The Fischer–Tropsch to olefins（FTO） process is a method for the direct conversion of synthesis gas to lower C–Colefins. Carbon-supported iron carbide nanoparticles are attractive catalysts for this reaction.The ca...The Fischer–Tropsch to olefins（FTO） process is a method for the direct conversion of synthesis gas to lower C–Colefins. Carbon-supported iron carbide nanoparticles are attractive catalysts for this reaction.The catalytic activity can be improved and undesired formation of alkanes can be suppressed by the addition of sodium and sulfur as promoters but the influence of their content and ratio remains poorly understood and the promoted catalysts often suffer from rapid deactivation due to particle growth. A series of carbon black-supported iron catalysts with similar iron content and nominal sodium/sulfur loadings of 1–30/0.5–5 wt% with respect to iron are prepared and characterized under FTO conditions at 1and 10 bar syngas pressure to illuminate the influence of the promoter level on the catalytic properties.Iron particles and promoters undergo significant reorganization during FTO operation under industrially relevant conditions. Low sodium content（1–3 wt%） leads to a delay in iron carbide formation. Sodium contents of 15–30 wt% lead to rapid loss of catalytic activity due to the covering of the iron surface with promoters during particle growth under FTO operation. Higher activity and slower loss of activity are observed at low promoter contents（1–3 wt% sodium and 0.5–1 wt% sulfur） but a minimum amount of alkali is required to effectively suppress methane and C–Cparaffin formation. A reference catalyst support（carbide-derived carbon aerogel） shows that the optimum promoter level depends on iron particle size and support pore structure.展开更多
We report the assisted role of water vapor in crystallographic cutting of graphene via iron catalysts in reduced atmosphere. Without water, graphene can be tailored with smooth trenches composed of straight lines with...We report the assisted role of water vapor in crystallographic cutting of graphene via iron catalysts in reduced atmosphere. Without water, graphene can be tailored with smooth trenches composed of straight lines with angles of 60℃ or 120℃ between two adjacent trenches. After the addition of water, new chacteristics are found： such as almost no iron particles can be detected along the trenches; each trench becomes longer and lots of graphene nanoribbons can be generated. The underlying mechanism is proposed and discussed, which is attributed to stimulating and lengthening of the catalytic activity of iron particles by water vapor.展开更多
Nitrogen-doped carbon nanotubes （NCNTs） were used as a support for iron （Fe） nanoparticles applied in car- bon dioxide （CO_2） hydrogenation at 633 K and 25 bar （1 bar = 10-5 Pa）. The Fe/NCNT catalyst promoted ...Nitrogen-doped carbon nanotubes （NCNTs） were used as a support for iron （Fe） nanoparticles applied in car- bon dioxide （CO_2） hydrogenation at 633 K and 25 bar （1 bar = 10-5 Pa）. The Fe/NCNT catalyst promoted with both potassium （K） and manganese （Mn） showed high performance in CO_2 hydrogenation, reaching 34.9% conversion with a gas hourly space velocity （GHSV） of 3.1 L-（g·h）-1. Product selectivities were high for olefin products and low for short-chain alkanes for the K-promoted catalysts. When Fe/NCNT catalyst was promot- ed with both K and Mn, the catalytic activity was stable for 60 h of reaction time. The structural effect of the Mn promoter was demonstrated by X-ray diffraction （XRD）, temperature-programmed reduction （TPR） with molecular hydrogen （H2）, and in situ X-ray absorption near-edge structure （XANES） analysis. The Mn pro- moter stabilized wtistite （FeO） as an intermediate and lowered the TPR onset temperature. Catalytic ammo- nia （NH_3） decomposition was used as an additional probe reaction for characterizing the promoter effects. The Fe/NCNT catalyst promoted with both K and Mn had the highest catalytic activity, and the Mn-promoted Fe/NCNT catalysts had the highest thermal stability under reducing conditions.展开更多
FeOx-SiO2 catalysts prepared by a sol-gel method were studied for the selective oxidation of methane by oxygen. A single-pass formaldehyde yield of 2.0% was obtained over the FeOx-SiO2 with an iron content of 0.5 wt% ...FeOx-SiO2 catalysts prepared by a sol-gel method were studied for the selective oxidation of methane by oxygen. A single-pass formaldehyde yield of 2.0% was obtained over the FeOx-SiO2 with an iron content of 0.5 wt% at 898 K. This 0.5 wt% FeOx-SiO2 catalyst demonstrated significantly higher catalytic performances than the 0.5 wt% FeOx/SiO2 prepared by an impregnation method. The correlation between the catalytic performances and the characterizations with UV-Vis and H2-TPR suggested that the higher dispersion of iron species in the catalyst prepared by the sol-gel method was responsible for its higher catalytic activity for formaldehyde formation. The modification of the FeOx-SiO2 by phosphorus enhanced the formaldehyde selectivity, and a single-pass formaldehyde yield of 2.4% could be attained over a P-FeOx-SiO2 catalyst （P/Fe = 0.5） at 898 K. Raman spectroscopic measurements indicated the formation of FePO4 nanoclusters in this catalyst, which were more selective toward formaldehyde formation.展开更多
Direct oxidative coupling of an alcohol and amine,with air or molecular oxygen as the oxygen source,is an environmentally friendly method for imine synthesis.We developed an Fe catalyst supported on mesoporous carbon...Direct oxidative coupling of an alcohol and amine,with air or molecular oxygen as the oxygen source,is an environmentally friendly method for imine synthesis.We developed an Fe catalyst supported on mesoporous carbon（denoted by FeOx/HCMK-3） for this reaction with excellent activity and recyclability.FeOx/HCMK-3 was prepared by impregnating HNO3-treated mesoporous carbon（CMK-3） with iron nitrate solution.The highly dispersed FeOx species give FeOx/HCMK-3 high reducibility and are responsible for the high catalytic performance.Imine synthesis over FeOx/HCMK-3 follows a redox mechanism.The oxygen species in FeOx/HCMK-3 participate in the reaction and are then regenerated by oxidation with molecular O2.The reaction involves two consecutive steps：oxidative dehydrogenation of an alcohol to an aldehyde and coupling of the aldehyde with an amine to give an imine.Oxidative dehydrogenation of the alcohol is the rate-determining step in the reaction.展开更多
Surface morphology, physical-chemical properties of skeletal iron catalysts prepared by leaching of the rapidly quenched(RQ) and naturally quenched(NQ) Fe-Al alloys with an aqueous solution of NaOH were characterized...Surface morphology, physical-chemical properties of skeletal iron catalysts prepared by leaching of the rapidly quenched(RQ) and naturally quenched(NQ) Fe-Al alloys with an aqueous solution of NaOH were characterized by using a series of techniques including XRD, BET, XPS, SEM, H_2 and CO-TPD. It was found that the RQ skeletal iron catalyst exhibits a smaller particle size, larger specific surface area and pore volume than the NQ one. The H_2 and CO-TPD experiments showed that the RQ skeletal iron exhibits stronger affinity for H_2 and milder affinity for CO compared with the NQ one. But the NQ skeletal catalyst shows a better thermal stability than the RQ catalyst.展开更多
Selective production of specific products,such as jet fuel,in Fischer-Tropsch synthesis(FTS)is a huge challenge due to the Anderson-Schulz-Flory(ASF)distribution law.Herein,by filling K-promoted Fe-based active specie...Selective production of specific products,such as jet fuel,in Fischer-Tropsch synthesis(FTS)is a huge challenge due to the Anderson-Schulz-Flory(ASF)distribution law.Herein,by filling K-promoted Fe-based active species,which usually produces medium-to-short chain hydrocarbons in high-temperature FTS,into the hierarchical carbon nanocages(hCNC),jet fuel with high selectivity of 60% is directly obtained in FTS at 300℃,exceeding the ASF maximum limitation of ca.41%.Through the theoretical simulations,we attribute this performance to the CO enrichment inside the nanocavities due to the sieving effect of the micropores across the hCNC shells(~6A)and the increased collision frequency in confined space.These two factors thereby promote the CO conversion and carbon-chain growth longer over the catalytically active Fe_(5)C_(2) phase,resulting in the remarkable selectivity to jet fuel.The effects of the length and size of micropores on the CO/H_(2) diffusion and FTS performance are examined,which corroborate the crucial role of micropores in the high-selective FTS to jet fuel.This work not only provides a remarkable catalyst to the selective jet fuel synthesis,but also offers an alternative way to design advanced catalysts for FTS.展开更多
The widespread utilization of fossil fuels has caused an associated increase in CO_(2) emissions over the past few decades,which has resulted in global warming and ocean acidification.CO hydrogenation(Fischer‐Tropsch...The widespread utilization of fossil fuels has caused an associated increase in CO_(2) emissions over the past few decades,which has resulted in global warming and ocean acidification.CO hydrogenation(Fischer‐Tropsch synthesis,FTS)is considered a significant route for the production of liquid fuels and chemicals from nonpetroleum sources to meet worldwide demand.Conversion of CO_(2) with renewable H_(2) into valuable hydrocarbons is beneficial for reducing dependence on fossil fuels and mitigating the negative effects of high CO_(2) concentrations in the atmosphere.Iron‐based catalysts exhibit superior catalytic performance in both FTS and CO_(2) hydrogenation to value‐added hydrocarbons.The abundance and low cost of iron‐based catalysts also promote their wide application in CO_(x) hydrogenation.This paper provides a comprehensive overview of the significant developments in the application of iron‐based catalysts in these two fields.The active phases,promoter effect,and support of iron‐based catalysts are discussed in the present paper.Based on understanding of these three essential aspects,we also cover recent advances in the design and preparation of novel iron‐based catalysts for FTS and CO_(2) hydrogenation.Current challenges and future catalytic applications are also outlined.展开更多
We report the in situ transmission electron microscope (TEM) observation of the catalytic gasification and growth of carbon nanotubes (CNTs). It was found that iron catalysts can consume the CNTs when pumping out the ...We report the in situ transmission electron microscope (TEM) observation of the catalytic gasification and growth of carbon nanotubes (CNTs). It was found that iron catalysts can consume the CNTs when pumping out the precursor gas, acetylene, at the growth temperature, and reinitiate the growth when acetylene is re-introduced. The switching between gasification and growth of CNTs can be repeated many times with the same catalyst. To understand the phenomenon, thermogravimetric analysis (TGA) coupled with mass spectroscopy was used to study the mechanism involved. It was shown that the residual water molecules in the growth chamber of the TEM react with and remove carbon atoms of CNTs as carbon monoxide vapor under the action of the catalyst, when the precursor gas is pumped out. This result contributes to a better understanding of the water-assisted and oxygen-assisted synthesis of CNT arrays, and provides useful clues on how to extend the lifetime and improve the activity of the catalysts.展开更多
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 encapsula...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.展开更多
CO_(2)hydrogenation is an attractive way to store and utilize carbon dioxide generated by industrial processes,as well as to produce valuable chemicals from renewable and abundant resources.Iron catalysts are commonly...CO_(2)hydrogenation is an attractive way to store and utilize carbon dioxide generated by industrial processes,as well as to produce valuable chemicals from renewable and abundant resources.Iron catalysts are commonly used for the hydrogenation of carbon oxides to hydrocarbons.Iron-molybdenum catalysts have found numerous applications in catalysis,but have been never evaluated in the CO_(2)hydrogenation.In this work,the structural properties of iron-molybdenum catalysts without and with a promoting alkali metal(Li,Na,K,Rb,or Cs)were characterized using X-ray diffraction,hydrogen temperatureprogrammed reduction,CO_(2)temperature-programmed desorption,in-situ^(57)Fe Mossbauer spectroscopy and operando X-ray adsorption spectroscopy.Their catalytic performance was evaluated in the CO_(2)hydrogenation.During the reaction conditions,the catalysts undergo the formation of an iron(Ⅱ)molybdate structure,accompanied by a partial reduction of molybdenum and carbidization of iron.The rate of CO_(2)conversion and product selectivity strongly depend on the promoting alkali metals,and electronegativity was identified as an important factor affecting the catalytic performance.Higher CO_(2)conversion rates were observed with the promoters having higher electronegativity,while low electronegativity of alkali metals favors higher light olefin selectivity.展开更多
K-promoted iron/carbon nanotubes composite（i.e., Fe K-OX） was prepared by a redox reaction between carbon nanotubes and K2FeO4followed by thermal treatments on a purpose as the Fischer–Tropsch catalyst for the dire...K-promoted iron/carbon nanotubes composite（i.e., Fe K-OX） was prepared by a redox reaction between carbon nanotubes and K2FeO4followed by thermal treatments on a purpose as the Fischer–Tropsch catalyst for the direct conversion of syngas to lower olefins. Its catalytic behaviors were compared with those of the other two Fe-IM and Fe K-IM catalysts prepared by impregnation method followed by thermal treatments. The novel Fe K-OX composite catalyst is found to exhibit higher hydrocarbon selectivity,lower olefins selectivity and chain growth probability as well as better stability. The catalyst structureperformance relationship has been established using multiple techniques including XRD, Raman, TEM and EDS elemental mapping. In addition, effects of additional potassium into the Fe K-OX composite catalyst on the FTO performance were also investigated and discussed. Additional potassium promoters further endow the catalysts with higher yield of lower olefins. These results demonstrated that the introduction method of promoters and iron species plays a crucial role in the design and fabrication of highly active,selective and stable iron-based composite catalysts for the FTO reaction.展开更多
The N,N,N'-ferrous chloride complexes,[2-{CMeN(2,4-(CHPh)_(2)-6-FC_(6)H_(2))}-6-(CMeNAr)C_(5)H_(3)N]FeCl_(2)(Ar=2,6-Me_(2)C_(6)H_(3) Fe1,2,6-Et_(2)C_(6)H_(3)Fe2,2,6-^(i)Pr_(2)C_(6)H_(3) Fe3,2,4,6-Me_(3)C_(6)H_(2) ...The N,N,N'-ferrous chloride complexes,[2-{CMeN(2,4-(CHPh)_(2)-6-FC_(6)H_(2))}-6-(CMeNAr)C_(5)H_(3)N]FeCl_(2)(Ar=2,6-Me_(2)C_(6)H_(3) Fe1,2,6-Et_(2)C_(6)H_(3)Fe2,2,6-^(i)Pr_(2)C_(6)H_(3) Fe3,2,4,6-Me_(3)C_(6)H_(2) Fe4 and 2,6-Et_(2)-4-MeC_(6)H_(2) Fe5),each possessing one N-2,4-dibenzhydryl-6-fluorophenyl group,were readily synthesized from their respective unsymmetrical bis(imino)pyridines,L1-L5.Structural identification of Fe2 highlighted the variation in the steric properties provided by the dissimilar N-aryl groups.Following pre-treatment with either MAO or MMAO,complexes Fe1-Fe5 all displayed,at an operating temperature of 80℃,high activities for ethylene polymerization with levels falling in the order:Fe4> Fe1> Fe5> Fe2> Fe3.Notably,Fe4/MAO displayed the highest activity of 1.94×10^(7) g_(PE)·mol_(Fe)^(-1)·h^(-1) of the study with only a modest loss in performance at 90℃.Generally,the resulting polyethylenes were highly linear(T_(m) range:122-132℃),narrowly disperse and of low molecular weight(M_(w) range:6.73-46.04kg·mol^(-1)),with the most sterically hindered Fe3 forming the highest molecular weight polymer of the series.End-group analysis by ^(1)H-and ^(13)CNMR spectroscopy revealed saturated alkyl(n-propyl and i-propyl) and unsaturated vinyl chain ends indicative of the role of both β-H elimination and chain transfer to aluminum as termination pathways.By comparison with previou sly reported iron precatalysts with similar tridentate ligand skeletons,it is evident that the introduction of a large benzhydryl group in combination with a fluorine as the ortho-substituents of one N-aryl group has the effect of enhancing thermal stability of the iron polymerization catalyst whilst maintaining appreciable polymer molecular weight.展开更多
Ammonia is essential for agriculture and,as a next-generation carbon-free fuel,typically produced through the Haber-Bosch method.This process requires high temperature and pressure,leading to significant energy consum...Ammonia is essential for agriculture and,as a next-generation carbon-free fuel,typically produced through the Haber-Bosch method.This process requires high temperature and pressure,leading to significant energy consumption and greenhouse gas emissions.Therefore,achieving ammonia synthesis under milder conditions has been a long-standing goal.In this study,we design and synthesize a series of CeO_(2)-modified Fe/carbon-based catalysts with varying amounts of CeO_(2)(Ce_(x)Fe_(y)/C).The catalyst Ce_(2)Fe_(5)/C demonstrates an ammonia yield rate of 3.5 mmol/(g·h),which is 44 times greater than that of Fe/C and 8 times greater than that of commercial Fe-based catalysts at 300℃and 1 MPa.Temperature-programmed desorption experiments show that Ce_(2)Fe_(5)/C has enhanced nitrogen adsorption capabilities.Multiple analyses confirm that the CeO_(2)in Ce_(2)Fe_(5)/C is rich in oxygen vacancies,which can provide electrons to Fe,facilitating nitrogen adsorption,dissociation,and activity in low-temperature ammonia synthesis.展开更多
In this study, a series of aryloxy-aluminoxanes originated directly from the hydrolysis of reaction products of A1Me3 and phenols were synthesized, which could serve as effective polymer-retarding activators for the i...In this study, a series of aryloxy-aluminoxanes originated directly from the hydrolysis of reaction products of A1Me3 and phenols were synthesized, which could serve as effective polymer-retarding activators for the iron-catalyzed ethylene oligomerization. The molar ratios of [PhOH]/[AlMe3] and [H2O]/[Al] during the preparation were explored and their impacts on the oligomerization activity and product distribution were discussed. To obtain the effective activators with good polymer-retarding effect and relatively high activity, the optimized conditions were proposed to be [PhOH]/[AlMe3] = 0.5 and [H2O]/[Al] = 0.7. Various aluminoxanes with different [-OH] sources confirmed the importance of using phenols in preparing the effective polymer-retarding activators. By utilizing these aryloxy-aluminoxanes, the mass fraction of polymers in the total products could be reduced to lower than 1.0 wt%, which is much lower than that of the MAO-activated systems （〉 30 wt%）. This is a potential benefit for the industrial application of the iron-catalyzed oligomerization process.展开更多
Rare earth gangue, which mainly consists of mixtures of light rare earths such as lanthana, ceria, neodymium oxide and praseodymium oxide, was used as the promoter of fused iron catalysts for ammonia synthesis. The re...Rare earth gangue, which mainly consists of mixtures of light rare earths such as lanthana, ceria, neodymium oxide and praseodymium oxide, was used as the promoter of fused iron catalysts for ammonia synthesis. The result showed that the activity of the catalyst promoted with rare earth gangue was comparable with those of commercial iron catalysts with high amount of cobalt. The role of rare earths was owed to their advantages for favoring the deep reduction of the main composite in catalyst, i.e., iron oxide. This fmding indicated that the use of rare earth gangue could decrease the content of cobalt or even completely replace cobalt, which was used to be regarded as unsub- stitutable promoters for high performance ammonia catalyst; therefore, the cost of fused iron catalysts would decrease significantly.展开更多
A series of both unsupported and coal‐supported iron–oxygen compounds with gradual changes in microstructure were synthesized by a precipitation‐oxidation process at 20 to 70°C.The relationship between the mic...A series of both unsupported and coal‐supported iron–oxygen compounds with gradual changes in microstructure were synthesized by a precipitation‐oxidation process at 20 to 70°C.The relationship between the microstructures and catalytic activities of these precursors during direct coal liquefaction was studied.The results show that the microstructure could be controlled through adjusting the synthesis temperature during the precipitation‐oxidation procedure,and that compounds synthesized at lower temperatures exhibit higher catalytic activity.As a result of their higher proportions ofγ‐FeOOH orα‐FeOOH crystalline phases,the unsupported iron–oxygen compounds synthesized at 20–30°C,which also had high specific surface areas and moisture levels,generate oil yields 4.5%–4.6%higher than those obtained with precursors synthesized at 70°C.It was also determined that higher oil yields were obtained when the catalytically‐active phase formed by the precursors during liquefaction(pyrrhotite,Fe1-xS)had smaller crystallites.Feed coal added as a carrier was found to efficiently disperse the active precursors,which in turn significantly improved the catalytic activity during coal liquefaction.展开更多
Activated carbon-supported Ru-based catalyst and A301 iron catalyst were prepared,and the influences of reaction temperature,space velocity,pressure,and H2/N2 ratio on performance of iron catalyst coupled with Ru cata...Activated carbon-supported Ru-based catalyst and A301 iron catalyst were prepared,and the influences of reaction temperature,space velocity,pressure,and H2/N2 ratio on performance of iron catalyst coupled with Ru catalyst in series for ammonia synthesis were investigated.The activity tests were also performed on the single Ru and Fe catalysts as comparison.Results showed that the activity of the Ru catalyst for ammonia synthesis was higher than that of the iron catalyst by 33.5%-37.6% under the reaction conditions：375-400 °C,10 MPa,10000 h-1,H2︰N2 3,and the Ru catalyst also had better thermal stability when treated at 475 °C for 20 h.The outlet ammonia concentration using Fe-Ru catalyst was increased by 45.6%-63.5% than that of the single-iron catalyst at low tem-perature （375-400 °C）,and the outlet ammonia concentration increased with increasing Ru catalyst loading.展开更多
A series of monolithic MnO_(2)/iron mesh (IM) catalysts for oxidation of toluene were successfully prepared by using in situ hydrothermal growth.MnO_(2)can grow firmly on the IM substrates surface with a shedding rate...A series of monolithic MnO_(2)/iron mesh (IM) catalysts for oxidation of toluene were successfully prepared by using in situ hydrothermal growth.MnO_(2)can grow firmly on the IM substrates surface with a shedding rate of only 0.14%.Due to the highest O_(ads) and high-valent Mn^(4+) and Fe^(3+) elements,the temperature at 50% and 90% toluene conversion (T_(50%) and T_(90%)) was 252 and 265℃,respectively for the best performance catalyst (hydrothermal temperature of 80℃,hydrothermal time of 12 h,and precursor manganese ion concentration of 0.03 mol/L).The catalysts also presented good water resistance and cycle performance.In-situ DRIFTS results suggesting that toluene was first rapid transformed into the reaction intermediate species (benzoate species) and then converted to CO_(2)and H_(2)O.Therefore,this work provides a new direction for the research and application of IM-based monolithic catalysts.展开更多
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 activ...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.展开更多
基金supported by a Post Doc grant of the German Academic Exchange Service(Deutscher Akademischer Austauschdienst,DAAD grant no.91552012)by the European Research Council(EU FP7 ERC advanced grant no.338846)
文摘The Fischer–Tropsch to olefins（FTO） process is a method for the direct conversion of synthesis gas to lower C–Colefins. Carbon-supported iron carbide nanoparticles are attractive catalysts for this reaction.The catalytic activity can be improved and undesired formation of alkanes can be suppressed by the addition of sodium and sulfur as promoters but the influence of their content and ratio remains poorly understood and the promoted catalysts often suffer from rapid deactivation due to particle growth. A series of carbon black-supported iron catalysts with similar iron content and nominal sodium/sulfur loadings of 1–30/0.5–5 wt% with respect to iron are prepared and characterized under FTO conditions at 1and 10 bar syngas pressure to illuminate the influence of the promoter level on the catalytic properties.Iron particles and promoters undergo significant reorganization during FTO operation under industrially relevant conditions. Low sodium content（1–3 wt%） leads to a delay in iron carbide formation. Sodium contents of 15–30 wt% lead to rapid loss of catalytic activity due to the covering of the iron surface with promoters during particle growth under FTO operation. Higher activity and slower loss of activity are observed at low promoter contents（1–3 wt% sodium and 0.5–1 wt% sulfur） but a minimum amount of alkali is required to effectively suppress methane and C–Cparaffin formation. A reference catalyst support（carbide-derived carbon aerogel） shows that the optimum promoter level depends on iron particle size and support pore structure.
基金supported by the National Natural Science Foundation of China(Grant No.10774032)the Instrument Developing Project of the Chinese Academy of Sciences(Grant No.Y2010031)
文摘We report the assisted role of water vapor in crystallographic cutting of graphene via iron catalysts in reduced atmosphere. Without water, graphene can be tailored with smooth trenches composed of straight lines with angles of 60℃ or 120℃ between two adjacent trenches. After the addition of water, new chacteristics are found： such as almost no iron particles can be detected along the trenches; each trench becomes longer and lots of graphene nanoribbons can be generated. The underlying mechanism is proposed and discussed, which is attributed to stimulating and lengthening of the catalytic activity of iron particles by water vapor.
基金supported by the Synchrotron Light Research Institute(Public Organization)Thailand(GS-54-D01)+7 种基金the Commission on Higher EducationMinistry of EducationThailandperformed under the project"Sustainable Chemical Synthesis(Sus Chem Sys)"which is co-financed by the European Regional Development Fund(ERDF)the state of North Rhine-WestphaliaGermanyunder the Operational Programme"Regional Competitiveness and Employment"2007–2013
文摘Nitrogen-doped carbon nanotubes （NCNTs） were used as a support for iron （Fe） nanoparticles applied in car- bon dioxide （CO_2） hydrogenation at 633 K and 25 bar （1 bar = 10-5 Pa）. The Fe/NCNT catalyst promoted with both potassium （K） and manganese （Mn） showed high performance in CO_2 hydrogenation, reaching 34.9% conversion with a gas hourly space velocity （GHSV） of 3.1 L-（g·h）-1. Product selectivities were high for olefin products and low for short-chain alkanes for the K-promoted catalysts. When Fe/NCNT catalyst was promot- ed with both K and Mn, the catalytic activity was stable for 60 h of reaction time. The structural effect of the Mn promoter was demonstrated by X-ray diffraction （XRD）, temperature-programmed reduction （TPR） with molecular hydrogen （H2）, and in situ X-ray absorption near-edge structure （XANES） analysis. The Mn pro- moter stabilized wtistite （FeO） as an intermediate and lowered the TPR onset temperature. Catalytic ammo- nia （NH_3） decomposition was used as an additional probe reaction for characterizing the promoter effects. The Fe/NCNT catalyst promoted with both K and Mn had the highest catalytic activity, and the Mn-promoted Fe/NCNT catalysts had the highest thermal stability under reducing conditions.
基金supported by the National Natural Science Foundation of China (Nos.20625310,20773099 and 20873110)the National Basic Programof China (No. 2005CB221408)the National Science Fund for Talent Training in Basic Science (No.J0630429)
文摘FeOx-SiO2 catalysts prepared by a sol-gel method were studied for the selective oxidation of methane by oxygen. A single-pass formaldehyde yield of 2.0% was obtained over the FeOx-SiO2 with an iron content of 0.5 wt% at 898 K. This 0.5 wt% FeOx-SiO2 catalyst demonstrated significantly higher catalytic performances than the 0.5 wt% FeOx/SiO2 prepared by an impregnation method. The correlation between the catalytic performances and the characterizations with UV-Vis and H2-TPR suggested that the higher dispersion of iron species in the catalyst prepared by the sol-gel method was responsible for its higher catalytic activity for formaldehyde formation. The modification of the FeOx-SiO2 by phosphorus enhanced the formaldehyde selectivity, and a single-pass formaldehyde yield of 2.4% could be attained over a P-FeOx-SiO2 catalyst （P/Fe = 0.5） at 898 K. Raman spectroscopic measurements indicated the formation of FePO4 nanoclusters in this catalyst, which were more selective toward formaldehyde formation.
基金supported by the National Natural Science Foundation of China(21473073,21473074)the "13th Five-Year" Science and Technology Research of the Education Department of Jilin Province(2016403)~~
文摘Direct oxidative coupling of an alcohol and amine,with air or molecular oxygen as the oxygen source,is an environmentally friendly method for imine synthesis.We developed an Fe catalyst supported on mesoporous carbon（denoted by FeOx/HCMK-3） for this reaction with excellent activity and recyclability.FeOx/HCMK-3 was prepared by impregnating HNO3-treated mesoporous carbon（CMK-3） with iron nitrate solution.The highly dispersed FeOx species give FeOx/HCMK-3 high reducibility and are responsible for the high catalytic performance.Imine synthesis over FeOx/HCMK-3 follows a redox mechanism.The oxygen species in FeOx/HCMK-3 participate in the reaction and are then regenerated by oxidation with molecular O2.The reaction involves two consecutive steps：oxidative dehydrogenation of an alcohol to an aldehyde and coupling of the aldehyde with an amine to give an imine.Oxidative dehydrogenation of the alcohol is the rate-determining step in the reaction.
基金Supported by the State Key L aboratory of Coal Conversion ICC CAS and the Key L aboratory of Science and Technology of Controllable Chemical Reactions BU CT of Ministry of Education of China
文摘Surface morphology, physical-chemical properties of skeletal iron catalysts prepared by leaching of the rapidly quenched(RQ) and naturally quenched(NQ) Fe-Al alloys with an aqueous solution of NaOH were characterized by using a series of techniques including XRD, BET, XPS, SEM, H_2 and CO-TPD. It was found that the RQ skeletal iron catalyst exhibits a smaller particle size, larger specific surface area and pore volume than the NQ one. The H_2 and CO-TPD experiments showed that the RQ skeletal iron exhibits stronger affinity for H_2 and milder affinity for CO compared with the NQ one. But the NQ skeletal catalyst shows a better thermal stability than the RQ catalyst.
基金jointly supported by the National Key Research and Development Program of China(No.2021YFA1500900)the National Natural Science Foundation of China(Nos.21972061 and 52071174)+1 种基金the Natural Science Foundation of Jiangsu Province,Major Project(No.BK20212005)the Foundation of Science and Technology of Suzhou(No.SYC2022102).
文摘Selective production of specific products,such as jet fuel,in Fischer-Tropsch synthesis(FTS)is a huge challenge due to the Anderson-Schulz-Flory(ASF)distribution law.Herein,by filling K-promoted Fe-based active species,which usually produces medium-to-short chain hydrocarbons in high-temperature FTS,into the hierarchical carbon nanocages(hCNC),jet fuel with high selectivity of 60% is directly obtained in FTS at 300℃,exceeding the ASF maximum limitation of ca.41%.Through the theoretical simulations,we attribute this performance to the CO enrichment inside the nanocavities due to the sieving effect of the micropores across the hCNC shells(~6A)and the increased collision frequency in confined space.These two factors thereby promote the CO conversion and carbon-chain growth longer over the catalytically active Fe_(5)C_(2) phase,resulting in the remarkable selectivity to jet fuel.The effects of the length and size of micropores on the CO/H_(2) diffusion and FTS performance are examined,which corroborate the crucial role of micropores in the high-selective FTS to jet fuel.This work not only provides a remarkable catalyst to the selective jet fuel synthesis,but also offers an alternative way to design advanced catalysts for FTS.
文摘The widespread utilization of fossil fuels has caused an associated increase in CO_(2) emissions over the past few decades,which has resulted in global warming and ocean acidification.CO hydrogenation(Fischer‐Tropsch synthesis,FTS)is considered a significant route for the production of liquid fuels and chemicals from nonpetroleum sources to meet worldwide demand.Conversion of CO_(2) with renewable H_(2) into valuable hydrocarbons is beneficial for reducing dependence on fossil fuels and mitigating the negative effects of high CO_(2) concentrations in the atmosphere.Iron‐based catalysts exhibit superior catalytic performance in both FTS and CO_(2) hydrogenation to value‐added hydrocarbons.The abundance and low cost of iron‐based catalysts also promote their wide application in CO_(x) hydrogenation.This paper provides a comprehensive overview of the significant developments in the application of iron‐based catalysts in these two fields.The active phases,promoter effect,and support of iron‐based catalysts are discussed in the present paper.Based on understanding of these three essential aspects,we also cover recent advances in the design and preparation of novel iron‐based catalysts for FTS and CO_(2) hydrogenation.Current challenges and future catalytic applications are also outlined.
基金Acknowle dgements This work was financially supported by the National Natural Science Foundation of China （NSFC） （Nos. 10704044 and 50825201）, Fok Ying Tung Education Foundation （No. 111049）, and the National BasicResearch Program of China （No. 2007CB935301）. We thank Qingyu Zhao and Xiaoyang Lin for the help in the STA experiments. RS and SWC acknowledge the support from NSF-CBET （#0625340）. We gratefully acknowledge the use of facilities within the LeRoy Eyring Center for Solid State Science at Arizona State University.
文摘We report the in situ transmission electron microscope (TEM) observation of the catalytic gasification and growth of carbon nanotubes (CNTs). It was found that iron catalysts can consume the CNTs when pumping out the precursor gas, acetylene, at the growth temperature, and reinitiate the growth when acetylene is re-introduced. The switching between gasification and growth of CNTs can be repeated many times with the same catalyst. To understand the phenomenon, thermogravimetric analysis (TGA) coupled with mass spectroscopy was used to study the mechanism involved. It was shown that the residual water molecules in the growth chamber of the TEM react with and remove carbon atoms of CNTs as carbon monoxide vapor under the action of the catalyst, when the precursor gas is pumped out. This result contributes to a better understanding of the water-assisted and oxygen-assisted synthesis of CNT arrays, and provides useful clues on how to extend the lifetime and improve the activity of the catalysts.
文摘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.
基金financial support from European Union(Interreg FWVL V project PSYCHE)from the French National Research Agency(Multiprobe project,ANR-20-CE42-0007)。
文摘CO_(2)hydrogenation is an attractive way to store and utilize carbon dioxide generated by industrial processes,as well as to produce valuable chemicals from renewable and abundant resources.Iron catalysts are commonly used for the hydrogenation of carbon oxides to hydrocarbons.Iron-molybdenum catalysts have found numerous applications in catalysis,but have been never evaluated in the CO_(2)hydrogenation.In this work,the structural properties of iron-molybdenum catalysts without and with a promoting alkali metal(Li,Na,K,Rb,or Cs)were characterized using X-ray diffraction,hydrogen temperatureprogrammed reduction,CO_(2)temperature-programmed desorption,in-situ^(57)Fe Mossbauer spectroscopy and operando X-ray adsorption spectroscopy.Their catalytic performance was evaluated in the CO_(2)hydrogenation.During the reaction conditions,the catalysts undergo the formation of an iron(Ⅱ)molybdate structure,accompanied by a partial reduction of molybdenum and carbidization of iron.The rate of CO_(2)conversion and product selectivity strongly depend on the promoting alkali metals,and electronegativity was identified as an important factor affecting the catalytic performance.Higher CO_(2)conversion rates were observed with the promoters having higher electronegativity,while low electronegativity of alkali metals favors higher light olefin selectivity.
基金supported by the China Scholarship Council (CSC) for the research at Norwegian University of Science and Technologysupported by the Natural Science Foundation of China (21306046)+2 种基金the Open Project of State Key Laboratory of Chemical Engineering (SKL-Che-15C03)the Fundamental Research Funds for the Central Universities (WA1514013)the 111 Project of Ministry of Education of China (B08021)
文摘K-promoted iron/carbon nanotubes composite（i.e., Fe K-OX） was prepared by a redox reaction between carbon nanotubes and K2FeO4followed by thermal treatments on a purpose as the Fischer–Tropsch catalyst for the direct conversion of syngas to lower olefins. Its catalytic behaviors were compared with those of the other two Fe-IM and Fe K-IM catalysts prepared by impregnation method followed by thermal treatments. The novel Fe K-OX composite catalyst is found to exhibit higher hydrocarbon selectivity,lower olefins selectivity and chain growth probability as well as better stability. The catalyst structureperformance relationship has been established using multiple techniques including XRD, Raman, TEM and EDS elemental mapping. In addition, effects of additional potassium into the Fe K-OX composite catalyst on the FTO performance were also investigated and discussed. Additional potassium promoters further endow the catalysts with higher yield of lower olefins. These results demonstrated that the introduction method of promoters and iron species plays a crucial role in the design and fabrication of highly active,selective and stable iron-based composite catalysts for the FTO reaction.
基金Chinese Academy of Sciences for a President's International Fellowship for Visiting Scientists。
文摘The N,N,N'-ferrous chloride complexes,[2-{CMeN(2,4-(CHPh)_(2)-6-FC_(6)H_(2))}-6-(CMeNAr)C_(5)H_(3)N]FeCl_(2)(Ar=2,6-Me_(2)C_(6)H_(3) Fe1,2,6-Et_(2)C_(6)H_(3)Fe2,2,6-^(i)Pr_(2)C_(6)H_(3) Fe3,2,4,6-Me_(3)C_(6)H_(2) Fe4 and 2,6-Et_(2)-4-MeC_(6)H_(2) Fe5),each possessing one N-2,4-dibenzhydryl-6-fluorophenyl group,were readily synthesized from their respective unsymmetrical bis(imino)pyridines,L1-L5.Structural identification of Fe2 highlighted the variation in the steric properties provided by the dissimilar N-aryl groups.Following pre-treatment with either MAO or MMAO,complexes Fe1-Fe5 all displayed,at an operating temperature of 80℃,high activities for ethylene polymerization with levels falling in the order:Fe4> Fe1> Fe5> Fe2> Fe3.Notably,Fe4/MAO displayed the highest activity of 1.94×10^(7) g_(PE)·mol_(Fe)^(-1)·h^(-1) of the study with only a modest loss in performance at 90℃.Generally,the resulting polyethylenes were highly linear(T_(m) range:122-132℃),narrowly disperse and of low molecular weight(M_(w) range:6.73-46.04kg·mol^(-1)),with the most sterically hindered Fe3 forming the highest molecular weight polymer of the series.End-group analysis by ^(1)H-and ^(13)CNMR spectroscopy revealed saturated alkyl(n-propyl and i-propyl) and unsaturated vinyl chain ends indicative of the role of both β-H elimination and chain transfer to aluminum as termination pathways.By comparison with previou sly reported iron precatalysts with similar tridentate ligand skeletons,it is evident that the introduction of a large benzhydryl group in combination with a fluorine as the ortho-substituents of one N-aryl group has the effect of enhancing thermal stability of the iron polymerization catalyst whilst maintaining appreciable polymer molecular weight.
基金the Haihe Laboratory of Sus-tainable Chemical Transformations for financial support(No.24HHWCSS00009).
文摘Ammonia is essential for agriculture and,as a next-generation carbon-free fuel,typically produced through the Haber-Bosch method.This process requires high temperature and pressure,leading to significant energy consumption and greenhouse gas emissions.Therefore,achieving ammonia synthesis under milder conditions has been a long-standing goal.In this study,we design and synthesize a series of CeO_(2)-modified Fe/carbon-based catalysts with varying amounts of CeO_(2)(Ce_(x)Fe_(y)/C).The catalyst Ce_(2)Fe_(5)/C demonstrates an ammonia yield rate of 3.5 mmol/(g·h),which is 44 times greater than that of Fe/C and 8 times greater than that of commercial Fe-based catalysts at 300℃and 1 MPa.Temperature-programmed desorption experiments show that Ce_(2)Fe_(5)/C has enhanced nitrogen adsorption capabilities.Multiple analyses confirm that the CeO_(2)in Ce_(2)Fe_(5)/C is rich in oxygen vacancies,which can provide electrons to Fe,facilitating nitrogen adsorption,dissociation,and activity in low-temperature ammonia synthesis.
基金support and encouragement of the National Natural Science Foundation of China(Nos.U1663222 and 21176208)
文摘In this study, a series of aryloxy-aluminoxanes originated directly from the hydrolysis of reaction products of A1Me3 and phenols were synthesized, which could serve as effective polymer-retarding activators for the iron-catalyzed ethylene oligomerization. The molar ratios of [PhOH]/[AlMe3] and [H2O]/[Al] during the preparation were explored and their impacts on the oligomerization activity and product distribution were discussed. To obtain the effective activators with good polymer-retarding effect and relatively high activity, the optimized conditions were proposed to be [PhOH]/[AlMe3] = 0.5 and [H2O]/[Al] = 0.7. Various aluminoxanes with different [-OH] sources confirmed the importance of using phenols in preparing the effective polymer-retarding activators. By utilizing these aryloxy-aluminoxanes, the mass fraction of polymers in the total products could be reduced to lower than 1.0 wt%, which is much lower than that of the MAO-activated systems （〉 30 wt%）. This is a potential benefit for the industrial application of the iron-catalyzed oligomerization process.
基金the National Natural Science Foundation of China (20576021)Science & Technology Priority Project of Fujian Province (2005HZ01-2)National Key Technology R&D Program of China (2007BAE08B02)
文摘Rare earth gangue, which mainly consists of mixtures of light rare earths such as lanthana, ceria, neodymium oxide and praseodymium oxide, was used as the promoter of fused iron catalysts for ammonia synthesis. The result showed that the activity of the catalyst promoted with rare earth gangue was comparable with those of commercial iron catalysts with high amount of cobalt. The role of rare earths was owed to their advantages for favoring the deep reduction of the main composite in catalyst, i.e., iron oxide. This fmding indicated that the use of rare earth gangue could decrease the content of cobalt or even completely replace cobalt, which was used to be regarded as unsub- stitutable promoters for high performance ammonia catalyst; therefore, the cost of fused iron catalysts would decrease significantly.
文摘A series of both unsupported and coal‐supported iron–oxygen compounds with gradual changes in microstructure were synthesized by a precipitation‐oxidation process at 20 to 70°C.The relationship between the microstructures and catalytic activities of these precursors during direct coal liquefaction was studied.The results show that the microstructure could be controlled through adjusting the synthesis temperature during the precipitation‐oxidation procedure,and that compounds synthesized at lower temperatures exhibit higher catalytic activity.As a result of their higher proportions ofγ‐FeOOH orα‐FeOOH crystalline phases,the unsupported iron–oxygen compounds synthesized at 20–30°C,which also had high specific surface areas and moisture levels,generate oil yields 4.5%–4.6%higher than those obtained with precursors synthesized at 70°C.It was also determined that higher oil yields were obtained when the catalytically‐active phase formed by the precursors during liquefaction(pyrrhotite,Fe1-xS)had smaller crystallites.Feed coal added as a carrier was found to efficiently disperse the active precursors,which in turn significantly improved the catalytic activity during coal liquefaction.
基金Supported by the National Natural Science Foundation of China（20803064） the Natural Science Foundation of Zhejiang Province（Y409034）
文摘Activated carbon-supported Ru-based catalyst and A301 iron catalyst were prepared,and the influences of reaction temperature,space velocity,pressure,and H2/N2 ratio on performance of iron catalyst coupled with Ru catalyst in series for ammonia synthesis were investigated.The activity tests were also performed on the single Ru and Fe catalysts as comparison.Results showed that the activity of the Ru catalyst for ammonia synthesis was higher than that of the iron catalyst by 33.5%-37.6% under the reaction conditions：375-400 °C,10 MPa,10000 h-1,H2︰N2 3,and the Ru catalyst also had better thermal stability when treated at 475 °C for 20 h.The outlet ammonia concentration using Fe-Ru catalyst was increased by 45.6%-63.5% than that of the single-iron catalyst at low tem-perature （375-400 °C）,and the outlet ammonia concentration increased with increasing Ru catalyst loading.
基金supported by the Fundamental Research Funds for the Central Universities (No. 2021ZY79)Beijing Municipal Education Commission through the Innovative Transdisciplinary Program "Ecological Restoration Engineering” (No. GJJXK210102)+2 种基金National Natural Science Foundation of China (Nos. 42075169, U1810209)National Key R&D Program of China (No. 2021YFE0110800)Chinese-Serbian collaboration project (No. 451-03-1205/2021-09)。
文摘A series of monolithic MnO_(2)/iron mesh (IM) catalysts for oxidation of toluene were successfully prepared by using in situ hydrothermal growth.MnO_(2)can grow firmly on the IM substrates surface with a shedding rate of only 0.14%.Due to the highest O_(ads) and high-valent Mn^(4+) and Fe^(3+) elements,the temperature at 50% and 90% toluene conversion (T_(50%) and T_(90%)) was 252 and 265℃,respectively for the best performance catalyst (hydrothermal temperature of 80℃,hydrothermal time of 12 h,and precursor manganese ion concentration of 0.03 mol/L).The catalysts also presented good water resistance and cycle performance.In-situ DRIFTS results suggesting that toluene was first rapid transformed into the reaction intermediate species (benzoate species) and then converted to CO_(2)and H_(2)O.Therefore,this work provides a new direction for the research and application of IM-based monolithic catalysts.
基金supported by the Foundation of China Postdoctoral Science Foundation (20080430734)
文摘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.
