Fe2O3 Catalyst Research Articles

Synthesis of Fe3O4 Derived from Acid Mine Drainage (AMD) Sludge and Catalytic Degradation of Tetracycline.

Acid mine drainage (AMD) sludge is waste generated in the process of acid mine wastewater treatment, and the use of AMD sludge to prepare Fe3O4 to activate H2O2 degradation pollutants is an effective means of resource utilization. In this study, the heterogeneous catalyst Fe3O4-based composites were synthesized by a one-step method using AMD sludge as a raw material, and the Fe3O4-based materials before and after catalysis were characterized by powder diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), thermogravimetric analysis (TGA), and scanning electron microscopy (SEM). The effects of several key factors (pH values, H2O2 content, TC concentration, and Fe3O4 content) of tetracycline (TC) degradation were evaluated. The results revealed that the TC removal rate reached up to 95% within 120 min under optimal conditions (pH 3; H2O2, 5 mmol/L; TC concentration, 25 mg/L; Fe3O4 content, 1g/L). Moreover, •OH and •O2- radicals were generated during the Fenton-like degradation process, and the plausible degradation mechanism was discussed. Besides, the Fe3O4 catalyst exhibited fantastic stability after five cycles. In conclusion, this study is expected to promote the resource utilization of industrial sludge and provide a new material for the treatment of antibiotic-contaminated wastewater.

Constructing frustrated Lewis pairs on Mo-doped Fe2O3 catalyst to enhance oxidative desulfurization efficiency

The emission of sulfur oxides will not only cause a series of environmental pollution but also threaten human health. At present, oxidative desulfurization is considered one of the technologies to achieve high-efficiency conversion of sulfur-containing compounds. Herein, the special frustrated Lewis pairs (FLPs) for efficient oxidative desulfurization are created by regulating surface doping in a redox iron-based oxide. According to experimental results, the Lewis acidic sites can be considered as the iron atoms adjacent to the molybdenum dopant, while the doped metal proximal to the oxygen vacancies serves as Lewis basic sites to create FLPs in redox iron-based oxide. This reactivity of FLPs is further adapted to the chemical activation of molecular oxygen and aromatic sulfur-containing compounds. The Fe2O3-FLP catalyst can achieve 100 % sulfur removal at 3 h and maintains 96.9 % after seven cycles, higher than other previously reported iron-based oxidative desulfurization catalysts. In addition, the design of FLPs offers a promising approach for developing high-efficiency catalysts in the oxidative desulfurization process.

Revealing the differences in CO oxidation activity of Fe-CeO2, Fe2O3, and CeO2 using operando CO2-DRIFTS-MS: Carbonate species and desorption process

The carbonate on the catalyst surface is the key factor limiting carbon monoxide (CO) oxidation activity. However, the relationship between different carbonate species and surface oxygen species is not clear. In this paper, Fe-CeO2, Fe2O3, and CeO2 catalysts prepared by aerosol method are selected as the research target, and operando DRIFTS-MS is used as the main characterization method. Fe-CeO2 has good redox properties resulting in the best CO oxidation activity (350°C) and CO2 selectivity (98 %). Operando DRIFTS-MS results indicate that surface M=O species play a crucial role in the catalyst's activity, demonstrating the ability to react with CO at low temperatures. Notably, a high concentration of M=O facilitates the formation of monodentate carbonate (vas(CO32−)) (vas(CO32−) decomposes at 100°C). With increasing temperature, CeO and M-O-Ce also react with CO and produce M-Ov-Ce (oxygen vacancy). CO adsorption on M2+-O22− or M sites to form vas(OCO) or vs(OCO). The decomposition temperature of vs(OCO) exceeds that of vas(CO32−) significantly, and its presence serves as the crucial step in the oxidation of CO. The above conclusions reveal the relationship between surface carbonate and oxygen, and provide a theoretical basis for regulating the surface structure of catalysts.

Effect of cobalt-doped iron oxide as an electrocatalyst for water splitting and photocatalytic hydrogen evolution

Developing cost-effective and efficient electrocatalysts for the oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) is a significant challenge for economically viable energy conversion devices, such as electrolyzers, rechargeable metal-air batteries, and regenerative fuel cells. Here, we have synthesized cobalt doped iron oxides (CoFe2O3) with different Co:Fe wt%. Among them, Co[1:3]Fe2O3 catalyst demonstrated outstanding performance and stability positioning it as a standard electrocatalyst for OER and HER, and as a photocatalyst for H2 production. The catalysts were characterized using various techniques, including field emission scanning electron microscopy (FESEM), X-ray diffraction spectroscopy (XRD), and energy dispersive X-ray spectroscopy (EDS) demonstrating successful application in water electrolysis. Specifically, the onset potentials for OER and HER were 1.63 V/RHE and −0.23 V/RHE, respectively. The overpotential (η) required to achieve 10 mA/cm2 for OER (in alkaline medium) and HER (in acidic medium) was 0.44 and −0.3 V/RHE, respectively. Additionally, the developed OER and HER catalyst exhibited high current and potential stability over a 13-hour period. This approach is considered a promising avenue for making water electrolysis for hydrogen (H2) energy viable by minimizing the energy requirements of the electrolytic process. Similarly, the performance of the fabricated catalyst was also examined for the photocatalytic generation of H2 gas in a photo-reactor. Where the highest generation rate of 97.77 mL. (g.min−1) was recorded for Co[1:3]Fe2O3 as a photocatalyst. As a result, the Co[1:3]Fe2O3 catalyst has the potential to function as both a photocatalyst and an electrocatalyst for water splitting.

Mn3O4-FeS2/Fe2O3 composite as peroxidase-mimics for the degradation of Bisphenol A

Due to the benefits of artificial peroxidase-like enzymes, Flower-like Mn3O4-FeS2/Fe2O3 composites with multiple active sites prepared by a one-step solvothermal method.The synergistic cyclic reaction between Mn and Fe on the catalyst surface enhances the generation of active radicals, which together promote the efficient degradation of BPA. In the presence of hydrogen peroxide (H2O2), Mn3O4-FeS2/Fe2O3 could generate hydroxyl radicals (·OH) and superoxide radicals (·O2-) in buffer solution of pH=4.5 and catalyze the oxidation of 3,3′,5,5′-tetramethylbenzidine (TMB) to blue oxidation products (ox TMB). The steady-state kinetic constants (Km) of TMB and H2O2 were obtained by Michaelis-Menten and Lineweaver-Burk models, which are 1.34 mM and 1.00 mM, respectively. This reveals the nice catalytic efficiency of Mn3O4-FeS2/Fe2O3 as enzyme mimics. Under the condition of 10 mg Mn3O4-FeS2/Fe2O3 catalyst, 100 μL H2O2 and pH = 4.5, the degradation efficiency of Bisphenol A (BPA) reaches 100 % when treating 40 mL of 50 mg L−1 BPA for 30 min at room temperature. Moreover, after 5 cycles of degradation, the BPA degradation efficiency of 85.8 % was still maintained. Therefore, the as-prepared Mn3O4-FeS2/Fe2O3 sample could potentially be applied in wastewater treatment.

Structure-activity relationship and deactivation behavior of iron oxide during CO2 hydrogenation

Identifying the dynamic structural evolution of iron during the thermocatalytic conversion of CO2 into liquid hydrocarbons is a promising approach for understanding the deactivation behavior and to design an efficient catalyst. Despite the understanding of the oxidation of χ-Fe5C2 to high-valent iron oxides (e.g., Fe3O4, Fe2O3) caused by water formed as the byproduct, the deactivation mechanism depending on the particle size during a long-term reaction remains unclear. Herein, the structural evolution and deactivation mechanism of Na-promoted Fe2O3 catalysts with varying particle sizes were investigated. The catalyst activity and deactivation behavior were highly dependent on the initial morphology of the calcined catalysts. The reduced iron catalyst with an average particle size (dave) of 0.52 μm maintained its domain integrity, whereas that with a dave value of 2.18 μm was severely pulverized during the CO2 hydrogenation. The pulverized particles exposed a new surface, making it highly susceptible to re-oxidation and catalyst deactivation. Conversely, maintenance of the iron integrity suppressed the re-oxidation, whereas the excess formation of graphitic carbon on the χ-Fe5C2 site was the main deactivation mechanism during long-term CO2 hydrogenation.

Multi-dimensional, multi-interface Fe3C/carbon sheets/carbon tubes nanoarchitecture towards high-performance microwave absorption

The serious problem of electromagnetic (EM) interference brings growing demand for developing high-performance electromagnetic shielding materials. In this study, three-dimensional (3D) Fe3C/carbon/carbon tubes (Fe3C/C/CT) absorber with multi-heterointerface was prepared by a facile self-propagating followed by chemical vapor deposition (CVD) strategy. Initially, Fe3O4 nanoparticles were anchored onto carbon nanosheets through the self-propagating process. After different etching times with diluted acid, CTs with diverse dimensions and quantities were catalyzed by the modified Fe3O4 catalysts during the CVD approach and grown from the carbon sheets. Such a special nanoarchitecture, which consists of carbon sheets and carbon tubes, acts as the source of dielectric loss. Meanwhile, Fe3C nanoparticles provide magnetic loss, and the abundant interfaces facilitate synergistic electromagnetic loss. Moreover, large numbers of heterointerfaces from the unique multidimensional nanoarchitecture significantly enhance the impedance matching and produce abundant dipole polarization. Ultimately, with etching time of 30 min, the Fe3C/C/CT-30 achieves excellent electromagnetic wave (EMW) absorption property with a minimum reflection loss of −46.4 dB at 10.56 GHz with a thickness of 3.0 mm. When the thickness is 3.57 mm, the effective absorption bandwidth (EAB) can extend up to 4.48 GHz. Moreover, the practical application of the absorbers was evaluated using radar cross-section (RCS) simulation, indicating that Fe3C/C/CT-30 achieves a maximum RCS reduction value of 58 dBm2. The multi-dimensional and multi-heterointerface absorber presented in this work might offer valuable insights for optimizing electromagnetic absorbers.

Allothermally Heated Reactors for Solar-Powered Implementation of Sulphur-Based Thermochemical Cycles

Catalytic sulphur trioxide splitting is the highest-temperature (650-950oC), endothermic step of several sulphur-based thermochemical cycles targeted to production of hydrogen or solid sulphur. Concentrated solar power tower plants are an attractive renewable energy source to provide the necessary heat. Furthermore, the development of solar receivers capable of delivering solid or gaseous heat transfer fluids at these temperature ranges enable the implementation of such endothermic reactions in allothermally-heated reactors/heat exchangers placed away from the solar receiver. In this context, a 2-kW laboratory-scale shelland-tube reactor/heat exchanger to perform thermal sulphuric acid decomposition and catalytic sulphur trioxide splitting was in-house designed, built and tested with electrically heated bauxite particles, in the perspective of eventually coupling such a reactor with a centrifugal particle solar receiver. Thermal test runs demonstrated the in-principle feasibility of the concept. The temperatures reached were sufficient to ensure complete sulphuric acid evaporation. However, the ones in the SO3 splitting zone were of the order of 750°C, high enough to demonstrate SO3 splitting but not reaching the levels required for close-toequilibrium conversion of the Fe2O3 catalyst system used (~ 850oC). An improved version of the reactor is under construction incorporating design modifications based on lessons learned from the test campaigns, in the perspective of scaling up the process.

Fabrication of Z-scheme Fe2O3/g-C3N4 nanocomposite with improved visible light induced photodegradation of pharmaceutical pollutants and photoelectrochemical water oxidation

The photodegradation and photoelectrochemical performance of Fe2O3 catalyst is an encouraging visible-light induced catalyst owing to its less harmfulness, cheap and ecofriendly. However, owing to its quick charge carriers recombination rate and less lifespan of charge carriers obstructs its catalyst application. Therefore, it has been lately established that the construction of heterojunction with other semiconductor might be a possible method to improve its catalytic activity. Herein, a novel Z-scheme Fe2O3/g-C3N4 heterostructure catalyst has been synthesized by a simple hydrothermal technique and studied its photoelectrochemical and photodegradation activity. The addition of g-C3N4 greatly improves the light absorption ability light, reduced charge recombination rate and progress the charge transportation. The composite catalyst exhibited the superior photodegradation performance (97.8 %) of sulfamethoxazole antibiotic remedy within 30 min of visible light illumination. •OH and •O2– radicals show a key role for dye degradation activity, and proposed a possible photodegradation charge carrier transfer mechanism based on a potential band structures of composite catalyst. Furthermore, the prepared catalysts are further used to examine the photoelectrochemical properties for hydrogen generation. The Fe2O3/g-C3N4 nanocomposite photoelectrode exhibited enriched photocurrent density (0.764 mA/cm2) than g-C3N4 (0.271 mA/cm2) and Fe2O3 (0.370 mA/cm2) photoelectrodes, which ∼ 2.8 and ∼2.1 folds greater photocurrent density than pure photoelectrodes. Electrochemical impedance spectroscopy analysis revealed that the composite electrode has minimal charge transfer resistance and greater electron transfer ability. Therefore, the current study presents a facile formation of Z-scheme catalyst and offers a sustainable method to eradicate water impurities and hydrogen generation by renewable solar energy.

Effect of CaO/Fe2O3 Ratio and Oil/Methanol Molar Ratio on Biodiesel Production from Waste Cooking Oil

Biodiesel is a renewable liquid fuel that can be produced through the transesterification reaction of biomass. The objective of this research was to examine the effect of comparative composition of CaO and Fe2O3 on CaO/Fe2O3 catalysts from eggshells and Fe2O3 in the production of biodiesel from waste cooking oil. In addition, it was also studied the effect of the ratio of oil and methanol on the yield and characteristics of the biodiesel produced. Catalysts were prepared through impregnation. The esterification-transesterification process was carried out with the conditions WCO:methanol molar ratio of 1:3, 1:6, 1:9, 1:12 and 1:15, catalyst (3%wt oil), heated at 65°C for 3 hours with a stirring scale of 1200 rpm. The results showed biodiesel production using CaO: Fe2O3 catalyst with the ratio of CaO: Fe2O3 70:30 and WCO:methanol molar ratio of 1:9 obtained higher yield (84.5%) compared to others. The best biodiesel yield produced is the CaO:Fe2O3 catalyst ratio of 70:30 and the WCO:methanol molar ratio of 1:9 with a biodiesel yield of 84.50% with a methyl ester content of 99.63% and a FAME yield of 84.14%. The biodiesel produced has met the requirements of the Indonesian National Standard (SNI) in terms of density and viscosity.

Eley−Rideal path enhanced NH3-SCR: Central Fe atoms activation for electron transfer promotion

Manganese modified Fe2O3 catalyst is a promising candidate to replace the commercial NH3-SCR catalyst for controlling NOx emission due to its superior performance and N2 selectivity at low temperature. In order to elucidate the effects of different modification methods of Mn on physicochemical properties and reaction mechanism in Fe-Mn binary catalysts, two kinds of Mn modified Fe2O3 are prepared by co-precipitation and impregnation method, respectively. Compared with MnO2 loaded Fe2O3, Mn doped Fe2O3 achieves above 85 % of NOx conversion with 20 % increase in N2 selectivity within 100–200°C. Transient reaction experiments and DFT calculation results prove that doping Mn effectively increases the reaction rate of the main reaction and reduces the formation of N2O through Eley−Rideal path. The formation of multiple Fe-O-Mn structures after Mn doping facilities the formation of coordination bond between the central Fe atoms and NH3 via modulating local charge density of Fe atoms, effectively improving the adsorption of NH3 and preventing its excessive oxidation, which leads to high activity and N2 selectivity at low temperature. This mechanism provides theoretical support for increasing the activity and N2 selectivity of NH3-SCR catalysts at low temperature and gains clear insight on the interaction between binary metal oxides.

Synthesis of Co/Ni-Doped mesoporous spinel ferrite microspheres for enhanced Low-Temperature SCR performance

The iron-based catalysts commonly used in the selective catalytic reduction (SCR) process cannot meet the increasingly stringent low-temperature NOx emission targets. In this study, mesoporous microspherical MFe2O4 (M=Co, Ni) spinel ferrite catalysts were synthesized by hydrothermal method and applied to the SCR of ammonia (NH3-SCR) reaction. Compared to Fe3O4, both NiFe2O4 and CoFe2O4 catalysts showed higher SCR catalytic activity at low temperature. The NiFe2O4 catalyst achieved a NO conversion of 95.5 % at 240 °C, while CoFe2O4 exhibited a high NO conversion of 97.6 % at 180 °C and a N2 selectivity of 99.6 %. Various characterization experiments revealed that the introduction of Co and Ni resulted in the formation of a specific mesoporous microsphere morphology in CoFe2O4 and NiFe2O4 catalysts, along with the generation of a large number of oxygen vacancies and acidic sites on the surface. These features facilitate the sequential adsorption and activation of NH3 and NOx species, resulting in excellent catalytic activity at low temperatures. Detailed in situ diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS) measurements showed that on NiFe2O4 the reaction follows the Eley–Rideal (E–R) mechanism, whereas it proceeds through the Langmuir–Hinshelwood (L–H) and Eley–Rideal (E–R) mechanisms on the CoFe2O4 catalyst. This work provides a feasible strategy for enhancing the low-temperature SCR reaction over iron-based catalysts; moreover, the elucidation of the complete reaction mechanism offers a solid foundation for future improvements in denitrification catalysts.

Photocatalytic removals of imidacloprid insecticide in TiO2- and Fe2O3-immobilized porous geopolymer granules

In this study, geopolymer catalysts were synthesized by incorporating different TiO2 (0, 7, and 14 wt%) and Fe2O3 content (0, 7, 14, and 20 wt%) into porous metakaolin-based geopolymer granules. TiO2- and Fe2O3-immobilized geopolymer granules were applied for photocatalytic removals of imidacloprid under UV-C irradiation. The analysis of the surface morphology of the Fe2O3 catalyst revealed its larger surface area predominated with meso- and macro-pores thus providing a larger area for photocatalysis. Meanwhile, the TiO2 catalyst had TiO2 nanoparticles filled up those mesopores and macropores in geopolymer resulting in its denser structure therefore limiting access of imidacloprid to the reactive sites. To maximize its photocatalytic activities, Fe2O3 and TiO2 could be immobilized into porous geopolymer matrix up to 20 and 14 wt%, respectively. The developed porous geopolymer had relatively stable imidacloprid adsorption capacities regardless of the TiO2 and Fe2O3 contents in their texture. After UV irradiation, their removal efficiencies were 94.85–100% and the photocatalytic degradation increased with the increase in TiO2 content (from 0 to 14 wt%) and Fe2O3 content (from 14 to 20 wt%). Nevertheless, Fe2O3-immobilized geopolymer granules posed a significantly higher kinetic rate (1.966 h−1) compared to that of TiO2 (0.154 h−1) at the same catalyst content (14 wt%). The newly developed Fe2O3-immobilized porous geopolymer catalysts could be effectively reused over 10 successive cycles during which the imidacloprid could be completely removed.

Kinetics insights into size effects of carbon nanotubes’ growth and their supported platinum catalysts for 4,6-dinitroresorcinol hydrogenation

Size effects are a well-documented phenomenon in heterogeneous catalysis, typically attributed to alterations in geometric and electronic properties. In this study, we investigate the influence of catalyst size in the preparation of carbon nanotube (CNT) and the hydrogenation of 4,6-dinitroresorcinol (DNR) using Fe2O3 and Pt catalysts, respectively. Various Fe2O3/Al2O3 catalysts were synthesized for CNT growth through catalytic chemical vapor deposition. Our findings reveal a significant influence of Fe2O3 nanoparticle size on the structure and yield of CNT. Specifically, CNT produced with Fe2O3/Al2O3 containing 28% (mass) Fe loading exhibits abundant surface defects, an increased area for metal-particle immobilization, and a high carbon yield. This makes it a promising candidate for DNR hydrogenation. Utilizing this catalyst support, we further investigate the size effects of Pt nanoparticles on DNR hydrogenation. Larger Pt catalysts demonstrate a preference for 4,6-diaminoresorcinol generation at (1 0 0) sites, whereas smaller Pt catalysts are more susceptible to electronic properties. The kinetics insights obtained from this study have the potential to pave the way for the development of more efficient catalysts for both CNT synthesis and DNR hydrogenation.

A review on Fe2O3‐based catalysts for toluene oxidation: catalysts design and optimization with the formation of abundant oxygen vacancies

Volatile organic compounds (VOCs) are typical pollutants with hazards for humans and the environment, and can be efficiently mitigated by catalytic combustion. Fe2O3‐based catalysts are a promising choice due to their low cost and strong redox ability. Several attempts have been made to promote the catalytic performance of Fe2O3 at low temperatures. This review summarizes the research progress on Fe2O3‐based catalysts for the oxidation of toluene, one of the most common and harmful VOC. Firstly, the properties and catalytical performance for Fe2O3‐based catalysts were summarized, and the reaction mechanisms for toluene oxidation on the surface of Fe2O3 were detailed to comprehend the role of oxygen vacancy. Then, the modification for single Fe2O3 catalysts, including synthesis parameters, structure and morphology control, has been introduced to reveal the correlation between physicochemical properties of catalysts and their activity. In addition, composite Fe2O3 catalysts, which can promote catalytic performance significantly due to the synergetic effect between different components, were comprehended. Finally, waste‐derived Fe2O3 catalysts with sustainable merit as converting waste into worth have been discussed. Moreover, the advanced machine learning tools, which are helpful in accelerating catalyst design, configuration optimization and reactivity prediction, have been introduced as an emerging research opportunity for the future.

An eco-efficient dual-function technology: Magnetically recoverable rGO-WO3/Fe3O4 ternary heterojunction catalytic system simultaneously performing malachite green photolysis and Cr(VI) reduction

This study focuses on developing a system that efficiently removes two contaminants simultaneously: malachite green (MG), an organic dye, and chromium (Cr) ions, which are used as oxidizing agents in the dyeing process. A dual-functional heterojunction photocatalyst was prepared by combining tungsten oxide (WO3, the main photocatalyst) and iron oxide (Fe3O4, a visible light absorber) on a reduced graphene oxide (rGO) support. The 10% rGO-WO3/Fe3O4 catalyst decomposes malachite green in 6 h and reduces Cr(VI) to Cr(III) in 2 h (both at 100 ppm). A mixed solution of MG and Cr(VI) required treatment for only 2 h, showing that the intermediates generated during the reaction positively synergized with each other. Here, the junction of WO3 and Fe3O4, which strongly induces a Z-scheme charge transfer, facilitates photo-charge separation and suppresses exciton recombination. The rGO extended the photocatalytic activity while continuously supplying electrons to the valence band of WO3. Finally, the rGO-WO3/Fe3O4 catalyst was completely recovered after the reaction using a magnet. Ultimately, this system will be useful for the quick, clean, and safe treatment of wastewater containing toxic heavy metals and organic pollutants.

Modulating the Activity and SO2 Resistance of α-Fe2O3 Catalysts for NH3-SCR of NOx via Crystal Facet Engineering.

The development of Fe-based catalysts for the selective catalytic reduction of NOx by NH3 (NH3-SCR of NOx) has garnered significant attention due to their exceptional SO2 resistance. However, the influence of different sulfur-containing species (e.g., ferric sulfates and ammonium sulfates) on the NH3-SCR activity of Fe-based catalysts as well as its dependence on exposed crystal facets of Fe2O3 has not been revealed. This work disclosed that nanorod-like α-Fe2O3 (Fe2O3-NR) predominantly exposing (110) facet performed better than nanosheet-like α-Fe2O3 (Fe2O3-NS) predominantly exposing (001) facet in NH3-SCR reaction, due to the advantages of Fe2O3-NR in redox properties and surface acidity. Furthermore, the results of the SO2/H2O resistance test at a critical temperature of 250 °C, catalytic performance evaluations on Fe2O3-NR and Fe2O3-NS sulfated by SO2 + O2 or deposited with NH4HSO4 (ABS), and systematic characterization revealed that the reactivity of ammonium sulfates on Fe2O3 catalysts to NO(+O2) contributed to their improved catalytic performance, while ferric sulfates showed enhancing and inhibiting effects on NH3-SCR activity on Fe2O3-NR and Fe2O3-NS, respectively; despite this, Fe2O3-NR showed higher affinity for SO2 + O2. This work set a milestone in understanding the NH3-SCR reaction on Fe2O3 catalysts in the presence of SO2 from the aspect of crystal facet engineering.

Surface exsolved NiFeOx nanocatalyst for enhanced alkaline oxygen evolution catalysis

A synergistically improved alkaline oxygen evolution catalyst of the NiFeOx nanoalloy oxide structure is introduced using an in-situ exsolution method. The separately doped Ni and Fe ions are exsolved on the surface of the perovskite as homogeneously distributed NiFeOx oxide alloy catalysts via following reduction and oxidation processes. The incorporation of additional Fe into the surface embedded NiFeOx catalyst improved the inherent oxygen evolution reaction (OER) property with fast reaction kinetics. Density functional theory (DFT) result indicates the lowest OER overpotential of NiFeOx catalyst is originated from the reduced energy barrier of surface *O formation from *OH group. The NiFeOx exsolved catalyst shows the smallest overpotential of 0.49 V (j = 10 mA∙cm−2) and Tafel slope (93 mV∙dec-1), compared with that of single NiO (0.54 V, 132 mV∙dec-1) and Fe3O4 catalyst. This study provides an effective method for developing nanosized OER catalysts for various energy conversion and storage electrode materials.

Iron oxide-based catalyst of (Fe1-xMgx)O·Fe2O3 with well-dispersed active sites favoring carbon nanotubes growth for high-performance microwave absorption

Traditional catalysts for carbon nanotubes growth require specific substrates to prevent catalyst aggregation, then designing environmentally friendly and efficient catalysts remains enormous challenges. Herein, we developed an iron oxide-based catalyst of (Fe1-xMgx)O·Fe2O3 with catalytic active sites for the low-cost growing of carbon nanotubes (CNT) in chemical vapor deposition (CVD) system. This (Fe1-xMgx)O·Fe2O3 was prepared by solid-phase sintering of iron oxide and magnesium oxide uniformly mixed in mass ratio of 3%∼20 wt% MgO at 1400 °C. The introduction of magnesium oxide possesses some advantages of reducing the decomposition temperature of iron oxide and hindering the aggregation of as-formed Fe catalyst during CVD process. Furthermore, the in-situ growing CNT wrapped up the magnetic (Fe1-xMgx)O·Fe2O3 catalyst to form the 3D CNT/(Fe1-xMgx)O·Fe2O3 with the high-performance of microwave absorption. The maximum absorption of the three-dimensional carbon nanocomposites at 11.8 GHz with a thickness of 2.0 mm is −37.3 dB. The coupling of dielectric loss of CNTs and magnetic loss of (Fe1-xMgx)O·Fe2O3 results in the enhancement of microwave absorption. Therefore, this study provides a low-cost and green route to design the efficient catalyst for carbon nanotubes as well as high-performance absorbing materials.

Superior room-temperature efficacy of selective catalytic reduction of NOx by CO utilizing metal-modified Fe2O3 catalysts

Fe2O3-based catalysts demonstrate significant potential for the selective catalytic reduction (SCR) of nitrogen oxides (NOx) by CO. However, their effectiveness is limited at lower temperatures, impeding widespread industrial adoption. To overcome this, we optimize the Fe2O3-based catalyst component through 3 wt% cobalt (Co) loading, which improves the synergistic removal of CO and NOx pollutants. Our developed catalyst, Co-Fe2O3 on an amorphous SiO2 substrate, exhibits superior room-temperature activity in CO-SCR, achieving CO and NOx conversion ratios as well as N2 selectivity above 80 % at 25 °C, and over 93 % at 100–500 °C. The enhancement in catalyst performance is elucidated through density functional theory calculations and experimental investigations, revealing the creation of heteronuclear active sites via metal modification, and consequent improvements in redox characteristics and acidity. Our findings offer a robust pathway towards the industrial implementation of ammonia-free-SCR technology with synergistic removal of CO and NOx and provide insights for designing superior heterogeneous catalysts.