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J.w. Niemantsverdriet - One of the best experts on this subject based on the ideXlab platform.
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Fundamental issues on practical Fischer–Tropsch Catalysts : how surface science can help
Catalysis Today, 2014Co-Authors: C.j. Weststrate, D.j. Moodley, A.m. Saib, Im Ionel Ciobica, J.w. NiemantsverdrietAbstract:The present article highlights the contribution of surface science and molecular modeling to the understanding of Fischer–Tropsch catalysis, in particular related to carbon-induced Co Fischer–Tropsch Catalyst deactivation. The role of atomic and graphitic carbon in surface restructuring is discussed. Both forms of surface carbon stabilize surface roughness, while molecular CO promotes mobility of Co surface atoms. In a proposed chain growth mechanism on Co(0 0 0 1) chain elongation proceeds via alkylidyne + CH. The resulting acetylenic species is hydrogenated to alkylidyne, the route to further growth. (Cyclo-)polymerization of acetylenic species produces (aromatic) forms of polymeric surface carbon, a slow side reaction.
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cobalt fischer tropsch Catalyst regeneration the crucial role of the kirkendall effect for cobalt redispersion
Topics in Catalysis, 2011Co-Authors: C.j. Weststrate, M M Hauman, D.j. Moodley, A.m. Saib, E. Van Steen, J.w. NiemantsverdrietAbstract:Redispersion of cobalt is a key process during Fischer–Tropsch Catalyst regeneration. Using model Catalysts we show that redispersion is a two step process. Oxidation of supported metallic cobalt nanoparticles produces hollow oxide particles by the Kirkendall effect; reduction leads to break-up of these hollow oxide shells, forming multiple metallic particles. This mechanism is to a large extent independent of the support.
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Cobalt Fischer–Tropsch Catalyst Regeneration: The Crucial Role of the Kirkendall Effect for Cobalt Redispersion
Topics in Catalysis, 2011Co-Authors: C.j. Weststrate, M M Hauman, D.j. Moodley, A.m. Saib, E. Van Steen, J.w. NiemantsverdrietAbstract:Redispersion of cobalt is a key process during Fischer–Tropsch Catalyst regeneration. Using model Catalysts we show that redispersion is a two step process. Oxidation of supported metallic cobalt nanoparticles produces hollow oxide particles by the Kirkendall effect; reduction leads to break-up of these hollow oxide shells, forming multiple metallic particles. This mechanism is to a large extent independent of the support.
Anders Holmen - One of the best experts on this subject based on the ideXlab platform.
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The effect of aerosol-deposited ash components on a cobalt-based Fischer–Tropsch Catalyst
Reaction Kinetics Mechanisms and Catalysis, 2019Co-Authors: Ljubiša Gavrilović, Jan Brandin, Rune Myrstad, Hilde J. Venvik, Anders Holmen, Edd Anders BlekkanAbstract:The effect of ash salts on Co-based Fisher–Tropsch Catalysts was studied using an aerosol deposition technique. The major elements in the ash were found to be K, S and Cl. The ash was deposited on a calcined Catalyst as dry particles with an average diameter of approx. 350 nm. The loading of ash particles was varied by varying the time of exposure to the particles in a gas stream. Catalyst characterization did not reveal significant differences in cobalt dispersion, reducibility, surface area, pore size, or pore volume between the reference and the Catalysts with ash particles deposited. Activity measurements showed that following a short exposure to the mixed ash salts (30 min), there were no significant loss of activity, but a minor change in selectivity of the Catalyst . Extended exposure (60 min) led to some activity loss and changes in selectivity. However, extending the exposure time and thus the amount deposited as evidenced by elemental analysis did not lead to a further drop in activity. This behavior is different from that observed with pure potassium salts, and is suggested to be related to the larger size of the aerosol particles deposited. The large aerosol particles used here were probably not penetrating the Catalyst bed, and to some extent formed an external layer on the Catalyst bed. The ash salts are therefore not able to penetrate to the pore structure and reach the Co active centers, but are mixed with the Catalyst and detected in the elemental analysis.
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Charge-Tuned CO Activation over a χ-Fe5C2 Fischer–Tropsch Catalyst
ACS Catalysis, 2018Co-Authors: Bingxu Chen, Anders Holmen, Di Wang, Xuezhi Duan, Wei Liu, Gang Qian, Wei-kang Yuan, Xinggui Zhou, De ChenAbstract:We performed DFT calculations to understand CO activation over a χ-Fe5C2 Fischer–Tropsch Catalyst. The χ-Fe5C2 Catalyst exhibits unique CO activation behaviors, and the BEP relation is nearly valid for this system. The physical basis of this relation mainly originates from the site-dependent charge of the involved surface Fe atoms for the CO activation. This descriptor is also applicable to describe the CO activation on the χ-Fe5C2 Catalyst with more complex surface properties involving K promoter, nonstoichiometric termination, and/or carbon vacancy. The insights revealed here might guide the rational Catalyst design via surface electronic modification.
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Deactivation of Co-Based Fischer–Tropsch Catalyst by Aerosol Deposition of Potassium Salts
Industrial & Engineering Chemistry Research, 2018Co-Authors: Ljubisa Gavrilovic, Jan Brandin, Rune Myrstad, Hilde J. Venvik, Anders Holmen, Edd Anders BlekkanAbstract:A 20%Co/0.5%Re/γAl2O3 Fischer–Tropsch Catalyst was poisoned by four potassium salts (KNO3, K2SO4, KCl, and K2CO3) using the aerosol deposition technique, depositing up to 3500 ppm K as solid particles. Standard characterization techniques (H2 chemisorption, BET, TPR) showed no difference between treated samples and their unpoisoned counterpart. The Fischer–Tropsch activity was investigated at industrially relevant conditions (210 °C, H2:CO = 2:1, 20 bar). The catalytic activity was significantly reduced for samples exposed to potassium, and the loss of activity was more severe with higher potassium loadings, regardless of the potassium salt used. A possible dual deactivation effect by potassium and the counterion (chloride and sulfate) is observed with the samples poisoned by KCl and K2SO4. The selectivity toward heavier hydrocarbons (C5+) was slightly increased with increasing potassium loading, while the CH4 selectivity was reduced for all the treated samples. The results support the idea that potassium...
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fischer tropsch synthesis an xas xrpd combined in situ study from Catalyst activation to deactivation
Journal of Catalysis, 2012Co-Authors: Nikolaos E Tsakoumis, Erling Rytter, Øyvind Borg, Alexey Voronov, Magnus Ronning, Wouter Van Beek, Anders HolmenAbstract:A rhenium promoted (1 wt.%Re/20 wt.%Co/c-Al2O3) and an un-promoted (20 wt.%Co/c-Al2O3) Fischer– Tropsch Catalyst were studied in situ throughout the common steps of laboratory Catalyst testing, that is, reduction, pressurization, the initial period before reaching pseudo-steady state, deactivation, and post-mortem analysis. High-resolution X-ray powder diffraction (HR-XRPD) was combined with X-ray absorption spectroscopy (XAS) in order to reveal the changes occurring during the experimental procedure. A mass spectrometer (MS) connected to the reactor outlet allow monitoring of the gas phase and accordingly the Catalyst performance with respect to activity. Fischer–Tropsch synthesis was performed at 493 K, 18 bar, H2/CO = 2.1, and >50% CO conversion. The reduction at 673 K confirmed the transition from Co3O4 to CoO and eventually a mixture of face-centered cubic (fcc) metallic cobalt, hexagonal close packed (hcp) metallic cobalt and a fraction of unreduced cobalt. The promoted Catalyst exhibits a transformation during the initial stages of the Fischer–Tropsch synthesis possibly associated with minor reoxidation of cobalt to Co
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A Highly Active and Selective Manganese Oxide Promoted Cobalt-on-Silica Fischer–Tropsch Catalyst
Topics in Catalysis, 2011Co-Authors: Johan P. Den Breejen, Anders Holmen, Frank M F De Groot, Anne M. Frey, Jia Yang, Matti M. Schooneveld, Odile Stephan, Johannes H. Bitter, Krijn P. JongAbstract:A highly active and selective manganese oxide-promoted silica-supported cobalt Catalyst for the Fischer–Tropsch reaction is reported. Co/MnO/SiO_2 Catalysts were prepared via impregnation of a cobalt nitrate and manganese nitrate precursor, followed by drying and calcination in an NO/He flow. The Catalysts were studied with STEM–EELS, infrared spectroscopy measurements of adsorbed CO and Steady-State Isotopic Transient Kinetic Analysis experiments. Based on those experiments, a relation between C_5+-selectivity and surface-coverages of CH_ x -intermediates on cobalt was found.
Erling Rytter - One of the best experts on this subject based on the ideXlab platform.
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fischer tropsch synthesis an xas xrpd combined in situ study from Catalyst activation to deactivation
Journal of Catalysis, 2012Co-Authors: Nikolaos E Tsakoumis, Erling Rytter, Øyvind Borg, Alexey Voronov, Magnus Ronning, Wouter Van Beek, Anders HolmenAbstract:A rhenium promoted (1 wt.%Re/20 wt.%Co/c-Al2O3) and an un-promoted (20 wt.%Co/c-Al2O3) Fischer– Tropsch Catalyst were studied in situ throughout the common steps of laboratory Catalyst testing, that is, reduction, pressurization, the initial period before reaching pseudo-steady state, deactivation, and post-mortem analysis. High-resolution X-ray powder diffraction (HR-XRPD) was combined with X-ray absorption spectroscopy (XAS) in order to reveal the changes occurring during the experimental procedure. A mass spectrometer (MS) connected to the reactor outlet allow monitoring of the gas phase and accordingly the Catalyst performance with respect to activity. Fischer–Tropsch synthesis was performed at 493 K, 18 bar, H2/CO = 2.1, and >50% CO conversion. The reduction at 673 K confirmed the transition from Co3O4 to CoO and eventually a mixture of face-centered cubic (fcc) metallic cobalt, hexagonal close packed (hcp) metallic cobalt and a fraction of unreduced cobalt. The promoted Catalyst exhibits a transformation during the initial stages of the Fischer–Tropsch synthesis possibly associated with minor reoxidation of cobalt to Co
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Development of an Attrition Resistant Fischer–Tropsch Catalyst for Slurry Operation
Topics in Catalysis, 2011Co-Authors: Erling Rytter, Dag Schanke, Hanne Wigum, Torild Hulsund Skagseth, Øyvind Borg, Edvard BergeneAbstract:Resistance towards attrition, sufficient activity at end-of-run and high selectivity to desired products are some of the requirements for a slurry Fischer–Tropsch Catalyst. We have found that modifying an alumina support by 2-valent metals, including magnesium, nickel and zinc, followed by high temperature firing, results in superior mechanical and ‘chemical attrition’ (dissolution) resistance of the Catalyst. Further, a sufficiently high surface area is being stabilized. The Catalyst performance has been verified in a long term test in a semi-commercial plant, including very good wax separation and high wax purity. Combined with appropriate process conditions, stable long-term operation of the Catalyst is secured.
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In-Situ Reduction of Promoted Cobalt Oxide Supported on Alumina by Environmental Transmission Electron Microscopy
Catalysis Letters, 2011Co-Authors: Roya Dehghan, Anders Holmen, Erling Rytter, Øyvind Borg, Thomas W. Hansen, Jakob B. Wagner, John C. WalmsleyAbstract:Reduction of 12wt.%Co/0.5wt.%Re/α-Al_2O_3 Fischer–Tropsch Catalyst has been studied in-situ in an environmental transmission electron microscope. Reduction of Co_3O_4 to metallic cobalt was observed dynamically at 360 °C under 3.4 mbar H_2. Structural and morphological changes were observed by high resolution transmission electron microscopy and scanning transmission electron microscopy imaging. The cobalt particles were mainly face centred cubic while some hexagonal close packed particles were also found. Reoxidation of the sample upon cooling to room temperature, still under flowing H_2, underlines the reactivity of the nanoparticles and the importance of controlling the gas composition and specimen temperature during this type of experiment. Similar behaviour was observed for a non-promoted Catalyst. Imaging and analysis of the promoted sample before and after reduction indicated a uniform distribution of the promoter. Graphical Abstract STEM images before and after reduction
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effect of biomass derived synthesis gas impurity elements on cobalt fischer tropsch Catalyst performance including in situ sulphur and nitrogen addition
Journal of Catalysis, 2011Co-Authors: Øyvind Borg, Rune Myrstad, Torild Hulsund Skagseth, Nina Hammer, Bjorn Christian Enger, O A Lindvag, Sigrid Eri, Erling RytterAbstract:Abstract The effect of 10 typical biomass-derived synthesis gas impurities on cobalt Fischer–Tropsch Catalyst performance was investigated at industrially relevant conditions. Impurities (0–1000 ppmw) were introduced ex situ by incipient wetness impregnation to give 23 different compositions. The presence of alkali (Na, K) and alkaline earth elements (Ca, Mg) did not affect the ex situ -measured cobalt surface area but decreased the in situ activity, thereby decreasing the apparent turnover frequency. The C 5+ selectivity increased and decreased upon addition of alkali and alkaline earth metals, respectively. Mn, Fe, and P had minor effects on Catalyst performance. The presence of Cl decreased cobalt surface without affecting activity, thus increasing the turnover frequency. The changes in turnover frequency correlated with element electronegativity. In situ addition of H 2 S and (CH 3 ) 2 S (2.5–10 ppm) decreased activity at all concentrations. However, product selectivity was not affected. Addition of NH 3 (4 ppm) did not change catalytic performance.
Andrei Y Khodakov - One of the best experts on this subject based on the ideXlab platform.
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Effect of Different Reaction Conditions on the Deactivation of Alumina-Supported Cobalt Fischer-Tropsch Catalysts in a Milli-Fixed-Bed Reactor: Experiments and Modeling
Industrial, 2014Co-Authors: Majid Sadeqzadeh, Stephane Chambrey, Pascal Fongarland, Daniel Schweich, D. Curulla-ferre, J. P. Hong, F. Luck, J. Bousquet, Andrei Y KhodakovAbstract:This paper focuses on the deactivation of a cobalt-based alumina-supported Fischer-Tropsch Catalyst in a milli-fixed-bed reactor under different operating conditions. Different Catalyst deactivation behaviors were observed at different syngas H-2/CO ratios and temperatures. The deactivation follows a two-step profile, where the initial deactivation is attributed to sintering, whereas the long-term deactivation is due to carbon deposition or cobalt oxidation on the surface. An unsteady-state semimechanistic model has been developed to represent the data at different temperatures and syngas ratios. This model takes into account cobalt sintering, coke deposition, and surface oxidation.
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deactivation of a co al2o3 fischer tropsch Catalyst by water induced sintering in slurry reactor modeling and experimental investigations
Catalysis Today, 2013Co-Authors: Majid Sadeqzadeh, Stephane Chambrey, S Piche, Pascal Fongarland, Francis Luck, Daniel Curullaferre, Daniel Schweich, Jacques Bousquet, Andrei Y KhodakovAbstract:Abstract The deactivation of cobalt based Catalysts in slurry Fischer–Tropsch reactor has been modeled assuming a sintering mechanism which involves the intermediate formation of cobalt oxide layer on metallic nanoparticles. The mechanism, correlating the crystallite size growth to the water to hydrogen concentration ratio in the liquid phase, has been used to describe the activity decline with time on stream. The effect of operating conditions on the rate of sintering is considered. It is found that at the same initial conversion, sintering rate is higher for lower H 2 /CO ratios, whereas higher ratios could lead to larger crystallites once operated at constant gas flow rate. The presence of water in the inlet syngas stream also accelerates sintering. The sintering model is then used to describe the deactivation in laboratory-scale slurry reactor.
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Deactivation of a Co/Al2O3 Fischer-Tropsch Catalyst by water-induced sintering in slurry reactor: Modeling and experimental investigations
Catalysis Today, 2013Co-Authors: Majid Sadeqzadeh, Stephane Chambrey, S Piche, Pascal Fongarland, Francis Luck, Daniel Schweich, Jacques Bousquet, D. Curulla-ferre, Andrei Y KhodakovAbstract:The deactivation of cobalt based Catalysts in slurry Fischer-Tropsch reactor has been modeled assuming a sintering mechanism which involves the intermediate formation of cobalt oxide layer on metallic nanoparticles. The mechanism, correlating the crystallite size growth to the water to hydrogen concentration ratio in the liquid phase, has been used to describe the activity decline with time on stream. The effect of operating conditions on the rate of sintering is considered. It is found that at the same initial conversion, sintering rate is higher for lower H-2/CO ratios, whereas higher ratios could lead to larger crystallites once operated at constant gas flow rate. The presence of water in the inlet syngas stream also accelerates sintering. The sintering model is then used to describe the deactivation in laboratory-scale slurry reactor. (C) 2013 Elsevier B.V. All rights reserved.
Øyvind Borg - One of the best experts on this subject based on the ideXlab platform.
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fischer tropsch synthesis an xas xrpd combined in situ study from Catalyst activation to deactivation
Journal of Catalysis, 2012Co-Authors: Nikolaos E Tsakoumis, Erling Rytter, Øyvind Borg, Alexey Voronov, Magnus Ronning, Wouter Van Beek, Anders HolmenAbstract:A rhenium promoted (1 wt.%Re/20 wt.%Co/c-Al2O3) and an un-promoted (20 wt.%Co/c-Al2O3) Fischer– Tropsch Catalyst were studied in situ throughout the common steps of laboratory Catalyst testing, that is, reduction, pressurization, the initial period before reaching pseudo-steady state, deactivation, and post-mortem analysis. High-resolution X-ray powder diffraction (HR-XRPD) was combined with X-ray absorption spectroscopy (XAS) in order to reveal the changes occurring during the experimental procedure. A mass spectrometer (MS) connected to the reactor outlet allow monitoring of the gas phase and accordingly the Catalyst performance with respect to activity. Fischer–Tropsch synthesis was performed at 493 K, 18 bar, H2/CO = 2.1, and >50% CO conversion. The reduction at 673 K confirmed the transition from Co3O4 to CoO and eventually a mixture of face-centered cubic (fcc) metallic cobalt, hexagonal close packed (hcp) metallic cobalt and a fraction of unreduced cobalt. The promoted Catalyst exhibits a transformation during the initial stages of the Fischer–Tropsch synthesis possibly associated with minor reoxidation of cobalt to Co
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Development of an Attrition Resistant Fischer–Tropsch Catalyst for Slurry Operation
Topics in Catalysis, 2011Co-Authors: Erling Rytter, Dag Schanke, Hanne Wigum, Torild Hulsund Skagseth, Øyvind Borg, Edvard BergeneAbstract:Resistance towards attrition, sufficient activity at end-of-run and high selectivity to desired products are some of the requirements for a slurry Fischer–Tropsch Catalyst. We have found that modifying an alumina support by 2-valent metals, including magnesium, nickel and zinc, followed by high temperature firing, results in superior mechanical and ‘chemical attrition’ (dissolution) resistance of the Catalyst. Further, a sufficiently high surface area is being stabilized. The Catalyst performance has been verified in a long term test in a semi-commercial plant, including very good wax separation and high wax purity. Combined with appropriate process conditions, stable long-term operation of the Catalyst is secured.
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In-Situ Reduction of Promoted Cobalt Oxide Supported on Alumina by Environmental Transmission Electron Microscopy
Catalysis Letters, 2011Co-Authors: Roya Dehghan, Anders Holmen, Erling Rytter, Øyvind Borg, Thomas W. Hansen, Jakob B. Wagner, John C. WalmsleyAbstract:Reduction of 12wt.%Co/0.5wt.%Re/α-Al_2O_3 Fischer–Tropsch Catalyst has been studied in-situ in an environmental transmission electron microscope. Reduction of Co_3O_4 to metallic cobalt was observed dynamically at 360 °C under 3.4 mbar H_2. Structural and morphological changes were observed by high resolution transmission electron microscopy and scanning transmission electron microscopy imaging. The cobalt particles were mainly face centred cubic while some hexagonal close packed particles were also found. Reoxidation of the sample upon cooling to room temperature, still under flowing H_2, underlines the reactivity of the nanoparticles and the importance of controlling the gas composition and specimen temperature during this type of experiment. Similar behaviour was observed for a non-promoted Catalyst. Imaging and analysis of the promoted sample before and after reduction indicated a uniform distribution of the promoter. Graphical Abstract STEM images before and after reduction
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effect of biomass derived synthesis gas impurity elements on cobalt fischer tropsch Catalyst performance including in situ sulphur and nitrogen addition
Journal of Catalysis, 2011Co-Authors: Øyvind Borg, Rune Myrstad, Torild Hulsund Skagseth, Nina Hammer, Bjorn Christian Enger, O A Lindvag, Sigrid Eri, Erling RytterAbstract:Abstract The effect of 10 typical biomass-derived synthesis gas impurities on cobalt Fischer–Tropsch Catalyst performance was investigated at industrially relevant conditions. Impurities (0–1000 ppmw) were introduced ex situ by incipient wetness impregnation to give 23 different compositions. The presence of alkali (Na, K) and alkaline earth elements (Ca, Mg) did not affect the ex situ -measured cobalt surface area but decreased the in situ activity, thereby decreasing the apparent turnover frequency. The C 5+ selectivity increased and decreased upon addition of alkali and alkaline earth metals, respectively. Mn, Fe, and P had minor effects on Catalyst performance. The presence of Cl decreased cobalt surface without affecting activity, thus increasing the turnover frequency. The changes in turnover frequency correlated with element electronegativity. In situ addition of H 2 S and (CH 3 ) 2 S (2.5–10 ppm) decreased activity at all concentrations. However, product selectivity was not affected. Addition of NH 3 (4 ppm) did not change catalytic performance.