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.     

Cobalt supported on CNTs-covered γ-and nano-structured alumina catalysts utilized for wax selective Fischer-Tropsch synthesis

Cobalt supported on carbon nanotubes(CNTs)-covered alumina has been recently developed and successfully utilized as a catalyst in Fischer-Tropsch synthesis(FTS).Problems associated with shaping of Co/CNTs into extrudates or pellets as well as catalyst attrition rendered these materials unfavorable for industrial applications.In this investigation regularγ-and nano-structured(N-S)alumina as well as CNTs-covered regularγ-and N-S-alumina supports were impregnated by cobalt nitrate solution to make new cobalt-based catalysts which were also promoted by Ru.The catalysts were characterized and tested in a micro reactor to evaluate their applicability in FTS.γ-Al2O3 was prepared by calcination of bohemite and N-S-Al2O3 was prepared by sol-gel method using aluminum chloride as starting material.Catalyst evaluations indicated that N-S-Al2O3 was superior to regularγ-Al2O3 and that CNTs-covered alumina supports were favored over non-covered ones in terms of activity and heavy hydrocarbon selectivity.These were justified by porosimetric characteristics of the catalysts and existence of CNTs points of view. CNTs-covered catalysts also showed higher wax selectivity and better resistance to deactivation.Furthermore,TPR analysis indicated that the cobalt aluminate phase,which is responsible for the permanent deactivation of alumina supported Co-based catalysts,did not form on alumina supported Co-based catalysts covered with CNTs due to weaker interactions between cobalt and alumina.     

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.     

Characterization and catalytic behavior of EDTA modified silica nanosprings (NS)-supported cobalt catalyst for Fischer-Tropsch CO-hydrogenation

The effect of ethylene diamine tetraacetic acid(EDTA) modification on the physico-chemical properties and catalytic performance of silica nanosprings(NS) supported cobalt(Co) catalyst was investigated in the conversion of syngas(H~(2+) CO) to hydrocarbons by Fischer-Tropsch synthesis(FTS). The unmodified Co/NS and modified Co/NS-EDTA catalysts were synthesized via an impregnation method. The prepared Co/NS and Co/NS-EDTA catalysts were characterized before the FTS reaction by BET surface area,X-ray diffraction(XRD),transmission electron microscopy(TEM),temperature programmed reduction(TPR),X-ray photoelectron spectroscopy(XPS),differential thermal analysis(DTA) and thermogravimetric analysis(TGA) in order to find correlations between physico-chemical properties of catalysts and catalytic performance. FTS was carried out in a quartz fixedbed microreactor(H_2/CO of 2 ∶1,230 ℃ and atmospheric pressure) and the products trapped and analyzed by GC-TCD and GC-MS to determine CO conversion and reaction selectivity. The experimental results indicated that the modified Co/NS-EDTA catalyst displayed a more-dispersed phase of Co_3O_4 nanoparticles(10.9%) and the Co_3O_4 average crystallite size was about 12.4 nm. The EDTA modified catalyst showed relatively higher CO conversion(70.3%) and selectivity toward C_(6-18)(JP-8,Jet A and diesel) than the Co/NS catalyst(C_(6-14))(JP-4).     

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.     

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.     

Recent Technological Developments in Cobalt Catalysts for Fischer-Tropsch Synthesis

Co-based catalysts are often utilized due to their high Fischer-Tropsch synthesis (FT) activity, G5+ hydrocarbon selectivity, low water-gas shift reaction (WGS) activity and relatively low cost. Selective control of C5+ hydrocarbons and the catalyst longevity are critical in the design of cobalt catalysts. Thus, various methods to improve the performance of Co catalysts have been suggested. The progress in cobalt catalysts reviewed in the last few decades, mainly involved the support, promoter, preparation and deactivation of Co-based catalysts.     

Environment friendly hydrothermal synthesis of carbon–Co_3O_4 nanorods composite as an efficient catalyst for oxygen evolution reaction

The design of cost-effective, highly active catalysts for hydrogen energy production is a vital element in the societal pursuit of sustainable energy. Water electrolysis is one of the most convenient processes to produce high purity hydrogen. Cobalt-based catalysts are well-known electrocatalysts for oxygen evolution reaction(OER). In this article, all these merits indicate that the present cobalt nanocomposite is a promising electrocatalyst for OER. C–Co_3O_4-nanorods catalyst with nanorod structure was synthesized by hydrothermal treatment of CoCl_2·6H_2O/dextrose/urea mixture at 180 °C for 18 h and then calcined at400 °C for 3.5 h. The role of dextrose percentage in solution to achieve the uniform coating of carbon on the surface of Co_3O_4-nanorods has been demonstrated. The prepared materials were characterized by X-ray diffraction(XRD), X-ray photoelectron spectrum(XPS), field emission scanning electron microscopy(FE-SEM), high-resolution transmission electron microscopy(HR-TEM), and Brunauer–Emmett–Teller instrument(BET). Due to its unique morphology, the C–Co_3O_4-nanorods catalyst exhibited better activity than Co_3O_4-microplates catalyst for OER in 1 M KOH aqueous solution. The results showed a highly efficient, scalable, and low-cost method for developing highly active and stable OER electrocatalysts in alkaline solution.     

Comparing the deactivation behaviour of Co/CNT and Co/γ-Al2O3 nano catalysts in Fischer-Tropsch synthesis

An extensive study of Fischer-Tropsch (FT) synthesis on cobalt nano particles supported on γ-alumina and carbon nanotubes (CNTs) catalysts is reported.20 wt% of cobalt is loaded on the supports by impregnation method.The deactivation of the two catalysts was studied at 220 C,2 MPa and 2.7 L/h feed flow rate using a fixed bed micro-reactor.The calcined fresh and used catalysts were characterized extensively and different sources of catalyst deactivation were identified.Formation of cobalt-support mixed oxides in the form of xCoO yAl2O3 and cobalt aluminates formation were the main sources of the Co/γ-Al2O3 catalyst deactivation.However sintering and cluster growth of cobalt nano particles are the main sources of the Co/CNTs catalyst deactivation.In the case of the Co/γ-Al2O3 catalyst,after 720 h on stream of continuous FT synthesis the average cobalt nano particles diameter increased from 15.9 to 18.4 nm,whereas,under the same reaction conditions the average cobalt nano particles diameter of the Co/CNTs increased from 11.2 to 17.8 nm.Although,the initial FT activity of the Co/CNTs was 26% higher than that of the Co/γ-Al2O3,the FT activity over the Co/CNTs after 720 h on stream decreased by 49% and that over the Co/γ-Al2O3 by 32%.For the Co/γ-Al2O3 catalyst 6.7% of total activity loss and for the Co/CNTs catalyst 11.6% of total activity loss cannot be recovered after regeneration of the catalyst at the same conditions of the first regeneration step.It is concluded that using CNTs as cobalt catalyst support is beneficial in carbon utilization as compared to γ-Al2O3 support,but the Co/CNTs catalyst is more susceptible for deactivation.     

Effects of ultrasonic impregnation combined with calcination in N_2 atmosphere on the property of Co_3O_4/CeO_2 composites for catalytic methane combustion

Co_3O_4/CeO_2 composites with high surface areas and ultrafine crystalline sizes for catalytic combustion of methane were firstly prepared by a new sol-gel method which combined ultrasonic impregnation treatment and calcination in N_2 atmosphere. The samples were characterized by various means such as nitrogen adsorption/desorption, X-ray diffraction(XRD), H_2 temperature-programmed reduction(H_2-TPR),X-ray photoelectron spectroscopy(XPS) and transmission electron microscopy(TEM). Results showed that the modified catalyst had the mesoporous structure, comparatively higher amount of surface oxygen and larger oxygen vacancies than others. As a result of the structure and surface composition merits, a high methane combustion conversion(50%) could be obtained at a low temperature of 262 °C for the modified Co_3O_4/CeO_2 composites catalysts. The experimental results demonstrated that ultrasonic impregnation treatment combined with the N_2 thermal treatment prior to calcination in air had a promising application for preparation of Co_3O_4/CeO_2 composites catalysts for low-temperature catalytic combustion of methane.     

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.     

Low-temperature hydrogenation of maleic anhydride to succinic anhydride and γ-butyrolactone over pseudo-boehmite derived alumina supported metal(metal = Cu,Co and Ni) catalysts

The pseudo-boehmite derived alumina supported metal(Cu,Co and Ni) catalysts prepared by the impregnation method were investigated in hydrogenation of maleic anhydride(MA) to succinic anhydride(SA) and γ-butyrolactone.The catalysts were characterized by ICP-AES,N_2 adsorptiondesorption,XRD,H_2-TPR,CO-TPD,dissociative N_2O adsorption and TEM and the results showed that the alumina possessed mesoporous feature and the metal species were well dispersed on the support.Compared to Cu/Al_2O_3 and Co/Al_2O_3,Ni/Al_2O_3 exhibited higher catalytic activity in the MA hydrogenation with 92%selectivity to SA and nearly 100%conversion of MA at 140 °C under 0.5 MPa of H_2 with a weighted hourly space velocity of 2 h ~1(MA).The stability of Ni/Al_2O_3 catalyst was also investigated.     

Effect of catalyst confinement and pore size on Fischer-Tropsch synthesis over cobalt supported on carbon nanotubes

This paper studies the impact of structure of cobalt catalysts supported on carbon nanotubes(CNT) on the activity and product selectivity of Fischer-Tropsch synthesis(FTS) reaction.Three types of CNT with average pore sizes of 5,11,and 17 nm were used as the supports.The catalysts were prepared by selectively impregnating cobalt nanoparticles either inside or outside CNT.The TPR results indicated that the catalyst with Co particles inside CNT was easier to be reduced than those outside CNT,and the reducibility of cobalt oxide particles inside the CNT decreased with the cobalt oxide particle size increasing.The activity of the catalyst with Co inside CNT was higher than that of catalysts with Co particles outside CNT.Smaller CNT pore size also appears to enhance the catalyst reduction and FTS activity due to the little interaction between cobalt oxide with carbon and the enhanced electron shift on the non-planar carbon tube surface.     

Ruthenium promotion of Co/SBA-15 catalysts for Fischer-Tropsch synthesis in slurry-phase reactors

The aim of this work was to evaluate the catalytic properties of a Ru promoted Co/SBA-15 catalyst for Fischer-Tropsch synthesis(FTS).The Ru promoted Co/SBA-15 catalyst was prepared by wet impregnation method and was characterized by X-ray diffraction,X-ray energy dispersion spectrophotometer,N2 adsorption-desorption,temperature-programmed reduction and transmission electron microscopy.The Fischer-Tropsch synthesis using the catalyst was carried out to evaluate the catalyst activity and its effect on FTS product distribution.The synthesis was carried out in a slurry reactor operating at 513 K,20 atm,CO:H2 molar ratio of 1:1.X-ray diffraction showed that the calcined cobalt catalyst did not modify the structure of SBA-15,proving that Co was present in the form of Co3O4 in the catalyst.The addition of cobalt in SBA-15 decreased the specific superficial area of the molecular sieve.Fischer-Tropsch synthesis activity and C5+hydrocarbon selectivity increased with the addition of Ru.The increases in activity and selectivity were attributed to the increased number of active sites resulting from higher reducibility and the synergetic effect of Ru and Co.Ru/Co/SBA-15 catalysts showed moderate conversion(40%)and high selectivity towards the production of C5+(80 wt%).     

Studies on accelerated deactivation of ruthenium-promoted alumina-supported alkalized cobalt Fischer-Tropsch synthesis catalyst

Accelerated deactivation of ruthenium-promoted alumina-supported alkalized cobalt (K-Ru-Co/γ-Al 2 O 3 ) Fischer-Tropsch (FT) synthesis catalyst along the catalytic bed over 120 h of time-on-stream (TOS) was investigated. Catalytic bed was divided into three parts and structural changes of the spent catalysts collected from each catalytic bed after FT synthesis were studied using different techniques. Rapid deactivation was observed during the reaction due to high reaction temperature and low feed flow rates. The physico-chemical properties of the catalyst charged in the Bed #1 of the reactor did not change significantly. Interaction of cobalt with alumina and the formation of CoAl 2 O 4 increased along the catalytic bed. Reducibility percentage decreased by 4.5%, 7.5% and 12.9% for the catalysts in the Beds #1, #2 and #3, respectively. Dispersion decreased by 8.8%, 14.4% and 26.6% for the catalysts in the Beds #1, #2 and #3, respectively. Particle diameter increased by 0.6%, 2.4% and 10.4% for the catalysts in the Beds #1, #2 and #3, respectively, suggesting higher rate of sintering at the last catalytic bed. The amount of coke at the last catalytic bed was significantly higher than those of Beds #1 and #2.     

Performance enhancement of bimetallic Co-Ru/CNTs nano catalysts using microemulsion technique

Bimetallic cobalt-ruthenium nano catalysts supported on carbon nanotubes(CNTs)are prepared using microemultion technique with water-to-surfactant ratios of 0.5—1.5.The nano catalysts were extensively characterized by different methods and their activity and selectivity in Fischer-Tropsch synthesis(FTS)have been assessed in a fixed-bed microreactor.The physicochemical properties and performance of the nanocatalysts were compared with the catalyst prepared by impregnation method.Very narrow particle size distribution has been produced by the microemulsion technique at relatively high loadings of active metals(15 wt%Co and 1 wt%Ru).According to TEM images,small Co particles(2—7 nm)were mostly confined inside the CNTs.Comparing with the catalyst prepared by impregnation,the use of microemulsion technique with water to surfactant ratio of 0.5 decreased the average cobalt oxide particle size to 4.8 nm,the dispersion was almost doubled and the reduction increased by 28%.Activity and selectivity were found to be dependent on the catalyst preparation method and water-to-surfactant ratio(as well as cobalt particle sizes).CO conversion increased from 59.1%to 75.1%and the FTS rate increased from 0.291 to0.372 gHC/(gcath).C5+liquid hydrocarbons selectivity decreased from 92.4%to 87.6%.     

The Dramatic Effect of Metal Precursor on the Catalytic Performance of Co/SiO2 Catalyst for CO2 Reforming of CH4

The catalytic reforming of CH. with COZ over Ni- and Co-based catalysts for theproduction of synthesis gas with low H=/CO ratios is of attraction in industrial FischerTropsch synthesis. One of major problems for this process is catalyst deactivation bycarbon deposition and/or active metal sintering. For Co-based catalysts, Co(NO,), isgenerally used as starting salt and much effort was devoted to the effects of promoter,supporter and preparation conditions'~#. The effect of cobalt precurs…     

Effect of support modification on the characterization and catalytic activity of Mo/Al_2O_3 catalysts

Molybdenum catalysts(15 wt% Mo O3loading) supported on alumina,alumina–magnesia,and alumina–chromia were prepared via impregnation technique and studied for the reaction of methyl-cyclohexane dehydrogenation. The catalysts were evaluated by means of FT-IR,XRD,DSC,TPR,and N2adsorption–desorption isotherms. The results clarified that Mo/alumina–magnesia catalyst possesses small crystallite size and high surface area(240 m2/g) and is selective toward the formation of dehydrogenated product(96.5%). The yield to ring-opening products is higher on Mo/alumina–chromia catalyst due to its higher acidity and larger metal crystals,which favor the ring-opening reaction and lower metallic activity with selectivity toward ringopening products(32%).     

Effects of impregnation sequence on the microstructure and performances of Cu-Co based catalysts for the synthesis of higher alcohols

Silica-supported CuCo catalysts were prepared by impregnation method with different impregnation sequence for higher alcohols synthesis. These catalysts were characterized by H2-TPR, XRD, N2 adsorption, XPS techniques and CO selective hydrogenation reaction measurement. The effects of impregnation sequence on the structure and performance of catalysts were investigated, and there were important influences on the selectivity to higher alcohols. There was a strong synergistic effect between copper and cobalt for the co-impregnated sample. The CuCo/SiO2 catalyst prepared by co- impregnation showed a better yield of total alcohols, and a higher selectivity to total alcohols which reached 51.5%.     

Promoted porous Co_3O_4-Al_2O_3 catalysts for ammonia decomposition

Transition metal catalysts have been considerably used for NH_3 decomposition because of the potential application in CO_x-free H_2 generation for fuel cells.However,most transition metal catalysts prepared via traditional synthetic approaches performed the inferior stability due to the agglomeration of active components.Here,we adopted an efficient method,aerosol-assisted selfassembly approach(AASA),to prepare the optimized cobalt-alumina(Co_3O_4-Al_2O_3)catalysts.The Co_3O_4-Al_2O_3catalysts exhibited excellent catalytic performance in the NH_3 decomposition reaction,which can reach 100%conversion at 600°C and maintain stable for 72 h at a gaseous hourly space velocity(GHSV)of 18000 cm~3g~(-1)_(cat)h~(-1).The catalysts were characterized by various techniques including transmission electron microscope(TEM),scanning electron microscope(SEM),nitrogen sorption,temperature-programmed reduction by hydrogen(H_2-TPR),ex-situ/in-situ Raman and ex-situ/in-situ X-ray diffraction(XRD)to obtain the information about the structure and property of the catalysts.H_2-TPR and in-situ XRD results show that there is strong interaction between the cobalt and alumina species,which influences the redox properties of the catalysts.It is found that even a low content of alumina(10 at%)is able to stabilize the catalysts due to the adequate dispersion and rational interaction between different components,which ensures the high activity and superior stability of the cobalt-alumina catalysts.