Thermodynamics of oxidation of an alumina-supported cobalt catalyst by water in F-T synthesis

Hou, Chaopeng; Xia, Guofu; Sun, Xiuyun; Wu, Yu; Jin, Chao; Yan, Zhennan; Li, Mingfeng; Hu, Zuming; Nie, Hong; Li, Dadong

doi:10.1016/j.cattod.2015.08.042

Cited by 20 publications

(11 citation statements)

References 30 publications

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“…Some authors operating just above 673 K found the Gibbs free energy of Co 3 O 4 formation to be negative at 730 K (

Δ G_{f}

= −81 kJ · mol −1 ) . However, this has been contradicted by other findings that predicted the

Δ G_{f}

of Co 3 O 4 at 673 K to be +190 kJ · mol −1 probably due to different reaction conditions (in this case, under FTS) . It means that if the

Δ G_{f}

is larger than zero, the formation of Co 3 O 4 under FTS reaction conditions will be nonspontaneous and that the probability of Co 3 O 4 formation is highly dependent on the prevailing reaction conditions.…”

Section: Discussionmentioning

confidence: 72%

Activation and deactivation scenarios in a plasma‐synthesized Co/C catalyst for Fischer‐Tropsch synthesis

Aluha

Abatzoglou

2018

Can J Chem Eng

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A carbon‐supported cobalt nano‐catalyst (Co/C) synthesized through plasma was tested for Fischer‐Tropsch activity. Catalyst deactivation and activation protocols studied included in situ sample pre‐treatment at 673 K in gas flowing at the rate of 250 cm3 · min−1 in: (a) H2 only, (b) CO only, and (c) CO followed by H2, with each cycle lasting 24 h. The so‐treated catalyst samples were then tested for FTS activity for over 50 h of time‐on‐stream (TOS), at 2.2 MPa pressure and 493 or 518 K temperature in a 3‐phase continuously‐stirred tank slurry reactor (3‐φ‐CSTSR) using squalane (C30H62) as the carrier liquid phase. The feed gas composition of molar H2:CO = 1.7 comprising 50 % H2, 30 % CO, and 10 % CO2 balanced in Ar for mass balance determination, flowing at a gas hourly space velocity (GHSV) of 3360 cm3 · h−1 · g−1 of catalyst. Fresh catalysts and those reduced by CO‐only were completely inactive at 493 K and initial inactivity was attributed to the excessive C matrix formed around the metal nanoparticles during catalyst synthesis. The sample that was reduced by H2 only was the most active, although it showed the fastest declining activity due to cumulative high H2O vapour pressure in the FTS reactor, while the sample pre‐treated in both CO and H2 demonstrated a higher degree of stability with TOS.

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“…Some authors operating just above 673 K found the Gibbs free energy of Co 3 O 4 formation to be negative at 730 K (

Δ G_{f}

= −81 kJ · mol −1 ) . However, this has been contradicted by other findings that predicted the

Δ G_{f}

of Co 3 O 4 at 673 K to be +190 kJ · mol −1 probably due to different reaction conditions (in this case, under FTS) . It means that if the

Δ G_{f}

Section: Discussionmentioning

confidence: 72%

Activation and deactivation scenarios in a plasma‐synthesized Co/C catalyst for Fischer‐Tropsch synthesis

Aluha

Abatzoglou

2018

Can J Chem Eng

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“…Possible mechanisms proposed for deactivation include: reoxidation of small metallic cobalt cluster to inactive CoO X ; sintering; some carbon deposition or solid-state reaction between cobalt and the support [4,25,26]. Thermodynamic calculations show that when the cobalt crystallites have a diameter lower than 4.4 nm, they may be reoxidized in the steam/hydrogen environments of FTS [7,8], but this may occur rapidly before the first measurement is taken. The initial decline and leveling off period for CO conversion typical of cobalt-based catalysts was not observed for the nickel promoted catalysts.…”

Section: Discussionmentioning

confidence: 99%

Substitution of Co with Ni in Co/Al2O3 Catalysts for Fischer–Tropsch Synthesis

et al. 2020

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The effect of cobalt substitution with nickel was investigated for the Fischer–Tropsch synthesis reaction. Catalysts having different Ni/Co ratios were prepared by aqueous incipient wetness co-impregnation, characterized, and tested using a continuously stirred tank reactor (CSTR) for more than 200 h. The addition of nickel did not significantly modify the morphological properties measured. XRD, STEM, and TPR-XANES results showed intimate contact between nickel and cobalt, strongly suggesting the formation of a Co-Ni solid oxide solution in each case. Moreover, TPR-XANES indicated that nickel addition improves the cobalt reducibility. This may be due to H2 dissociation and spillover, but is more likely the results of a chemical effect of intimate contact between Co and Ni resulting in Co-Ni alloying after activation. FTS testing revealed a lower initial activity when nickel was added. However, CO conversion continuously increased with time on-stream until a steady-state value (34%–37% depending on Ni/Co ratio) was achieved, which was very close to the value observed for undoped Co/Al2O3. This trend suggests nickel can stabilize cobalt nanoparticles even at a lower weight percentage of Co. Currently, the cobalt price is 2.13 times the price of nickel. Thus, comparing the activity/price, the catalyst with a Ni/Co ratio of 25/75 has better performance than the unpromoted catalyst. Finally, nickel-promoted catalysts exhibited slightly higher initial selectivity for light hydrocarbons, but this difference typically diminished with time on-stream; once leveling off in conversion was achieved, the C5+ selectivities were similar (≈ 80%) for Ni/Co ratios up to 10/90, and only slightly lower (≈ 77%) at Ni/Co of 25/75.

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“…In fact, polymorphism of the carrier materials is an important parameter affecting the formation of MSCs. For example, crystal structures for Al 2 O 3 other than the a-Al 2 O 3 have been reported to show a higher tendency towards the formation of cobalt aluminates 17,25,83,84 or nickel aluminate. 22 While thermodynamics suggest the formation of aluminate from Ni 0 and a-Al 2 O 3 at a p H 2 O /p H 2 ratio of $50 for temperatures exceeding 900 C (Fig.…”

Section: Thermodynamic Predictions On Oxidation Of Bulk Metalmentioning

confidence: 99%

Thermodynamic assessment of the stability of bulk and nanoparticulate cobalt and nickel during dry and steam reforming of methane

Wolf

2021

RSC Adv.

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Thermodynamics of oxidation of an alumina-supported cobalt catalyst by water in F-T synthesis

Cited by 20 publications

References 30 publications

Activation and deactivation scenarios in a plasma‐synthesized Co/C catalyst for Fischer‐Tropsch synthesis

Activation and deactivation scenarios in a plasma‐synthesized Co/C catalyst for Fischer‐Tropsch synthesis

Substitution of Co with Ni in Co/Al2O3 Catalysts for Fischer–Tropsch Synthesis

Thermodynamic assessment of the stability of bulk and nanoparticulate cobalt and nickel during dry and steam reforming of methane

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