Solvent-free synthesis of alumina supported cobalt catalysts for Fischer–Tropsch synthesis

A novel mechano-synthesis method has been elaborated in this work for the design of efficient cobaltbased Fischer–Tropsch catalysts. The process aims to reduce the total number of steps involved in the synthesis of solid catalysts and thus to avoid relevant toxic solutions generated during the catalyst preparation. The mechano-synthesis of the Co/Al_2O_3 catalyst was processed in a low-energy vibratory micro mill and high energy planetary ball mill. Porous spherical γ-aluminas(1860 μm and 71 μm mean particle diameter) were used in this work as host compounds. Co_3O_4(3 μm mean particle diameter) has provided guest particles for mechano-synthesis. The catalysts were characterized by textural(surface area, porosity and particle size) and structural analyses(X-ray diffraction, TPR, SEM-EDX and microprobe). The microprobe images show deposition of Co_3O_4 on the surface of the alumina and indicated no Co_3O_4 diffusion inside the alumina pores. SEM-EDX mapping illustrated that cobalt coating tended to occur on surface of rounded shape of cracked alumina fragments. After milling, the crystallite size of Co_3O_4 decreased to 15 nm from 30 to 50 nm. The TPR profiles indicated very low concentrations of inactive cobalt aluminate mixed compounds which are usually produced during the catalyst preparation by impregnation.In Fischer–Tropsch synthesis, the catalysts prepared using mechano-synthesis methods showed catalytic performance comparable to the catalysts prepared by impregnation.     

Effects of cobalt carbide on Fischer–Tropsch synthesis with MnO supported Co-based catalysts

Cobalt carbide(Co_2C)was considered as potential catalysts available for large-scale industrialization of transforming syngas(H_2 and CO)to clean fuels.Herein,we successfully synthesized Co-based catalysts with MnO supported,to comprehend the effects of Co_2C for Fischer–Tropsch synthesis(FTS)under ambient conditions.The huge variety of product selectivity which was contained by different active sites(Co and Co_2C)has been found.Furthermore,density functional theory(DFT)shows that Co_2C is efficacious of CO adsorption,whereas is weaker for H adsorption than Co.Combining the advantages of Co and Co_2C,the catalyst herein can not only obtain more C_(5+)products but also suppress methane selectivity.It can be a commendable guide for the design of industrial application products in FTS.     

Fischer–Tropsch synthesis over iron catalysts with corncob-derived promoters

A sustainable strategy for Fischer–Tropsch iron catalysts is successfully achieved by embedding of synergistic promoters from a renewable resource, corncob. The iron-based catalysts, named as "corncob-driven"catalysts, are composed of iron species supported on carbon as primary active components and various minerals(K, Mg, Ca, and Si, etc.) as promoters. The corncob-driven catalysts are facilely synthesized by a one-pot hydrothermal treatment under mild conditions. The characterization results indicate that the formation of iron carbides from humboldtine is clearly enhanced and the morphology of catalyst particles tends to be more regular microspheres after adding corncob. It is observed that the optimized corncob-driven catalyst exhibits a higher conversion than without promoters' catalyst in Fischer–Tropsch synthesis(ca. 73% vs. ca. 49%). More importantly, a synergistic effect exists in multiple promoters from corncob that can enhance heavy hydrocarbons selectivity and lower CO_2 selectivity, obviously different from the catalyst with promoters from chemicals. The proposed synthesis route of corncob-driven catalysts provides new strategies for the utilization of renewable resources and elimination of environmental pollutants from chemical promoters.     

Fischer–Tropsch synthesis over CNT-supported cobalt catalyst: effect of magnetic field

In the present work, the cobalt catalysts supported on carbon nanotubes (CNTs) were prepared by impregnation method in the presence and absence of magnetic field. The prepared catalysts were employed to yield higher hydrocarbons via Fischer–Tropsch synthesis. It is explored that using magnetized water can effectively change the catalyst geometry in impregnation catalyst preparation method. For the preparation of different sizes of cobalt particles on the CNTs support, the physical properties of solvent (water) in impregnation process were changed using the magnetizing process. The results showed that the average particle sizes of impregnated cobalt nanoparticles were decreased by using magnetized water in impregnation step. In addition, in the magnetized treated cobalt catalyst, the cobalt particles mostly dispersed outside the tubes because the capillary forces decreased by reducing water surface tension. Furthermore, the experimental results showed that the probability of chain growth (α) and selectivity to heavier hydrocarbons increased in magnetized water treatment catalysts.     

Metal–organic frameworks of zeolitic imidazolate framework-7 and zeolitic imidazolate framework-60 for fast mercury and methylmercury speciation analysis

A fluorescence sensing platform based on metal–organic frameworks (MOFs) nanoparticles (NPs) of both zeolitic imidazolate framework-7 (ZIF-7) and zeolitic imidazolate framework-60 (ZIF-60) was developed for speciation analysis of inorganic Hg [Hg(II)] and methylmercury (MeHg⁺). Microwave-ultrasound assisted synthesis was employed for the preparation of ZIF-7 and ZIF-60 NPs, with short reaction time, easy procedure, and small particle size obtained. Based on strict cavity confinement of the ZIF-7 and ZIF-60 structures, the proposed method exhibited excellent selectivity for both Hg(II) and MeHg⁺, even in the presence of the other Hg species or various cations or anions with the concentration of 50 times high. Effect of pH and ionic strength on sensing behaviour of the ZIF MOF was studied as well. The calculated detection limit is 3 ng mL⁻¹ and 6 ng mL⁻¹ for Hg(II) and MeHg⁺, respectively. Furthermore, the application of the developed method to the analysis of local drinking water was demonstrated to be feasible, and the obtained recovery was 102% and 96.2% for Hg(II) and MeHg⁺, respectively.     

Controlled synthesis of cobalt nanocrystals on the carbon spheres for enhancing Fischer–Tropsch synthesis performance

Non-porous carbon sphere was used as support to synthesize supported cobalt Fischer-Tropsch catalysts with high activity and durability. Strong metal-support interaction was avoided and intrinsic activity of pristine cobalt nano-particles was studied. Thermal decomposition synthesis method was applied to obtain cobalt catalysts with high dispersion and narrow particle size distribution. Furthermore the cobalt size can be controlled by the molar ratio of o-dichlorobenzene/benzylamine. Compared with supported cobalt catalysts prepared by incipient wetness impregnation method and ultrasonic impregnation method,the catalyst prepared by thermal decomposition method showed higher catalytic activity, higher long chain hydrocarbons selectivity and lower methane selectivity.     

Cobalt–copper based catalysts for higher terminal alcohols synthesis via Fischer–Tropsch reaction

The production of higher terminal alcohols through CO hydrogenation according to the Fischer–Tropsch(F–T) process has been a topic of interest since the Institut Fran?ais du Pétrole(IFP) demonstrated shortchain C_1–C_6mixed alcohols production over cobalt–copper based catalysts. A number of catalyst formulations were screened for their suitability at that time. In particular, the addition of Cr, Zn, Al, Mn and V to Co Cu was investigated. In a number of patents, it was shown that catalyst preparation is crucial in these catalyst formulations and that high alcohols selectivity can only be achieved by carefully respecting the procedures and recipes. This short critical review highlights recent developments in Co Cu-based catalysts for higher terminal alcohols synthesis via F–T synthesis. Special attention will be given to catalyst preparation which according to developments in our group is based on oxalate precipitation. This way we show that the close association of Co and Cu on the one hand and promoter/dispersant on the other are of utmost importance to ensure high performance of the catalysts. We shall concentrate on "Co Cu Mn","Co Cu Mo" and "Co Cu Nb" catalyst formulations, all prepared via oxalate precipitation and combined with"entrainment techniques" if necessary, and show high total alcohols selectivity can be obtained with tunable Anderson-Schulz-Flory chain-lengthening probability. Either long-chain C_8–C_(14)terminal alcohols as feedstock for plasticizers, lubricants and detergents, or short-chain C_2–C_5alcohols as "alkanol" fuels or fuel additives can be formed this way.     

Effect of introduced zeolite on the Fischer–Tropsch synthesis over a cobalt catalyst

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Synthesis and characterization of Al-modified SBA-15 for Fischer–Tropsch synthesis (FTS) reaction

Research on Chemical Intermediates - In this work, we synthesized a Co-based catalyst supported on modified SBA-15 to obtain the uniform particle size of active metal and selective products with...     

Promotion of cobalt catalyst for Fischer–Tropsch synthesis by molybdenum as protection against sulfur poisoning

Molybdenum promotion was used to increase the resistance of a cobalt catalyst for the Fischer–Tropsch synthesis to sulfur poisoning. A series of experiments on adding 1,3,5-trithiane to synthesis gas (sulfur content of 1 ppm) showed that the Co–Mo /Al₂O₃ catalyst regained its initial activity after 8 h of operation. In comparison, catalysts not containing molybdenum experienced a significant irreversible loss of activity that was not recovered after stopping the addition of 1,3,5-trithiane to the feed.     

Fischer–Tropsch synthesis on impregnated cobalt-based catalysts:New insights into the effect of impregnation solutions and pH value

The Co-based catalysts were prepared with different cobalt acetate solutions. Effects of p H value were studied deeply on Fischer–Tropsch synthesis(FTS) through a semi-batch reactor. Among all impregnation solutions(water, butanol, amyl alcohol, acetic acid, nitric acid and ammonium nitrate), the catalyst prepared by NH_4NO_3 solution showed the highest catalytic activity due to its small particle size and high reduction degree. However, the catalyst with the smallest particle size derived from water as impregnation solution exhibited low activity as well as high methane selectivity since it was difficult to be reduced and inactive in FTS. According to FT-IR spectra results, the low intensity of absorbed CO on the catalyst prepared from water solution resulted in low FTS activity. Whereas, the high activity of catalysts prepared from NH_4NO_3 solution could be explained by the high intensity of absorbed CO on the catalysts.The cobalt species on the catalysts prepared under lower p H conditions exhibited smaller particle size distribution as well as lower CO conversion than those prepared at higher p H value.     

Effect of preparation methods on Co/ZrO2 catalysts in Fischer–Tropsch synthesis

Cobalt was incorporated into the zirconia support by different methods. The reducibility and activity of the catalysts was directly related to the preparation methods. Impregnated Co/ZrO₂ catalyst showed the highest reduction degree and the highest CO hydrogenation activity.     

Fabrication of K-promoted iron/carbon nanotubes composite catalysts for the Fischer–Tropsch synthesis of lower olefins

K-promoted iron/carbon nanotubes composite(i.e., Fe K-OX) was prepared by a redox reaction between carbon nanotubes and K_2FeO_4followed by thermal treatments on a purpose as the Fischer–Tropsch catalyst for the direct conversion of syngas to lower olefins. Its catalytic behaviors were compared with those of the other two Fe-IM and Fe K-IM catalysts prepared by impregnation method followed by thermal treatments. The novel Fe K-OX composite catalyst is found to exhibit higher hydrocarbon selectivity,lower olefins selectivity and chain growth probability as well as better stability. The catalyst structureperformance relationship has been established using multiple techniques including XRD, Raman, TEM and EDS elemental mapping. In addition, effects of additional potassium into the Fe K-OX composite catalyst on the FTO performance were also investigated and discussed. Additional potassium promoters further endow the catalysts with higher yield of lower olefins. These results demonstrated that the introduction method of promoters and iron species plays a crucial role in the design and fabrication of highly active,selective and stable iron-based composite catalysts for the FTO reaction.     

Thermokinetic study of Fischer–Tropsch synthesis on Fe2Cu1 and FeCu surfaces with comparison to Fe(110) and Cu(111) catalysts by the UBI-QEP method

The purpose of this study is to predict the activation barriers and enthalpy for elementary steps in the process of Fischer–Tropsch (F-T) on the surfaces of Fe(110), Cu(111) and Fe/Cu alloys catalyst using “Unity Bond Index-Quadratic Exponential Potential” method aimed at predicting the activity and selectivity on the basis of energy criteria. The elementary steps, such as dissociation of CO, hydrogenation of carbidic carbon, C–C chain growth by insertion of CH₂ versus CO into the metal-alkyl bonds, and chain termination, which lead to hydrocarbons (alkanes versus α-olefins) or oxygenates are discussed in detail. The results show that metallic Fe(110) is necessary to produce the carbidic carbon from CO dissociation, but the synthesis of hydrocarbons and oxygenates can effectively proceed on Cu(111) surface. For optimum performance of F-T synthesis catalyst, these conflicting properties must be optimized. In this regard, we studied Fe/Cu alloy catalyst. On all the catalyst surfaces, the energetically preferred path to initiate the alkyl chain growth is via insertion of a CH_2,s group into the carbon–metal bond of a CH_3,s group. On FeCu catalyst surface, the activation barrier for termination of alkyl chain growth by β-elimination of hydrogen is found to be lower than that for α-addition of hydrogen and consequently for this catalyst, olefins are expected to form more readily than paraffins. The results of the model for a single metal surface are in agreement with the experimental data.     

Novel Co/graphene oxide and Co/nanoporous graphene catalysts for Fischer–Tropsch reaction

For the first time, nanoporous graphene and graphene oxide sheets have been synthesized and used as supports for preparation of Co/graphene-based catalysts to evaluate their efficiency in Fischer–Tropsch synthesis and for comparison with the performance of Co/Al₂O₃ to study the effects of the carbon supports on the reaction. Outstanding results were obtained compared with the alumina counterpart. Application of nanoporous graphene yielded heavier hydrocarbons compared with the Co/Al₂O₃ catalyst, possibly due to the high surface area and intrinsic properties of the carbon nanostructures as effective hydrogen carriers. Use of graphene oxide and nanoporous graphene supports also resulted in high CO₂ selectivity. However, the graphene-supported catalysts displayed lower C₁–C₄ hydrocarbon selectivity compared with the Al₂O₃ catalyst.     

Enantioselective catalytic synthesis of ethyl mandelate derivatives using Rh(I)–NHC catalysts and organoboron reagents

Herein we describe for the first time the enantioselective catalytic arylation of ethyl glyoxalate using phenylboron reagents and chiral rhodium(I)–NHC catalysts. KO^tBu was the base of choice, along with tert-amyl alcohol as the solvent. A novel chiral bis-imidazolium salt was synthesized and evaluated for the first time in this catalytic transformation. Although moderate enantioselectivities (up to 34% ee) were obtained for the phenylation reaction, despite the excellent yields, very low enantioselectivities were obtained using other arylboronic acids with a variety of chiral rhodium(I)–NHC catalysts.     

A novel hybrid electrode of zeolitic imidazolate framework–derived carbon encapsulated in reduced-TiO2 nanotube arrays: Fabrication and photoelectrocatalytic activity

Constructing high-efficient photoelectrodes is one of the promising tasks in photoelectrocatalytic (PEC) technology. Al-reduced TiO₂ nanotube arrays (R-TNTAs) exhibit distinct improved visible-light response ability in comparison with traditional TiO₂ nanomaterials. In addition, metal–organic framework (MOF)-derived porous carbon materials possess versatile advantages partly due to preserved geometry configuration of MOF. Inspired by these characteristics, in this work, we synthesized the novel hybrid electrodes of C–N (Zn)@R-TNTAs through the pyrolysis of ZIF-8@R-TNTAs at controlled temperatures, which were pre-synthesized by coating zeolitic imidazolate frameworks (ZIF-8) onto R-TNTAs. The resulting hybrid electrodes were characterized using field-emission scanning electron microscopy, powder X-ray diffraction, X-ray photoelectron spectra, and Fourier-transform infrared techniques. The EC property and PEC activity of the composite electrodes were also analyzed, and the dependence of these on the pyrolysis temperature was also explored. The results showed that the pyrolyzed carbon materials were uniformly deposited in the inner TiO₂ nanotubes and thus effectively enhanced their EC and PEC activities. The best EC and PEC capacities were obtained by C–N (Zn)@R-TNTAs (600); the maximum photocurrent density was 0.85 mA cm⁻², which is ~1.5 times that of single R-TNTAs; and the maximum H₂ evolution rate was 58.83 μmol h⁻¹ cm⁻², being ~2.3 times that of R-TNTAs. In addition, C–N (Zn)@R-TNTAs (600) exhibited the best PEC activity in the degradation of rhodamine B with excellent catalytic stability. Based on EC analyses, a possible band structure and enhanced PEC mechanism for C–N (Zn)@R-TNTAs were proposed. There are only a few reports related to reduced TiO₂ nanotubes, and this work highlights the ideas of designing the hybrid electrodes based on reduced TNTAs and MOF-derived carbon materials, which may find broad applications in PC and PEC processes.     

Dynamics of carbide formation in iron-supported catalysts of the Fischer–Tropsch process promoted by copper and potassium

The kinetics of the formation of iron carbides during the activation of iron-coated catalyst for Fischer–Tropsch synthesis promoted by copper and potassium, and by carbon monoxide and syngas, is studied. It is established that the presence of copper lowers the initial temperature of hematite reduction to magnetite and leads to the formation of carbide in both CO and СО/Н₂. Potassium slows the rate of magnetite formation, but it accelerates the formation of iron oxide. It is shown that the rate of carbide formation during magnetite reduction for catalysts is half that in the reaction of hematite reduction to magnetite in both CO and СО/Н₂.