Production
of Fischer–Tropsch catalysts is challenging because
it involves controlling and optimizing multiple parameters in numerous
technical steps. Here, we present C-supported nanometric Fe and Co
catalysts synthesized by plasma spraying, a method that contracts
catalyst production into a single step, in contrast to traditional
multistep catalyst production by precipitation or impregnation. The
catalysts were reduced in situ and then tested for
Fischer–Tropsch synthesis in a gas–solid fixed-bed reactor
at 230 °C and 30-bar pressure for 24 h. The performance of plasma-synthesized
catalysts was superior at a gas hourly space velocity of 6,000 mL·g
cat
–1·h–1, with Fe/C catalysts showing about 30%
CO conversion per pass while Co/C catalysts yielded about 20% CO conversion.
Identical C-supported Co and Fe catalysts prepared by impregnation
or precipitation gave CO conversions of about 7% under similar reaction
conditions.
Cu-ZnO-based catalysts are of importance for CO2 utilization to synthesize methanol. However, the mechanisms of CO2 activation, the split of the C=O double bond, and the formation of C-H and O-H bonds are still debatable. To understand this mechanism and to improve the selectivity of methanol formation, the combination of strong electronic adsorption (SEA) and atomic layer deposition (ALD) was used to form catalysts with Cu nanoparticles surrounded by a non-uniform ZnO layer, uniform atomic layer of ZnO, or multiple layers of ZnO on porous SiO2. N2 adsorption, H2 temperature-programmed reduction (H2-TPR) X-ray diffraction (XRD), transmission electron microscope (TEM), energy-dispersive X-ray spectroscopy (EDX), CO-chemisorption, CO2 temperature-programmed desorption (CO2-TPD), X-ray adsorption near edge structure (XANES), and extended X-ray absorption fine structure (EXAFS) were used to characterize the catalysts. The catalyst activity was correlated to the number of metallic sites. The catalyst of 5 wt% Cu over-coated with a single atomic layer of ZnO exhibited higher methanol selectivity. This catalyst has comparatively more metallic sites (smaller Cu particles with good distribution) and basic site (uniform ZnO layer) formation, and a stronger interaction between them, which provided necessary synergy for the CO2 activation and hydrogenation to form methanol.
In this study, two catalyst grain sizes (fine powders and pellets) have been investigated to elucidate the effects of both external and internal mass transfer diffusion as well as particle size during the CO hydrogenation reaction to produce higher alcohols. Catalyst grain sizes of 88 and 254 μm were advisedly chosen based on our previous investigations with a similar catalyst matrix for the higher alcohol synthesis (HAS) reaction. The focus in this work was to explore the attractive textural properties of CNH support for CO hydrogenation reaction to produce higher alcohols under specified reaction conditions. Also, to ascertain the possibilities of commercialization of the developed carbon nanohorn (CNH)-supported KCoRhMo catalyst, bentonite clay was added to the pristine support as a binder to enhance its mechanical/crushing strength and kinetic analyses of such catalyst assessed. The influence of bentonite clay was investigated by incorporating 5 wt % of this binder into the formulation of the KCoRhMo/CNH catalyst. For mass transfer considerations, the finely ground KCoRhMo/CNH catalyst powder of 88 μm particle size was used so as to eradicate mass transfer resistance. CO hydrogenation experiments were carried out using a twophase fixed-bed reactor system to ascertain the intrinsic kinetics of the liquid alcohol products (methanol, ethanol, higher alcohols) as well as the gaseous products generated by the reaction. Syngas of H 2 /CO ratio of 1.25 was used as feedstock at temperatures, pressures, and gas hourly space velocity ranges of 290−350 °C, 800−1400 psig, and 2.4−4.8 m 3 STP/kg cat /h, respectively. The power law model was used to fit experimental data to evaluate kinetic parameters for the HAS reaction on the catalyst surface. Fitting of the experimental data with the developed power law models showed good fits with high R 2 values in the range of 0.88−0.96 for the components evaluated. The activation energies computed for ethanol and propanol in the HAS reaction over CNH-supported KCoRhMo catalyst were 54.4 and 92.2 kJ/mol, which are low compared to values obtained by other researchers in similar studies.
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