Electron Energy Loss Spectroscopy (EELS) of Iron Fischer–Tropsch Catalysts

Jin, Yaming; Xu, Huifang; Datye, Abhaya K.

doi:10.1017/s1431927606060144

Cited by 50 publications

(41 citation statements)

References 21 publications

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“…Due to the mixing of C1s and 3d orbitals (hybridization) of carbon and metal atoms, such a structure also occurs for chromium and iron carbides [57,58]. Due to the superposition of the carbides and metal oxides structures in the NEXAFS C1s X-ray spectra, their study by spectral methods is impossible.…”

Section: Near-edge X-ray Absorption Fine Structure (Nexafs) Spectroscmentioning

confidence: 99%

The Structure and Chemical Composition of the Cr and Fe Pyrolytic Coatings on the MWCNTs’ Surface According to NEXAFS and XPS Spectroscopy

et al. 2020

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The paper is devoted to the structure and properties of the composite material based on multi-walled carbon nanotubes (MWCNTs) covered with pyrolytic iron and chromium. Fe/MWCNTs and Cr/MWCNTs nanocomposites have been prepared by the metal organic chemical vapor deposition (MOCVD) growth technique using iron pentacarbonyl and bis(arene)chromium compounds, respectively. Composites structures and morphologies preliminary study were performed using X-ray diffraction, scanning and transmission electron microscopy and Raman scattering. The atomic and chemical composition of the MWCNTs’ surface, Fe-coating and Cr-coating and interface—(MWCNTs surface)/(metal coating) were studied by total electron yield method in the region of near-edge X-ray absorption fine structure (NEXAFS) C1s, Fe2p and Cr2p absorption edges using synchrotron radiation of the Russian-German dipole beamline (RGBL) at BESSY-II and the X-ray photoelectron spectroscopy (XPS) method using the ESCALAB 250 Xi spectrometer and charge compensation system. The absorption cross sections in the NEXAFS C1s edge of the nanocomposites and MWCNTs were measured using the developed approach of suppressing and estimating the contributions of the non-monochromatic background and multiple reflection orders radiation from the diffraction grating. The efficiency of the method was demonstrated by the example of the Cr/MWCNT nanocomposite, since its Cr2p NEXAFS spectra contain additional C1s NEXAFS in the second diffraction order. The study has shown that the MWCNTs’ top layers in composite have no significant destruction; the MWCNTs’ metal coatings are continuous and consist of Fe3O4 and Cr2O3. It is shown that the interface between the MWCNTs and pyrolytic Fe and Cr coatings has a multilayer structure: a layer in which carbon atoms along with epoxy –C–O–C– bonds form bonds with oxygen and metal atoms from the coating layer is formed on the outer surface of the MWCNT, a monolayer of metal carbide above it and an oxide layer on top. The iron oxide and chromium oxide adhesion is provided by single, double and epoxy chemical binding formation between carbon atoms of the MWCNT top layer and the oxygen atoms of the coating, as well as the formation of bonds with metal atoms.

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Section: Near-edge X-ray Absorption Fine Structure (Nexafs) Spectroscmentioning

confidence: 99%

The Structure and Chemical Composition of the Cr and Fe Pyrolytic Coatings on the MWCNTs’ Surface According to NEXAFS and XPS Spectroscopy

et al. 2020

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“…The slight increase of intensity that can be seen at energies above the L3 edge is caused by electron scattering processes. The shift indicates the presence of metallic Fe for the oleic acid capped nanoparticles [25,26].…”

Section: Resultsmentioning

confidence: 99%

Synthesis of Fe Nanoparticles Functionalized with Oleic Acid Synthesized by Inert Gas Condensation

Silva

Solís-Pomar

Gutiérrez-Lazos

et al. 2014

Journal of Nanomaterials

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In this work, we study the synthesis of monodispersed Fe nanoparticles (Fe-NPs)in situfunctionalized with oleic acid. The nanoparticles were self-assembled by inert gas condensation (IGC) technique by using magnetron-sputtering process. Structural characterization of Fe-NPs was performed by transmission electron microscopy (TEM). Particle size control was carried out through the following parameters: (i) condensation zone length, (ii) magnetron power, and (iii) gas flow (Ar and He). Typically the nanoparticles generated by IGC showed diameters which ranged from ~0.7 to 20 nm. Mass spectroscopy of Fe-NPs in the deposition system allowed the study ofin situnanoparticle formation, through a quadrupole mass filter (QMF) that one can use together with a mass filter. When the deposition system works without quadrupole mass filter, the particle diameter distribution is around +/−20%. When the quadrupole is in line, then the distribution can be reduced to around +/−2%.

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“…Probing by EELS is a very sensitive technique and very low concentration of elements can be detected. The carbon K-edge structure clearly shows a weak p* shoulder peak and an intense r* peak, which are characteristic of amorphous carbon species [20]. Since the EELS spectra of the rim do not contain any characteristic edge for Fe or oxygen, it can be concluded that the outer rim consists of amorphous carbon only.…”

Section: Morphologymentioning

confidence: 92%

“…High-resolution STEM imaging coupled with EELS analysis was utilized to determine the chemical nature of any particular structure of interest in different catalyst samples mentioned in Table 1. To identify the elemental composition in EELS spectra, characteristic edge structure of Fe (L 2,3 edge at about 720-740 eV), oxygen (K edge at about 530-535 eV) and carbon (K edge at about 285-310 eV) are considered [20].…”

Section: Morphology and Phase Transformation By Hrtem Stem And Eelsmentioning

confidence: 99%

Fischer–Tropsch Synthesis: Morphology, Phase Transformation and Particle Size Growth of Nano-scale Particles

et al. 2007

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An unpromoted ultrafine iron nano-particle catalyst was used for Fischer-Tropsch synthesis (FTS) in a CSTR at 270°C, 175 psig, H 2 /CO = 0.7, and a syngas space velocity of 3.0 sl/h/g Fe. Prior to FTS, the catalyst was activated in CO for 24 h which converted the initial hematite into a mixture of 85% v-Fe 5 C 2 and 15% magnetite, as found by Mössbauer measurement. The activated catalyst results in an initial high conversion (ca. 85%) of CO and H 2 ; however the conversions decreased to ca. 10% over about 400 h of synthesis time and after that remained nearly constant up to 600 h. Mössbauer and EELS measurement revealed that the catalyst deactivation was accompanied by gradual in situ re-oxidation of the catalyst from initial nearly pure v-Fe 5 C 2 phase to pure magnetite after 400 h of synthesis time. Experimental data indicates that the nucleation for carbide/oxide transformation may initiates at the center of the particle by water produced during FTS. Small amount of e¢-Fe 2.2 C phase was detected in some catalyst samples collected after 480 h of FTS which are believed to be generated by syngas during FTS.Particle size distribution (PSD) measurements indicate nano-scale growth of individual catalyst particle. Statistical average diameters were found to increase by a factor of 4 over 600 h of FTS. Large particles with the largest dimension larger than 150 nm were also observed. Chemical compositions of the larger particles were always found to be pure single crystal magnetite as revealed by EELS analysis. Small number of ultrafine carbide particles was identified in the catalyst samples collected during later period of FTS. The results suggest that carbide/oxide transformation and nano-scale growth of particles continues either in succession or at least simultaneously; but definitely not in the reverse order (in that case some larger carbide particles would have observed). EELS-STEM measurement reveals amorphous carbon rim of thickness 3-5 nm around some particles after activation and during FTS. Well ordered graphitic carbon layers on larger single crystal magnetite particles were found by EELS-STEM measurement. However the maximum thickness of the carbon (amorphous or graphitic) rim does not grow above 10 nm suggesting that the growths of particles are not due to carbon deposition.

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Electron Energy Loss Spectroscopy (EELS) of Iron Fischer–Tropsch Catalysts

Cited by 50 publications

References 21 publications

The Structure and Chemical Composition of the Cr and Fe Pyrolytic Coatings on the MWCNTs’ Surface According to NEXAFS and XPS Spectroscopy

The Structure and Chemical Composition of the Cr and Fe Pyrolytic Coatings on the MWCNTs’ Surface According to NEXAFS and XPS Spectroscopy

Synthesis of Fe Nanoparticles Functionalized with Oleic Acid Synthesized by Inert Gas Condensation

Fischer–Tropsch Synthesis: Morphology, Phase Transformation and Particle Size Growth of Nano-scale Particles

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