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Light olefins such as ethylene, propylene, and butylene are key compounds in the chemical industry. Iron catalyst supported on carbon nanotubes (CNTs) is an appropriate candidate for light olefins production using synthesis gas in Fischer-Tropsch synthesis (FTS). First, catalytic chemical vapor deposition (CCVD) method was applied to synthesize CNTs using Fe/CaCO 3 and acetylene as catalyst and hydrocarbon source, respectively. Applying response surface methodology, the optimum operating conditions were determined in CVD reactor for maximal yield and purity of CNTs. The effects of reaction time (30–60 min), reaction temperature (700–800 °C), and loading of the catalyst (10–30 wt% Fe) were investigated. The synthesized CNTs was characterized by Raman spectroscopy for its graphitic structure and purity. After acid-treatment of the synthesized CNTs, Fe/CNTs-synthesized catalyst was successfully fabricated by ultrasonic-assisted wet impregnation method. 20Fe/CNTs-synthesized, 20Fe/CNTs-commercial, and 20Fe/Al 2 O 3 were analyzed in terms of physio-chemical properties and FTS catalytic performance. Comparison of transmission electron microscopy (TEM) and CO-chemisorption results showed that 20Fe/CNTs-synthesized reduces iron oxide agglomeration resulting in metal particles well-dispersed among the studied Fe-based catalysts. The catalytic performance of Fe-based catalysts was investigated using a fixed-bed reactor at 280 °C under 290 psi. 20Fe/CNTs-synthesized exhibited a lower rate of water-gas-shift (WGS) reaction compared with 20Fe/CNTs-commercial, with C 2 -C 4 selectivity of 23.6% which is slightly less than that of its commercial counterpart. Analysis of FTS liquid products revealed that 20Fe/CNTs-synthesized provides liquid hydrocarbons in the range of C 8 -C 18 , while 20Fe/CNTs-commercial and 20Fe/Al 2 O 3 obtained C 9 -C 52 and C 10 -C 20 , respectively. After 120 h time on stream under steady state condition, higher activity had been maintained by the 20Fe/CNTs-synthesized catalyst compared to the 20Fe/CNTs-Commercial and 20Fe/Al 2 O 3 catalysts. [Display omitted] • Evaluation of the effects of growth parameters on carbon nanotubes yield and purity. • High CO conversion obtained by Fe-synthesised CNTs. • Higher iron time yields obtained by Fe-synthesised CNTs. • Lighter hydrocarbons production via Fe-synthesised CNTs compared to reference catalysts. [ABSTRACT FROM AUTHOR]

Iron-based catalysts have been explored for selective catalytic reduction (SCR) of NO due to environmentally benign characters and good SCR activity. Mn-W-Sb modified siderite catalysts were prepared by impregnation method based on siderite ore, and SCR performance of the catalysts was investigated. The catalysts were analyzed by X-ray diffraction, H 2 -temperature-programmed reduction, Brunauer-Emmett-Teller, Thermogravimetry-derivative thermogravimetry and in-situ diffused reflectance infrared Fourier transform spectroscopy (DRIFTS). The modified siderite catalysts calcined at 450°C mainly consist of Fe 2 O 3 , and added Mn, W and Sb species are amorphous. 3Mn-5W-1.5Sb-siderite catalyst has a wide temperature window of 180-360°C and good N 2 selectivity at low temperatures. In-situ DRIFTS results show NH 4 +, coordinated NH 3 , NH 2 , NO 3 − species (bidentate), NO 2 − species (nitro, nitro-nitrito, monodentate), and adsorbed NO 2 can be discovered on the surface of Mn-W-Sb modified siderite catalysts, and doping of Mn will enhance adsorbed NO 2 formation by synergistic catalysis with Fe3+. In addition, the addition of Sb can inhibit sulfates formation on the surface of the catalyst in the presence of SO 2 and H 2 O. Time-dependent in-situ DRIFTS studies also indicate that both of Lewis and Brønsted acid sites play a role in SCR of NO by ammonia at low temperatures. The mechanism of NO removal on the 3Mn-5W-1.5Sb-siderite catalyst can be discovered as a combination of Eley-Rideal and Langmuir-Hinshelwood mechanisms with three reaction pathways. The mechanism of NO, oxidized by synergistic catalysis of Fe3+ and Mn4+/3+ to form NO 2 among three pathways, reveals the reason of high NO x conversion of the catalyst at medium and low temperatures. [Display omitted] [ABSTRACT FROM AUTHOR]

The research progress and shortcomings of Fenton technology of iron-based catalyst were discussed. The redox characteristics, advantages and potential application fields of non-iron-based Fenton catalysts (such as cerium, chromium, cobalt, copper, manganese, ruthenium, polymetallic oxyhydrochloric acid and gold nanomaterials, etc.) are emphatically introduced. The shortcomings of non-iron based catalysts in practical application are summarized, and it is pointed out that in the future, efficient and stable catalysts, non-iron-based enhanced Fenton-like technology and the combination/coupling technology of non-iron-based Fenton/Fenton-like technology with other processes are the main research areas. [ABSTRACT FROM AUTHOR]

[Display omitted] • Evaluation platform of syngas-derived LT-FTS process based on iron-based catalysts. • Final products (trade-off between wax and gasoline) were controlled by acidity of LT-FTS catalysts. • Reverse water–gas-shift reaction-derived LT-FTS has the greatest potential to reduce CO 2 emission. • Combined reforming shows the best process performance from both economic and environmental perspectives. Fischer–Tropsch synthesis (FTS) is currently garnering significant attention owing to its ability to utilize syngas derived from diverse feedstocks. With the increasing emphasis on achieving net-zero emissions and utilization of alternative sources, determining which syngas production methods to integrate with the FTS process has become crucial. This study analyzed various syngas production methods (natural gas, coal, biomass, and CO 2 /H 2 -based technologies) and their potential combinations with iron-based low-temperature FTS from both economic and environmental perspectives. Our FTS catalyst enables to control product distribution through acidity variation. Therefore, 25 extensive analyzes were performed with different types of syngas production method and final products. As a result, the reverse water–gas-shift reaction using CO 2 and H 2 showed the greatest potential to reduce CO 2 emissions, and combined reforming showed an appropriate environmental and economic balance, showing the best performance among the evaluations conducted in this study. Wax production by LT-FTS, which consumes the least energy, is advantageous regardless of the syngas production method in the unified process standard. Furthermore, we provide the operating strategy of the proposed syngas-derived LT-FTS process considering both the environment and economics. This analysis indicated the potential developmental trajectory of the FTS process as a future carbon–neutral strategy. [ABSTRACT FROM AUTHOR]

• The flower-like spherical, sea urchin-like and tubular MnO 2 were prepared via hydrothermal synthesis. • The promotional effects of different morphology MnO 2 on iron-based Fischer-Tropsch synthesis catalysts are investigated. • The different morphology MnO 2 exhibits observably distinct promotion functions on iron-based FTS catalysts. In this work, flower-like spherical, sea urchin-like and tubular MnO 2 are prepared via hydrothermal synthesis and used as promoters of iron-based Fischer-Tropsch synthesis (FTS) catalysts to investigate their morphological effects. It is found that the different morphology of MnO 2 exhibits observably distinct promotion functions on iron-based FTS catalysts. Tubular MnO 2 contains moderate amount of surface oxygen vacancies accompany with weak Fe-Mn electronical interaction, as a result, tubular MnO 2 promotes the formation of long-chain hydrocarbon and olefins, and restrains the generation of CH 4. Flower-like spherical MnO 2 presents negative roles in the CO conversion and formation of long-chain hydrocarbon, due to its insufficient oxygen vacancies and moderate Fe-Mn electronical interaction. With the most abundance of oxygen vacancies and strongest Fe-Mn interaction, sea urchin-like MnO 2 modified catalysts exhibits the highest initial CO conversion, but deactivates rapidly. Besides, the sea urchin-like MnO 2 enhances the formation of long-chain paraffins. This work presents new insights of the promotion roles of Mn additive, which is beneficial for the rational design of efficient iron-based FTS catalysts. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Pure Fe 5 C 2 were prepared to explore the relationship of catalytic phase-catalytic performance-reaction pathways. • The main hydrocarbon products were alkanes over Fe 5 C 2. • The alkenes selectivity increased obviously over K-modified Fe 5 C 2. • Fe 5 C 2 can catalyze both RWGS and FTS process. • The combination of Fe 3 O 4 and Fe 5 C 2 is beneficial for the long-chain hydrocarbons. Iron-based catalysts have been widely used to synthesize value-added hydrocarbons through CO 2 hydrogenation. Fe carbide, Fe 5 C 2 , was proposed as the active phase responsible for C C coupling during the chain growth. However, the reaction mechanism over iron-based catalysts is still under debate due to the presence of multiple phases of Fe species. In this work, Fe 5 C 2 and K-modified Fe 5 C 2 were prepared and used to study the relationship between the Fe phase, catalytic performance and reaction pathways. CH 4 and CO selectivities of 46.1 C-mol% and 2.8 C-mol% were obtained on Fe 5 C 2 at a CO 2 conversion of 49.8 %, with the main hydrocarbon products being alkanes. With the addition of the promoter K, the C 2 -C 4 = selectivity increased to above 38.0 C-mol%, and the selectivity to C 5+ hydrocarbons increased to 23.9 C-mol% at a similar CO 2 conversion. CH 4 and C 2+ hydrocarbons formed through the CO 2 →CO→hydrocarbons (indirect) route over K-modified Fe 5 C 2 , whereas the direct hydrogenation route occurred on unmodified Fe 5 C 2 in addition to the indirect route of CO 2 to CO to hydrocarbons through Fischer-Tropsch synthesis (FTS) processes. This work offers insights in direct CO 2 hydrogenation over Fe 5 C 2 and Fe 3 O 4 -Fe 5 C 2 catalysts, which advances the understanding of the functions of active phases and reaction pathways of CO 2 hydrogenation over iron-based catalysts. [ABSTRACT FROM AUTHOR]

• Successfully prepared N-doped catalysts built by iron-based metal–organic framework. • Explored the different effects of different types of N sources on the same catalyst. • The addition of N improved the stability and dispersion of the metal–organic frame. Tetracycline, one of the most commonly used antibiotics, has emerged as a critical concern in water pollution treatment. N-doped iron-based catalysts were prepared by one-step pyrolysis with MIL-101 (Fe) as precursors in this study. The effects of doping ratio, material dosage, anions and other factors on the degradation efficiency of tetracycline were investigated. In best conditions, the removal rate of tetracycline has reached 91%, which was attributed to the synergistic effect of free radical (i.e., SO 4 •−, •OH) and non free radical pathways (i.e., 1O 2). And the ion leaching of N doped catalysts was investigated. The iron ion leaching was maintained at a relatively low level. Then, LC-MS was used to study the pathway of tetracycline degradation. ECOSAR assessments had demonstrated that tetracycline and its intermediates exhibited significantly reduced levels of acute toxicity, developmental toxicity, and mutagenicity. These studies indicated that the derivative of N-doped iron-based MOFs was a highly promising, environmentally friendly catalyst for practical wastewater treatment applications. [ABSTRACT FROM AUTHOR]

CO₂ utilisation is increasingly important, and CO₂-hydrogenation represents a potential route for (re)-utilizing of CO₂ in hydrocarbon synthesis, especially when using renewable hydrogen. A large number of data-points in CO 2 hydrogenation have been collected over the last decade, which are re-analysed in this study. This meta-analysis shows that the direct hydrogenation of CO 2 yielding hydrocarbons (with the parallel formation of CO) is evidenced in more than 25% of published data. The meta-analysis further indicates that iron-catalysts may be promising as catalysts for CO 2 hydrogenation, although the obtained chain growth probability is still too low to convert CO 2 to liquid hydrocarbons at a high selectivity. [Display omitted] • Re-analysis of over 1000 data points on activity/selectivity in CO 2 -hydrogenation. • Criterium developed for the evaluation of the reaction pathway in CO 2 -hydrogenation. • Ca. 25% of published data indicate that CO 2 is directly converted into hydrocarbons. [ABSTRACT FROM AUTHOR]

• Iron oxide nanoparticles are highly dispersed on h-BN. • Cu can facilitate the reduction of catalyst by introducing more sites dissociating H 2. • Mn can weaken strong metal support interaction by altering the electron structure of iron species. • A higher activity can be realized due to the synergistic effect of Mn and Cu. A series of Fe/h-BN catalysts promoted with Cu or Mn were prepared for Fischer-Tropsch synthesis (FTS). The physicochemical properties, crystal structures and morphologies of the catalysts were characterized by N 2 physisorption, FT-IR, TPR, XPS, XRD, MES and TEM. It is found that iron oxide nanoparticles are highly dispersed on h-BN matrix due to the anchoring effect of surface defects and the accommodation of porous structures of h-BN. The characterization results indicate that strong interaction between iron oxide and h-BN is present on un-promoted catalyst, which endows the h-BN supported iron catalyst with stable properties under FTS conditions but severely retards reduction of the catalyst. The addition of Cu to Fe/h-BN can to some extent overcome the strong interaction by introducing more sites for dissociating H 2. It is observed that Cu promoter can increase the reduction or carburization degree and thus enhance the FTS activity. The addition of Mn to Fe/h-BN can weaken the strong interaction by altering the electron structure of iron species. And the electron-rich Fe species are responsible for easy reduction and the enhanced FTS performance. Besides, a higher activity can be realized by co-adding Cu and Mn to the Fe/h-BN catalyst. These results suggest that the synergistic effect of Mn and Cu can largely improve the performance of Fe/h-BN catalyst without impairing the stability of the catalyst. The present study paves a way to tailor the performances of FTS catalysts with h-BN as support. [ABSTRACT FROM AUTHOR]

A series of Fe–Mn catalysts was prepared using different supports (kaolin, diatomite, and alumina) and used for NO abatement via low-temperature NH 3 -selective catalytic reduction (SCR). The results showed that 12Fe–10Mn/Kaolin (with the concentration of Fe and Mn 12 and 10 wt.%, respectively) exhibited the highest activity, and more than 95.8% NO conversion could be obtained within the wide temperature range of 120–300°C. The properties of the catalysts were characterized by inductively coupled plasma-atomic emission spectrometry (ICP-AES), thermogravimetry (TG), Brunner–Emmet–Teller (BET) measurements, X-ray diffraction (XRD), H 2 -temperature programmed reduction (H 2 -TPR), NH 3 -temperature programmed desorption (NH 3 -TPD), X-ray photoelectron spectroscopy (XPS), scanning electron microprobe (SEM) and energy dispersive spectroscopy (EDS) techniques. The support effects resulted in significant differences in the components and structures of catalysts. The 12Fe–10Mn/Kaolin catalyst exhibited better dispersion of active species, optimum low-temperature reduction behavior, the largest amount of normalized Brønsted acid sites, and the highest Mn4+/Mn and Fe3+/(Fe3+ + Fe2+), all of which may be major reasons for its superior catalytic activity. Unlabelled Image [ABSTRACT FROM AUTHOR]

Graphical abstract Note: These runs were under the same conditions (i.e. temperature, pressure SV etc.), sampled with the same time-on-stream and utilized the same amount of startup solvent. Thus, runs under the same activity displayed the same levels of start-up solvent. Highlights • Rb and Cs promoted iron catalysts were superior to the K promoted iron catalyst. • The initial overall CO 2 conversion is much higher for Cs and Rb. • These catalysts had a much higher selectivity toward C 5 + materials. • A synergistic effect for Rb and Cs promoters yield cheaper superior catalysts. • Degradation of these catalysts are mainly through coking, not oxidation. Abstract The effect of alkali promoter (K, Rb and Cs) on the performance of precipitated iron-based catalysts was investigated for carbon dioxide (CO 2) hydrogenation. Characterization by temperature-programmed reduction with CO, Mössbauer spectroscopy, and transmission electron microscopy were used to study the effect of alkali promoter interactions on the carburization and phase transformation behavior of the catalysts. Under similar reaction conditions, cesium (Cs) and rubidium (Rb) promoted catalysts exhibited the highest initial CO 2 conversions to higher hydrocarbons. CO 2 conversions then decreased to reach steady state conversions around 170 h on stream. At steady state conversion, all three catalysts exhibited similar CO 2 conversions and selectivities. For comparison, a lower loaded Cs (1.5 Cs) promoted iron-based catalyst was prepared. It exhibited slightly lower initial conversion than the higher loaded Cs catalyst, but remained very stable. Among all the catalysts at steady state conversion, the 1.5 Cs promoted catalyst exhibited the highest stability. Results indicate a synergistic effect brought on by these promoters that, if balanced, could potentially yield superior CO 2 hydrogenation catalysts. [ABSTRACT FROM AUTHOR]

The direct production of light α‐olefins (C2=‐C4=) from CO2 is of great importance as this process can convert the greenhouse gas into the desired chemicals. In this study, the crucial roles of Na and Mn promoter in CO2 hydrogenation to produce light α‐olefins via the Fischer‐Tropsch synthesis (FTS) over Fe3O4‐based catalysts are investigated. The results indicate that both Na and Mn promoter can enhance the reducibility of Fe3O4. In situ XPS and DFT calculations show that Na facilitates the reduction by electron donation from Na to Fe as the oxygen vacancy formation energy is reduced by Na. In contrast, Mn promotes the reduction by the presence of oxygen vacancy in MnO as the oxygen in Fe oxide can spillover to the vacancy in MnO spontaneously. For un‐promoted Fe3O4 catalysts, CO2 hydrogenation dominantly produces light n‐paraffins. The addition of Na remarkably shifts the selectivity to light α‐olefins with a sharp decline in the selectivity to light n‐paraffins, which is attributed to the electron donation from Na to Fe resulting in the promoted CO dissociation and the favorable β‐H abstraction of surface short alkyl‐metal intermediates. The addition of Mn into Na‐containing Fe3O4 catalysts can obviously further enhance the selectivity to light α‐olefins as the spatial hindrance of Mn suppresses the chain growth to increase the amount of surface short alkyl‐metal intermediates. Work together: The roles of Na and Mn promoter are clearly unraveled in CO2 hydrogenation over Fe3O4‐based catalysts for enhanced selectivity to light α‐olefins. Na−Mn synergy favors the selective production of C2=‐C4= from CO2 hydrogenation over Fe3O4‐based catalysts. [ABSTRACT FROM AUTHOR]

Abstract: An iron‐tungsten oxide catalyst was developed for selective catalytic reduction of NO with NH3 (NH3‐SCR) by supporting Fe2O3 nanoparticles onto hexagonal WO3 nanorods. The Fe2O3/WO3 catalyst showed much higher catalytic activity than Fe2O3 and WO3, as explained by the synergistic effects caused by acid sites (provided by WO3) and redox sites (provided by Fe2O3). X‐ray diffraction and transmission electron microscopy techniques revealed that the crystal structures and morphologies of Fe2O3 and WO3 kept unchanged during the preparation of Fe2O3/WO3. NH3 adsorption curves, NH3 temperature programmed desorption, and temperature programmed surface reaction of NO demonstrated that WO3 possessed strong acidity but poor redox ability, whereas Fe2O3 had high redox ability but inadequate acidic property. Therefore, the enhancement in catalytic activity (when using Fe2O3/WO3 as a catalyst) should originate from the redox‐acid synergy, as further evidenced by the low SCR activity of pure Fe2O3 and Fe2O3/TiO2 with low capacity for adsorbing NH3. In addition, Fe2O3/WO3 showed high activity and stability in the presence of K+, SO2, and H2O, demonstrating its potential in practical applications. [ABSTRACT FROM AUTHOR]

Finding a replacement for the toxic hexavalent chromium oxide in commercial iron oxide-based high temperature water-gas shift (HT-WGS) catalyst is of current environmental concern. Previous studies in developing Cr-free catalysts mainly focus on ex-situ characterization on catalysts bulk structure. In the present study, CuO/MO x -Fe 2 O 3 catalysts promoted by Si, Al, Cr or Mg were studied with XRD, in situ Raman, HS-LEIS, BET, transient C 16 O 2  → C 18 O 2 isotopic switch, steady-state WGS activity test and CO-TPR to elucidate their structure-activity relationships. The Mg and Al are homogeneously distributed within both fresh and activated catalysts as texture promoters, while the Si exists as discrete SiO 2 that is covered by iron oxides. During the HT-WGS reaction, the Mg promoter resulted in the poorest thermally stability and least amount of metal-metal oxide interface, and the Si promoter inhibited the reducibility of surface oxygen. Only the Al promoter was found to yield a catalyst that possessed similar catalyst structure, comparable thermostability and activity with the Cr-promoted catalyst. This work demonstrates the importance of in situ characterization to the rational design of Cr-free iron oxide based HT-WGS catalysts. [ABSTRACT FROM AUTHOR]

The interest for the electrodes based on conductive boron-doped diamond powder (BDDP) is increasing in recent years due to their excellent physical and chemical stability, the wide potential window in both aqueous and organic electrolytes, the relatively large specific surface area, and their versatility in comparison to boron-doped diamond thin film electrodes. These materials have been proposed as alternative cathode catalyst support due to their high corrosion resistance when subjected to the highly positive potentials originated during the start-stop operations in fuel cells, especially in automobiles. In this work, we present three BDDP supports with different particle sizes and different surface oxygen contents as supports of different iron species for oxygen reduction reaction in alkaline solution. BDDP supports were modified with carbon nitride (C 3 N 4) or phthalocyanines (Pc) as anchoring points for iron. The different electrocatalytic performance observed confirmed the strong influence of the surface chemistry of the BDDP supports on the activity of the metallic sites for FePc samples while, for Fe-C 3 N 4 samples, the determining effect was the particle size of the BDDP support. Additionally, DFT calculations were used to obtain some insights about the interaction of the FePc with the diamond surface. [ABSTRACT FROM AUTHOR]

Iron-based Fischer-Tropsch synthesis (FTS) has received renewable interests due to the gradual depletion of crude oil resources and its flexible product adjustment from lower olefins to long-chain hydrocarbons. However, one of the main challenges of iron-based FTS catalysts is the relative lower activity or productivity (per gram catalyst) at low or middle temperature. In this work, ultra-active iron-based FTS catalysts (Fe/SMC) were developed by loading iron over spherical mesoporous carbon (SMC) with huge porosity. The large pore volume (2.22 cm 3 /g) and high specific surface area (767 m 2 /g) of SMC allowed the high iron loading (up to 50 wt%) with proper dispersion. Weak C-Fe interaction was observed in the Fe/SMC catalysts, which was favorable for the reduction of iron and its further carburization to form more active sites of FTS. Activity tests showed that the Fe/SMC catalysts exhibited ultra-high activities in FTS. With the increase of iron loadings (30–50 wt%), the FTS rates (FTY, mmol CO/(h·g cat.)) of Fe/SMC catalysts increased due to the larger iron surfaces exposed at higher iron loadings. Small amount of K promoter significantly enhanced the FTY and apparent turnover frequency (TOF, S −1 ) of the Fe/SMC catalysts. The hydrocarbon productivity of K-promoted catalyst (40FeK/SMC) was up to 0.91 g HC/(h·g cat.) (260 °C, H 2 /CO = 1, 2 MPa), much higher than that of any other supported or unsupported iron-based FTS catalysts reported at similar reaction conditions. The results obtained in this work will open a new avenue for the development of highly active iron-based FTS catalysts. [ABSTRACT FROM AUTHOR]

Summary: Herein, we report four self-assembly Iron(II/III) complex consisting triethanolamine (TEOA) as ligand and an FeIII(TPA)Cl3 (TPA= 3-(2-pyridine methyl) amine) as contrast catalyst, for photochemical reduction of CO2 to CO under visible light. The photocatalytic systems were assembled by [Ru(bpy)3]Cl2 as photosensitizer, and 1,3 -dimethyl-2-phenyl-2,3-dihydro-1H-benzo-[d]-imidazole (BIH) as electron donor. Experiments are conducted to study the relationship between CO production and the external ions. Different external counterions are provided to assist the discussion of the influence of these external ions on catalysis. Density functional theory calculations confirmed that the external ions have an effect on the CO yield. Moreover, a mechanism involving proton-coupled electron transfer is proposed. [ABSTRACT FROM AUTHOR]

• The effects of four types of MnO 2 (α-, β-, γ- and δ-MnO 2) on iron-based FTS catalysts were investigated. • These four types of MnO 2 exhibit distinct roles in the structure evolution and catalytic performances. • The α- and δ-MnO 2 modifying remarkably improves the selectivity of LAOs and heavy hydrocarbon. • The modification of β- and γ-MnO 2 dramatically increases the catalytic activity. Manganese oxide additive is an effective promoter for modulating the catalytic performance of iron-based Fischer-Tropsch synthesis (FTS) catalysts and studied extensively, however, the promotion effects of MnO 2 crystal structures on iron-based FTS catalysts have never been reported. In this work, four types of MnO 2 with crystal phases corresponding to α-, β-, γ- and δ-MnO 2 were prepared, and their promotion functions on iron-based FTS catalysts were studied. These four types of MnO 2 exhibit dramatically distinct promotion effects on the structure evolution and catalytic performances. The ferrite MnFe 2 O 4 only forms in the α-MnO 2 modified catalysts, while the β-, γ- and δ-MnO 2 also present different existing forms in the catalysts. The presence of abundant oxygen vacancies on the surface of α- and δ-MnO 2 notably facilitates the cleavage of Fe-O bonds and the dissociation of CO, leading to the enhancing formation of iron carbides in the activated and spent catalysts. Meanwhile, the strong Mn-Fe electronical interactions formed in α- and δ-MnO 2 modified catalysts lead to high density of surface carbon species with a long residence time, dramatically improving the selectivity of linear high carbon α-olefins and heavy hydrocarbons. In contrast, the β- and γ-MnO 2 modifying dramatically increases the catalytic activity, but suppresses the formation of olefins and long chain hydrocarbons, due to their relatively few amounts of surface oxygen vacancies and moderate Mn-Fe electronical interactions. This work provides new insights and in-depth understanding of the promotion roles of Mn additive, benefiting for the rational design of high performance iron-based FTS catalysts. [ABSTRACT FROM AUTHOR]

• The effects of four types of MnO 2 (α-, β-, γ- and δ-MnO 2) on iron-based FTS catalysts were investigated. • These four types of MnO 2 exhibit distinct roles in the structure evolution and catalytic performances. • The α- and δ-MnO 2 modifying remarkably improves the selectivity of LAOs and heavy hydrocarbon. • The modification of β- and γ-MnO 2 dramatically increases the catalytic activity. Manganese oxide additive is an effective promoter for modulating the catalytic performance of iron-based Fischer-Tropsch synthesis (FTS) catalysts and studied extensively, however, the promotion effects of MnO 2 crystal structures on iron-based FTS catalysts have never been reported. In this work, four types of MnO 2 with crystal phases corresponding to α-, β-, γ- and δ-MnO 2 were prepared, and their promotion functions on iron-based FTS catalysts were studied. These four types of MnO 2 exhibit dramatically distinct promotion effects on the structure evolution and catalytic performances. The ferrite MnFe 2 O 4 only forms in the α-MnO 2 modified catalysts, while the β-, γ- and δ-MnO 2 also present different existing forms in the catalysts. The presence of abundant oxygen vacancies on the surface of α- and δ-MnO 2 notably facilitates the cleavage of Fe-O bonds and the dissociation of CO, leading to the enhancing formation of iron carbides in the activated and spent catalysts. Meanwhile, the strong Mn-Fe electronical interactions formed in α- and δ-MnO 2 modified catalysts lead to high density of surface carbon species with a long residence time, dramatically improving the selectivity of linear high carbon α-olefins and heavy hydrocarbons. In contrast, the β- and γ-MnO 2 modifying dramatically increases the catalytic activity, but suppresses the formation of olefins and long chain hydrocarbons, due to their relatively few amounts of surface oxygen vacancies and moderate Mn-Fe electronical interactions. This work provides new insights and in-depth understanding of the promotion roles of Mn additive, benefiting for the rational design of high performance iron-based FTS catalysts. [ABSTRACT FROM AUTHOR]

[Display omitted] • Silica-supported nano-Fe 2 O 3 for FTS was prepared by colloidal deposition method. • Nano-Fe/silica showed higher selectivity to light olefins than impregnated catalyst. • Nano-Fe/silica exhibited significantly superior durability over impregnated catalyst. • Nano-Fe particles were geometrically favorable for coking resistance. Nano-iron catalysts exhibit good performances in the Fischer–Tropsch synthesis to lower olefins (FTO), however, there is still a lack of simple methods for their preparation. In this work, we introduced a facile colloidal deposition (CD) method to fabricate silica-supported Fe 2 O 3 nanoparticles using a colloidal solution readily prepared from ferric hydroxide. With increasing the Fe loading from 16.3 % to 31.6 %, the Fe 2 O 3 particle size increased from 1.3 to 6.1 nm. The catalytic performances in FTO were tested at a H 2 /CO molar ratio of 1. At a Fe loading of 30.4 %, the catalyst having a particle size of 4.7 nm showed the highest lower olefin selectivity and the lowest CO 2 selectivity, outperforming analogs prepared by impregnation method. Furthermore, this catalyst showed good stability in a 200-hour durability test, while the impregnated analogue quickly deactivated due to serious coking. Presumably, the effective contact areas between the nanoparticles and the generated carbon sheets are geometrically small, which results in weak van der Waals forces between them, preventing the former from being heavily covered by the latter. Besides, from the point of view of the carbide decomposition mechanism of coking, due to the relatively low volume to surface area ratios of the intermediate carbide nanoparticles, the surface concentrations of carbon atoms released from them are low, which delays the coke formation. This study may provide a simple method to fabricate supported nano-iron catalysts, and cast some light on understanding catalyst durability in FTO. [ABSTRACT FROM AUTHOR]

[Display omitted] • Fenton sludge is used to prepare SCR iron-based catalyst. • Physical and chemical properties of the catalyst are characterized in detail. • An alternative method was provided to dispose Fenton sludge. • The optimum acid leaching conditions were explored in detail. • NO x conversion can reach 100% at 301–450 °C. Fenton sludge is a type of industrial hazardous waste produced after the Fenton reaction treats industrial wastewater that contains a large amount of iron oxide and other metallic elements. In this study, an efficient treatment method for preparing a selective catalytic reduction catalyst from Fenton sludge is proposed. Fenton sludge was treated using a selective acid leaching method, and the effects of four main factors were systematically studied. The experimental results showed that the dealkalization extent reached 94.8% and the retention extent of active components was 90.46% under the condition of the liquid-to-solid ratio of 6 mL/g, acid leaching temperature of 80 °C, acid leaching time of 60 min and acid dosage of 20%. The modified Fenton sludge catalyst (MFS) achieved 100% NO x conversion in the temperature range 301–450 °C, which is a wide reaction temperature range and excellent low-temperature catalytic activity. The selective dealkalization treatment can effectively inhibit the high-temperature sintering of the catalyst, increase the specific surface area and porosity of the catalyst and improve the redox performance of the catalyst. Moreover, the high O β concentration, Fe3+/Fe2+ ratio and number of oxygen vacancies contributed to the excellent catalytic performance of MFS. [ABSTRACT FROM AUTHOR]

Graphite is a widely used industrial material, which experienced a marked shortage caused by the growing demand for electrode anode material and the increased costs for raw material. Graphitic carbon from biomass is a promising approach that will result in low-cost and efficient preparation. Herein, Fe(NO 3) 3 was selected as the catalyst for pine sawdust, and the effects of temperature and iron content on the graphitization of biochar were investigated. Additionally, the formation mechanism of the graphitic crystallite structure was explored. Results showed that the formation of pyrolysis gas increased with the increase in the amount of catalyst added or pyrolysis temperature. The change in pyrolysis gas, such as H 2 and CO, was a critical auxiliary factor reflecting the conversion process. As temperature was increased from 600 °C to 800 °C, the solid products showed high graphitization and low solid yield. Graphite structure mainly formed at 700 °C because of the formation of Fe nanoparticles. The increase in the amount of catalyst could provide more reaction sites and promote the contact between Fe and C, showing that amorphous carbon is dissolved on Fe nanoparticles and precipitated into ordered graphitic carbon. On this basis, a mechanism of "carbon dissolution-precipitation" was proposed to explain the formation of graphite structure, and the whole pyrolysis process included the transformation of the iron element were analyzed. [Display omitted] • Low-temperature catalytic of iron nitrate on graphitization of sawdust was studied. • Fe nanoparticles promote graphitization of sawdust. • Temperature affects the graphitization degree by changing the morphology of Fe. • Reaction mechanism of biomass catalytic pyrolysis graphitization was proposed. [ABSTRACT FROM AUTHOR]

The catalysts with high activity and selectivity, especially the latter, play a key role in Fischer–Tropsch synthesis technology. Herein, a novel Fe-based confinement catalyst, Fe 2 O 3 encapsulated in TiO 2 nanotubes, was prepared by a method of vacuum-assisted impregnation. The catalyst presented an excellent yield of oil phase hydrocarbons and C 5+ selectivity due to the confinement effect. This interesting phenomenon was discussed from the view of the restrained molecular movement and enhanced readsorption of short-chain α-olefins in the confined space of TiO 2 nanotube channels. The results over this novel confinement catalyst revealed a promising research prospect on adjusting the product distribution to long-chain hydrocarbons for Fe-based Fischer–Tropsch catalyst. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effects of Fe 2 O 3 and waste hematite on rapid pyrolysis of coal were compared. • Fe 2 O 3 significantly increased CO, CH 4 and H 2 O production compared with hematite. • The kinetics of Fe 2 O 3 and hematite with coal were studied by KAS and FWO method. • The 3 and 4 ring compounds in MAH significantly decreased by iron-based catalyst. • The cracking mechanisms of pyrolysis volatile by iron-based catalyst were concluded. Pyrolysis plays a critical role in clean coal technology and energy conversion and is also conducive to the early peaking of carbon dioxide emissions. Light tar production from traditional coal pyrolysis using various iron-based catalysts for chemicals and fuel oil has gained attention recently. In this study, waste hematite was initially used for catalytic upgrading of rapid coal pyrolysis. Subsequently, thermogravimetric analyzer coupled with Fourier-transform infrared spectrometry (TG-FTIR) and pyrolysis gas chromatography mass spectrometry (Py-GC/MS) were utilized to compare the performances, kinetic parameters, and volatile composition of coal pyrolysis with Fe 2 O 3 and hematite. The results showed that the maximum weight loss rate of coal pyrolysis increased by 1.55 %/min and 0.32 %/min with the addition of Fe 2 O 3 and hematite, respectively, indicating that the pyrolysis reaction became more rapid and intense with iron-based catalysts. Both Kissinger Akahira Sunose (KAS) and Flynn-Wall-Ozawa (FWO) methods revealed that the catalysts reduced the apparent activation energy of coal pyrolysis. Online FTIR showed the emission temperature and content of coal volatiles, suggesting iron-based catalysts were conducive to the cracking of oxygen-containing functional groups and the directional cracking of groups to CO. Py-GC/MS illustrated the presence of Fe 2 O 3 and hematite could reduce polycyclic aromatic hydrocarbons and oxygenates. In addition, a mechanism for rapid coal pyrolysis with iron-based catalysts was proposed to provide fundamental information for the transformation of aliphatic hydrocarbons, oxygenates, and polycyclic aromatic hydrocarbons. It is believed that iron-based catalysts have great potential for future research on upgrading coal volatiles and tar. [ABSTRACT FROM AUTHOR]

A synthetic secondary effluent containing an aqueous mixture of emerging contaminants (ECs) has been treated by photocatalytic ozonation using Fe3+or Fe3O4as catalysts and black light lamps as the radiation source. For comparative purposes, ECs have also been treated by ultraviolet radiation (UVA radiation, black light) and ozonation (pH 3 and 7). With the exception of UVA radiation, O3-based processes lead to the total removal of ECs in the mixture. The time taken to achieve complete degradation depends on the oxidation process applied. Ozonation at pH 3 is the most effective technique. The addition of iron based catalysts results in a slight inhibition of the parent compounds degradation rate. However, a positive effect is experienced when measuring the total organic carbon (TOC) and the chemical oxygen demand (COD) removals. Photocatalytic oxidation in the presence of Fe3+leads to 81% and 88% of TOC and COD elimination, respectively, compared to only 23% and 29% of TOC and COD removals achieved by single ozonation. The RCTconcept has been used to predict the theoretical ECs profiles in the homogeneous photocatalytic oxidation process studied. Treated wastewater effluent was toxic toDaphnia magnawhen Fe3+was used in photocatalytic ozonation. In this case, toxicity was likely due to the ferryoxalate formed in the process. Single ozonation significantly reduced the toxicity of the treated wastewater. [ABSTRACT FROM AUTHOR]

[Display omitted] • Various iron-based catalysts used in SR-AOPs for soil remediation were summarized. • Iron-based catalysts exhibit considerable potential in SR-AOPs for soil remediation. • The mechanisms of iron-based catalysts that remove pollutants in soil were analyzed. • The properties of soil would be negatively affected after SR-AOPs treatment. • The applications of iron-based catalysts for SR-AOPs in soil remediation were presented. Accumulation of multiple organic pollutants in the soil is a huge threat to ecological systems and health of human beings. Iron-based catalysts, such as zero-valent iron (ZVI) catalysts, iron oxide catalysts, and supported iron-based catalysts are widely used in sulfate radicals (SO 4 •−)-based advanced oxidation process (SR-AOPs) for soil remediation as a result of their environmental friendliness, extensiveness, and low cost, etc. In recent years, SR-AOPs using iron-based catalysts have arousing attention for the degradation/mineralization of organic pollutants in polluted soil. It helps to accelerate the transformation of contaminants, as well as sustainable remediation and adaptability to complex soil environments. This paper concentrates on the progresses of the Fe-based catalysts in SR-AOPs for organically contaminated soil. General persulfate activation process and the radical free radicals generation are summarized in soil remediation. The changes of physicochemical properties (e.g. , organic matter, naturally occurring minerals, pH, and microbial community) in soil after SR-AOPs treatment are particularly discussed. The applications of Fe-based catalysts for SR-AOPs in soil remediation are thoroughly investigated from the perspective of the internal interaction among pollutants, catalysts, and soil. Finally, the existing challenges for SR-AOPs by Fe-based catalysts used in soil remediation are proposed. [ABSTRACT FROM AUTHOR]

As for the 3% Ce after treated by CO 2 /H 2 , when the reducing gas atmosphere is switched from CO to H 2 , the surface ratio of Na/Fe and the ratio of Fe 3 O 4 /Fe x C decreases, the CO 2 desorption temperature and the ratio of defect oxygen increases, and the adsorbed CO 2 on the surface of iron oxides probably react with the presence of H 2 to produce the surface oxygen ions, inhibiting the conversion of CO 2 to CO and the transformation of CO to hydrocarbons. Therefore, the conversion of CO 2 decreased from 36% to 12%, the selectivity of CO increased from 11% to 65%, the FTY decreased from 1.37*10-6 mol CO2 /g Fe •s to 0.13*10-6 mol CO2 /g Fe •s and the ratio of O/P decreased from 1.7 to 0.2. [Display omitted] • CO 2 conversion, CO selectivity and FTY over FeCeNa were regulated by reducing gas. • Reducing gas atmosphere can regulate the surface ratio of Fe 3 O 4 /Fe x C y and Na/Fe. • The CO 2 desorption temperature can be tuned by reducing gas atmosphere. • The adsorbed CO 2 can be turned into surface oxygen species in the presence of H 2. In this work, a series of FeCeNa catalyst were prepared and evaluated in the reducing gas atmosphere of CO and H 2 , respectively. The catalytic performance of hydrogenation of CO 2 to olefins show the reducing gas atmosphere has an apparent effect on the CO 2 conversion, CO selectivity, FTY and the ratio of O/P. In situ XRD, in situ XPS and TPSR were further carried out to investigate the effect of reducing gas atmosphere on the performance of FeCeNa catalyst for the hydrogenation of CO 2 to olefins. When the reducing gas atmosphere of 3% Ce is switched from CO to H 2 , the catalyst has lower Fe 3 O 4 /Fe x C y , higher ratio of defect oxygen and higher CO 2 desorption temperature. The adsorbed CO 2 on the surface can react with the presence of H 2 to produce higher ratio of the surface oxygen ions, which probably occupies the surface of the catalyst and inhibits the conversion of CO 2 to CO and the transformation of CO to hydrocarbons. Besides, the surface Na/Fe ratio of 3% Ce decreases when the reducing gas atmosphere is switched from CO to H 2 , inhibiting the formation of olefins. Therefore, as for 3% Ce, switching the reducing gas atmosphere from CO to H 2 can decrease the ratio of Fe 3 O 4 /Fe x C y , increase the ratio of defect oxygen and surface oxygen ion species, decrease the ratio of Na/Fe, and increase the CO 2 desorption temperature, subsequently affect the RWGS and FT reaction, leading to the conversion of CO 2 decreasing from 36% to 12%, the selectivity of CO increasing from 11% to 65%, the FTY decreasing from 1.37*10−6 mol CO2 /g Fe •s to 0.13*10−6 mol CO2 /g Fe •s and the ratio of O/P decreasing from 1.7 to 0.2. [ABSTRACT FROM AUTHOR]

The catalytic conversion of CO2 to value-added chemicals and fuels has been long regarded as a promising approach to the mitigation of CO2 emissions if green hydrogen is used. Light olefins, particularly ethylene and propylene, as building blocks for polymers and plastics, are currently produced primarily from CO2-generating fossil resources. The identification of highly efficient catalysts with selective pathways for light olefin production from CO2 is a high-reward goal, but it has serious technical challenges, such as low selectivity and catalyst deactivation. In this review, we first provide a brief summary of the two dominant reaction pathways (CO2-Fischer-Tropsch and MeOH-mediated pathways), mechanistic insights, and catalytic materials for CO2 hydrogenation to light olefins. Then, we list the main deactivation mechanisms caused by carbon deposition, water formation, phase transformation and metal sintering/agglomeration. Finally, we detail the recent progress on catalyst development for enhanced olefin yields and catalyst stability by the following catalyst functionalities: (1) the promoter effect, (2) the support effect, (3) the bifunctional composite catalyst effect, and (4) the structure effect. The main focus of this review is to provide a useful resource for researchers to correlate catalyst deactivation and the recent research effort on catalyst development for enhanced olefin yields and catalyst stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Influence factors of AOPs of iron-based catalysts were comprehensively summarized. • Active species and catalytic mechanism of iron-based catalysts were explored. • The key issues and possible research directions have made some corresponding outlooks. Sulfate radicals (SO 4 −)-based advanced oxidation processes have obtained far-reaching attention due to their high catalytic activity and selectively for intricate water environmental pollutants. The couple of cheap and readily available iron-based materials and peroxymonosulfate (PMS) or persulfate (PS) is an effective measure to generate incalculabe reactive sulfate radicals. The article analyzed the latest research progress on different typical heterogeneous iron-based catalysts for PMS or PS activation. The microstructure and electrical properties of these catalysts and the effects of different tailoring engineering approaches (such as structure defect, heteroatom doping, and rugulation of pore structure, etc) in PMS or PS activation were summarized. In addition, the environmental factors of iron-based materials-PMS (PS) systems in organic pollutants degradation and related advanced oxidation processes were also summarized. Finally, critical discussion and possible future prospects on challenges related to degradation mechanism exploration, potential catalysts development as well as practical catalytic system application were also proposed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Influence factors of AOPs of iron-based catalysts were comprehensively summarized. • Active species and catalytic mechanism of iron-based catalysts were explored. • The key issues and possible research directions have made some corresponding outlooks. Sulfate radicals (SO 4 −)-based advanced oxidation processes have obtained far-reaching attention due to their high catalytic activity and selectively for intricate water environmental pollutants. The couple of cheap and readily available iron-based materials and peroxymonosulfate (PMS) or persulfate (PS) is an effective measure to generate incalculabe reactive sulfate radicals. The article analyzed the latest research progress on different typical heterogeneous iron-based catalysts for PMS or PS activation. The microstructure and electrical properties of these catalysts and the effects of different tailoring engineering approaches (such as structure defect, heteroatom doping, and rugulation of pore structure, etc) in PMS or PS activation were summarized. In addition, the environmental factors of iron-based materials-PMS (PS) systems in organic pollutants degradation and related advanced oxidation processes were also summarized. Finally, critical discussion and possible future prospects on challenges related to degradation mechanism exploration, potential catalysts development as well as practical catalytic system application were also proposed. [ABSTRACT FROM AUTHOR]

Abstract: The production of hydrogen and filamentous carbon by means of methane decomposition was investigated in a fixed-bed reactor using iron-based catalysts. The effect of the textural promoter and the addition of Mo as a dopant affects the catalysts performance substantially: iron catalyst prepared with Al2O3 showed slightly higher catalytic performance as compared to those prepared with MgO; Mo addition was found to improve the catalytic performance of the catalyst prepared with MgO, whereas in the catalyst prepared with Al2O3 displayed similar or slightly poorer results. Additionally, the influence of the catalyst reduction temperature, the reaction temperature and the space velocity on the hydrogen yield was thoroughly investigated. The study reveals that iron catalysts allow achieving high methane conversions at operating temperatures higher than 800°C, yielding simultaneously carbon nanofilaments with interesting properties. Thus, at 900°C reaction temperature and 1lg−1 cat h−1 space velocity, ca. 93vol% hydrogen concentration was obtained, which corresponds to a methane conversion of 87%. Additionally, it was found that at temperatures higher than 700°C, carbon co-product is deposited mainly as multi walled carbon nanotubes. The textural and structural properties of the carbonaceous structures obtained are also presented. [Copyright &y& Elsevier]

Abstract: The Fischer–Tropsch synthesis (FTS) performances of iron-based catalysts promoted with/without potassium compounds containing different acidic structural promoters (Al2O3, SiO2, and ZSM-5) were studied in this research. Characterization technologies of temperature-programmed reduction with CO (CO-TPR), powder X-ray diffraction (XRD) and Mössbauer effect spectroscopy (MES) were used to study the effect of K–structural promoter interactions on the carburization behaviors of catalysts. It showed that the addition states of potassium (K–Al2O3, K–SiO2, K–ZSM-5 and K-free) have a significant influence on the formation of iron carbides, which shows a following sequence in promotion of carburization: K–Al2O3 >K–SiO2 >K–ZSM-5>K-free. The FTS reaction test was performed in a fixed bed reactor. It is found that Fe/K–Al2O3 catalyst leads to the highest CO conversion, Fe/K–ZSM-5 catalyst shows the highest H2 conversion, and Fe/K-free catalyst shows the lowest CO and H2 conversion. As for the hydrocarbon selectivity, Fe/K–SiO2 catalyst yields the lowest methane and the highest C5 + products, Fe/K–ZSM-5 catalyst yields higher methane and the highest liquid hydrocarbon product, whereas Fe/K-free catalyst yields the highest methane and the lowest C5 + products. These results can be explained from the interaction between potassium and structure promoters, and the spillover of reactants or intermediates from Fe sites to the surfaces of structural promoters. [Copyright &y& Elsevier]

Abstract: Chromium-free iron-based catalysts were prepared and studied in regard to their performance in the high-temperature water-gas shift reaction (HTS). The effects of various catalyst preparation variables (i.e., Fe/promoter ratio, pH of precipitation medium, calcination and reduction temperatures) and preparation methods were investigated. Aluminum is a potential chromium replacement in HTS catalysts. Further improvement in WGS activity of Fe–Al catalysts can be achieved by the addition of small amounts of copper or cobalt. Catalysts were characterized using BET surface area measurements, temperature-programmed reduction (TPR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). As a textural promoter, aluminum and chromium prevent the sintering of iron oxides and stabilize magnetite phase by retarding its further reduction to FeO and metallic Fe. The promotional effect of Cu is found to be strongly dependent on the preparation method. [Copyright &y& Elsevier]

The soluble system diethylbis(2,2′-bipyridine)Fe–MAO is very active for the polymerization of isoprene to predominantly 3,4 polymers (ca. 80%). The polymers obtained at 25 °C are amorphous by X-ray examination, while those obtained below 10 °C are crystalline. The identity period determined from the X-ray fiber spectrum, ca. 5.2 A˚, and the NMR analysis show that the polymer contains stereoregular sequences of 3,4 syndiotactic structure. An interpretation is given of the effect of polymerization temperature on stereospecificity. Some differences between the 1,2 polymerization of butadiene and the 3,4 polymerization of isoprene are examined. [Copyright &y& Elsevier]

The state and active site of iron-based catalysts in co-liquefaction of coal with low-density polyethylene (LDPE) have been discussed. The catalysts used were sulfur-promoted iron oxides (Fe2O3+S), ferrous sulfide (FeS), ferrous sulfate (FeSO4·7H2O) and the mineral pyrite (FeS2). It was found by X-ray photoelectron spectrometry that the active site in the working state of Fe2O3+S catalyst was not Fe1−XS and the main form of sulfur existing in the spent Fe2O3+S catalyst was sulfate, followed by sulfite (SO32−). A finding from autoclave tests was that the ferrous sulfate before and after oxidation treatments showed sufficiently high activity for the co-liquefaction of coal with LDPE. It was concluded that an active site of the iron-based catalysts was sulfate species formed on the catalyst surface during the hydroliquefaction process of coal. [Copyright &y& Elsevier]

Iron-based oxide catalysts for the NH3–SCR (selective catalytic reduction of NOx by NH3) reaction have gained attention due to their high catalytic activity and structural adjustability. In this work, iron–niobium, iron–titanate and iron–molybdenum composite oxides were synthesized by a co-precipitation method with or without the assistance of hexadecyl trimethyl ammonium bromide (CTAB). The catalysts synthesized with the assistance of CTAB (FeM0.3Ox-C, M = Nb, Ti, Mo) showed superior SCR performance in an operating temperature range from 150 °C to 400 °C compared to those without CTAB addition (FeM0.3Ox, M = Nb, Ti, Mo). To reveal such enhancement, the catalysts were characterized by N2-physisorption, XRD (Powder X-ray diffraction), NH3-TPD (temperature-programmed desorption of ammonia), DRIFTS (Diffuse Reflectance Infrared Fourier Transform Spectroscopy), XPS (X-ray Photoelectron Spectroscopy), and H2-TPR (H2-Total Physical Response). It was found that the crystalline phase of Fe2O3 formed was influenced by the presence of CTAB in the preparation process, which favored the formation of crystalline γ-Fe2O3. Owing to the changed structure, the redox-acid properties of FeM0.3Ox-C catalysts were modified, with higher exposure of acid sites and improved ability of NO oxidation to NO2 at low-temperature, both of which also contributed to the improvement of NOx conversion. In addition, the weakened redox ability of Fe prevented the over-oxidation of NH3, thus accounting for the greatly improved high-temperature activity as well as N2 selectivity. [ABSTRACT FROM AUTHOR]

The NH 3 -SCR reaction mechanism on FeS/(TiO 2 -ZrO 2) catalysts. • Fe 2 O 3.SO 4 2−/(TiO 2 -ZrO 2) is a promising catalyst to apply in NH 3 -SCR of flue gas. • Doping TiO 2 into ZrO 2 , the physical-chemical properties were improved totally. • The SCR reaction mechanism of Fe 2 O 3.SO 4 2−/(TiO 2 -ZrO 2) catalyst was Langmuir-Hinshelwood theory. Several Fe 2 O 3.SO 4 2−/(TiO 2 –ZrO 2) catalysts with different ratios of Ti/Zr were prepared by wet impregnation method. The Fe 2 O 3.SO 4 2−/Ti1Zr4 (TiO 2 :ZrO 2 = 1/4) exhibited the highest NO x conversions and N 2 selectivity in 300–500 °C. And the SO 2 resistance was well enhanced when TiO 2 adding to ZrO 2. The XRD, BET, H 2 -TPR, XPS, NH 3 -TPD, and DRIFTS characterization were conducted and it was concluded that the improvement of catalytic effect was closely related to the property's enhancement when TiO 2 adding to ZrO 2. With the introducing TiO 2 , the surface area of carrier would be greatly enhanced, while Fe 2 O 3 and SO 4 2− highly dispersed on binary metal oxide (TiO 2 –ZrO 2) supports, and the interaction between Ti and Zr would significantly lead to much more conversion of Fe3+ to Fe2+ on Ti1Zr4 support compared to TiO 2 or ZrO 2. A large number of Fe2+ might break a charge balance and accelerate to adsorb NH 3 molecules or oxidize NO to NO 2 in the SCR reaction. According to our DRIFTS results on FeS/(Ti1Zr4) catalyst, the introduction of TiO 2 further improved the NH 3 and NO x adsorption and activation over the surface of the Fe 2 O 3.SO 4 2−/(Ti1Zr4) catalysts, which might be the most important reason for Fe 2 O 3.SO 4 2−/(Ti1Zr4) catalyst possessed superior activity at high temperature. [ABSTRACT FROM AUTHOR]

The Fe/(SZr) and S(Fe/Zr) sulfated iron-based catalysts, prepared by impregnation methods through changing the loading order of Fe2O3 and SO42− on ZrO2, were investigated on selective catalytic reduction (SCR) of NOx by ammonia. It was studied that the existent forms of Fe2O3 and SO42− on the surface of catalysts were affected by the loading order. The Fe/(SZr) catalyst surface had isolated Fe2O3 and SO42− species and followed both the L-H mechanism and the E-R mechanism, whereas the S(Fe/Zr) catalyst contained SO42− specie and sulfate only and mainly followed the E-R pathway. These factors affected the redox ability and NH3 adsorption, which might be key to the SCR reaction. [ABSTRACT FROM AUTHOR]

Iron-based catalysts are promising catalysts in the direct coal liquefaction (DCL) process as they are inexpensive and environmentally friendly. However, most such iron-based catalysts show relatively low activity in coal conversion and oil yield. Common techniques for the synthesis of these catalysts with excellent catalytic performance remain a substantial challenge. We present a simple solid-state synthesis strategy for preparing CoFe2O4 nanoparticles and CoFe2O4 nanoparticles supported on coal (CoFe2O4@coal) composites for DCL. The obtained bimetallic oxide CoFe2O4 nanoparticles show an enhanced catalytic performance in the DCL compared with monometallic components Fe2O3 and Co(OH)2 nanoparticles. The synergistic effect between Co and Fe of CoFe2O4 nanoparticles promotes the catalytic hydrogenation of coal during the DCL process. Moreover, the catalytic performance of CoFe2O4 nanoparticles is further improved when they are loaded on the coal. The conversion, oil yield, liquefaction degree, and gas yield of Dahuangshan lignite are 99.44, 56.01, 82.18 and 19.30 wt %, respectively, with the CoFe2O4@coal composites involved. The smaller particle size and high dispersion of CoFe2O4 supported on coal are of great benefit to full contact between coal and active components. The in-situ solid-state synthesis with coal as support shows great potential to prepare effective iron-based catalysts toward DCL in practice. [ABSTRACT FROM AUTHOR]