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

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.

Plasma-Catalytic Fischer–Tropsch Synthesis at Very High Pressure

“…More current advancement in hydrocarbon synthesis through FTS has employed the application of induction suspension plasma technology [38], with reported preparation of nanometric C-supported catalysts [39]. These plasma-synthesized catalysts have been shown to have active catalytic species for FTS using Co-based and modified Co-Fe catalysts [40,41]. Aluha et al [42] provided a short review paper highlighting advances made from the introduction of plasma techniques for catalyst synthesis since its introduction four decades ago.…”

Plasma-Based Synthesis and Modification of Nanomaterials

“…This Special Issue of Nanomaterials, including nine original research works [ 1 , 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 ], is devoted to the application of different atmospheric pressure (APP) and low-pressure (LPP) plasmas for synthesis or modification of various nanomaterials (NMs) of exceptional properties. This is followed by their structural and morphological characterization and further interesting and unique applications in different areas of science and technology.…”

“…Among the discharges and plasmas applied for plasma-mediated synthesis or modification of NMs, the readers can find, for example: impulse plasma in a solution initiated by spark discharge between two metallic electrodes immersed in this solution [ 1 ]; atmospheric pressure plasma jets provided by dielectric barrier discharge (DBD) operated in Ar–H 2 [ 2 ] or Ar–O 2 , Ar–N 2 , and Ar–NH 3 [ 5 ] mixtures; atmospheric pressure glow discharges (APGDs) generated in air between solid metallic electrodes and flowing solutions [ 3 , 4 , 6 ]; low-pressure capacitively coupled plasma (CCP) sustained in O 2 or N 2 between two electrodes, one being at the end of a chamber field with ionic liquids or low boiling point solvents [ 7 ]; and contact glow discharge electrolysis (CGDE) [ 8 ] or liquid phase plasma (LPP) [ 9 ], operated in both cases between two electrodes immersed in solutions of different compositions. Plasma-chemical processes and reactions occurring directly in plasmas or at interfacial zones between gaseous phases of these plasmas and liquids led to the fabrication of various metal-, nonmetal- and carbon-based NMs, including bimetallic Pd–Fe nanoparticles (NPs) formed by melting and eroding Pd–Fe electrodes [ 1 ], fructose-functionalized AgNPs [ 3 ], PVP-stabilized PtNPs [ 4 ], and pectin-stabilized AgNPs [ 6 ] (all synthesized by the reduction of appropriate ions of these metals dissolved in solutions), carbon dots (CDs) formed by irradiation of aliphatic acids dispersed in viscous media, SiNPs fabricated by melting and eroding Si electrodes under plasma heat [ 8 ], and nanocomposites supported by Fe 3 O 4 NPs on N-doped activated carbon [ 9 ].…”

“…Plasma-chemical processes and reactions occurring directly in plasmas or at interfacial zones between gaseous phases of these plasmas and liquids led to the fabrication of various metal-, nonmetal- and carbon-based NMs, including bimetallic Pd–Fe nanoparticles (NPs) formed by melting and eroding Pd–Fe electrodes [ 1 ], fructose-functionalized AgNPs [ 3 ], PVP-stabilized PtNPs [ 4 ], and pectin-stabilized AgNPs [ 6 ] (all synthesized by the reduction of appropriate ions of these metals dissolved in solutions), carbon dots (CDs) formed by irradiation of aliphatic acids dispersed in viscous media, SiNPs fabricated by melting and eroding Si electrodes under plasma heat [ 8 ], and nanocomposites supported by Fe 3 O 4 NPs on N-doped activated carbon [ 9 ]. Interestingly, NMs were also synthesized by introducing suspensions of substrates into a plasma torch (suspension-plasma spray, SPS) [ 2 ] to form Co/C, Fe/C, and Co–Fe/C NMs, containing a nanometallic phase in addition to carbide and oxide phases of Co and Fe. Immersing plasma jets in liquid suspensions, it was possible to modify the surface of dispersed nanocellulose (NC) fibers [ 5 ].…”

“…The morphological, structural, and functional properties of NMs result in their having a wide variety of applications, e.g., as catalysts for the Fischer–Tropsch synthesis of CH 4 from H 2 and CO [ 2 ], antimicrobial agents against different phytopathogenic bacteria [ 3 ], heat conductive media in heat management systems [ 4 ], necrotic agents toward cancerous cells of the human melanoma cell line [ 6 ], fluorescence sensors for detecting and measuring metal ions and flavonoids in solutions [ 7 ], and materials for the production of anodes in lithium-ion batteries [ 8 ] or electrochemical capacitor electrodes [ 9 ].…”