Fischer–Tropsch Synthesis: Characterization and Reaction Testing of Cobalt Carbide

Mohandas, Janet Chakkamadathil; Gnanamani, Muthu Kumaran; Jacobs, Gary; Ma, Wanhong; Ji, Yaying; Khalid, Syed; Davis, Burtron H.

doi:10.1021/cs200236q

Cited by 132 publications

(110 citation statements)

References 23 publications

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“…However, when compared to the metal-Co standard, a shift of the edge peak in both the fresh and used Co/C catalysts was observed, particularly when the derivative plots were examined, as seen in Figure 5. The Co species in the catalysts seemed to have become 'more metallic' in the sense of its electron-donating capability and hence the edge shift to the lower energies of the spectrum [41]. This was perhaps due to the simultaneous presence of metallic and carbidic species in the Co/C catalyst samples, as discussed in …”

Section: Xanes Analysismentioning

confidence: 85%

Effect of CO Concentration on the α-Value of Plasma-Synthesized Co/C Catalyst in Fischer-Tropsch Synthesis

Aluha

Abatzoglou

2017

Catalysts

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Abstract:A plasma-synthesized cobalt catalyst supported on carbon (Co/C) was tested for Fischer-Tropsch synthesis (FTS) in a 3-phase continuously-stirred tank slurry reactor (3-φ-CSTSR) operated isothermally at 220 • C (493 K), and 2 MPa pressure. Initial syngas feed stream of H 2 :CO ratio = 2 with molar composition of 0.6 L/L (60 vol %) H 2 and 0.3 L/L (30 vol %) CO, balanced in 0.1 L/L (10 vol %) Ar was used, flowing at hourly space velocity (GHSV) of 3600 cm 3 ·h −1 ·g −1 of catalyst. Similarly, other syngas feed compositions of H 2 :CO ratio = 1.5 and 1.0 were used. Results showed~40% CO conversion with early catalyst selectivity inclined towards formation of gasoline (C 4 -C 12 ) and diesel (C 13 -C 20 ) fractions. With prolonged time-on-stream (TOS), catalyst selectivity escalated towards the heavier molecular-weight fractions such as waxes (C 21+ ). The catalyst's α-value, which signifies the probability of the hydrocarbon-chain growth was empirically determined to be in the range of 0.85-0.87 (at H 2 :CO ratio = 2), demonstrating prevalence of the hydrocarbon-chain propagation, with particular predisposition for wax production. The inhibiting CO effect towards FTS was noted at molar H 2 :CO ratio of 1.0 and 1.5, giving only~10% and~20% CO conversion respectively, although with a high α-value of 0.93 in both cases, which showed predominant production of the heavier molecular weight fractions.

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Section: Xanes Analysismentioning

confidence: 85%

Effect of CO Concentration on the α-Value of Plasma-Synthesized Co/C Catalyst in Fischer-Tropsch Synthesis

Aluha

Abatzoglou

2017

Catalysts

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“…Carbon formed in FTS under hydrogen deficient conditions by the Boudouard reaction (equation 4) or via CO dissociation may interact with the cobalt-based catalyst, [80] affecting CO conversion and selectivity by forming cobalt carbide (Co 2 C) [81]. Although Co is thought to be in the +2 oxidation state in Co 2 C, the carbide exhibits strong metallic properties (similar to most transition metal carbides) and therefore can be considered to be an hcp lattice with C incorporated at interstitial sites [81]. By observing the XANES derivative spectra of the cobalt species found during FTS (figure 10), the change in oxidation state of cobalt species can be portrayed by observing the shift of the peaks (with the aid of the line drawn through the centre of the tallest peak in spectrum g).…”

Section: X-ray Absorption Spectroscopy or X-ray Absorption Fine Strucmentioning

confidence: 99%

X-ray spectroscopic and scattering methods applied to the characterisation of cobalt-based Fischer–Tropsch synthesis catalysts

Herbert

Sénécal

Martin

et al. 2016

Catal. Sci. Technol.

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(2016) 'X-ray spectroscopic and scattering methods applied to the characterisation of cobalt-based FischerTropsch synthesis catalysts.', Catalysis science and technology., 6 (15). pp. 5773-5791. Further information on publisher's website:http://dx.doi.org/10.1039/C6CY00581KPublisher's copyright statement:Additional information: Use policyThe full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that:• a full bibliographic reference is made to the original source • a link is made to the metadata record in DRO • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders.Please consult the full DRO policy for further details. Abstract: This review aims to critically assess the use of X-ray techniques, both of a scattering (e.g. X-ray diffraction (XRD), Pair Distribution Function (PDF)) and spectroscopic nature (X-ray Absorption spectroscopy (XAFS)), in the study of cobalt-based Fisher-Tropsch Synthesis (FTS) catalysts. In particular, the review will focus on how these techniques have been successfully used to describe the salient characteristics of these catalysts that govern subsequent activity and selectivity, as well as to afford insight into deactivation phenomena that have seemingly stifled their application. We discuss how these X-ray-based techniques have been used to yield insight into the bulk structure, the catalyst surface, oxidation states, local (cobalt) geometry, and elemental composition of particles, primarily from a 1D perspective but we also highlight how, with recent developments in advanced X-ray characterisation methods, crucial information can now be obtained in 2D and 3D. The examples chosen focus on data acquired in situ/operando, under realistic operating conditions and during activation which often allow for obtaining a more relevant perspective on the changes in catalyst structure that accompany a change in catalyst performance. We conclude with a perspective on some of the challenges that beset the Co-based FTS technology and discuss how X-ray based techniques could be used to solve them.2

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“…Aging studies at CAER [85] over cobalt carbide catalysts and analysis of used samples withdrawn from the reactor and examined by XANES and EXAFS determined that cobalt carbides begin with low activity and high C 1 selectivity, but gradually exhibit greater Co metallic character and better -though not good -selectivities to FT products as a function of time on-stream (Fig. 46).…”

Section: Fig 38 Seementioning

confidence: 99%

“…By removing catalysts from the reactor with increasing time on stream or simulating a CO hydrogenation environment using CO, H 2 , and H 2 O, ex situ and in situ studies have provided information on changes in oxidation state and coordination environment occurring during aging [63,[82][83][84][85][86][87][88][89][90][91][92][93][94], during water co-feeding [95][96][97], during mildly oxidizing conditions using H 2 O/He addition [98], as a function of conversion (i.e., water partial pressure, since water is a product of FT) [63,70], and as a function of H 2 /CO ratio [72]. The recent coupling of synchrotron Raman spectroscopy with XRD and XAS to investigate both the activation and reaction testing of Fe catalysts is also discussed [94].…”

Section: Introductionmentioning

confidence: 99%

The application of synchrotron methods in characterizing iron and cobalt Fischer–Tropsch synthesis catalysts

Jacobs

Gao

et al. 2013

Catalysis Today

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Fischer–Tropsch Synthesis: Characterization and Reaction Testing of Cobalt Carbide

Cited by 132 publications

References 23 publications

Effect of CO Concentration on the α-Value of Plasma-Synthesized Co/C Catalyst in Fischer-Tropsch Synthesis

Effect of CO Concentration on the α-Value of Plasma-Synthesized Co/C Catalyst in Fischer-Tropsch Synthesis

X-ray spectroscopic and scattering methods applied to the characterisation of cobalt-based Fischer–Tropsch synthesis catalysts

The application of synchrotron methods in characterizing iron and cobalt Fischer–Tropsch synthesis catalysts

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