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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.
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TL;DR: In this paper, the photoactivity of the prepared coated particles was lower than that of single-phase TiO2 and was found to decrease with an increase in the heat treatment.
Abstract: Magnetic photocatalysts were synthesized by coating titanium dioxide particles onto colloidal magnetite and nano-magnetite particles. The photoactivity of the prepared coated particles was lower than that of single-phase TiO2 and was found to decrease with an increase in the heat treatment. These observations were explained in terms of an unfavorable heterojunction between the titanium dioxide and the iron oxide core, leading to an increase in electron−hole recombination. Interactions between the iron oxide core and the titanium dioxide matrix upon heat treatment were also seen as a possible cause of the observed low activities of these samples. Other issues considered include the physical and chemical characteristics of the samples, such as surface area and the presence of surface hydroxyl groups. Depending on the calcination conditions, these photocatalysts were found to suffer from varying degrees of photodissolution. Photodissolution tests revealed the greater the extent of the heat treatment, the low...

511 citations

Journal ArticleDOI
TL;DR: An exhaustive review on the photochemical properties of iron-doped TiO2 semiconductors is presented in this article, where different aspects relating to structural, surface and photophysical properties of these photocatalysts are extensively discussed.
Abstract: An exhaustive review on the photochemical properties of iron-doped TiO2 semiconductors is presented. Photocatalytic reactions (reductions and oxidations) using Fe-containing TiO2 on different organic and inorganic substrates are reported. Different aspects relating to structural, surface and photophysical properties of these photocatalysts are extensively discussed. The origin of the photoactivity of this kind of mixed oxides is considered with regards to previously proposed physical and chemical processes and on the role of the iron content.

421 citations

Journal ArticleDOI
TL;DR: In this article, a review of strong metal-support interactions (SMSI) is presented, which are responsible for the catalytic activity, selectivity and stability of various reaction systems, such as heterogeneous catalysis and electrocatalysis.
Abstract: Interactions between metals and supports are of fundamental interest in heterogeneous catalysis. The electronic, geometric and bifunctional effects originating from Strong Metal-Support Interactions (SMSI) that are responsible for the catalyst's activity, selectivity, and stability are key factors that determine performance. Research into SMSI is fast-growing with many revolutionary systems being developed to enhance our understanding of its nature and effects. This review starts with a brief overview of heterogeneous catalysis and SMSI; then three major mechanisms involving electronic, geometric and bifunctional effects are summarized to introduce the fundamental concepts, recent progress and disagreement remained. Subsequently, advanced analytical techniques are introduced as contemporary approaches to the investigation and understanding of SMSI. In addition, the effects of SMSI on the catalytic activity, selectivity and stability of various reaction systems, such as heterogeneous catalysis and electrocatalysis are examined. Additionally, a brief review of various protocols used for the manipulation of interactions between metals and supports is given. Lastly, the future of SMSI with respect to further developments and ongoing challenging issues is addressed.

221 citations

Journal ArticleDOI
01 Jun 2020
TL;DR: In this article, the particle size of the support (ceria-zirconia) can be used to tune the metal-support interactions, resulting in a substantially enhanced CO2 hydrogenation rate.
Abstract: Metal–support interactions have a strong impact on the performance of heterogeneous catalysts. Specific sites at the metal–support interface can give rise to unusual high reactivity, and there is a growing interest in optimizing not only the properties of metal particles but also the metal–support interface. Here, we demonstrate how varying the particle size of the support (ceria–zirconia) can be used to tune the metal–support interactions, resulting in a substantially enhanced CO2 hydrogenation rate. A combination of X-ray diffraction, X-ray absorption spectroscopy, near-ambient pressure X-ray photoelectron spectroscopy, transmission electron microscopy and infrared spectroscopy provides insight into the active sites at the interface between cobalt and ceria–zirconia involved in CO2 hydrogenation to CH4. Reverse oxygen spillover from the support during treatment in hydrogen results in the generation of oxygen vacancies. Stabilization of cobalt particles by ceria–zirconia particles of intermediate size leads to oxygen spillover to the support during the CO2 and CO dissociation steps, followed by further hydrogenation of the resulting intermediates on cobalt. Metal–support interactions can effectively modify the catalytic properties of heterogeneous composites. Here, the authors report the possibility of controlling the interaction between cobalt and a ceria–zirconia support by changing the particle size of the latter, resulting in a superior CO2 hydrogenation system.

215 citations

Journal ArticleDOI
TL;DR: In this article, a stable magnetic photocatalyst was prepared by coating a magnetic core with a layer of photoactive titanium dioxide, which inhibited the direct electrical contact and hence prevented the photodissolution of the iron oxide phase.
Abstract: A stable magnetic photocatalyst was prepared by coating a magnetic core with a layer of photoactive titanium dioxide. A direct deposition of titanium dioxide onto the surface of magnetic iron oxide particles proved ineffective in producing a stable magnetic photocatalyst, with high levels of photodissolution being observed with these samples. This observed photodissolution is believed to be due to the dissolution of the iron oxide phase, induced by the photoactive the titanium dioxide layer due to electronic interactions at the phase junction in these magnetic photocatalysts. The introduction of an intermediate passive SiO2 layer between the titanium dioxide phase and the iron oxide phase inhibited the direct electrical contact and hence prevented the photodissolution of the iron oxide phase. The magnetic photocatalyst is for use in slurry-type reactors from which the catalyst can be easily recovered by the application of an external magnetic field.

186 citations

References
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Journal ArticleDOI
TL;DR: In this article, it was shown that the anatase-rutile transformation of the TiO2 support is facilitated by the Fe2+ ions formed during the reduction process.
Abstract: Based onin-situ Mossbauer and X-ray diffraction studies, it is shown that in the Fe/TiO2 catalyst, the anatase-rutile transformation of the TiO2 support is facilitated by the Fe2+ ions formed during the reduction. The transformation occurs at lower temperatures in Th/TiO2 and Cu/TiO2 compared to pure TiO2. In general, the transformation of anatase to rutile seems to occur at or below the temperature (∼770 K) at which strong-metal-support-interaction manifests itself.

25 citations

Journal ArticleDOI
TL;DR: In this article, the authors examined the surface properties of iron sulfates at various temperatures ranging from 500 to 900 °C and found that the sulfates completely decomposes to form α-Fe2O3 at temperatures from 675 to 700 °C.

17 citations