Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2018 Oct 12;8(10):822.
doi: 10.3390/nano8100822.

Use of Plasma-Synthesized Nano-Catalysts for CO Hydrogenation in Low-Temperature Fischer⁻Tropsch Synthesis: Effect of Catalyst Pre-Treatment

James Aluha  1 , Stéphane Gutierrez  2 , François Gitzhofer  3 , Nicolas Abatzoglou  4
Affiliations

Use of Plasma-Synthesized Nano-Catalysts for CO Hydrogenation in Low-Temperature Fischer⁻Tropsch Synthesis: Effect of Catalyst Pre-Treatment

James Aluha et al. Nanomaterials (Basel). .

Abstract

A study was done on the effect of temperature and catalyst pre-treatment on CO hydrogenation over plasma-synthesized catalysts during the Fischer⁻Tropsch synthesis (FTS). Nanometric Co/C, Fe/C, and 50%Co-50%Fe/C catalysts with BET specific surface area of ~80 m² g⁻1 were tested at a 2 MPa pressure and a gas hourly space velocity (GHSV) of 2000 cm³ h-1 g-1 of a catalyst (at STP) in hydrogen-rich FTS feed gas (H₂:CO = 2.2). After pre-treatment in both H₂ and CO, transmission electron microscopy (TEM) showed that the used catalysts shifted from a mono-modal particle-size distribution (mean ~11 nm) to a multi-modal distribution with a substantial increase in the smaller nanoparticles (~5 nm), which was statistically significant. Further characterization was conducted by scanning electron microscopy (SEM with EDX elemental mapping), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The average CO conversion at 500 K was 18% (Co/C), 17% (Fe/C), and 16% (Co-Fe/C); 46%, 37%, and 57% at 520 K; and 85%, 86% and 71% at 540 K respectively. The selectivity of Co/C for C5+ was ~98% with 8% gasoline, 61%, diesel and 28% wax (fractions) at 500 K; 22% gasoline, 50% diesel, and 19% wax at 520 K; and 24% gasoline, 34% diesel, and 11% wax at 540 K, besides CO₂ and CH₄ as by-products. Fe-containing catalysts manifested similar trends, with a poor conformity to the Anderson⁻Schulz⁻Flory (ASF) product distribution.

Keywords: CO-hydrogenation; low-temperature Fischer–Tropsch; nano-catalysts; plasma synthesis; pre-treatment.

PubMed Disclaimer

Conflict of interest statement

The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript, and in the decision to publish the results.

Figures

Figure 1
Figure 1
The activity of (a) Co/C, (b) Fe/C, and (c) Co-Fe/C catalysts tested at 500 K, 520 K, and 540 K (pressure = 2 MPa; GHSV = 2000 cm3 h−1 g−1 of the catalyst) indicating the CO and H2 conversions.
Figure 2
Figure 2
The activity of the Co/C catalyst extended to 72 h on stream at 500 K, 2 MPa and GHSV = 2000 cm3 h−1 g−1 of the catalyst.
Figure 3
Figure 3
The sample pictures showing a massive wax formation in the reactor after an FTS reaction by carbon-supported catalysts that are evidently black with the wax being conspicuously white.
Figure 4
Figure 4
The H2:CO ratio, r, which indicates that all the catalysts, at higher temperatures, converted more CO to form CO2 and probably with increased water-gas shift, FTS demanded less H2.
Figure 5
Figure 5
The selectivity plots of the Co/C catalyst tested at 500 K, 520 K and 540 K, 2 MPa pressure, and GHSV = 2000 cm3 h−1 g−1 of the catalyst.
Figure 6
Figure 6
The aggregated product fractions of the Co/C catalyst tested at 500 K, 520 K, and 540 K (pressure = 2 MPa; GHSV = 2000 cm3 h−1 g−1 of the catalyst).
Figure 7
Figure 7
The aggregate selectivity of (a) Fe/C and (b) Co-Fe/C catalysts tested at 520 K and 540 K (pressure = 2 MPa; GHSV = 2000 cm3 h−1 g−1 of the catalyst).
Figure 8
Figure 8
Modeling the ASF kinetics from selectivity data of the Co/C sample (a) at 500, 520, and 540 K, and (b) at 520 and 540 K.
Figure 9
Figure 9
Modelling ASF kinetics using selectivity data of the (a) Co-Fe/C and (b) single-metal Co/C sample tested at 500 K, and the Fe/C sample tested at 520 K and 540 K.
Figure 10
Figure 10
Plots showing (a) the adsorption-desorption isotherms of the fresh Co-Fe/C sample, and (b) the pore size distribution by the BET surface area analysis.
Figure 11
Figure 11
Sample SEM images of the used catalysts: (i) Co/C (ii) Fe/C and (iii) Co-Fe/C displaying (a) secondary electron images. (b) elemental EDX mapping, and (c) EDX spectra.
Figure 12
Figure 12
The TEM images of the used (a) Co/C (b) Fe/C and (c) Co-Fe/C catalysts with some sections having nanoparticles predominantly below ~5 nm, or ~10 nm, and (d) sections of the Co-Fe/C catalyst with larger nanoparticles ~20 nm and CNFs.
Figure 13
Figure 13
TEM images of the Co-Fe/C catalyst (a) freshly synthesized by plasma, and (b) after pre-treatment in CO, indicating formation of carbon nanofilaments (CNFs).
Figure 14
Figure 14
The particle size analysis by TEM imaging showing (a) a mono-modal nanoparticle distribution in the fresh Co/C catalyst [47]. (b) Bi-modal distribution in the used Co/C. (c) Bi-modal distribution in the Fe/C sample, and (d) multi-modal distribution in the used Co-Fe/C catalyst.
Figure 15
Figure 15
The XPS analysis of the fresh (a) Co/C and (b) Fe/C catalysts. Reproduced with permission from Reference [48]. Copyright Springer, 2018.
Figure 16
Figure 16
The XPS analysis of (a) Co metal, and (b) Fe metal in the fresh Co-Fe/C catalyst samples collected from the main plasma reactor.
Figure 17
Figure 17
The XPS plots quantifying the C-support in the fresh Co-Fe/C catalyst samples collected from (a) the main plasma reactor and (b) the secondary plasma reactor.
Figure 18
Figure 18
The XRD patterns of the catalyst samples for (a) fresh Co/C (b) used Co/C (c) fresh Co-Fe/C, (d) used Co-Fe/C (e) fresh Fe/C and (f) used Fe/C.
Figure 19
Figure 19
The RQA curve fitting of the used (a) Co/C (b) Co-Fe/C, and (c) Fe/C catalyst samples by XRD analysis.
See this image and copyright information in PMC

References

    1. Raghubanshi H., Dikio E.D. Synthesis of helical carbon fibers and related materials: A review on the past and recent developments. Nanomaterials. 2015;5:937–968. doi: 10.3390/nano5020937. - DOI - PMC - PubMed
    1. Nasir S., Hussein M.Z., Zainal Z., Yusof N.A. Carbon-based nanomaterials/allotropes: A glimpse of their synthesis, properties and some applications. Materials. 2018;11:295. doi: 10.3390/ma11020295. - DOI - PMC - PubMed
    1. Avouris P., Chen Z., Perebeinos V. Carbon-based electronics. Nat. Nanotechnol. 2007;2:605–615. doi: 10.1038/nnano.2007.300. - DOI - PubMed
    1. Sun X., Suarez A.I.O., Meijerink M., van Deelen T., Ould-Chikh S., Zečević J., de Jong K.P., Kapteijn F., Gascon J. Manufacture of highly loaded silica-supported cobalt Fischer–Tropsch catalysts from a metal organic framework. Nat. Commun. 2017;8:1680. doi: 10.1038/s41467-017-01910-9. - DOI - PMC - PubMed
    1. Zaporotskova I.V., Boroznina N.P., Parkhomenko Y.N., Kozhitov L.V. Carbon nanotubes: Sensor properties. A review. Mod. Electron. Mater. 2016;2:95–105. doi: 10.1016/j.moem.2017.02.002. - DOI