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.
Highlights
Carbon is a very fascinating element because in the recent past, there has been substantial evidence showing how the final carbon nanomaterial, its growth process, structural morphology and microstructure can be modified by experimental parameters such as the source of carbon feedstock, gas flow rate, synthesis temperature, and the type of catalyst used, including its composition, shape, and particle size [1]
We showed that the CO-reduced CO conversion at K was 18% (Co/C) catalyst did not display the presence of CNFs [52], and the same has been confirmed in this study
The catalysts were synthesized through plasma and with a BET specific surface area of ~80 m2.g−1; they are remarkably identical in morphology too
Summary
Carbon is a very fascinating element because in the recent past, there has been substantial evidence showing how the final carbon nanomaterial, its growth process, structural morphology and microstructure can be modified by experimental parameters such as the source of carbon feedstock, gas flow rate, synthesis temperature, and the type of catalyst used, including its composition, shape, and particle size [1]. Magnetic carbon nanotubes (CNTs) can be found in biomedical applications [6], carbon nanotropes for drug delivery [7], CNTs in field emission devices [8], super-capacitors and batteries for energy storage [9], and high-performance energy conversion in solar cells and fuel cells [10]. In all these emerging fields, the properties of novel nanometric materials exhibit substantial variation from the bulk solid state due to their diminished size, for example, in data storage devices and sensors, finely divided magnetic nanoparticles are most desirable [11]. The single roller melt-spinning method has been used, which involves in situ carbidation through rapid quenching of skeletal nano-crystalline Fe [25]
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