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Andrei Y Khodakov - One of the best experts on this subject based on the ideXlab platform.
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agglomeration at the micrometer length scale of Cobalt nanoparticles in alumina supported fischer tropsch catalysts in a slurry reactor
Chemcatchem, 2013Co-Authors: Diego Pena, Anne Gribovalconstant, Fabrice Diehl, Vincent Lecocq, Andrei Y KhodakovAbstract:Fischer–Tropsch (FT) synthesis is a promising approach to produce ultraclean hydrocarbon fuels by using syngas obtained from natural gas, coal, or biomass. Alumina-supported Cobalt catalysts are generally preferred for FT synthesis because of their high activity, high selectivity to linear paraffins, and low water gas shift activity. [1–4] Nevertheless, structural changes to the Cobalt catalysts during the FT reaction may result in a decrease in catalytic activity. These changes may include catalyst contamination; transformations of metallic Cobalt into Cobalt carbides, Cobalt oxides, and/or Cobalt aluminates; Cobalt restructuring; agglomeration of the metallic Cobalt particles; carbon deposition; and catalyst attrition. It has been shown [3] that, because of thermodynamic reasons, Cobalt bulk oxidation does not occur and Cobalt particles with crystallite sizes larger than 2–3 nm remain in the metallic state under typical FT synthesis conditions. Long-term deactivation may involve carbon deposition and catalyst attrition. The loss of the active catalyst by attrition represents one of the major problems in slurry bubble column reactors in industry. [4] Cobalt sintering at the nanoscale level has been observed by both in situ and ex situ techniques. Cobalt sintering results in an increase in Cobalt particle size to several nanometers. [3, 5–7] The decrease in the active surface resulting from nanoscale sintering of metallic Cobalt particles is an irreversible process driven by thermodynamic forces. [2] It has been reported that agglomeration of smaller Cobalt nanoparticles by sintering could be responsible for a decrease in catalytic activity by approximately 30–40 % over the first few days of a reaction. [3, 7] A number of publications suggest that sintering levels off at Cobalt particle sizes of several nanometers, which correspond to the pore diameter of the catalysts. To the best of our knowledge, micron-sized Cobalt agglomerates produced during the FT reaction in slurry reactors have not been reported.
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Cobalt species and Cobalt support interaction in glow discharge plasma assisted fischer tropsch catalysts
Journal of Catalysis, 2010Co-Authors: P.a. Chernavskii, Jingping Hong, Andrei Y KhodakovAbstract:Abstract Cobalt species and Cobalt-support interaction in glow discharge plasma-assisted Fischer–Tropsch catalysts were studied using a combination of characterization techniques (X-ray diffraction, thermo-gravimetric analysis, temperature-programmed reduction, in situ magnetic measurements and in situ X-ray absorption). The catalysts were prepared by incipient impregnation using solutions of Cobalt nitrate and ruthenium nitrosyl nitrate followed by plasma or/and oxidative treatment. Cobalt dispersion in silica-supported catalysts was significantly enhanced by plasma pretreatment. Cobalt particle size was a function of glow discharge plasma intensity. The concentration of Cobalt silicate in plasma-assisted samples was low. No noticeable effect of the plasma pretreatment on the formation of barely reducible Cobalt silicate species was observed. Cobalt reducibility was to some extent hindered in the plasma-assisted catalysts, while promotion with ruthenium significantly enhanced Cobalt reducibility in silica-supported catalysts. Due to the combination of high Cobalt dispersion and optimized Cobalt reducibility, ruthenium-promoted plasma-assisted Cobalt catalyst exhibited an enhanced activity in Fischer–Tropsch synthesis.
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Cobalt species in promoted Cobalt alumina-supported Fischer–Tropsch catalysts
Journal of Catalysis, 2007Co-Authors: Wei Chu, P.a. Chernavskii, L. Gengembre, Galina A. Pankina, Pascal Fongarland, Andrei Y KhodakovAbstract:The structure of Cobalt species at different stages of the genesis of monometallic and Pt-promoted Cobalt alumina-supported Fischer–Tropsch catalysts was studied using X-ray diffraction, UV–visible spectroscopy, in situ X-ray absorption, in situ magnetic method, X-ray photoelectron spectroscopy, and DSC–TGA thermal analysis. The catalysts were prepared by incipient wetness impregnation using solutions of Cobalt nitrate and dihydrogen hexachloroplatinate. Both variation of catalyst calcination temperature between 473 and 773 K and promotion with 0.1 wt% of Pt had no significant affect on the size of supported Co3O4 crystallites. The size of Cobalt oxide particles in the calcined catalysts seems to be influenced primarily by the pore diameter of the support. Cobalt reducibility was relatively low in monometallic Cobalt alumina-supported catalysts and decreased as a function of catalyst calcination temperature. The effect was probably due to the formation of mixed surface compounds between Co3O4 and Al2O3 at higher calcination temperatures, which hinder Cobalt reduction. Promotion with platinum spectacularly increased the rate of Cobalt reduction; the promotion seemed to reduce the activation energy of the formation of Cobalt metallic phases. Analysis of the magnetization data suggests that the presence of Pt led to the reduction of smaller Cobalt oxide particles, which could not be reduced at the same conditions in the Cobalt monometallic catalysts. Promotion of Cobalt alumina-supported catalysts with small amounts of Pt resulted in a significant increase in Fischer–Tropsch Cobalt time yield. The efficient control of Cobalt reducibility through catalyst calcination and promotion seems to be one of the key issues in the design of efficient Cobalt alumina-supported Fischer–Tropsch catalysts.
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Characterization of the Genesis of Cobalt Metal Particles in Silica-Supported Fischer-Tropsch Catalysts using Foner Magnetic Method
Applied Catalysis A : General, 2006Co-Authors: Petr A. Chernavskii, Andrei Y Khodakov, Galina V. Pankina, Jean-sébastien Girardon, Elodie QuinetAbstract:The genesis of Cobalt metal particles in silica-supported Fischer-Tropsch catalysts was studied using in situ Foner vibrating-sample magnetic method. The Cobalt promoted and unpromoted catalysts were prepared by aqueous (co)-impregnation using Cobalt nitrate or acetate, ruthenium nitrosyl nitrate or perrhenic acid followed by oxidative pre-treatment in air and reduction in hydrogen. In several catalyst preparations, sucrose was added to the impregnating solutions. The genesis of Cobalt metal phases in these catalysts was monitored in situ by the magnetic method during the temperature-programmed reduction in pure hydrogen. A considerably higher extent of Cobalt reduction was found in the catalysts prepared from Cobalt nitrate than in those prepared from Cobalt acetate. Promotion with ruthenium and rhenium results in a considerable decrease in the temperature of the emergence of Cobalt metal phases. Small superparamagnetic, single-domain and multi-domain ferromagnetic Cobalt metal particles were observed in the reduced catalysts by the magnetic method. It was found that lower temperature calcination of the Cobalt catalysts prepared from Cobalt nitrate and addition of sucrose to the impregnating solution lead to a decrease in the concentration of multi-domain Cobalt ferromagnetic metal particles and to an increase in the fraction of superparamagnetic Cobalt particles. Superparamagnetic Cobalt particles smaller than 6-7 nm were detected in the reduced catalysts prepared from Cobalt nitrate with sucrose addition and in the catalysts prepared from Cobalt acetate. Catalyst characterization using X-ray diffraction and X-ray photoelectron spectroscopy has confirmed the results about Cobalt dispersion and reducibility in the Cobalt silica-supported catalysts obtained by the Foner magnetic method.
P.a. Chernavskii - One of the best experts on this subject based on the ideXlab platform.
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Cobalt species and Cobalt support interaction in glow discharge plasma assisted fischer tropsch catalysts
Journal of Catalysis, 2010Co-Authors: P.a. Chernavskii, Jingping Hong, Andrei Y KhodakovAbstract:Abstract Cobalt species and Cobalt-support interaction in glow discharge plasma-assisted Fischer–Tropsch catalysts were studied using a combination of characterization techniques (X-ray diffraction, thermo-gravimetric analysis, temperature-programmed reduction, in situ magnetic measurements and in situ X-ray absorption). The catalysts were prepared by incipient impregnation using solutions of Cobalt nitrate and ruthenium nitrosyl nitrate followed by plasma or/and oxidative treatment. Cobalt dispersion in silica-supported catalysts was significantly enhanced by plasma pretreatment. Cobalt particle size was a function of glow discharge plasma intensity. The concentration of Cobalt silicate in plasma-assisted samples was low. No noticeable effect of the plasma pretreatment on the formation of barely reducible Cobalt silicate species was observed. Cobalt reducibility was to some extent hindered in the plasma-assisted catalysts, while promotion with ruthenium significantly enhanced Cobalt reducibility in silica-supported catalysts. Due to the combination of high Cobalt dispersion and optimized Cobalt reducibility, ruthenium-promoted plasma-assisted Cobalt catalyst exhibited an enhanced activity in Fischer–Tropsch synthesis.
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Cobalt species in promoted Cobalt alumina-supported Fischer–Tropsch catalysts
Journal of Catalysis, 2007Co-Authors: Wei Chu, P.a. Chernavskii, L. Gengembre, Galina A. Pankina, Pascal Fongarland, Andrei Y KhodakovAbstract:The structure of Cobalt species at different stages of the genesis of monometallic and Pt-promoted Cobalt alumina-supported Fischer–Tropsch catalysts was studied using X-ray diffraction, UV–visible spectroscopy, in situ X-ray absorption, in situ magnetic method, X-ray photoelectron spectroscopy, and DSC–TGA thermal analysis. The catalysts were prepared by incipient wetness impregnation using solutions of Cobalt nitrate and dihydrogen hexachloroplatinate. Both variation of catalyst calcination temperature between 473 and 773 K and promotion with 0.1 wt% of Pt had no significant affect on the size of supported Co3O4 crystallites. The size of Cobalt oxide particles in the calcined catalysts seems to be influenced primarily by the pore diameter of the support. Cobalt reducibility was relatively low in monometallic Cobalt alumina-supported catalysts and decreased as a function of catalyst calcination temperature. The effect was probably due to the formation of mixed surface compounds between Co3O4 and Al2O3 at higher calcination temperatures, which hinder Cobalt reduction. Promotion with platinum spectacularly increased the rate of Cobalt reduction; the promotion seemed to reduce the activation energy of the formation of Cobalt metallic phases. Analysis of the magnetization data suggests that the presence of Pt led to the reduction of smaller Cobalt oxide particles, which could not be reduced at the same conditions in the Cobalt monometallic catalysts. Promotion of Cobalt alumina-supported catalysts with small amounts of Pt resulted in a significant increase in Fischer–Tropsch Cobalt time yield. The efficient control of Cobalt reducibility through catalyst calcination and promotion seems to be one of the key issues in the design of efficient Cobalt alumina-supported Fischer–Tropsch catalysts.
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Cobalt dispersion, reducibility, and surface sites in promoted silica-supported Fischer–Tropsch catalysts.
Journal of Catalysis, 2007Co-Authors: J.-s. Girardon, E. Quinet, Anne Griboval-constant, P.a. Chernavskii, L. Gengembre, A.y. KhodakovAbstract:Cobalt particle size, Cobalt reducibility, and metal surface sites in a series of ruthenium- and rhenium-promoted Cobalt silica-supported Fischer– Tropsch catalysts were studied by X-ray diffraction, UV–vis spectroscopy, in situ X-ray absorption, in situ magnetic method, X-ray photoelectron spectroscopy, DSC-TGA thermal analysis, and propene chemisorption. The catalysts were prepared by co-impregnation; in several catalyst syntheses, sucrose was added to the impregnating solutions. Mononuclear octahedral Cobalt complexes were observed in the catalysts after impregnation and drying. Cobalt repartition on silica in the impregnated and dried catalysts depended primarily on the pH of the impregnating solution. Cobalt repartition was uniform on the silica surface if the pH of the impregnating solution was higher than the point of zero charge (PZC) of silica, but was less uniform at pH below that of the PZC of silica. Cobalt dispersion proceeded during catalyst calcination in air. Decomposition of Cobalt nitrate and crystallization of Cobalt oxide seemed to be the crucial steps in the preparation of highly dispersed Cobalt catalysts. Promotion with noble metals resulted in greater Cobalt dispersion, probably due to higher concentrations of Cobalt oxide crystallization sites. Addition of sucrose modified the structure of supported Cobalt complexes and led to higher temperatures of crystallization of Cobalt oxide and to catalysts with extremely high Cobalt dispersion. In situ magnetization measurements show that promotion with Ru moderated the temperature of reduction of Cobalt oxide to metal phases, whereas the effect was less significant for Re-promoted catalysts. The addition of sucrose during impregnation, although significantly enhancing Cobalt dispersion, did not diminish Cobalt reducibility. Due to a combination of high Cobalt dispersion and reducibility, the ruthenium- and rhenium-promoted catalysts prepared using sucrose had the highest number of Cobalt metal surface sites. Fischer–Tropsch reaction rates were determined principally by the number of Cobalt surface sites, with high Cobalt dispersion and easy reducibility resulting in more active Fischer–Tropsch catalysts.
A.y. Khodakov - One of the best experts on this subject based on the ideXlab platform.
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Cobalt dispersion, reducibility, and surface sites in promoted silica-supported Fischer–Tropsch catalysts.
Journal of Catalysis, 2007Co-Authors: J.-s. Girardon, E. Quinet, Anne Griboval-constant, P.a. Chernavskii, L. Gengembre, A.y. KhodakovAbstract:Cobalt particle size, Cobalt reducibility, and metal surface sites in a series of ruthenium- and rhenium-promoted Cobalt silica-supported Fischer– Tropsch catalysts were studied by X-ray diffraction, UV–vis spectroscopy, in situ X-ray absorption, in situ magnetic method, X-ray photoelectron spectroscopy, DSC-TGA thermal analysis, and propene chemisorption. The catalysts were prepared by co-impregnation; in several catalyst syntheses, sucrose was added to the impregnating solutions. Mononuclear octahedral Cobalt complexes were observed in the catalysts after impregnation and drying. Cobalt repartition on silica in the impregnated and dried catalysts depended primarily on the pH of the impregnating solution. Cobalt repartition was uniform on the silica surface if the pH of the impregnating solution was higher than the point of zero charge (PZC) of silica, but was less uniform at pH below that of the PZC of silica. Cobalt dispersion proceeded during catalyst calcination in air. Decomposition of Cobalt nitrate and crystallization of Cobalt oxide seemed to be the crucial steps in the preparation of highly dispersed Cobalt catalysts. Promotion with noble metals resulted in greater Cobalt dispersion, probably due to higher concentrations of Cobalt oxide crystallization sites. Addition of sucrose modified the structure of supported Cobalt complexes and led to higher temperatures of crystallization of Cobalt oxide and to catalysts with extremely high Cobalt dispersion. In situ magnetization measurements show that promotion with Ru moderated the temperature of reduction of Cobalt oxide to metal phases, whereas the effect was less significant for Re-promoted catalysts. The addition of sucrose during impregnation, although significantly enhancing Cobalt dispersion, did not diminish Cobalt reducibility. Due to a combination of high Cobalt dispersion and reducibility, the ruthenium- and rhenium-promoted catalysts prepared using sucrose had the highest number of Cobalt metal surface sites. Fischer–Tropsch reaction rates were determined principally by the number of Cobalt surface sites, with high Cobalt dispersion and easy reducibility resulting in more active Fischer–Tropsch catalysts.
Carola Lidén - One of the best experts on this subject based on the ideXlab platform.
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Cobalt release from implants and consumer items and characteristics of Cobalt sensitized patients with dermatitis
Contact Dermatitis, 2011Co-Authors: Jacob P. Thyssen, Torkil Menné, Carola Lidén, Anneli Julander, Peter Østrup Jensen, Stig Storgaard Jakobsen, Kjeld Søballe, Klaus Gotfredsen, Morten Stendahl Jellesen, Jeanne D. JohansenAbstract:Background. Cobalt allergy is prevalent in dermatitis patients. Very little documentation exists about current sources of Cobalt exposure. Objectives. To investigate and discuss putative sources of Cobalt exposure and to present selected epidemiological data on Cobalt allergy from patch-tested dermatitis patients in an attempt to better understand Cobalt allergy. Materials and methods. 19 780 dermatitis patients aged 4–99 years were patch tested with nickel, chromium or Cobalt between 1985 and 2010. The Cobalt spot test was used to test for Cobalt ion release from mobile phones as well as Cobalt-containing dental alloys and revised hip implant components. Results. Six of eight dental alloys and 10 of 98 revised hip implant components released Cobalt in the Cobalt spot test, whereas none of 50 mobile phones gave positive reactions. The clinical relevance of positive Cobalt test reactions was difficult to determine in the majority of patients. Isolated patch test reactivity to Cobalt was less associated with occupational dermatitis and hand eczema than patch test reactivity to Cobalt in combination with other contact allergies. Conclusions. It is often difficult to interpret the relevance of a positive patch test reaction to Cobalt, and there is a need for further studies to determine sources of Cobalt exposure.
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Cobalt containing alloys and their ability to release Cobalt and cause dermatitis
Contact Dermatitis, 2009Co-Authors: Anneli Julander, Monica Hindsen, Lizbet Skare, Carola LidénAbstract:Cobalt, nickel, and chromium are important skin sensitizers. However, knowledge about Cobalt exposure and causes of Cobalt sensitization is limited. To study release of Cobalt, nickel, and chromium from some Cobalt-containing hard metal alloys and to test reactivity to the materials in Cobalt-sensitized patients. Discs suitable for patch testing were made of some hard metal alloys. Cobalt, nickel, and chromium release from the materials was determined by immersion in artificial sweat (2 min, 1 hr, 1 day, and 1 week). Patch test reactivity to the discs and to serial dilutions of Cobalt and nickel was assessed in previously patch-tested dermatitis patients (19 Cobalt positive and 18 Cobalt-negative controls). All discs released Cobalt, nickel, and chromium. Some discs released large amounts of Cobalt (highest concentration: 290 mu g/cm(2)/week). Seven discs elicited three or more positive test reactions. The concentration of released Cobalt was high enough to elicit allergic contact dermatitis in Cobalt-sensitized patients. As the materials in the discs are used in wear parts of hard metal tools, individuals with contact allergy to Cobalt may develop hand eczema when handling such materials. (Less)
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Cobalt‐containing alloys and their ability to release Cobalt and cause dermatitis
Contact Dermatitis, 2009Co-Authors: Anneli Julander, Monica Hindsen, Lizbet Skare, Carola LidénAbstract:Cobalt, nickel, and chromium are important skin sensitizers. However, knowledge about Cobalt exposure and causes of Cobalt sensitization is limited. To study release of Cobalt, nickel, and chromium from some Cobalt-containing hard metal alloys and to test reactivity to the materials in Cobalt-sensitized patients. Discs suitable for patch testing were made of some hard metal alloys. Cobalt, nickel, and chromium release from the materials was determined by immersion in artificial sweat (2 min, 1 hr, 1 day, and 1 week). Patch test reactivity to the discs and to serial dilutions of Cobalt and nickel was assessed in previously patch-tested dermatitis patients (19 Cobalt positive and 18 Cobalt-negative controls). All discs released Cobalt, nickel, and chromium. Some discs released large amounts of Cobalt (highest concentration: 290 mu g/cm(2)/week). Seven discs elicited three or more positive test reactions. The concentration of released Cobalt was high enough to elicit allergic contact dermatitis in Cobalt-sensitized patients. As the materials in the discs are used in wear parts of hard metal tools, individuals with contact allergy to Cobalt may develop hand eczema when handling such materials. (Less)
Jingping Hong - One of the best experts on this subject based on the ideXlab platform.
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Cobalt species and Cobalt support interaction in glow discharge plasma assisted fischer tropsch catalysts
Journal of Catalysis, 2010Co-Authors: P.a. Chernavskii, Jingping Hong, Andrei Y KhodakovAbstract:Abstract Cobalt species and Cobalt-support interaction in glow discharge plasma-assisted Fischer–Tropsch catalysts were studied using a combination of characterization techniques (X-ray diffraction, thermo-gravimetric analysis, temperature-programmed reduction, in situ magnetic measurements and in situ X-ray absorption). The catalysts were prepared by incipient impregnation using solutions of Cobalt nitrate and ruthenium nitrosyl nitrate followed by plasma or/and oxidative treatment. Cobalt dispersion in silica-supported catalysts was significantly enhanced by plasma pretreatment. Cobalt particle size was a function of glow discharge plasma intensity. The concentration of Cobalt silicate in plasma-assisted samples was low. No noticeable effect of the plasma pretreatment on the formation of barely reducible Cobalt silicate species was observed. Cobalt reducibility was to some extent hindered in the plasma-assisted catalysts, while promotion with ruthenium significantly enhanced Cobalt reducibility in silica-supported catalysts. Due to the combination of high Cobalt dispersion and optimized Cobalt reducibility, ruthenium-promoted plasma-assisted Cobalt catalyst exhibited an enhanced activity in Fischer–Tropsch synthesis.