Titania-Supported Cobalt and Cobalt–Phosphorus Catalysts: Characterization and Performances in Ethane Oxidative Dehydrogenation

Brik, Younes; Kacimi, M. El; Ziyad, Mahfoud; Bozon‐Verduraz, François

doi:10.1006/jcat.2001.3262

Cited by 227 publications

(142 citation statements)

References 34 publications

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“…The fraction of the nonreducible cobalt phase is thought to be present in intimate contact with the TiO 2 , presumably in the form of cobalt titanates, which are known to be hardly reducible. 23 On the other hand, Figures 13C and 13D show that, in the H-CoMn and Hcop-CoMn catalysts, manganese clearly influences the cobalt particle size. These images display larger cobalt clusters in the range 8-15 nm, in addition to smaller particles of around 3-6 nm.…”

Section: Tem Analysis Of Reduced Catalystsmentioning

confidence: 96%

X-ray Absorption Spectroscopy of Mn/Co/TiO₂ Fischer−Tropsch Catalysts: Relationships between Preparation Method, Molecular Structure, and Catalyst Performance

et al. 2006

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The effects of the addition of manganese to a series of TiO 2 -supported cobalt Fischer-Tropsch (FT) catalysts prepared by different methods were studied by a combination of X-ray diffraction (XRD), temperatureprogrammed reduction (TPR), transmission electron microscopy (TEM), and in situ X-ray absorption fine structure (XAFS) spectroscopy at the Co and Mn K-edges. After calcination, the catalysts were generally composed of large Co 3 O 4 clusters in the range 15-35 nm and a MnO 2 -type phase, which existed either dispersed on the TiO 2 surface or covering the Co 3 O 4 particles. Manganese was also found to coexist with the Co 3 O 4 in the form of Co 3-x Mn x O 4 solutions, as revealed by XRD and XAFS. Characterization of the catalysts after H 2 reduction at 350°C by XAFS and TEM showed mostly the formation of very small Co 0 particles (around 2-6 nm), indicating that the cobalt phase tends to redisperse during the reduction process from Co 3 O 4 to Co 0 . The presence of manganese was found to hamper the cobalt reducibility, with this effect being more severe when Co 3-x Mn x O 4 solutions were initially present in the catalyst precursors. Moreover, the presence of manganese generally led to the formation of larger cobalt agglomerates (∼8-15 nm) upon reduction, probably as a consequence of the decrease in cobalt reducibility. The XAFS results revealed that all reduced catalysts contained manganese entirely in a Mn 2+ state, and two well-distinguished compounds could be identified: (1) a highly dispersed Ti 2 MnO 4 -type phase located at the TiO 2 surface and (2) a less dispersed MnO phase being in the proximity of the cobalt particles. Furthermore, the MnO was also found to exist partially mixed with a CoO phase in the form of rock-salt Mn 1-x Co x O-type solid solutions. The existence of the later solutions was further confirmed by scanning transmission electron microscopy with electron energy loss spectroscopy (STEM-EELS) for a Mn-rich sample. Finally, the cobalt active site composition in the catalysts after reduction at 300 and 350°C was linked to the catalytic performances obtained under reaction conditions of 220°C, 1 bar, and H 2 /CO ) 2. The catalysts with larger Co 0 particles (∼ >5 nm) and lower Co reduction extents displayed a higher intrinsic hydrogenation activity and a longer catalyst lifetime. Interestingly, the MnO and Mn 1-x Co x O species effectively promoted these larger Co 0 particles by increasing the C 5+ selectivity and decreasing the CH 4 production, while they did not significantly influence the selectivity of the catalysts containing very small Co 0 particles.

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Section: Tem Analysis Of Reduced Catalystsmentioning

confidence: 96%

X-ray Absorption Spectroscopy of Mn/Co/TiO₂ Fischer−Tropsch Catalysts: Relationships between Preparation Method, Molecular Structure, and Catalyst Performance

et al. 2006

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“…To enhance the activity of cobalt catalysts the active compound precursors were dispersed on porous carriers with SiO 2 , Al 2 O 3 and TiO 2 being the most frequently used. The interaction between cobalt and the supports leads to the formation of Co-support compounds including Co 2 SiO 4 , COAl 2 O 4 and CoTiO 3 compounds, which can be only reduced or decomposed at elevated temperatures (>1000 K), and declines the activity of catalysts in FTS [5][6][7][8][9].…”

Section: Introductionmentioning

confidence: 99%

The formation of Co2C species in activated carbon supported cobalt-based catalysts and its impact on Fischer–Tropsch reaction

et al. 2005

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The cobalt carbide (Co 2 C) species was formed in some activated carbon supported cobalt-based (Co/AC) catalysts during the activation of catalysts. It was found that the activity of Fischer-Tropsch reaction over Co-based catalysts decreased due to the formation of cobalt carbide species. Some promoters and pretreatment of activated carbon with steam could restrain the formation of cobalt carbide.

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“…36 In addition, Figure 2. EDX analysis performed using TEM both from (a) the sidewalls and (b) the catalyst particle; iron, nickel, and chromium mixture, indicated the presence of phosphorus both inside the sidewalls and the catalyst particle.…”

Section: Resultsmentioning

confidence: 99%

Synthesis of Phosphorus Included Multiwalled Carbon Nanotubes by Pyrolysis of Sucrose

et al. 2013

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Multiwalled carbon nanotubes (MWCNT) were synthesized by a pyrolysis route which involves a dehydration step using phosphoric acid. The resultants were found to be mostly containing amorphous carbon with scattered MWCNTs using scanning electron and transmission electron microscopy techniques. These MWCNTs were smaller in size and limited in quantity compared to the ones synthesized using other common precursors. Energy dispersive X-ray and electron energy loss spectroscopy analysis indicated the presence of phosphorus both at the MWCNT sidewalls and in the catalyst particles encapsulated inside the MWCNTs. In addition, a comparative investigation for sulfur and phosphorus inclusion to the sidewalls of MWCNTs was carried out using density functional theory calculations. The results of the computational study showed that both phosphorus and sulfur atoms prefer to bind among themselves rather than adsorbing directly on carbon nanotubes (CNT). Furthermore, cluster calculations revealed that phosphorus atoms more likely form carbonaceous clusters which result in a decrease in the number of free carbon atoms that can be used for CNT formation. Therefore, we concluded that MWCNT growth might be hindered (promoted) in a phosphorus (sulfur) rich environment which results in needle like phosphorus containing MWCNTs.

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Titania-Supported Cobalt and Cobalt–Phosphorus Catalysts: Characterization and Performances in Ethane Oxidative Dehydrogenation

Cited by 227 publications

References 34 publications

X-ray Absorption Spectroscopy of Mn/Co/TiO₂ Fischer−Tropsch Catalysts: Relationships between Preparation Method, Molecular Structure, and Catalyst Performance

X-ray Absorption Spectroscopy of Mn/Co/TiO₂ Fischer−Tropsch Catalysts: Relationships between Preparation Method, Molecular Structure, and Catalyst Performance

The formation of Co2C species in activated carbon supported cobalt-based catalysts and its impact on Fischer–Tropsch reaction

Synthesis of Phosphorus Included Multiwalled Carbon Nanotubes by Pyrolysis of Sucrose

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Titania-Supported Cobalt and Cobalt–Phosphorus Catalysts: Characterization and Performances in Ethane Oxidative Dehydrogenation

Cited by 227 publications

References 34 publications

X-ray Absorption Spectroscopy of Mn/Co/TiO2 Fischer−Tropsch Catalysts: Relationships between Preparation Method, Molecular Structure, and Catalyst Performance

X-ray Absorption Spectroscopy of Mn/Co/TiO2 Fischer−Tropsch Catalysts: Relationships between Preparation Method, Molecular Structure, and Catalyst Performance

The formation of Co2C species in activated carbon supported cobalt-based catalysts and its impact on Fischer–Tropsch reaction

Synthesis of Phosphorus Included Multiwalled Carbon Nanotubes by Pyrolysis of Sucrose

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Product

Resources

About

X-ray Absorption Spectroscopy of Mn/Co/TiO₂ Fischer−Tropsch Catalysts: Relationships between Preparation Method, Molecular Structure, and Catalyst Performance

X-ray Absorption Spectroscopy of Mn/Co/TiO₂ Fischer−Tropsch Catalysts: Relationships between Preparation Method, Molecular Structure, and Catalyst Performance