications.Alkaline earth metal iron-based oxides are considered a promising candidate to replace graphite because of their low preparation cost,good thermal stability,superior stability,and high electrochemical performance.Nonetheless,many issues and challenges remain to be addressed.Herein,we systematically summarize the research progress of alkaline earth metal iron-based oxides as LIB anodes.Meanwhile,the material and structural properties,synthesis methods,electrochemical reaction mechanisms,and improvement strategies are introduced.Finally,existing challenges and future research directions are discussed to accelerate their practical application in commercial LIBs.

Physico-chemical structure evolution characteristics of coal char during gasification in the presence of iron-based waste catalyst

The present study aims to explore the physico-chemical structure evolution characteristic during Yangchangwan bituminous coal(YCW)gasification in the presence of iron-based waste catalyst(IWC).The catalytic gasification reactivity of YCW was measured by thermogravimetric analyzer.Scanning electron microscope–energy dispersive system,nitrogen adsorption analyzer and laser Raman spectroscopy were employed to analyze the char physico-chemical properties.The results show that the optimal IWC loading ratio was 5 wt%at 1000°C.The distribution of IWC on char was uneven and Fe catalyst concentrated on the surface of some chars.The specific surface area of YCW gasified semi-char decreased significantly with the increase of gasification time.i.e.,the specific surface area reduced from 382 m2/g(0 min)to 192 m2/g(3 min),meanwhile,the number of micropores and mesopores decreased sharply at the late gasification stage.The carbon microcrystalline structure of YCW gasified semi-char was gradually destroyed with the increase of gasification time,and the microcrystalline structure with small size was gradually generated,resulting in the decreasing order degree of carbon microcrystalline structure.IWC can catalyze YCW gasification which could provide theoretical guidance for industrial solid waste recycling.

Electronic Structure Investigation of 12442 Iron-Based Superconductors Based on Block-Layer Model

Superconducting transition temperature(Tc),as a crucial parameter,exploring its relationship with various macroscopic and microscopic factors helps to understand the mechanism of high-temperature superconductivity from multiple perspectives,aiding in a multidimensional comprehension of high-temperature superconductivity mechanisms.Drawing inspiration from the block-layer structure models of cuprate superconductors,we computationally investigated the interlayer interaction energies in the 12442-type iron-based superconducting materials AkCa_(2)Fe_(4)As_(4)F_(2)(Ak=K,Rb,Cs)systems based on the block-layer model and explored their relationship with Tc.We observed that an increase in interlayer combinative energy leads to a decrease in Tc,while conversely,a decrease in interlayer combination energy results in an increase in Tc.Further,we found that the contribution of the Fe 3d band structure,especially the 3dz2 orbital,to charge transfer is significant.

Direct decomposition of nitric oxide in low temperature over iron-based perovskite-type catalyst modified by Ru

Iron-based perovskite-type compounds modified by Ru were prepared through sol-gel process to study its catalytic activity of NOx direct decomposition at low temperature and evaluate the conversion of NO under the experimental conditions. The catalytic activity of La 0.9Ce 0.1Fe 0.8-nCo 0.2RunO3 （n=0.01,0.03,0.05,0.07,0.09）series for the NO, NO-CO two components, CO-HC-NO three components were also analyzed. The catalytic investigation evidenced that the presence of Ru is necessary for making highly activity in decomposition of nitric oxide even at low temperature（400 ℃）and La 0.9Ce 0.9Fe 0.75Co 0.2Ru 0.05O3 （n=0.05） has better activity in all the samples, the conversion of it is 58.5%. With the reducing gas（CO,C3H6）added into the gas, the catalyst displayed very high activity in decomposition of NO and the conversion of it is 80% and 92.5% separately.

Bimetallic Single‑Atom Catalysts for Water Splitting

Green hydrogen from water splitting has emerged as a critical energy vector with the potential to spearhead the global transition to a fossil fuel-independent society.The field of catalysis has been revolutionized by single-atom catalysts(SACs),which exhibit unique and intricate interactions between atomically dispersed metal atoms and their supports.Recently,bimetallic SACs(bimSACs)have garnered significant attention for leveraging the synergistic functions of two metal ions coordinated on appropriately designed supports.BimSACs offer an avenue for rich metal–metal and metal–support cooperativity,potentially addressing current limitations of SACs in effectively furnishing transformations which involve synchronous proton–electron exchanges,substrate activation with reversible redox cycles,simultaneous multi-electron transfer,regulation of spin states,tuning of electronic properties,and cyclic transition states with low activation energies.This review aims to encapsulate the growing advancements in bimSACs,with an emphasis on their pivotal role in hydrogen generation via water splitting.We subsequently delve into advanced experimental methodologies for the elaborate characterization of SACs,elucidate their electronic properties,and discuss their local coordination environment.Overall,we present comprehensive discussion on the deployment of bimSACs in both hydrogen evolution reaction and oxygen evolution reaction,the two half-reactions of the water electrolysis process.

Catalyst–Support Interaction in Polyaniline‑Supported Ni_(3)Fe Oxide to Boost Oxygen Evolution Activities for Rechargeable Zn‑Air Batteries

Catalyst–support interaction plays a crucial role in improving the catalytic activity of oxygen evolution reaction(OER).Here we modulate the catalyst–support interaction in polyaniline-supported Ni_(3)Fe oxide(Ni_(3)Fe oxide/PANI)with a robust hetero-interface,which significantly improves oxygen evolution activities with an overpotential of 270 mV at 10 mA cm^(-2)and specific activity of 2.08 mA cm_(ECSA)^(-2)at overpotential of 300 mV,3.84-fold that of Ni_(3)Fe oxide.It is revealed that the catalyst–support interaction between Ni_(3)Fe oxide and PANI support enhances the Ni–O covalency via the interfacial Ni–N bond,thus promoting the charge and mass transfer on Ni_(3)Fe oxide.Considering the excellent activity and stability,rechargeable Zn-air batteries with optimum Ni_(3)Fe oxide/PANI are assembled,delivering a low charge voltage of 1.95 V to cycle for 400 h at 10 mA cm^(-2).The regulation of the effect of catalyst–support interaction on catalytic activity provides new possibilities for the future design of highly efficient OER catalysts.