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.
Catalytic oxidative desulfurization (ODS) is emerging as a potential alternative to deep hydroprocessing as a result of its milder operating conditions and no hydrogen requirements. In this study, ODS catalysts based on a mesoporous TUD-1 support were developed to overcome the diffusion limitation of zeolite-based catalysts in oxidizing large-size organosulfur compounds present in real petroleum feedstocks. Different mesoporous oxidation catalysts were formed by substituting Ti in the TUD-1 framework and impregnating Keggin molybdenum heteropolyacid (HPA) on the TUD-1 support. The mesoporosity of TUD-1 and the presence of Ti(IV) and Mo Keggin units in the prepared catalysts were confirmed from the characterization results of X-ray diffraction, X-ray photoelectron spectroscopy, X-ray absorption near edge structure, and Brunauer−Emmett−Teller N 2 surface area analyses. The ODS performance of catalysts was studied using a mild hydrotreated bitumen-derived heavy gas oil feedstock. The HPA-dispersed Ti−TUD-1 catalyst was found to be most active for desulfurizing the heavy gas oil feedstock as a result of a strong synergy effect of Ti and Mo Keggin ions on catalyzing oxygen transfer from an oxidant to a substrate. Oxidants, such as hydrogen peroxide, cumene hydroperoxide, tert-butyl hydroperoxide, and molecular oxygen, were screened in this study. The first two oxidants were better than others and equally efficient. The HPA/Ti−TUD-1 catalyst was found to be suitable for ODS and oxidative denitrogenation (ODN) in both the batch stirred-tank reactor and continuous fixed-bed reactor systems.
In the present study, a series of monometallic Cu/SiO2-Al2O3 catalysts exhibited immense potential in the hydroprocessing of oleic acid to produce jet-fuel range hydrocarbons. The synergistic effect of Fe on the monometallic Cu/SiO2-Al2O3 catalysts of variable Cu loadings (5–15 wt%) was ascertained by varying Fe contents in the range of 1–5 wt% on the optimized 13% Cu/SiO2-Al2O3 catalyst. At 340 °C and 2.07 MPa H2 pressure, the jet-fuel range hydrocarbons yield and selectivities of 51.8% and 53.8%, respectively, were recorded for the Fe(3)-Cu(13)/SiO2-Al2O3 catalyst. To investigate the influence of acidity of support on the cracking of oleic acid, ZSM-5 (Zeolite Socony Mobil–5) and HZSM-5(Protonated Zeolite Socony Mobil–5)-supported 3% Fe-13% Cu were also evaluated at 300–340 °C and 2.07 MPa H2 pressure. Extensive techniques including N2 sorption analysis, pyridine- Fourier Transform Infrared Spectroscopy (Pyridine-FTIR), X-ray Diffraction (XRD), X-ray Photoelectron Spectroscopy (XPS), and H2-Temperature Programmed Reduction (H2-TPR) analyses were used to characterize the materials. XPS analysis revealed the existence of Cu1+ phase in the Fe(3)-Cu(13)/SiO2-Al2O3 catalyst, while Cu metal was predominant in both the ZSM-5 and HZSM-5-supported FeCu catalysts. The lowest crystallite size of Fe(3)-Cu(13)/SiO2-Al2O3 was confirmed by XRD, indicating high metal dispersion and corroborated by the weakest metal–support interaction revealed from the TPR profile of this catalyst. CO chemisorption also confirmed high metal dispersion (8.4%) for the Fe(3)-Cu(13)/SiO2-Al2O3 catalyst. The lowest and mildest Brønsted/Lewis acid sites ratio was recorded from the pyridine–FTIR analysis for this catalyst. The highest jet-fuel range hydrocarbons yield of 59.5% and 73.6% selectivity were recorded for the Fe(3)-Cu(13)/SiO2-Al2O3 catalyst evaluated at 300 °C and 2.07 MPa H2 pressure, which can be attributed to its desirable textural properties, high oxophilic iron content, high metal dispersion and mild Brønsted acid sites present in this catalyst.
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