Iron-based Catalysts Research Articles

Insight into degradation mechanism of PCBs from thermal desorption off-gas over iron-based catalysts

Iron-based catalysts were developed to achieve the hydrodechlorination (HDC)/oxidation of polychlorinated biphenyls (PCBs) from thermal desorption off-gas, and Fe3O4/γ-Al2O3 showed higher dechlorination efficiency than Fe2O3/γ-Al2O3. The optimal Fe loading resulted in 95.5% degradation efficiency and 76.9% toxicity reduction of gaseous PCBs, and the optimal Fe3O4/γ-Al2O3 exhibited excellent stability during a 60-h test. The gas chromatography–mass spectrometry analysis of intermediate products indicated the presence of two competitive degradation pathways, namely, hydrodechlorination and oxidation with Fe3O4/γ-Al2O3 as catalyst. During the first stage (reductive dechlorination), the reductive activity of iron-based catalysts was effectively enhanced in the presence of water, which was confirmed by density functional theory (DFT) calculations. The removal of chlorine atoms was found in the order of meta > para > ortho. During the second stage (oxidation), hydroxyl and superoxide anion radicals were found to attack PCBs on the surface of Fe3O4/γ-Al2O3. This study provides an insight into the HDC and oxidation mechanism of gaseous PCBs over iron-based catalysts.

Continuous synthesis of isobutylaluminoxanes in a compact and integrated approach

We present a 3D-printed continuous flow platform for controllable synthesis of isobutylaluminoxanes (IBAO), an effective olefin polymerization co-catalyst, via the highly exothermic hydrolytic reaction of triisobutylaluminum (TIBA). This platform encompasses modules of mixing and reaction, in-line separation, and in situ UV–vis characterization. In addition, two NMR protocols are established to validate the results of in-line UV–vis analysis (by 31P NMR) and reveal product structures (by 1H NMR). Measured temperature profiles over the reactor indicate essentially fast heat removal, ensuring inherent safety. Co-catalytic activities of IBAO are obtained from ethylene oligomerization experiments using an iron-based catalyst system at atmospheric pressure. Furthermore, we investigate the influence of key operating parameters including temperature, initial molar ratio between water and TIBA, initial TIBA concentration, and residence time. A high IBAO yield over 98% and a superior co-catalytic activity of ~ 5000 kg·(mol Fe)–1·h−1 are achieved with optimal parameters in this single-pass platform, demonstrating the advantages of process.

In-situ impregnation of β-FeOOH on coal by solid-state reaction toward direct coal liquefaction

Herein, β-FeOOH nanoparticles supported on coal (β-FeOOH@C) were prepared by a solid-state in-situ impregnation and tested for the direct coal liquefaction (DCL) process. The β-FeOOH nanoparticles with ~10–50 nm were uniformly loaded over coal through a solid-state reaction among ferrous chloride, sodium hydroxide and coal. The obtained β-FeOOH@C solid showed enhanced catalytic performance for DCL compared with unsupported β-FeOOH nanoparticles. The conversion and oil yield achieved by β-FeOOH@C were 92.88 and 48.78% in the catalytic liquefaction of Dahuangshan lignite. The solid-state in-situ impregnation with coal as support shows great potential to prepare effective iron-based catalysts toward practical DCL.

Activation of peroxymonosulfate by iron oxychloride with hydroxylamine for ciprofloxacin degradation and bacterial disinfection

Iron oxychloride (FeOCl) is a known effective iron-based catalyst and has been used in advanced oxidation processes (AOPs). This study intends to achieve more facile free radicals generation from peroxymonosulfate (PMS) activation by exploring the Fe(III)/Fe(II) cycle of FeOCl in the presence of hydroxylamine (HA). With 0.2 g/L FeOCl, 1.5 mM PMS, and 1 mM HA, the PMS/FeOCl/HA system could effectively achieve 98.88% of the oxidative degradation of 5 mg/L ciprofloxacin (CIP) in 15 min and quickly inactivate 99.99% of E. coli (108 CFU/mL) in 5 min at near-neutral pH. HA played an important role in promoting the Fe(III)/Fe(II) cycle, thereby greatly improving the oxidation activity of the system. The reactive oxygen species (ROS) such as HO, SO4− and O2− were identified as the dominated free radicals produced in the system. The intermediate products of CIP detected by liquid chromatograph-mass spectrometer (LC-MS) and three possible degradation pathways of CIP were proposed. The presence of common anions in the PMS/FeOCl/HA system, including HCO3−, Cl−, SO42−, and NO3−, enhanced the degradation efficiency of CIP to varying degrees at the concentrations of 10 mM. Moreover, FeOCl maintained a high degradation capability for CIP after several recycles. This work offers a new promising means of catalyzing the PMS-based AOPs in the degradation of refractory organics.

Catalytic Pyrolysis of Methane to Hydrogen over Carbon (from cellulose biochar) Encapsulated Iron Nanoparticles

The catalytic performance of carbon encapsulated iron nanoparticles (CEINPs) for methane decomposition was investigated over a range of temperatures between 700 and 800 °C with varying iron concentrations (20, 30, and 40 wt %) in a semicontinuous flow fixed bed reactor. CEINPs were prepared by impregnating a cellulose biochar support (carbon source) with iron nitrate solution. This mixture was dried at 110 °C for 72 h in air followed by pyrolysis at 1000 °C in a N2 atmosphere. Unlike conventional iron-based catalysts, in CEINPs, the iron nanoparticles were encapsulated in a graphitic shell that prevented atmospheric oxidation and sintering at high temperature, improving the thermal stability of the catalysts. The fresh CEINPs did not contain any metal oxides and had only the following phases: elemental iron, iron carbides, activated carbon, and graphitic carbon, which allowed for the catalyst reduction step (in H2) to be eliminated. The decomposition of methane being an endothermic reaction showed better catalytic activity with an increase in temperature with the highest conversion of 95.7% observed at 800 °C. There are four different active sites in the catalyst, namely, graphite, graphite encapsulated iron nanoparticles, uncovered iron nanoparticles, and activated carbon. In the case of 20 wt % CEINP, the presence of higher amounts of activated carbon and graphite with a lower amount of Fe negatively impacted methane decomposition, confirming the importance of Fe as an active site. At 800 °C, the maximum catalytic performance was exhibited by 30 wt % CEINP where the initial methane conversion was 95.7% and dropped to 36.8% after 180 min of reaction. The higher conversion was due to the combined optimum amounts of Fe, graphite, and activated carbon active sites. In the case of 40 wt % CEINP, the higher amount of Fe resulted in the agglomeration of Fe nanoparticles and reduction in surface area, leading to lower methane conversions. The surface area of the spent catalysts reduced appreciably in all cases due to carbon deposition from CH4 in the form of coke and graphite (on non-encapsulated Fe nanoparticles), resulting in catalyst deactivation.

Catalytic performance and reaction mechanisms of NO removal with NH3 at low and medium temperatures on Mn-W-Sb modified siderite catalysts

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, H2-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 Fe2O3, 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 N2 selectivity at low temperatures. In-situ DRIFTS results show NH4+, coordinated NH3, NH2, NO3− species (bidentate), NO2− species (nitro, nitro-nitrito, monodentate), and adsorbed NO2 can be discovered on the surface of Mn-W-Sb modified siderite catalysts, and doping of Mn will enhance adsorbed NO2 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 SO2 and H2O. 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 NO2 among three pathways, reveals the reason of high NOx conversion of the catalyst at medium and low temperatures. [Display omitted]

Research Progress on degradation of Organic pollutants in Water Body by Iron-based Materials activated persulfate

The advanced persulfate oxidation technology has shown great potential in the efficient degradation of organic pollutants in water body, owing to its strong oxidation ability, easy operation and many other advantages. At present, the development of this technology focuses on the choice of activation mode of persulfate, and its essence lies in the cleavage of O-O bond in persulfate. Iron-based catalysts have been widely used in persulfate activation because of their advantages such as earth abundance, eco-friendliness and cost-effectiveness. In this paper, the methods and research progress of activating persulfate by iron-based materials (including nanometer zero-valent iron, common zero-valent iron, nanometer iron tetroxide) are reviewed. Finally, the existing problems and development direction of persulfate advanced oxidation technology in the current application are analyzed, in order to promote the development of related research work.

Fe based catalysts for petroleum coke graphitization for Lithium Ion battery application

Graphitic carbon materials are synthesized by mixing petroleum coke with Fe-based catalysts, followed with annealing under N2 atmosphere at various iron-based catalysts at 1300 °C. We have found that the utilization of iron or iron oxide as catalyst lead to similar graphitic structure formation during heat treatment of petroleum coke. X-ray Diffraction (XRD) pattern showed that iron oxide catalyst leads to the formation of ordered graphitic structure. The use of iron-based catalyst tends to decrease the turbostratic peak, lead to a higher ordered graphite peak. Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM) showed that the morphology structure of graphite powder synthesized using iron or iron oxide is similar. From the full cell testing using NMC-622 cathode, the as-synthesized sample shows good electrochemical properties and comparable to graphite commercial.

Development of an Iron-Based Fischer—Tropsch Catalyst with High Attrition Resistance and Stability for Industrial Application

In order to develop an iron-based catalyst with high attrition resistance and stability for Fischer–Tropsch synthesis (FTS), a series of experiments were carried out to investigate the effects of SiO2 and its hydroxyl content and a boron promoter on the attrition resistance and catalytic behavior of spray-dried precipitated Fe/Cu/K/SiO2 catalysts. The catalysts were characterized by means of N2 physisorption, nuclear magnetic resonance (NMR), X-ray diffraction (XRD), Raman spectrum, X-ray photoelectron spectroscopy (XPS), H2-thermogravimetric analysis (H2-TGA), temperature-programmed reduction and hydrogenation (TPR and TPH), and scanning and transmission electron microscopy (SEM and TEM). The FTS performance of the catalysts was tested in a slurry-phase continuously stirred tank reactor (CSTR), while the attrition resistance study included a physical test with the standard method and a chemical attrition test under simulated reaction conditions. The results indicated that the increase in SiO2 content enhances catalysts’ attrition resistance and FTS stability, but decreases activity due to the suppression of further reduction of the catalysts. Moreover, the attrition resistance of the catalysts with the same silica content was greatly improved with an increase in hydroxyl number within silica sources, as well as the FTS activity and stability to some degree. Furthermore, the boron element was found to show remarkable promotion of FTS stability, and the promotion mechanism was discussed with regard to probable interactions between Fe and B, K and B, and SiO2 and B, etc. An optimized catalyst based on the results of this study was finalized, scaled up, and successfully applied in a megaton industrial slurry bubble FTS unit, exhibiting excellent FTS performance.

Interfacial engineering of vacancy-rich nitrogen-doped FexOy@MoS2 Co-catalytic carbonaceous beads mediated non-radicals for fast catalytic oxidation

How to accelerate the Fe3+/Fe2+ conversion and fabricate recyclable iron-based catalysts with high reactivity and stability is highly desired yet challenging. Herein, vacancy-rich N@FexOy@MoS2 carbonaceous beads were firstly developed via employing sodium alginate, molybdenum disulfide (MoS2), and Fe-ZIFs through sol-gel self-assembly, followed by in-situ growth and pyrolysis strategies. As expected, A series of characterizations reflected that N@FexOy@MoS2 had high dispersibility and conductivity for fast mass and electron transport, and MoS2 as co-catalyst accelerated the circulation of Fe3+ to Fe2+ that attained 99.4% (0.345 min−1) norfloxacin degradation via PMS activation in a synergistic ‘‘adsorption-driven-oxidation’’ process, which much outperformed those of pure MoS2 (32.4%) and N@FexOy powder catalyst (45.3%). Moreover, confined Fe species, graphitic N, pyrrolic N, pyridinic N, and sulfur/oxygen vacancies were found as highly exposed active sites that contributed to the activation of PMS to dominate non-radicals (1O2 and O2·-) and other radicals following a contribution order 1O2 > O2·- > SO4·- > ·OH. More importantly, a fluidized-bed catalytic unit was evaluated and maintained the continuous zero discharge of NX. Overall, this study offered a generally applicable approach to fabricate removable Fe-based catalysts for contaminants remediation.

Supercritical water gasification of fuel gas production from waste lignin: The effect mechanism of different oxidized iron-based catalysts

Iron and iron oxides have been employed to catalyze supercritical water gasification (SCWG) of lignin, a typical component of pulp and paper mill wastewater. To investigate the effects of different oxidation sates of Fe-based catalysts during SCWG process, all simulations were carried out through ReaxFF molecular dynamics method. During the catalytic SCWG process, the degradation rate of guaiacyl dimer lignin (GDL) molecule was inversely proportional to the valence state of iron, the higher oxidation state of Fe in iron-based catalyst was, the lower the catalytic degradation ability would be, and then GDL molecule underwent a series of reactions, accompanying with the generation of small molecules, among most of them were fuel gas products. In terms of gas products, Fe catalyst had a unique advantage in catalytic hydrogen production. Moreover, it is found that iron with low oxidation state was beneficial to the formation of CO, while iron with high oxidation state was CO2. Our simulation results further revealed the formation mechanisms of CO, CO2 and CH4. Migration of lattice oxygen in iron oxides was also visualized through figure, and spent catalyst showed different sources in the final, demonstrating that SCW participates in the entire reaction providing not only H but also O free radicals.

Effect of iron-based catalyst from coal liquefaction on coal char gasification reactivity and kinetics

Gasification technology can help the resource recovery of solid product from coal liquefaction, where the iron-based catalyst widely exists. In the present work, the effects of iron-based catalysts from coal liquefaction on the coal structure and reactivity were studied, using the Hami raw coal and demineralized coal. The surface morphology, element distribution and mesoporous characteristics of coal char were investigated by SEM-EDS and physical adsorption analyzer. The gasification reactivity was performed in a thermogravimetric analyzer. The gasification kinetics was studied through the model-fitting and model-free methods. The results showed that the demineralization and catalyst loading had more obvious effect on the surface attachments than the carbon matrix. The coal char with catalyst loading had significant larger specific surface area (SSA). The reactivity improvement by iron-based catalyst could be attributed to the enrichment of Fe and AAEMS and increase of SSA for coal char. More pronounced relative catalytic activity was observed for the catalytic gasification of demineralized coal char, and its activity was not sensitive to the change of heating rate and carbon conversion. The gasification characteristics difference would be reduced with the increase of heating rate. The iron-based catalyst can increase the pre-exponential factor A for the demineralized coal char gasification, and reduce the activation energy Ea for the raw coal char gasification. Under non-isothermal conditions, the Ea decreased with conversion. According to fitting performance and kinetic compensation effect, the random pore model was the best model to describe gasification, especially for the (catalytic) gasification of the demineralized coal char.

Effect of potassium on GO-modified large Fe3O4 microspheres for the production of α-olefins

Despite that iron-based catalysts are preferred for the high selectivity to value-added α-olefins via Fischer-Tropsch synthesis (FTS) reaction, the carbon deposition leads to deactivate catalyst more readily and CO2 selectivity as high as ~50% leads to low carbon efficiency. Herein, we developed an innovative approach to fabricate iron-based catalysts to deal with this issue. In detail, prepare Fe3O4 microsphere with an average particle size of ~580 nm via hydrothermal method and mix it with GO. The GO modification could effectively inhibit the sintering and coking of the large Fe3O4 microspheres (580 nm) by assisting its evolution into much smaller iron carbide nanocapsules (~9.1 nm). And the obtained catalyst exhibited excellent reaction activity, stability and high α-olefin selectivity. The addition of K into Fe3O4 microsphere produces major ɛ’-Fe2.2C about 58.9% in the evolution process and facilitates lower CO2 emission obviously.

Spatially-resolved reaction profiles in Fischer-Tropsch synthesis – influence of operating conditions and promotion for iron-based catalysts

The complex reaction mechanism of iron-based Fischer-Tropsch synthesis comprises of manifold primary and secondary reaction pathways. Within this work, an experimental setup for spatially-resolved measurements on promoted iron-based Fischer-Tropsch catalysts is presented, allowing for a general study of the influence of operating conditions and promotion as well as of the influence of secondary reactions on product selectivity. It was found that, depending on catalyst composition, considerable hydrogenation of 1-alcohols and olefins occurs, while no considerable influence of reinitiation of chain growth on product distribution could be found.

The role of chromium in iron-based high-temperature water-gas shift catalysts under industrial conditions

Chromium promotion of iron oxide based water-gas shift (WGS) catalysts prepared via co-precipitation/calcination was investigated. Mössbauer spectroscopy and XRD evidence that chromium is incorporated in the calcined hematite (α-Fe2O3) precursor irrespective of the doping level (0−12 wt.%). CO-TPR shows chromium delays the reduction of hematite and the active magnetite (Fe3O4) phase. WGS activity was evaluated under realistic conditions for 4 days. Enhanced CO conversion was observed with increased chromium doping. Mössbauer spectra indicate that chromium incorporates into octahedral sites of magnetite and prevents reduction of Fe3+ to Fe2+ during formation of the active phase, leading to an increased Fe3+/Fe2+ ratio in octahedral sites. The higher Fe3+/Fe2+ ratio did not affect the high CO conversion associated with the structural stabilization mechanism of Cr-doping. Interpretation of the Mössbauer spectra was supported by computational modelling of various chromium and vacancy-doped magnetite structures. The bulk structure of an in situ prepared chromium-doped high-temperature WGS catalyst is best described as a partially oxidized chromium-doped magnetite phase. No surface effects of Cr-doping were found.

Boosting Efficient Ammonia Synthesis over Atomically Dispersed Co-Based Catalyst via the Modulation of Geometric and Electronic Structures

Boosting Efficient Ammonia Synthesis over Atomically Dispersed Co-Based Catalyst via the Modulation of Geometric and Electronic Structures

Reduced formation of peroxide and radical species stabilises iron-based hybrid catalysts in polymer electrolyte membrane fuel cells

The incorporation of Pt into an iron-nitrogen-carbon (FeNC) catalyst for the oxygen reduction reaction (ORR) was recently shown to enhance catalyst stability without Pt directly contributing to the ORR activity. However, the mechanistic origin of this stabilisation remained obscure. It is established herein with rotating ring disc experiments that the side product, H2O2, which is known to damage FeNC catalysts, is suppressed by the presence of Pt. The formation of reactive oxygen species is additionally inhibited, independent of intrinsic H2O2 formation, as determined by electron paramagnetic resonance. Transmission electron microscopy identifies an oxidised Fe-rich layer covering the Pt particles, thus explaining the inactivity of the latter towards the ORR. These insights develop understanding of FeNC degradation mechanisms during ORR catalysis, and crucially establish the required properties of a precious metal free protective catalyst to improve FeNC stability in acidic media.

Facile synthesis of oxygen vacancies enriched α-Fe2O3 for peroxymonosulfate activation: A non-radical process for sulfamethoxazole degradation

Hematite (α-Fe2O3) has been commonly used as an eco-friendly catalyst for peroxymonosulfate (PMS) to generate free radicals (SO4•- and/or •OH). However, the activation efficiency of PMS relies heavily on the conversion of Fe(III) to Fe(II) that is slow and rate-limiting. In this study, oxygen vacancies enriched α-Fe2O3 was prepared from thermally treated goethite (α-FeOOH) and employed as a PMS activator. Systematic characterization demonstrated that α-Fe2O3 with most abundant oxygen vacancies could be obtained by heating α-FeOOH at 300 °C. The as-prepared α-Fe2O3 exhibited excellent catalytic activity in activation of PMS for oxidation of sulfamethoxazole (SMX, k = 0.04 min−1). The SMX degradation rate was found to be positively correlated with the concentration of oxygen vacancies. Quenching experiments, EPR, LC/MS and XPS analysis revealed that singlet oxygen (1O2) was the predominant reactive oxygen species. The effects of pH, PMS dosage, catalyst loading, temperature, and anions on SMX degradation were comprehensively investigated. Moreover, the plausible degradation pathways of SMX in the α-Fe2O3/PMS system were proposed. This work not only provides a valuable insight into the mechanism of PMS activation by α-Fe2O3 but also establishes a new strategy for the design of more efficient and practical iron-based catalyst for PMS activation.

Chain Propagation Mechanism of Fischer–Tropsch Synthesis: Experimental Evidence by Aldehyde, Alcohol and Alkene Addition

Fischer–Tropsch synthesis (FTS) produces hundreds of hydrocarbons and oxygenates by simple reactants (CO + H2) and the detailed chain propagation mechanism is still in dispute. An industrial iron-based catalyst was used to further clarify the mechanism by adding aldehyde, alcohol and alkene species into a fixed-bed tubular reactor. The added species were investigated in H2 and syngas atmospheres, respectively. 1-alkene in the H2 atmosphere presented an obvious hydrogenolysis, in which the produced C1 species participated in C–C bond formation simultaneously. Co-feeding Cn alkene with syngas showed remarkable Cn+1 alcohol selectivity compared to the normal FTS reaction. In addition, the carbonyl group of aldehyde was extremely unstable over the iron-based catalyst and could easily be hydrogenated to an alcohol hydroxyl group, which could even undergo dehydration for hydrocarbon species formation. Experimental data confirmed that both heavier alkenes and alcohols added can be converted to chain growth intermediates and then undergo monomer insertion for chain propagation. These results provide strong evidence that the chain propagation in the FTS reaction is simultaneously controlled by the surface carbide mechanism and the CO insertion mechanism, with surface CHx species and CO as monomers, respectively. The study is of guiding significance for FTS mechanism understanding and kinetic modeling.

Performance of Mg-Ti modified iron-based catalyst in NH3-SCR of NO at the presence of arsenic: Influence of oxygen and temperature

Impact of arsenic on the performance of Mg-Ti modified iron-based catalyst during selective catalytic reduction of NOx with ammonia was studied. The results indicated that Mg and Ti modification not only improved the catalytic activity at 100–350 °C, but also exhibited remarkable anti-arsenic ability. Mg was dominant in the excellent anti-arsenic performance, and this role was firstly recognized. The anti-arsenic mechanism of Mg-Ti modified iron-based catalyst was ascribed to two aspects. One side, Mg exhibited well reactivity with arsenic which competed with Fe for the adsorption of arsenic and protected active iron sites from arsenic occupation. The other side, presence of Mg promoted the formation of MgFe2O4 in view of the strong interactions between Mg and Fe, suppressing the interactions between arsenic and Fe. Instead, gaseous arsenic turned to bond with Mg-O sites. Consequently, surface acid sites and function Fe-OH/ Fe = O bonds were preserved for de-NOx. Moreover, increase of oxygen content and temperature weakened the deactivation of Mg-Ti modified iron-based catalyst by arsenic. It was due to the oxidation of As2O3 with oxygen content increase and the strengthened reactivity of non-active iron sites with arsenic and Mg with arsenic as temperature elevation, inhibiting the interactions between active iron sites with arsenic.