Fischer–Tropsch synthesis of hydrocarbons over mesoporous Co/SBA-15 catalysts: the influence of metal loading, cobalt precursor, and promoters

Martı́nez, Agustı́n; López, Carlos A.; Márquez, Francisco; Dı́az, Isabel

doi:10.1016/s0021-9517(03)00289-6

Cited by 444 publications

(230 citation statements)

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“…As reported in the literature, the existence of unreduced cobalt species (e.g., titanates or CoO x ) is known to catalyze the WGS reaction, thus increasing the effective H 2 /CO ratio at the surface of the catalyst. [37][38][39] Hence, a first explanation for the higher CH 4 is the increase of the WGS activity leading to higher hydrogenation rates and, consequently, to a higher CH 4 selectivity. The presence of these unreduced phases has been suggested by the XANES analysis.…”

Section: Tem Analysis Of Reduced Catalystsmentioning

confidence: 99%

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: 99%

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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“…Re promotion has also been widely investigated in Cobased F-T catalysis. [85][86][87][88][89][90][91][92][93][94][95][96][97][98]153,168,171,174,177,253 Re is regarded as a structural promoter and it has been frequently reported to increase the Co reducibility via a hydrogen spillover effect, leading to catalysts with enhanced Co dispersions. Re reduces to a metallic state at higher temperatures than Ru and therefore, can facilitate the second cobalt reduction step, from CoO to Co 0 .…”

Section: Overview Of the Promoter Elements Used Inmentioning

confidence: 99%

“…168 On the other hand, the selectivity of the Co sites is generally expected to be not directly affected by the presence of Re, 153 although some authors have reported improvements in the C 51 selectivity when using Re. 94,171 A possible explanation may be the influence of Re on the Co particle sizes distribution, which may also have an indirect effect on the selectivity due to the changes in the Co surface density. Some differences found in literature may also arise from comparisons of the catalysts at different conversions, which lead to significant variations in selectivities.…”

Section: Overview Of the Promoter Elements Used Inmentioning

confidence: 99%

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Promotion Effects in Co‐Based Fischer—Tropsch Catalysis

Morales¹,

Weckhuysen²

2006

ChemInform

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“…10,11,[20][21][22][23][24][25] Basic issues on the nanocasting strategy have been recently reviewed. 26 However, very few published results are available on the reactive crystal planes of Co 3 O 4 materials prepared using the nanocasting method and their correlation with catalytic reaction activity.…”

Section: Introductionmentioning

confidence: 99%

Mesoporous Co₃O₄ and Au/Co₃O₄ Catalysts for Low-Temperature Oxidation of Trace Ethylene

et al. 2010

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Low-temperature catalysts of mesoporous Co 3 O 4 and Au/Co 3 O 4 with high catalytic activities for the trace ethylene oxidation at 0°C are reported in this paper. The catalysts were prepared by using the nanocasting method, and the mesostructure was replicated from three-dimensional (3D) cubic KIT-6 silicas. High resolution transmission electron microscopy (HRTEM) studies revealed that {110} facets were the exposed active surfaces in the mesoporous Co 3 O 4 , whereas the Co 3 O 4 nanosheets prepared by the precipitation method exhibited the most exposed {112} facets. We found that the mesoporous Co 3 O 4 was significantly more active for ethylene oxidation than the Co 3 O 4 nanosheets. The results indicated that the crystal facet {110} of Co 3 O 4 played an essential role in determining its catalytic oxidation performance. The synthesized Au/Co 3 O 4 materials, in which the gold nanoparticles were assembled into the pore walls of the Co 3 O 4 mesoporous support, exhibited stable, highly dispersed, and exposed gold sites. Gold nanoparticles present on Co 3 O 4 readily produced surface-active oxygen species and promoted ethylene oxidation to achieve a 76% conversion at 0°C, which is the highest conversion reported yet.

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Fischer–Tropsch synthesis of hydrocarbons over mesoporous Co/SBA-15 catalysts: the influence of metal loading, cobalt precursor, and promoters

Cited by 444 publications

References 32 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

Promotion Effects in Co‐Based Fischer—Tropsch Catalysis

Mesoporous Co₃O₄ and Au/Co₃O₄ Catalysts for Low-Temperature Oxidation of Trace Ethylene

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Fischer–Tropsch synthesis of hydrocarbons over mesoporous Co/SBA-15 catalysts: the influence of metal loading, cobalt precursor, and promoters

Cited by 444 publications

References 32 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

Promotion Effects in Co‐Based Fischer—Tropsch Catalysis

Mesoporous Co3O4 and Au/Co3O4 Catalysts for Low-Temperature Oxidation of Trace Ethylene

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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

Mesoporous Co₃O₄ and Au/Co₃O₄ Catalysts for Low-Temperature Oxidation of Trace Ethylene