Ce Fe Mixed Oxides Research Articles

Vacancy-rich Fe-Ce mixed oxides as nanoenzymes for efficient antioxidant activity in vitro

Traditional anti-oxidant drugs possess limited active sites and short half-lives that hamper the efficiency of the removal of excessive reactive oxygen species (ROS) that are linked to various diseases. On this point, the CeO2 nanozyme has recently attracted much attention because of its anti-oxidant ability to act as a ROS scavenger. While introducing trivalent ions into CeO2 helps induce the increasing Ce3+, it may damage the auto-regenerative ability and finally lead to decreased ROS activities. Here, Fe-Ce mixed oxides (Fe-CeO2) is developed as a nanozyme with adjustable oxygen vacancies. The ROS scavenging capabilities of Fe-CeO2 outperformed those of CeO2, primarily due to a higher concentration of oxygen vacancies. Moreover, the auto-regenerative properties of CeO2 are still retained after forming Fe-Ce mixed oxides. To delve into the enhanced scavenging activity driven by the increasing oxygen vacancies, we employ density functional theory (DFT) calculations to provide a comprehensive explanation, which can be attributed to the stimulated generation of oxygen vacancies and the more energetically favorable reaction path. This study provides a more profound understanding of the structure–activity relationship in nanozymes and inspires a novel approach for a highly efficient ROS scavenger via defect engineering.

Catalytic fast pyrolysis of steam-exploded biomass for long-chain ethers precursors

A novel valorization pathway for steam-exploded corn stalk conversion to long-chain ethers was proposed in the work. The procedure enabled the transformation of multifunctional components in catalytic fast pyrolysis (CFP) vapors using Fe-Ce mixed oxides into carbonyl compounds (ketones, aldehydes and furans with carbonyl group) suitable for preparing long-chain oxygenated fuels in a fluidized-bed/fixed-bed consolidation reactor. A series of Fe-Ce bimetallic oxides were explored and the results indicated that the catalyst with 0.3 of molar ratio of Fe to Ce (Fe/Ce(0.3)) showed highly active in converting levoglucosan and acetic acid into linear and cyclic ketones. Moreover, the conversion rate of acetic acid and levoglucosan in pyrolytic vapors was close to 100% and 90.07%, respectively. The carbon yield of carbonyl compounds (28.91%) in ex-situ CFP was achieved under optimal conditions. The continuous operation showed that Fe/Ce(0.3) remained highly active and there was little coke and carboxylates on the catalyst surface after 200 min.

NO reduction by CO on Ce-Fe mixed oxides and gold nanoparticles

Gold nanoparticles were synthesized by a colloidal method and deposited on a Ce0.8Fe0.2O2-δ mixed oxide. The resulting material was characterized by High-Resolution Scanning Transmission Electron Microscopy, Temperature-Programmed Reduction, Mössbauer Spectroscopy, Oxygen Storage Capacity, Adsorption and Temperature-Programmed Desorption (NO and CO) and DRIFT Spectroscopy in order to elucidate the influence of gold nanoparticles and oxygen vacancies of Ce0.8Fe0.2O2-δ support on the selective catalytic reduction of NO by CO. Ce0.8Fe0.2O2-δ support presented a higher NO conversion (95% at 250 °C; and 99% at 350 °C) than Au/Ce0.8Fe0.2O2-δ catalyst (48% at 250 °C). We propose that gold deposition changed the support surface sites by blocking oxygen vacancies, which are the dissociation centers of NO molecules, decreasing thereby the catalytic activity of the gold-based catalyst. On the other hand, gold nanoparticles improved the reducibility and the oxygen storage capacity of the mixed oxide because isolated Fe3+ (in OFeCe3 sites) become more reducible, which could be evidenced by the increased oxidation of CO to CO2 at room temperature. On Au/Ce0.8Fe0.2O2-δ, the oxygen needed for CO oxidation can be supplied by the mixed oxide crystalline lattice, possibly from interface sites between gold nanoparticles and the mixed oxide, once the oxygen from NO dissociation becomes less abundant.

Synthesis and crystal structure of a novel cyano-bridged Fe2+- Ce4+ supracomplex, designed to produce an effective catalyst for clean fuel production

A new cyano-bridged, FeII–CeIV hetero-binuclear supra-complex formulated as [(FeII)2(CN)6(CeIV)2(CN)6(H2O)3]n.nH2O (1), has been synthesized. Depending on the synthetic conditions, different morphology has been obtained. Using hydrothermal synthesis lead to a micro-structured of complex 1 (MS), while using ultrasonic irradiation resulted a nano-structured of complex 1 (NS). The synthesized complexes were characterized by elemental analysis, Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), differential thermal analysis (DTA) and scanning electron microscopy (SEM). The crystals of complex 1 have been fully characterized by single-crystal X-ray diffraction (SC-XRD), which revealed an orthorhombic system with space group Cmcm of expected composition. Also, the results of SEM show that the synthesized complexes have the different morphology and particle size. In the following, catalysts of Ce–Fe/SiO2-MS and Ce–Fe/SiO2-NS were prepared by thermal decomposition of MS and NS complexes, respectively, and characterized by FT-IR spectroscopy, SEM, powder X-ray diffraction (PXRD), and Brunauer–Emmett–Teller (BET) N2 adsorption-desorption analysis. The catalytic activity of Ce–Fe/SiO2 -MS and Ce–Fe/SiO2 -NS was evaluated in the high-temperature water-gas shift reaction (HT-WGS) for hydrogen production. The high CO conversion (93 and 85.5%) was achieved by Ce–Fe/SiO2 –NS, Ce–Fe/SiO2 –MS, respectively, which can be mainly ascribed to physicochemical features of these catalysts, such as mesoporous nature, particle size, BET surface area and strong synergistic effects between the Ce and Fe in the Ce–Fe mixed oxides.

Highly dispersed Fe–Ce mixed oxide catalysts confined in mesochannels toward low-temperature oxidation of formaldehyde

Highly dispersed Fe–Ce mixed oxides confined in mesochannels are prepared by two-step impregnation–calcination, achieving superior catalytic oxidation of HCHO (9.8 μg L−1) with 65 and 94.9% at 30 and 60 °C, respectively.

Promotional mechanism of activity via three-dimensional ordered macroporous Cu-doped Ce–Fe mixed oxides for the CO-SCR reaction

Mechanism illustration of 3DOM Ce0.7Fe0.2Cu0.1O2 catalyst for NO + CO reaction.

Removal of Elemental Mercury from Coal Pyrolysis Gas Using Fe–Ce Oxides Supported on Lignite Semi-coke Modified by the Hydrothermal Impregnation Method

In this paper, Fe–Ce mixed oxides supported on lignite semi-coke were prepared by the hydrothermal impregnation method. The sorbents were employed to capture elemental mercury from coal pyrolysis gas. The influences of hydrothermal impregnation temperature, mole ratio of Fe/Ce, reaction temperature, and H2S concentration on Hg0 removal efficiency were investigated in a fixed-bed reactor. The physicochemical properties of the sorbent samples were characterized by X-ray diffraction, Brunauer–Emmett–Teller, scanning electron microscopy, and X-ray photoelectron spectroscopy (XPS). The results showed that the Fe/Ce-modified semi-coke sorbents, synthesized by hydrothermal impregnated at 200 °C, had larger specific surface areas and pore volumes than the original semi-coke. The sorbent with a Fe/Ce molar ratio of 0.4:0.2 exhibited the highest Hg0 removal efficiency of 83.5% at 150 °C. On the basis of the XPS characterization of the sorbent, a mechanism of Hg0 removal over the Fe0.4Ce0.2/SC200 sorbent was propose...

Adsorption and catalytic oxidation of elemental mercury over regenerable magnetic Fe[sbnd]Ce mixed oxides modified by non-thermal plasma treatment

This study proposes the novel application of non-thermal plasma treatment to improve the oxidation capacity of regenerable magnetic FeCe mixed oxides (FCs) for the efficient removal of elemental mercury (Hg0) from coal combustion flue gas. Sample characterization shows that the textural property, crystalline phases, and magnetic property of FCs undergo no obvious changes after plasma treatment. But greater Ce4+ concentration and richer lattice oxygen are generated on the treated FCs. The treated FCs exhibit far better Hg0 removal performance compared to raw FC. The effects of treatment time (0–20 min), reaction temperature (100–250 °C), and flue gas components (SO2, NO, O2, HCl and H2O) on Hg0 removal performance are also discussed. Both Hg0 adsorption capacity and adsorption rate evaluated at 150 °C for the treated FCs are extremely close to those obtained with a commercial activated carbon manufactured specifically for mercury removal from flue gas. Furthermore, the Hg0 removal mechanism is proposed for the treated FCs. The treated FCs include separate active sites for Hg0 adsorption and catalytic oxidation. Ce4+ species with greater oxidation state and lattice oxygen are largely consumed during the Hg0 removal process. However, these components are replenished by subsequent non-thermal plasma treatment. Finally, the spent FCs can be effectively recycled through magnetic separation, thermal desorption, and non-thermal plasma treatment.

Fe–Ce Mixed Oxides Supported on Carbon Nanotubes for Simultaneous Removal of NO and Hg0 in Flue Gas

Developing simultaneous removal technology of NOx and Hg0 in flue gas is highly desirable but remains challenging. Multiwalled carbon nanotube supported Fe–Ce mixed oxide nanoparticles (Fe(2)Ce(0.5)Ox/MWCNTs) were prepared using the ethanol impregnation method for DeNOx and Hg0 removal. The NO and Hg0 removal efficiencies over catalyst reached to 99.1% and 88.9% at 240 °C and a space velocity of 30 000 h–1. The Fe–Ce mixed oxides supported both inside and outside of MWCNTs in highly dispersed form with particle size of 3–5 nm. The Ce4+ existed on MWCNTs in two forms, some of which are the fluorite-like crystal CeO2; the other portion of Ce4+ entered the spinel structure of γ-Fe2O3 and led to the distortion of the γ-Fe2O3 lattice. Furthermore, it is evident that the chemisorbed oxygen content and oxidation activity of catalysts increased dramatically after Ce doping, which could be attributed to the excellent NH3-SCR and Hg0 removal performance.

Chemical-looping water splitting over ceria-modified iron oxide: Performance evolution and element migration during redox cycling

Ceria-modified iron oxide exhibits high redox performance superior to that of pure iron oxide, which can inhibit the deactivation caused by sintering of materials. In the present work, the ceria-modified iron oxide is investigated as an oxygen carrier for hydrogen production via chemical-looping water splitting process (CLWS). To identify the role of CeO2, the performance evolution and element migration of the mixed oxides during redox cycling were discussed in detail. Comparing the obvious deactivation of pure iron oxide sample, ceria-modified iron oxide shows relative constant production of hydrogen during the successive recycling water splitting. FeCe20 sample with a CeO2 mole percent of 20% shows the highest average yield of hydrogen (8651 μmol/g) with a Fe average oxygen recovery rate of 67.7% among Fe-Ce mixed oxides with different Ce molar percentage (x = 0, 10, 20 and 40%). In spite of materials sintering, the oxygen releasing/acquiring capacity and reactivity of Fe-Ce mixed oxides are three times higher than that of pure iron oxide after redox treatment. This can be ascribed to the preferable dispersion of Ce-based sub-micro particles (CeO2 and CeFeO3) and enhanced Fe-Ce interactions generated from active sites at the contact interface between iron oxides (mainly Fe3O4 particles) and Ce-based sub-micro particles (CeO2 and CeFeO3) after cycling.

Chemical interaction of Ce-Fe mixed oxides for methane selective oxidation

Chemical interaction of Ce-Fe mixed oxides was investigated in methane selective oxidation via methane temperature programmed reduction and methane isothermal reaction tests over Ce-Fe oxygen carriers. In methane temperature programmed reduction test, Ce-Fe oxide behaved complete oxidation at the lower temperature and selective oxidation at higher temperatures. Ce-Fe mixed oxides with the Fe content in the range of 0.1–0.5 was able to produce syngas with high selectivity in high-temperature range (800–900 °C), and a higher Fe amount over 0.5 seemed to depress the CO formation. In isothermal reaction, complete oxidation occurred at beginning following with selective oxidation later. Ce1–xFexO2–δ oxygen carriers (x≤0.5) were proved to be suitable for the selective oxidation of methane. Ce-Fe mixed oxides had the well-pleasing reducibility with high oxygen releasing rate and CO selectivity due to the interaction between Ce and Fe species. Strong chemical interaction of Ce-Fe mixed oxides originated from both Fe* activated CeO2 and Ce3+ activated iron oxides (FeOm), and those chemical interaction greatly enhanced the oxygen mobility and selectivity.

CeO2 modified Fe2O3 for the chemical hydrogen storage and production via cyclic water splitting

The chemical hydrogen storage (hydrogen reduction) and production (water splitting) behaviour of Ce-modified Fe2O3 mixed oxides were investigated. Fe1−xCexO2−δ (x = 0, 0.05, 0.1, 0.2, 0.3, 0.4 and 1) oxides prepared by chemical precipitation were characterized by XRD (X-ray diffraction), H2-TPR (hydrogen temperature-programmed reduction) and H2O-TPO (steam temperature-programmed oxidation) tests. XRD results showed that two kinds of Fe–Ce–O solid solutions (Ce-based and Fe-based) coexisted in Fe–Ce mixed oxides. H2-TPR experiment suggested that Ce addition could reduce hydrogen reduction temperature while H2O-TPO experiments over reduced oxides showed that Fe–Ce mixed oxides could split water to produce hydrogen at a lower temperature and complete in a shorter time. Both redox reactions (hydrogen reduction and water splitting) were sensitive to the temperature and active at a high temperature. The successive redox cycles were carried out over the Fe0.7Ce0.3O2−δ mixed oxide at 750 °C. It kept a stable production of hydrogen in the successive redox process at the condition of serious agglomeration of the materials. The highest hydrogen storage amount was up to 1.51 wt% for the Fe–Ce sample with a 30% substitution of Ce for Fe.

Physicochemical characterization and catalytic CO oxidation performance of nanocrystalline Ce–Fe mixed oxides

Fe-doped CeO2 nano-oxide exhibited superior CO oxidation activity compared to pristine CeO2 due to its facile reducible nature, enhanced lattice strain, and ample oxygen vacancies.

Microstructure and oxygen evolution of Fe–Ce mixed oxides by redox treatment

The relationship between structure and reduction/redox properties of Fe–Ce mixed oxides with a Fe content of 5, 10, 20 or 30mol%, prepared by a coprecipitation method, were investigated by XRD, Raman, TEM, TPR and TPO techniques. It is found that all the iron ions can be incorporated into the ceria lattice to form a solid solution for the FeCe 5 (Fe 5%) sample, but amorphous or crystal Fe2O3 particles were found to be present on the Fe–Ce oxide samples with higher the iron content. The reducibility of single solid solution was much better than the pure CeO2, and the appearance of dispersed Fe2O3 particles improved the surface reducibility of materials. The iron ions incorporated into the CeO2 lattice accelerated the oxygen release from bulk to surface, and surface Fe2O3 particles in close contact to CeO2 acted as a catalyst for the reaction between solid solution and hydrogen. The microstructure of exposed Fe2O3 with Ce–Fe–O solid solution allows the Fe–Ce mixed oxides to own good reducibility and high OSC, which also counteracts the deactivation of the reducibility resulting from the sintering of materials in the redox cycling.

Oxygen release–absorption properties and structural stability of Ce0.8Fe0.2O2−x

Oxygen release–absorption properties and structural stability of Ce–Fe mixed oxides (Ce0.8Fe0.2O2−x) with different calcination temperatures (600–1000 °C) were investigated and correlated to their oxygen storage capacity. Iron ions could be incorporated into the CeO2 lattice to form a solid solution after calcination at low temperatures, but such solid solution was unstable under high-temperature thermal treatments. High-temperature (≥800 °C) calcination resulted in the appearance of exposed Fe2O3 phases on the surface of the solid solution, and this structural evolution finally affected the reduction behavior. The Fe3+ reduction from the Ce–Fe oxide solid solution was easier than the bulk Fe2O3 particles, while the small Fe2O3 particles in close contact with CeO2 could enhance the reducibility of cerium oxides. The strong interaction between the exposed small Fe2O3 particles and the solid solution made the Ce–Fe mixed oxides possess good reduction stability and high oxygen storage capacity (OSC) even after repeated redox treatments. Such interactions were absent toward the physically mixed sample. An unusual enhancement on the reducibility of Ce–Fe mixed oxides was observed after a successive redox treatment. Large oxygen evolution appeared at around 600 °C for the recycled samples, and the OSC rose to 1.31 mmol-O2/g after six redox cycles. The XRD, Raman, and TEM analyses revealed that the material structure of the mixed oxides was stabilized to have an inter-region between the Fe2O3 particles and the solid solution after the redox treatment. It was concluded that such microstructural evolutions of composite particle from solid solution under redox conditions brought beneficial property to the OSC of the Ce–Fe mixed oxides.

Impact of Ce–Fe synergism on the catalytic behaviour of Au/CeO2–FeOx/Al2O3for pure H2production

In this work the development of a series of gold catalysts, essentially based on γ-alumina promoted with a small superficial fraction of Ce–Fe mixed oxides, is reported. The catalytic behaviour is evaluated in the water gas shift reaction. The formation of a Ce–Fe solid solution is evidenced by XRD and related to the catalytic activity where the importance of the Ce–Fe interaction is demonstrated. The best catalyst reached CO conversions very close to the equilibrium limit. A long-term stability test is performed and the loss of activity is observed and attributed to reaction intermediates. Almost complete recovery of the initial conversion is achieved after oxidation treatment, suggesting that the problem of stability could be overcome by a suitable change in the reaction parameters thus leading to a highly efficient catalyst for future applications in H2 production and clean-up

Low-temperature CO oxidation on multicomponent gold based catalysts.

In this work the development of gold catalysts, essentially based on γ-alumina with small superficial fraction of Ce-Fe mixed oxides as support for the low temperature CO oxidation is proposed. Characterization results obtained by means of TEM, OSC, XPS, UV-Vis spectroscopy and H2-TPR are employed to correlate the activity data with the catalysts composition. The bare γ-alumina supported gold catalyst demonstrates the poorest activity within the series. The addition of CeO2 or FeOX improves the catalytic performance, especially observed for the CeO2-FeOx mixed oxide doped samples. This enhanced CO oxidation activity was related to the Ce-Fe interaction producing materials with promoted redox properties and therefore oxidation activity.

Promoting effect of Fe in preferential oxidation of carbon monoxide reaction (PROX) on Au/CeO2

Ce–Fe mixed oxides were prepared by impregnation (IM) method and co-precipitation method (CP). Gold supported on Ce–Fe mixed oxides prepared by direct anionic exchange (DAE) was used as catalyst for preferential oxidation of carbon monoxide (PROX). The influence of the atomic ratio Ce/Fe and of the preparation method (CP or IM) was investigated. It was found that gold supported on modified ceria by iron displayed better catalytic performances. However, the selectivity of Au/CeFe-CP was lower than that of Au/CeO2 catalyst, which could be ascribed to the formation of defects in CeFe support prone to accumulate carbonate species on the surface. The characterization by means of XRD, XPS, H2-TPR and HRTEM indicated that the doping of iron in ceria prepared by CP promoted the formation of a Ce–Fe solid solution, decreased the particle size of ceria and enhanced the dispersion of gold. In the case of the IM catalysts, iron is segregated in the form of Fe2O3, which impedes the activity in PROX. The strong interaction between CeO2 and Fe2O3 supports led to higher oxygen mobility and to the formation of Au3+, which may also contribute to the higher catalytic activity of Au/Ce85Fe15.

Enhancement of Reducibility and Oxygen Storage Capacity (OSC) of Ce–Fe Mixed Oxides by Repetitive Redox Treatment

Abstract The reduction properties and oxygen storage capacity (OSC) of Ce–Fe mixed oxide (Ce/Fe = 4/1) were investigated. When TPR/OSC cycle was repeated, Ce–Fe mixed oxide gave a new reduction peak at 600 °C, suggesting the enhancement of the reducibility of iron ions. This was accounted by the formation of a solid solution and the participation of Fe2O3 as catalyst for the reduction of Ce–Fe mixed oxide.

Partial oxidation of methane to syngas with air by lattice oxygen transfer over ZrO 2-modified Ce–Fe mixed oxides

Catalytic performance of Ce–Fe mixed oxides promoted with ZrO 2 was investigated for methane partial oxidation to syngas via gas–solid reactions. The results showed that moderate amounts of ZrO 2 could strongly enhance the interaction between iron and cerium oxides via increasing the oxygen vacancy concentration and improving the dispersion of free Fe 2O 3, which improved the activity of Ce–Fe material for methane partial oxidation. However, heavy loading of ZrO 2 would lead to a phase segregation of CeO 2 and Fe 2O 3 from the Ce–Fe solid solution, resulting in a decrease in syngas selectivity. Among the tested samples, Ce–Fe–Zr (0.05) sample showed the best catalytic performance (with both high methane conversion and syngas selectivity). Despite severe sintering, the Ce–Fe–Zr (0.05) oxides presented high catalytic stability during the repetitive redox process (methane reduction/air re-oxidation) for the continuous production of syngas. This property should be attributed to the increased oxygen vacancy concentration on the mixed oxides after cycling, which could improve the lattice oxygen mobility, counteracting the native effect of material sintering on the catalytic activity for methane partial oxidation.