Synthesis of cobalt nanodumbbells and their thermal stability under H2, H2/CO and O2 atmospheres

González-Carballo, Juan M.; Sadasivan, Sajanikumari; Landon, Philip; Tooze, Robert P.

doi:10.1016/j.matchar.2016.06.031

Cited by 12 publications

(15 citation statements)

References 44 publications

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“…To our knowledge, no mechanistic study was done on ferromagnetic metals, despite the fact that such methods were developed by several groups in the past decade. Among the different chemical solution routes for metal ferromagnetic nanoparticle synthesis, the polyol process is one of the favorites since it is cost-effective and easy to implement, the polyol acting both as the solvent and the reducing agent. , One-pot in situ SMG, i.e., following a protocol where noble metal seeds are generated in situ from a noble metal precursor added concomitantly with the Co precursor at the beginning of the reaction, was developed by several groups to synthesize cobalt − and cobalt–nickel − nanorods or nanowires, as building blocks for permanent magnet materials , or as catalysts. ,− The one-pot in situ SMG methods present the advantage to be scalable to several grams per batch, , but the drawback compared to the ex situ methods is the difficulty to study properly the nucleation steps as far as the seeds are not isolated. Several studies reported that the addition of a small amount of nucleating agent was mandatory to induce cobalt anisotropic growth and formation of nanowires, ,,, but despite this empirical support on the role of the noble metal, no clear mechanism of the seeding process was described.…”

Section: Resultsmentioning

confidence: 99%

“…following a protocol where noble metal seeds are generated in situ from a noble metal precursor added concomitantly with the Co precursor at the beginning of the reaction, was developed by several groups to synthesize cobalt 33,34,35 and cobalt-nickel 36,37,38,39,40 nanorods or nanowires, as building blocks for permanent magnet materials 41,42 or as catalysts. 33,43,44,45,46 The one-pot in situ SMG methods present the advantage to be scalable to several grams per batch 42,47 but the drawback compared to the ex situ methods is the difficulty to study properly the nucleation steps as far as the seeds are not isolated. Several studies reported that the addition of a small amount of nucleating agent was mandatory to induce cobalt anisotropic growth and formation of nanowires, 38,43,48,49 but despite this empirical support on the role of the noble metal, no clear mechanism of the seeding process was described.…”

Section: Introductionmentioning

confidence: 99%

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One-Pot Seed-Mediated Growth of Co Nanoparticles by the Polyol Process: Unraveling the Heterogeneous Nucleation

et al. 2019

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The one-step seed-mediated synthesis is widely used for the preparation of ferromagnetic metal nanoparticles (NPs) since it offers a good control of particle morphology. Nevertheless, this approach suffers from a lack of mechanistic studies because of the difficulties to follow in real time the heterogeneous nucleation and to predict structure effects with seeds that are generated in situ. Here, we propose a complete scheme of the hetero-nucleation process involved in onepot seed-mediated syntheses of cobalt nanoparticles in liquid polyols, relying on geometrical phase analysis (GPA) of high-resolution HAADF-STEM images and in situ measurements of the molecular hydrogen evolution. Cobalt particles of different shapes (rods, platelets or hourglass like particles) were grown by reducing cobalt carboxylate in liquid polyols in presence of iridium or ruthenium chloride as nucleating agent. A reaction scheme was established by monitoring the H2 evolution resulting from the decomposition of metal hydrides, formed in situ by β-elimination of metal alkoxides, and from the polyol dehydrogenation, catalytically activated by the metal particles. This is a very good probe for both the noble metal nucleation and the heterogeneous 2 nucleation of cobalt, showing a good separation of these two steps. Ir and Ru seeds with a size in the range 1-2 nm were found exactly in the center of the cobalt particles, whatever the cobalt particle shape, and high-resolution images revealed an epitaxial growth of the hcp Co on fcc Ir or hcp Ru seeds. The microstructure analysis around the seeds evidenced two different ways of relaxing the lattice mismatch between the seeds and the cobalt, with the presence of dislocations around the Ir seeds and compression zones of the cobalt lattice near the Ru seeds. The relationship between the nature of the nucleating agent, the reaction steps and the microstructure is discussed.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

One-Pot Seed-Mediated Growth of Co Nanoparticles by the Polyol Process: Unraveling the Heterogeneous Nucleation

et al. 2019

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“…The reduction of the Co 3 O 4 phase was caused by the abundant H 2 in the feed (~50 vol.% in the study by Nyathi et al [18]), which also causes the reduction of other base metal oxides used to catalyze CO-PrOx [7]. Other studies have shown that the reaction environment can influence the reduction onset temperature and DoR to Co 0 , where the presence of H 2 O or O 2 delays the reduction onset and minimizes the DoR to Co 0 [17,[19][20][21][22].…”

Section: Introductionmentioning

confidence: 97%

Magnesium as a Methanation Suppressor for Iron- and Cobalt-Based Oxide Catalysts during the Preferential Oxidation of Carbon Monoxide

2022

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The preferential oxidation of CO (CO-PrOx) to CO2 is an effective catalytic process for purifying the H2 utilized in proton-exchange membrane fuel cells for power generation. Our current work reports on the synthesis, characterization and CO-PrOx performance evaluation of unsubstituted and magnesium-substituted iron- and cobalt-based oxide catalysts (i.e., Fe3O4, Co3O4, MgFe2O4 and MgCo2O4). More specifically, the ability of Mg to stabilize the MgFe2O4 and MgCo2O4 structures, as well as suppress CH4 formation during CO-PrOx was of great importance in this study. The cobalt-based oxide catalysts achieved higher CO2 yields than the iron-based oxide catalysts below 225 °C. The highest CO2 yield (100%) was achieved over Co3O4 between 150 and 175 °C, however, undesired CH4 formation was only observed over this catalyst due to the formation of bulk fcc and hcp Co0 between 200 and 250 °C. The presence of Mg in MgCo2O4 suppressed CH4 formation, with the catalyst only reducing to a CoO-type phase (possibly containing Mg). The iron-based oxide catalysts did not undergo bulk reduction and did not produce CH4 under reaction conditions. In conclusion, our study has demonstrated the beneficial effect of Mg in stabilizing the active iron- and cobalt-based oxide structures, and in suppressing CH4 formation during CO-PrOx.

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“…This good correlation could be tentatively rationalized by the fact that sintering [93] and cobalt oxidation [94] should be favored with small cobalt particles [95]. Furthermore, the high stability of the Co hcp phase under FTS conditions has been reported [66,67,96,97], and some studies have pointed out that this phase is more stable under FTS conditions than the Co fcc one [98,99]. Finally, for the ex-nitrate catalysts containing a significant amount of confined particles, we noticed a template effect of the CNT cavity, since the sintering was more pronounced for the Co particles located on the external surface of the CNT (Figure S19).…”

Section: Structure/performance Relationshipsmentioning

confidence: 80%

Beyond confinement effects in Fischer-Tropsch Co/CNT catalysts

Ghogia

Machado

Cayez

et al. 2021

Journal of Catalysis

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Fischer-Tropsch catalyst preparation parameters, such as cobalt precursor and impregnation solvent, determine structure and in fine catalytic performances of Co-based catalysts. Co particles of 3-7 nm mean size were prepared by incipient wetness impregnation on surface-oxidized CNT. In this work the crucial impact of the chemistry operating between the Co precursor and the support during catalyst preparation on the catalyst properties is demonstrated and the influence of CNT surface chemistry on catalyst characteristics has been assessed. Very good correlations were found between: i) the reduction degree of the catalysts and the concentration of the Co(OOC-) surface species; ii) the Co hcp /Co fcc ratio and the amount of CO-releasing groups on the support surface; iii) the extent of hydrogen spillover and the concentration of quinone surface groups. The initial catalytic activity could only be correlated to a combination of catalyst features: percentage of Co hcp , Co confinement, hydrogen spillover, and surprisingly the inverse of the Co initial particle size. No significant differences in S C5+ selectivity were observed, in accordance with comparable final Co particle size. Finally, the stability of the catalyst can be correlated with the initial Co particle size and the percentage of Co hcp in the catalyst. These results confirm the significant impact of the precursor/support couple on the structure and performance of Co/CNT catalysts, and reveal for the first time an inverse correlation between Co particle size and activity, which is attributed to the confined Co hcp phase.

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Synthesis of cobalt nanodumbbells and their thermal stability under H2, H2/CO and O2 atmospheres

Cited by 12 publications

References 44 publications

One-Pot Seed-Mediated Growth of Co Nanoparticles by the Polyol Process: Unraveling the Heterogeneous Nucleation

One-Pot Seed-Mediated Growth of Co Nanoparticles by the Polyol Process: Unraveling the Heterogeneous Nucleation

Magnesium as a Methanation Suppressor for Iron- and Cobalt-Based Oxide Catalysts during the Preferential Oxidation of Carbon Monoxide

Beyond confinement effects in Fischer-Tropsch Co/CNT catalysts

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