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Journal ArticleDOI

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.
Citations
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Journal ArticleDOI
TL;DR: In this article, the authors investigated the correlation between the heat treatment and the observed photoactivities and found that an increase in the applied heat treatment, either by increasing the temperature or increasing the heat treatments duration, led to a decrease in the activities of the catalyst particles.
Abstract: Magnetic iron oxide–titania photocatalysts (Fe 3 O 4 –TiO 2 ) were prepared using a coating technique in which the photoactive titanium dioxide was deposited onto the surface of a magnetic iron oxide core. These particles had a core–shell structure. The prepared particles were heat treated at high temperature in order to transform the amorphous titanium dioxide into a photoactive crystalline phase. The heat treatment temperature and duration were varied, and the correlation between the heat treatment and the observed photoactivities was investigated. An increase in the applied heat treatment, either by increasing the temperature or increasing the heat treatment duration, led to a decrease in the activities of the catalyst particles. A decrease in surface area due to sintering, along with the diffusion of Fe ions into the titanium dioxide coating are seen as contributing factors to the decline in photoactivity which accompanied an increase in the heat treatment. Differential scanning calorimetry analysis (DSC) results confirmed that the presence of the iron oxide core did not have an effect on the phase transformation of titania under the experimental conditions investigated. In this study we also present surface charge measurements which show that the surface of the particles became more positive as the heat treatment was increased. This is an indication of changing surface properties as heat treatment is applied. For single-phase TiO 2 powders, this is postulated to be due to a decrease in the surface hydroxyl (OH) groups and/or residual organics (OR) groups. For the Fe 3 O 4 –TiO 2 powders, in addition to the loss of OH and OR groups, the diffusion of the Fe into the titania shell is postulated to also play a role in the changing surface properties with applied heat treatment. Experiments aimed at reducing the duration of the heat treatment revealed that a heat treatment duration of 20 min at 450 °C was sufficient to transform amorphous titanium dioxide into a photoactive crystalline phase. This does not only minimise loss of surface hydroxyl groups but it also has the potential to limit the oxidation of the magnetic core, which occurs due to the porosity of the coating. This has practical implications in terms of separating the magnetic particles from the treated waste waters under the application of an external magnetic field. It also presents an opportunity to produce photoactive composite particles while limiting the interactions between the core and the shell during the heat treatment.

155 citations

Journal ArticleDOI
TL;DR: In this article, a visible-light-active TiO2/ZnFe2O4 photocatalyst was prepared by liquid catalytic phase transformation and the sol−gel method.
Abstract: A visible-light-active TiO2/ZnFe2O4 photocatalyst was prepared by liquid catalytic phase transformation and the sol−gel method. The diffuse reflection spectra results show that TiO2/ZnFe2O4 photocatalyst can absorb visible light. The photocatalytic experimental result demonstrates that TiO2/ZnFe2O4 powder can effectively photodegrade methyl orange under visible light irradiation. The analysis of XRD indicated that the highly dispersed ZnFe2O4 nanoparticles prevented the formation of the rutile phase to some extent. A transmission electron microscope was used to characterize the structure of the photocatalyst, indicating that the ZnFe2O4 nanoparticles are highly dispersed among TiO2 nanoparticles. In TiO2/ZnFe2O4 photocatalyst, the relatively narrow bandgap ZnFe2O4 as the light-absorbing semiconductor and the wide bandgap titanium oxide formed a coupled semiconductor system resulting in an efficient primary charge separation and photocatalytic activity under visible light irradiation. The effect of calcina...

132 citations

Journal ArticleDOI
TL;DR: In this paper, the degradation of ortho-cresol assisted by Fe/TiO2 photocatalysts was investigated in oxygenated aqueous suspension in a spiral glass flow reactor.
Abstract: The degradation of ortho-cresol (o-cresol) assisted by Fe/TiO2 photocatalysts was investigated in oxygenated aqueous suspension in a spiral glass flow reactor. Iron–titania (1–10 wt.% Fe) mixed catalysts have been prepared by sol–gel impregnation method using metal alkoxide precursors. The surface structure of Fe/TiO2 catalyst was studied by surface analysis with XPS and TEM techniques. Characterization of these catalysts, fired at different temperatures (in the range 500–900°C) using X-ray diffraction (XRD) showed that the sintering temperature and incorporation of iron ions mediate the phase transformation and growth of pseudobrookite (Fe2TiO5) phase at higher temperatures. The rate of degradation of o-cresol decreases with the increasing sintering temperature and iron content of the catalysts and the initial pH of the aqueous solution of o-cresol changes with the illumination time due to the formation of various acidic intermediate photoproducts.

86 citations

Journal ArticleDOI
TL;DR: In this article, the authors studied the cyclohexane with molecular oxygen (1 atm) in the presence of isobutyraldehyde catalyzed by nanostructured iron and cobalt oxides and iron supported on titania and found that highly dispersed transition metals oxide is more effective for oxidation than the corresponding zero valent powders.
Abstract: The oxidation of cyclohexane with molecular oxygen (1 atm) in the presence of isobutyraldehyde catalyzed by nanostructured iron and cobalt oxides and iron supported on titania has been studied. It was found that highly dispersed transition metals oxide is more effective for oxidation than the corresponding zero valent powders. In the titania supported catalysts iron exists as iron (III) oxide segregated to the surface layers and stabilized by titania. This form is the most active in the cyclohexane oxidation under mild conditions.

79 citations

Journal ArticleDOI
TL;DR: In this article, a continuous fixed-bed micro-reactor was used for naphthalene hydrogenation over various supported Pt catalysts and the reaction order was independent of the support and the pre-reduction temperature.
Abstract: Vapor-phase naphthalene hydrogenation over various supported Pt catalysts was studied in a continuous fixed-bed micro-reactor Experimental results indicated that the catalytic activity of the catalyst strongly depended on the nature of the support and the pre-reduction temperature Reaction order was independent of the support as the reaction was pseudo-first-order with respect to naphthalene in the temperature range studied By comparing the apparent rate constant over various supported Pt catalysts, Pt supported on TiO2–ZrO2 (1 : 1) reduced at a low temperature showed the highest activity For higher pre-reduction temperatures, Pt/TiO2–ZrO2 (1 : 1) exhibited the least suppression of H2 uptake, due to a stabilization effect exerted by ZrO2, which prevents the migration of TiOx moieties and the blockage of the Pt surface However, the apparent depression of the hydrogenation activity of high-temperature reduced Pt/TiO2–ZrO2 (1 : 1) was significantly greater than the suppression of its hydrogen uptake Furthermore, the decreasing value of the hydrogenation activity relative to the hydrogen uptake demonstrates electron perturbations between the support and the Pt metal

76 citations

References
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Journal ArticleDOI
C.R. Brundle1, T. J. Chuang1, Klaus Wandelt1
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

Journal ArticleDOI
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

Journal ArticleDOI
S. Matsuda1, A. Kato1
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

Journal ArticleDOI
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

Journal ArticleDOI
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