Yolk–shell structured iron carbide/N-doped carbon composite as highly efficient and stable oxygen reduction reaction electrocatalyst

We report a simple route to synthesize iron carbide/carbon yolk–shell composite via a facile two-step process including polymerization of pyrrole using Fe₃O₄ as a sacrificial template to form a Fe₃O₄/polypyrrole composite, followed by annealing at high temperature in N₂ atmosphere. The yolk–shell composite, with iron carbide (Fe_2.5C) embedded in nitrogen-doped carbon layers, shows impressively high catalytic activity and stability for oxygen reduction reaction in alkaline solution. Both the pyridinic-N and graphic-N in the shell of Fe₃O₄–PPy-700, together with the Fe_2.5C confined in carbon layers are believed to be the active sites for the ORR.     

Sol–gel derived CeO2–Fe2O3 nanoparticles: Synthesis,characterization and solar thermochemical application

Synthesis of CeO₂–Fe₂O₃ nanoparticles via propylene oxide (PO) aided sol–gel method for the production of solar fuels via thermochemical H₂O/CO₂ splitting cycles is reported in this paper. For the synthesis of CeO₂–Fe₂O₃, cerium nitrate hexahydrate and iron nitrate nonahydrate were first dissolved in ethanol and then PO was added to this mixture as a proton scavenger to achieve the gel formation. Synthesized CeO₂–Fe₂O₃ gel was aged, dried, and then calcined in air to achieve the desired phase composition. Influence of different synthesis parameters on physico-chemical properties of sol-gel derived CeO₂–Fe₂O₃ was explored in detail by using various analytical methods such as powder x-ray diffraction (PXRD), BET surface area analyzer (BET), x-ray energy dispersive spectrometer (EDS), scanning electron microscopy (SEM), and high resolution transmission electron microscopy (HR–TEM). According to the findings, at all experimental conditions, phase/chemical composition of sol–gel derived CeO₂–Fe₂O₃ was observed to be unaltered. The SSA and pore volume was increased with the upsurge in the amount of PO used during sol–gel synthesis and decreased with the rise in the calcination temperature and dwell time. In contrast, the crystallite size was enlarged with the increase in the calcination temperature and dwell time. The nanoparticle morphology of the sol–gel derived CeO₂–Fe₂O₃ was verified with the help of SEM/TEM analysis. Thermochemical CO production ability of sol–gel derived CeO₂–Fe₂O₃ was investigated by performing thermogravimetric thermal reduction and CO₂ splitting experiments in the temperature range of 1000–1400 °C. Reported results indicate that the sol–gel derived CeO₂–Fe₂O₃ produced higher amounts of O₂ (69.134 μmol/g) and CO (124.013 μmol/g) as compared to previously investigated CeO₂ and CeO₂–Fe₂O₃ in multiple thermochemical cycles. It was also observed that the redox reactivity and thermal stability of sol–gel derived CeO₂–Fe₂O₃ remained unchanged as it produced constant amounts of O₂ and CO in eight successive thermochemical cycles.     

Axial gas profiles in a bubbling fluidised bed biomass gasifier

A 200 mm laboratory-scale atmospheric bubbling fluidised bed reactor has been used to obtain experimental data for the air/steam gasification of eucalyptus red gum wood chips and commercial wood pellets. The unique feature of this gasifier is the ability to examine the variations to axial gas composition along the bed height. At present no such data is available in the literature for biomass gasification. Gasification tests were performed using beds of; silica sand, char or clay to determine the effect of bed type on the gas composition. The behaviour of the major gas species (CO, H₂, CO₂) were observed to be strongly influenced by the water–gas shift reaction within the freeboard of the gasifier resulting in the exit gas being relatively similar in composition as compared to the in-bed variations. These small differences in gas composition for all bed types tested are the result of the achievement of equilibrium in the water–gas shift reaction. The influence of bed type exerted the most impact on the C₂–C₃ emissions (tar proxy) with the char bed found to best aid in their breakdown and to limit the amount of hydrocarbons surviving into the freeboard. The reduction of iron oxide (Fe₂O₃) content in the clay to a more reactive form of magnetite Fe₃O₄ by CO and H₂ in the product gas resulted in the clay bed to also exhibit a reduction in C₂–C₃ emissions compared to silica sand but less then char. The clay bed produced the highest calorific values for the producer gas. However, operation of the clay bed above 800 °C exhibits the potential for over reduction to form iron with subsequent agglomeration of the bed. Changing the fuel type to a biomass pellet resulted in higher emissions of C₁–C₃ hydrocarbons and in part its contribution is the result of primary particle fragmentation during screw feed conveying to the bed. Feeder location and bed design (conical or cylindrical) also exhibit an influence on hydrocarbon emissions.     

Study on an iron–manganese Fischer–Tropsch synthesis catalyst prepared from ferrous sulfate

A systematic study was undertaken to investigate the effects of the initial oxidation degree of iron on the bulk phase composition and reduction/carburization behaviors of a Fe–Mn–K/SiO₂ catalyst prepared from ferrous sulfate. The catalyst samples were characterized by powder X-ray diffraction (XRD), Mössbauer spectroscopy, X-ray photoelectron spectroscopy (XPS) and H₂ (or CO) temperature-programmed reduction (TPR). The Fischer–Tropsch synthesis (FTS) performance of the catalysts was studied in a slurry-phase continuously stirred tank reactor (CSTR). The characterization results indicated that the fresh catalysts are mainly composed of α-Fe₂O₃ and Fe₃O₄, and the crystallite size of iron oxides is decreased with the increase of the initial oxidation degree of iron. The catalyst with high content of α-Fe₂O₃ in its as-prepared state has high content of iron carbides after being reduced in syngas. However, the catalyst with high content of Fe₃O₄ in its as-prepared state cannot be easily carburized in CO and syngas. FTS reaction study indicates that Fe-05 (Fe³⁺/Fe_total = 1.0) has the highest CO conversion, whereas Fe-03 (Fe³⁺/Fe_total = 0.55) has the lowest activity. The catalyst with high CO conversion has a high selectivity to gaseous hydrocarbons (C₁–C₄) and low selectivity to heavy hydrocarbons (C₅₊).     

Oxygen carriers for chemical looping combustion of solid fuels

A thermal analyzer-differential scanning calorimeter-mass spectrometer (TG-DSC-MS) was used to study oxygen carriers (OC) for their potential use for the application of chemical looping combustion (CLC) to solid fuels. Reaction rates, changes in reaction rates with repeated oxidation-reductions, exothermic heats during oxidation, and the effect of changing reduction gas compositions were studied. Oxidation rates were greater than reduction rates and reaction rates were reproducible through multiple oxidation-reduction cycles except where agglomeration occurred with powders. Iron oxide (Fe₂O₃ powder) and iron-based catalysts were found suitable for CLC of solid fuels having rapid reduction rates which increased with higher reducing gas concentrations. Fe₂O₃ powder was used to oxidize a high carbon coal char in an inert gas removing 88% of the carbon from the char. Other properties such as cost and durability indicated iron oxide OCs potential use for CLC of solid fuels.     

Direct conversion of methane to synthesis gas using lattice oxygen of CeO2–Fe2O3 complex oxides

Three kinds of complex oxides oxygen carriers (CeO₂–Fe₂O₃, CeO₂–ZrO₂ and ZrO₂–Fe₂O₃) were prepared and tested for the gas–solid reaction with methane in the absence of gaseous oxidant. These oxides were prepared by co-precipitation method and characterized by means of XRD, H₂-TPR and Raman. The XRD measurement shows that Fe₂O₃ particles well disperse on ZrO₂ surface and Ce–Zr solid solution forms in CeO₂–ZrO₂ sample. For CeO₂–Fe₂O₃ sample, only a small part of Fe³⁺ has been incorporated into the ceria lattice to form solid solutions and the rest left on the surface of the oxides. Low reduction temperature and low lattice oxygen content are observed over ZrO₂–Fe₂O₃ and CeO₂–ZrO₂ samples, respectively by H₂-TPR experiments. On the other hand, CeO₂–Fe₂O₃ shows a rather high reduction peak ascribed to the consuming of H₂ by bulk CeO₂, indicating high lattice oxygen content in CeO₂–Fe₂O₃ complex oxides. The gas–solid reaction between methane and oxygen carriers are strongly affected by the reaction temperature and higher temperature is benefit to the methane oxidation. ZrO₂–Fe₂O₃ sample shows evident methane combustion during the reducing of Fe₂O₃, and then the methane conversion is strongly enhanced by the reduced Fe species through catalytic cracking of methane. CeO₂–ZrO₂ complex oxides present a high activity for methane oxidation due to the formation of Ce–Zr solid solution, however, the low synthesis gas selectivity due to the high density of surface defects on Ce–Zr–O surface could also be observed. The highly selective synthesis gas (with H₂/CO ratio of 2) can be obtained over CeO₂–Fe₂O₃ oxygen carrier through gas–solid reaction at 800 °C. It is proposed that the dispersed Fe₂O₃ and Ce–Fe solid solution interact to contribute to the generation of synthesis gas. The reduced oxygen carrier could be re-oxidized by air and restored its initial state. The CeO₂–Fe₂O₃ complex oxides maintained very high catalytic activity and structural stability in successive redox cycles. After a long period of successive redox cycles, there could be more solid solutions in the CeO₂–Fe₂O₃ oxygen carrier, and that may be responsible for its favorable successive redox cycles performance.     

Anchoring mesoporous Fe3O4 nanospheres onto N-doped carbon nanotubes toward high-performance composite electrodes for supercapacitors

Fe-based oxide electrodes for practical applications in supercapacitors (SCs) suffer from low conductivity and poor structural stability. To settle these issues, we report on the design and synthesis of Fe₃O₄/carbon nanocomposites via firmly anchoring mesoporous Fe₃O₄ nanospheres onto N-doped carbon nanotubes (N-CNTs) via C–O–Fe bonds. Mesoporous Fe₃O₄ nanospheres are featured by rich electroactive sites and short ion diffusion pathways. The N-CNTs, on the other hand, serve as the scaffolds, which not only provide conductive networks but also suppress the accumulation between mesoporous Fe₃O₄ nanospheres as well as alleviate volume changes during charge/discharge cycles. Accordingly, the constructed Fe₃O₄/N-CNTs nanocomposite electrode demonstrates improved specific capacity values of up to 314 C g⁻¹ at 1 A g⁻¹, with 92% retention of the initial capacity after 5000 cycles at 10 A g⁻¹. In addition, the assembled Fe₃O₄/N-CNTs//active carbon (AC) asymmetric supercapacitor (ASC) device possesses an energy density of 25.3 Wh kg⁻¹, suggesting that the prepared Fe₃O₄/N-CNTs nanocomposites are promising electrode materials for use in SCs.     

Effects of Zn, Cu, and K Promoters on the Structure and on the Reduction, Carburization, and Catalytic Behavior of Iron-Based Fischer–Tropsch Synthesis Catalysts

Zn, K, and Cu effects on the structure and surface area and on the reduction, carburization, and catalytic behavior of Fe–Zn and Fe oxides used as precursors to Fischer–Tropsch synthesis (FTS) catalysts, were examined using X-ray diffraction, kinetic studies of their reactions with H₂ or CO, and FTS reaction rate measurements. Fe₂O₃ precursors initially reduce to Fe₃O₄ and then to metallic Fe (in H₂) or to a mixture of Fe_2.5C and Fe₃C (in CO). Zn, present as ZnFe₂O₄, increases the surface area of precipitated oxide precursors by inhibiting sintering during thermal treatment and during activation in H₂/CO reactant mixtures, leading to higher FTS rates than on ZnO-free precursors. ZnFe₂O₄ species do not reduce to active FTS structures, but lead instead to the loss of active components; as a result, maximum FTS rates are achieved at intermediate Zn/Fe atomic ratios. Cu increases the rate of Fe₂O₃ reduction to Fe₃O₄ by providing H₂ dissociation sites. Potassium increases CO activation rates and increases the rate of carburization of Fe₃O₄. In this manner, Cu and K promote the nucleation of oxygen-deficient FeO _x species involved as intermediate inorganic structures in reduction and carburization of Fe₂O₃ and decrease the ultimate size of the Fe oxide and carbide structures formed during activation in synthesis gas. As a result, Cu and K increase FTS rates on catalysts formed from Fe–Zn oxide precursors. Cu increases CH₄ and the paraffin content in FTS products, but the additional presence of K inhibits these effects. Potassium titrates residual acid and hydrogenation sites and increases the olefin content and molecular weight of FTS products. K increases the rate of secondary water–gas shift reactions, while Cu increases the relative rate of oxygen removal as CO₂ instead of water after CO is dissociated in FTS elementary steps. Through these two different mechanisms, K and Cu both increase CO₂ selectivities during FTS reactions on catalysts based on Fe–Zn oxide precursors.     

Reduction and oxidation properties of Fe2O3/ZrO2 oxygen carrier for hydrogen production

Fe₂O₃ is a promising oxygen carrier for hydrogen production in the chemical-looping process. A set of kinetic studies on reduction with CH₄, CO and H₂ respectively, oxidation with water and oxygen containing Ar for chemical-looping hydrogen production was conducted. Fe₂O₃ (20 wt.%)/ZrO₂ was prepared by a co-precipitation method. The main variables in the TGA (thermogravimetric analyzer) experiment were temperatures and gas concentrations. The reaction kinetics parameters were estimated based on the experimental data. In the reduction by CH₄, CO and H₂, the reaction rate changed near FeO. Changes in the reaction rate due to phase transformation were observed at low temperature and low gas concentration during the reduction by CH₄, but the phenomenon was not remarkable for the reduction by CO and H₂. The reduction rate achieved using CO and H₂ was relatively faster than achieved using CH₄. The Hancock and Sharp method of comparing the kinetics of isothermal solid-state reactions was applied. A phase boundary controlled model (contacting sphere) was applied to the reduction of Fe₂O₃ to FeO by CH₄, and a different phase boundary controlled model (contacting infinite slab) was fit well to the reduction of FeO to Fe by CH₄. The reduction of Fe₂O₃ to Fe by CO and H₂ can be described by the former phase boundary controlled model (contacting sphere). This phase boundary controlled model (contacting sphere) also fit well for the oxidation of Fe to Fe₃O₄ by water and FeO to Fe₂O₃ by oxygen containing Ar. These kinetics data could be used to design chemical-looping hydrogen production systems.     

Fe2O3/粉煤灰载氧体化学链燃烧实验与机理研究

提出了一种以粉煤灰为载体制备的新型铁基载氧体。采用同步热重分析仪、小型流化床以及DFT分别研究了新型载氧体的活性与热稳定性,发泡剂含量与反应温度以及粉煤灰主要组分之间的协同作用对新型载氧体性能的影响。研究结果表明,新型载氧体在以CO为燃料的化学链系统中具有较高的活性;新型载氧体较大的孔隙率以及粉煤灰多组分间的协同作用促使850℃下发泡剂含量为10.0%(质量)的新型铁基载氧体的最大转化率(84.9%)比Fe₂O₃/Al₂O₃的最大转化率(54.3%)高30%,且新型铁基载氧体在30个循环测试中表现出良好的热稳定性。载体制备采用的发泡剂含量以及反应温度对新型铁基载氧体性能影响很大,适当的发泡剂含量(约10%(质量))可提高新型载氧体性能。此外,高温下会造成载氧体的烧结现象。最后,采用密度泛函理论(DFT)研究了粉煤灰与载氧体之间的界面作用以及协同氧化CO的电子特性。计算结果表明,粉煤灰和Fe₂O₃之间的界面电荷转移使Fe₂O₃为电正性,促使CO在表面的相互作用,载体和活性组分之间的协同作用降低了载氧体与CO前线轨道能量差,进而促进了CO与Fe₂O₃的反应。     

Prevention of bed agglomeration with iron oxide during fluidized bed incineration of refuse-derived fuels

The present study was performed to evaluate the effect of iron oxide addition on the prevention of bed agglomeration during the fluidized bed incineration of refuse-derived fuels (RDFs) having different alkali contents. To investigate the extent of bed agglomeration as a function of the Fe₂O₃/(K₂O+Na₂O) molar ratio, a simulation was performed by using a thermodynamic equilibrium model. Based on this simulation, potassium (K) component exhibited a much higher affinity for iron (Fe) component than for silicon (Si) component, and the extent of agglomeration was remarkably reduced. Therefore, a small amount of iron oxide added to the bed effectively reduced the extent of bed agglomeration in the fluidized bed incineration process. Furthermore, the extent of agglomeration decreased as the molar ratio of Fe₂O₃/(K₂O+Na₂O) increased until unity was attained. In excess Fe₂O₃, no potassium silicate melts existed in the products, while the amount of sodium silicate melts remained constant.     

Electroreduction of cation-deficient oxide and dioxygen at a passive iron electrode

The electrochemical characterization of the cation-deficient Fe₂O₃ or passive film with adsorbed oxygen atoms has been given which was produced on iron under the strongly oxidizing conditions of higher potentials. The reduction potential of the cation-deficient Fe₂O₃ lay about 0.5 V anodic to that of the ordinary passive film on iron. The reduction of dioxygen has been studied at a rotating platinum ring-passive iron disk electrode. The passive film was first reduced to porous intermediate [Fe(OH)₂]_ads, and dioxygen was reduced by a four electron process on a film (Fe₃O₄)-covered iron.     

Rh–Fe/Ca–Al2O3: A Unique Catalyst for CO-Free Hydrogen Production in Low Temperature Ethanol Steam Reforming

Low temperature ethanol steam reforming (ESR) was studied over a series of 1 wt% Rh–x % Fe catalysts with various Fe loading (x = 0–10 wt%) and on different supports (Ca–Al₂O₃, SiO₂ and ZrO₂). The results show that close interaction between Rh and Fe is required to reduce the CO selectivity to almost negligible values. In addition, Rh–Fe supported on Ca–Al₂O₃ exhibits the best performance in terms of CO selectivity and hydrogen yield as compared to other supports. Characterization by XPS and XANES indicates the presence of Fe_xO_y species upon reduction, resulting in the formation of coordinatively unsaturated ferrous (CUF) active sites along the Rh–Fe_xO_y interface. These CUF sites promote water–gas shift reaction during low temperature ESR. Temperature programmed oxidation and Raman spectroscopy of spent catalysts also indicate that the addition of iron oxide reduces coke deposition and forms more reactive coke. Hence, the catalyst lifespan is significantly extended.     

Effectiveness of Ni incorporation in iron oxide crystal structure towards thermochemical CO2 splitting reaction

In this study, Ni-doped iron oxide (Ni_xFe_3−xO₄) materials were synthesized via the 1,2-epoxypropane assisted sol-gel method by varying the molar concentration of Ni from x=0.2 to 1. Sol-gel derived Ni_xFe_3−xO₄ gels were dried and the dried powder was further calcined upto 600 °C in air for 90 min. Obtained calcined Ni_xFe_3−xO₄ powders were further analyzed to determine the phase composition, crystallite size, specific surface area, pore volume, and morphology via powder X-ray diffraction (PXRD), BET surface area analysis (BET), as well as scanning and transmission electron microscopy (SEM and TEM). The obtained results in the synthesis and characterization section indicate formation of Ni_xFe_3−xO₄ nanoparticles with high specific surface area. Thermal reduction and re-oxidation of the sol-gel synthesized Ni_xFe_3−xO₄ materials were determined by using the high temperature thermogravimetry. Obtained results indicate that the amount of O₂ released during the thermal reduction step (at 1400 °C) and quantity of CO produced during the CO₂ splitting step (at 1000 °C) increases as the concentration of Ni inside the iron oxide crystal structure increases. The highest amounts of O₂ released (221.88 μmol/g) and CO produced (375.01 μmol/g) in case of NiFe₂O₄ (NF10 material).     

In situ sonochemical synthesis of Fe3O4–graphene nanocomposite for lithium rechargeable batteries

In this paper, we have presented experimental results for preparation of Fe₃O₄–graphene nanocomposite that uses an ultrasound assisted method. The graphene oxide (GO) was prepared from graphite powder using modified Hummers–Offeman method. Subsequently, the synthesis of graphene-Fe₃O₄ nanocomposite was carried out by ultrasound assisted co-precipitation of iron (II) and (III) chlorides in the presence of GO. The formation of GO and graphene-Fe₃O₄ nanocomposite was confirmed by X-ray diffraction (XRD), Energy dispersive X-ray (EDX) analysis and Fourier transform-infrared (FTIR) analysis. The particle size of Fe₃O₄ nanoparticles loaded on graphene nanosheets (observed from TEM image) was found to be smaller than 20 nm. The use of ultrasonic irradiations during synthesis of graphene-Fe₃O₄ nanocomposite resulted in uniform loading of Fe₃O₄ nanoparticles on graphene nanosheets. The prepared graphene-Fe₃O₄ nanocomposite material was used for the preparation of anode for lithium ion batteries. The electrochemical performance of the material was tested by cyclic voltammetry (CV) and charge/discharge cycles. It was observed that the capacity of Li-battery when the anode material was made using graphene-Fe₃O₄ nanocomposite showed stable electrochemical performance for around 120 cycles and the battery could repeat stable charge–discharge reaction.     

Effect of iron oxide content on the crystallisation of a diopside glass–ceramic glaze

The effect of iron oxide content on the crystallisation of a diopside glass–ceramic glaze was investigated using a glass–ceramic frit in the K₂O–ZnO–MgO–CaO–Al₂O₃–SiO₂ system and a granite waste glass. Measurements by X-ray diffraction (XRD) combined with scanning electron microscopy (SEM) and EDX microanalysis showed that the distribution of Fe³⁺ ions among different crystalline phases such as franklinite (ZnFe₂O₄) and hematite Fe₂O₃ depends on the iron content in the original diopside mixture. Thus, the original glaze crystallises to franklinite or hematatite when iron content is greater than 2 and 15%, respectively.     

Low temperature synthesis and formation mechanism of carbon encapsulated nanocrystals by electrophilic oxidation of ferrocene

A novel method is developed for low temperature synthesis of carbon encapsulated spherical Fe₇S₈, equiaxed Fe₃O₄ and spherical porous FeOOH nanocrystals with a core–shell structure via a solid–solid reaction of ferrocene with (NH₄)₂S₂O₈, (NH₄)₂Cr₂O₇ and NH₄ClO₄ in an autoclave, respectively. Samples were characterized by X-ray diffraction, scanning electron microscopy and transmission electron microscopy. It is found that the median size of Fe₇S₈, Fe₃O₄ and FeOOH nanocrystals is about 28.99, 52.68 and 25.66 nm, respectively. The hollow worm-like carbon shell provides exclusive rooms for tens to hundreds of nanocrystals separated from each other. The cooperative effect of ammonium and strong oxidizing ion on electrophilic oxidation of ferrocene contributes to the in situ formation of carbon shell on the nanocrystals. The metal–π interaction of iron atom with cyclopentadienone oligomers enables ordered self-assembling of carbon rings, resulting in the formation of graphitizable carbon shell with roughly parallel fringes at low temperature.     

Study on Fe–Al2O3 interaction over precipitated iron catalyst for Fischer–Tropsch synthesis

Two model spherical iron catalysts (100Fe/0Al₂O₃ and 100Fe/15Al₂O₃) with free Cu and K promoters were prepared by the combination of co-precipitation and spray drying method for the application of slurry Fischer–Tropsch synthesis (FTS). The effect of Fe–Al₂O₃ interaction on the reduction/carburization behavior in H₂/CO/syngas, surface basicity and the change of phase structure were comparatively studied by means of H₂ or CO temperature-programmed reduction (TPR), CO₂ temperature-programmed desorption (TPD) and Mössbauer effect spectroscopy (MES). The results showed that the catalyst incorporated with Al₂O₃ exhibits a strong Fe–Al₂O₃ interaction, which obviously weakens the surface basicity, stabilizes the FeO phase and inhibits the reduction of iron catalyst in H₂ or syngas. Furthermore, Fe–Al₂O₃ interaction also restrains the carburization of iron catalyst in CO or syngas. In slurry FTS process, it was found that the strong Fe–Al₂O₃ interaction decreases the FTS activity and suppresses the water gas shift (WGS) reaction, but can stabilize the active sites of iron catalyst and improve its run stability. Due to the strong Fe–Al₂O₃ interaction, the weak surface basicity on the catalyst incorporated with Al₂O₃ greatly decreases the selectivity of heavy hydrocarbon products.     

The use of ilmenite as an oxygen carrier in chemical-looping combustion

The feasibility of using ilmenite as oxygen carrier in chemical-looping combustion has been investigated. It was found that ilmenite is an attractive and inexpensive oxygen carrier for chemical-looping combustion. A laboratory fluidized-bed reactor system, simulating chemical-looping combustion by exposing the sample to alternating reducing and oxidizing conditions, was used to investigate the reactivity. During the reducing phase, 15 g of ilmenite with a particle size of 125–180 μm was exposed to a flow of 450 mL_n/min of either methane or syngas (50% CO, 50% H₂) and during the oxidizing phase to a flow of 1000 mL_n/min of 5% O₂ in nitrogen. The ilmenite particles showed no decrease in reactivity in the laboratory experiments after 37 cycles of oxidation and reduction. Equilibrium calculations indicate that the reduced ilmenite is in the form FeTiO₃ and the oxidized carrier is in the form Fe₂TiO₅ + TiO₂. The theoretical oxygen transfer capacity between these oxidation states is 5%. The same oxygen transfer capacity was obtained in the laboratory experiments with syngas. Equilibrium calculations indicate that ilmenite should be able to give high conversion of the gases with the equilibrium ratios CO/(CO₂ + CO) and H₂/(H₂O + H₂) of 0.0006 and 0.0004, respectively. Laboratory experiments suggest a similar ratio for CO. The equilibrium calculations give a reaction enthalpy of the overall oxidation that is 11% higher than for the oxidation of methane per kmol of oxygen. Thus, the reduction from Fe₂TiO₅ + TiO₂ to FeTiO₃ with methane is endothermic, but less endothermic compared to NiO/Ni and Fe₂O₃/Fe₃O₄, and almost similar to Mn₃O₄/MnO.     

Preparation of a new precipitated iron catalyst for Fischer–Tropsch synthesis

It is well known that a typical precipitated iron catalyst was prepared by iron(III) nitrate (Fe(NO₃)₃). The modified iron catalyst was prepared by iron(II) sulfate in our laboratory. The results from catalytic performance tests showed that the iron catalyst prepared from iron sulfate (cat-S) has the higher activity for Fischer–Tropsch synthesis (FTS) than the catalyst prepared from iron nitrate (cat-N). The results from XRD of catalyst before use showed the difference definitely. The XRD patterns of these catalysts indicate that the main phase of cat-N is Fe₂O₃, whereas the phases of cat-S are a mixture of Fe₂O₃ and Fe₃O₄. It is considered that magnetite was directly formed during precipitation and contained in the catalyst before use enhances the activity for FTS.