Strong metal support interaction state in the Fe/TiO2 system- an XPS study
01 Oct 1995-Journal of Materials Science (Kluwer Academic Publishers-Plenum Publishers)-Vol. 30, Iss: 19, pp 4980-4985
TL;DR: In this article, strong metal support interaction with supported group VIII metals is associated with the phase transformation of the support employed, which is identified to have arisen from the formation of a ternary oxide phase and its subsequent reorganization under high temperature reduction conditions.
Abstract: Strong metal support interaction with supported group VIII metals is associated with the phase transformation of the support employed. The reduced uptake of hydrogen and the enhanced reactivity in CO hydrogenation in these systems are associated with the geometrical dispersion of the metal species, which is identified to have arisen from the formation of a ternary oxide phase and its subsequent reorganization under high temperature reduction conditions. XPS experimental evidence is provided for this postulate.
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TL;DR: In this paper, commercial rutile TiO2 particles (200-300 nm) were modified by the temperature-regulated chemical vapor deposition (tr-CVD) of Fe-oxide and subsequent annealing at various temperatures (300~750 °C).
Abstract: Commercial rutile TiO2 particles (200–300 nm) were modified by the temperature-regulated chemical vapor deposition (tr-CVD) of Fe-oxide and subsequent annealing at various temperatures (300~750 °C). As a result of the modification, the photocatalytic activity of the TiO2 regarding acetaldehyde removal under visible light was enhanced, and the enhancement effects were dependent on the annealing temperature. Specifically, the enhancement effects of the modification were most pronounced when Fe-TiO2 was annealed at 375 °C, whereas the effects were significantly reduced by annealing at higher temperatures (525 and 750 °C). The analytical results with various techniques, including two surface-sensitive methods (XPS (X-ray photoelectron spectroscopy) and TOF-SIMS (time of fight-secondary ion mass spectrometry)), revealed that the stronger metal support interaction between TiO2 and the loaded Fe-oxide at high temperature (>375 °C) resulted in the decreased charge separation efficiency and photocatalytic activity of the Fe-TiO2 under light irradiation. The production scale for the Fe-TiO2 photocatalysts can be easily increased (from 200 g to 8 kg per the unit process) by upsizing the reactor volume. The mass-produced samples exhibited similar activity to the samples produced at small scale, and they were photocatalytically active after being spread on a cement block (stainless steel plate) using a surface hardening agent (paint), showing the high applicability in real applications.
9 citations
TL;DR: In this article, the solubility of Fe in reduced rutile TiO2 crystals and the followed precipitation on the (001) surface have been studied using X-ray photoelectron spectroscopy (XPS) and scanning tunneling microscopy (STM) in ultra-high vacuum.
6 citations
TL;DR: In this article, a series of well-defined and uniform pore-structure (WDUPS) TiO2/SiO2 supports with various percentages of rutileTiO2 was developed.
Abstract: A series of well-defined and uniform pore-structure (WDUPS) TiO2/SiO2 supports with various percentages of rutile TiO2 was developed. Then Fe was introduced into the as-prepared WDUPS supports by incipient wetness impregnation to obtain WDUPS Fe/TiO2/SiO2 catalysts for the Fischer–Tropsch (FT) synthesis. Due to a similar surface OH density in the supports and the same pore structure and Fe loading, the catalytic performance of WDUPS catalysts dominated by percentages of rutile TiO2. Based on the catalytic performance for FT synthesis and the characterization of the H2 temperature-programmed reduction (H2-TPR) and the X-ray photoelectron spectroscopy (XPS), the results suggested that rutile TiO2 acted as a structure promoter in titania-supported iron catalysts and led to an increase in the catalytic activity during FT synthesis. The C5+ selectivity had an increase as the percentage of the rutile phase increased, which was also probably because of rutile TiO2 as a structure promoter for enhancing chain growth.
2 citations
Journal Article•
TL;DR: In this paper, the authors studied the oxidation of cyclohexane with molecular oxygen in the presence of isobutyraldehyde catalyzed by nanostructured iron and cobalt oxides and iron oxide supported on titania.
Abstract: The oxidation of cyclohexane with molecular oxygen in the presence of isobutyraldehyde catalyzed by nanostructured iron and cobalt oxides and iron oxide supported on titania has been studied. It was found that highly dispersed transition metal oxide is more effective for oxidation than the corresponding zero-valent metal powders. Nanostructured cobalt oxide on MCM-41 is found to be efficient for catalytic aerobic epoxidation of olefins. The catalyst is reusable and gives moderate to high regio- and stereoselectivity.
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References
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IBM1
TL;DR: The core and valence level XPS spectra of FexO (x ~ 0.90-0.95), Fe2O3 (α and γ), Fe3O4; and FeOOH have been studied under a variety of sample surface conditions as discussed by the authors.
577 citations
TL;DR: The metal-support interaction between iron and titania, which is initiated by reduction at 800 K and is responsible for the changes in ammonia synthesis kinetics, is due to titanium species at the surface of the metallic iron particles as mentioned in this paper.
220 citations
TL;DR: In this article, the application and physico-chemical properties of TiO2-based catalysts are discussed and the preparation procedure of a high surface area TiO 2 support is briefly summarized.
207 citations
TL;DR: In this paper, surface compositional changes were observed for TiO2 single crystal electrodes used for photo-electrolysis of water, and they were compared with a variety of titanium, titanium oxide and titanium hydride standard materials.
198 citations
TL;DR: In this paper, the authors studied the kinetics of the transformation of anatase from titanium sulphate to rutile and found that the transformation becomes immeasurably slow below ~695±10°C compared to ~610°C for pure anatase.
Abstract: The particle size and crystallite size of anatase increase markedly in the region of the crystal structure transformation. The unit cell of anatase seems to expand prior to the transformation to rutile. This expansion has been attributed to a displacive transformation of the type defined by Buerger. Smaller particle size and larger surface area seem to favour the transformation. The kinetics of the transformation of anatase prepared by the hydrolysis of titanium sulphate have been studied at different temperatures and are found to be considerably different from the kinetics of the transformation of pure anatase. The transformation becomes immeasurably slow below ~695±10°C compared to ~610°C for pure anatase. An induction period is observed in the transformation of anatase obtained from sulphate hydrolysis and the duration decreases with increase in temperature. The activation energy is ~120 kcal/mole, a value higher than that for the pure anatase-rutile transformation. The results have been interpreted in terms of the relative rates of nucleation and propagation processes. The activation energy for the nucleation process seems to be much larger than for the propagation process. The kinetics of the transformation of anatase samples doped with different amounts of sulphate ion impurity have also been studied and the transformation is found to be progressively decelerated with increase in the impurity concentration. The energy of activation for the transformation appears to increase progressively with increase in impurity concentration.
163 citations