Synthesis and characterization of multiwall carbon nanotubes/alumina nanohybrid-supported cobalt catalyst in Fischer-Tropsch synthesis

Multiwall carbon nanotubes (MWNTs) and alumina are combined to give a new type of nanohybrid for Fisher-Tropsch synthesis (FTS) catalyst support. Alumina nano-particles (10 wt%) were introduced directly on functionalized MWNTs by a modified sol-gel method. Microstructure observations show that alumina particles were homogeneously dispersed on the inside and outside of modified MWNTs surfaces. 15 wt% cobalt loading catalysts were prepared with this nanohybrid and γ-alumina as a reference, using a sol-gel technique and wet impregnation method respectively. These catalysts were characterized by TEM, XRD, N₂-adsorption, H₂ chemisorption and TPR. The deposition of cobalt nanoparticles synthesized by sol-gel technique on the MWNTs nanohybrid shift the reduction peaks to a low temperature, indicating higher reducibility for uniform cobalt particles. Nanohybrid also aided in high dispersion of metal clusters and high stability and performance of catalyst. The proposed MWNTs nanohybrid-supported cobalt catalysts showed the improved FTS rate (g_HC/(g_cat·min)), CO conversion (%), and water gas shift rate (WGS)(g_CO2/(g_cat·h)) of 0.012, 52, and 30E-3, respectively, as compared to those of 0.007, 25, and 18E-3, respectively, on the γ-alumina-supported cobalt catalysts with the same Co loading.     

Effect of cobalt weight content on the structure and catalytic properties of Co/CNT catalysts in the fischer–tropsch synthesis

Cobalt-based Fischer–Tropsch synthesis (FTS) catalysts containing 1 to 40 wt % cobalt supported on multi-walled carbon nanotubes (CNTs) have been investigated. The CNTs have been characterized by low-temperature nitrogen adsorption, scanning electron microscopy, and X-ray photoelectron spectroscopy. All catalysts have been prepared by impregnating, with an ethanolic solution of cobalt nitrate, the CNTs preoxidized with concentrated nitric acid and have been tested in the FTS at 220°C and atmospheric pressure. Correlations have been established between the cobalt weight content of the catalyst and the Co particle size determined by transmission electron microscopy and X-ray diffraction. The Co content and particle size have an effect on the activity and selectivity of the catalyst and on the target fraction (C₅₊) yield in the FTS. The highest CO conversion is observed for the catalyst containing 20 wt % Co; the highest selectivity and activity, for the catalyst containing 5 wt % Co; the highest C₅₊ yield, for the catalyst containing 10 wt % Co.     

Carbon nanotubes decorated α-Al2O3 containing cobalt nanoparticles for Fischer-Tropsch reaction

A new hierarchical composite consisted of multi-walled carbon nanotubes (CNTs) layer anchored on macroscopic α-Al₂O₃ host matrix was synthesized and used as support for Fischer-Tropsch synthesis (FTS). The composite constituted by a thin shell of a homogeneous, highly entangled and structure-opened carbon nanotubes network and it exhibited a relatively high and fully accessible specific surface area of 76 m²·g^?1, compared with that of 5 m²·g^?1 of the original α-Al₂O₃ support. The metal-support interaction between carbon nanotubes surface and cobalt precursor and high effective surface area led to a relatively high dispersion of cobalt nanoparticles. This hierarchically supported cobalt catalyst exhibited a high FTS activity along with an extremely high selectivity towards liquid hydrocarbons compared with the cobalt-based catalyst supported on pristine α-Al2O₃ or on CNTs carriers. This improvement can attribute to the high accessibility of composite surface area comparing with the macroscopic host structure alone or to the bulk CNTs where the nanoscopic dimension induced a dense packing with low mass transfer which favoured the problem of reactants competitive diffusion towards the cobalt active site. In addition, intrinsic thermal conductivity of decorated CNTs could help the heat dissipating throughout the catalyst body, thus avoiding the formation of local hot spots which appeared in high CO conversion under pure syngas feed in FTS reaction. Cobalt supported on CNTs decorated α-Al₂O₃ catalyst also exhibited satisfied high stability during more than 200 h on stream under relatively severe conditions compared with other catalysts reported in the literature. Finally, the macroscopic shape of such composite easily rendered its usage as catalyst support in a fixed-bed configuration without facing problems of transport and pressure drop as encountered with the bulk CNTs.     

Effect of niobium promoter on iron-based catalyst for Fischer-Tropsch reaction

Niobium-promoted Fe/CNTs catalysts were prepared using a wet impregnation method.Samples were characterized by nitrogen adsorption,H2-TPR,TPD,XRD and TEM.The Fischer-Tropsch Synthesis(FTS) was carried out in a fixed-bed microreactor at 220 ℃,1 atm and H2/CO=2 for 5 h.Addition of niobium into Fe/CNTs increased the dispersion,decreased the average size of iron oxide nanoparticles and the catalyst reducibility.Niobium-promoted Fe catalyst resulted in appreciable increase in the selectivity of C5+ hydrocarbons and suppressed methane formation.These effects were more pronounced for the 0.04%Nb/Fe/CNTs catalyst,compared to those observed from other niobium compositions.The 0.04%Nb/Fe/CNTs catalyst enhanced the C5+ hydrocarbons selectivity by a factor of 67.5% and reduced the methane selectivity by a factor of 59.2%.     

Iron-based catalysts encapsulated by nitrogen-doped graphitic carbon for selective synthesis of liquid fuels through the Fischer-Tropsch process

Fischer-Tropsch synthesis (FTS) has the potential to be a powerful strategy for producing liquid fuels from syngas if highly selective catalysts can be developed. Herein, a series of iron nanoparticle catalysts encapsulated by nitrogen-doped graphitic carbon were prepared by a one-step pyrolysis of a ferric L-glutamic acid complex. The FeC-800 catalyst pyrolyzed at 800 °C showed excellent catalytic activity (239.4 μmol_CO g_Fe^–1 s^–1), high C₅–C₁₁ selectivity (49%), and good stability in FTS. The high dispersion of ferric species combined with a well-encapsulated structure can effectively inhibit the migration of iron nanoparticles during the reaction process, which is beneficial for high activity and good stability. The nitrogen-doped graphitic carbon shell can act as an electron donor to the iron particles, thus promoting CO activation and expediting the formation of Fe₅C₂, which is the key factor for obtaining high C₅–C₁₁ selectivity.     

Fischer-Tropsch synthesis by nano-structured iron catalyst

Effects of nanoscale iron oxide particles on textural structure, reduction, carburization and catalytic behavior of precipitated iron catalyst in Fischer-Tropsch synthesis (FTS) are investigated. Nanostructured iron catalysts were prepared by microemulsion method in two series. Firstly, Fe2O3, CuO and La2O3 nanoparticles were prepared separately and were mixed to attain Fe/Cu/La nanostructured catalyst (sep-nano catalyst); Secondly nanostructured catalyst was prepared by co-precipitation in a water-in-oil microemulsion method (mix-nano catalyst). Also, conventional iron catalyst was prepared with common co-precipitation method. Structural characterizations of the catalysts were performed by TEM, XRD, H2 and CO-TPR tests. Particle size of iron oxides for sep-nano and mix-nano catalysts, which were determined by XRD pattern (Scherrer equation) and TEM images was about 20 and 21.6 nm, respectively. Catalyst evaluation was conducted in a fixed-bed stainless steel reactor and compared with conventional iron catalyst. The results revealed that FTS reaction increased while WGS reaction and olefin/paraffin ratio decreased in nanostructured iron catalysts.     

TiO2 supported cobalt-manganese nano catalysts for light olefins production from syngas

Cobalt-manganese nano catalysts were prepared by sol-gel method. This research investigated the effects of different cobalt-manganese (Co/Mn = 1/1) loading, pH and calcination conditions on the catalytic performance of Co-Mn/TiO₂ catalysts for Fischer-Tropsch synthesis (FTS) in a fixed bed reactor. It was found that the catalyst containing 30wt%(Co-Mn)/TiO₂ was an optimal catalyst for the conversion of synthesis gas to light olefins especially propylene. The activity and selectivity of optimal catalyst were studied under different operational conditions. The results showed that the best operational conditions were H₂/CO= 1/1 molar feed ratio at 250 °C and GHSV= 1300 h^?1 under atmospheric pressure. Characterization of catalysts was carried out by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), N₂ adsorption-desorption measurements.     

Promotion of Mn Doped Co/CNTs Catalysts for CO Hydrogenation to Light Olefins

With various contents, Mn was introduced into carbon nanotubes (CNTs) supported cobalt catalysts and the obtained Mn‐Co/CNTs catalysts were investigated for CO hydrogenation to light alkenes and characterized by N₂ adsorption, X‐ray diffraction (XRD), X‐ray photoelectron spectra (XPS), H₂ temperature programmed reduction (TPR), CO temperature programmed desorption (TPD) and transmission electron microscope (TEM). The results indicate that the addition of a small amount of Mn (0.3 wt%) to CNTs‐supported Co catalyst significantly increased the selectivity of C₂–C₄ olefins and decreased the selectivity of CH₄. However, with further addition of Mn to the cobalt catalysts, the CH₄ selectivity decreased obviously along with the increase of the C₅₊ selectivity. Compared with the unpromoted catalysts, the Mn‐promoted cobalt catalysts increased the C₂^?–C₄^?/C₂⁰–C₄⁰ molar ratio.     

助剂对Ni基催化剂结构及甲烷化性能的影响

本文采用等体积浸渍制备了掺杂不同金属助剂改性的Ni基催化剂,考察了其催化浆态床CO甲烷化的性能。通过XRD、H2-TPR、HR-TEM等表征对催化剂进行了分析,结果表明,掺杂Zr、Co、Ce、Zn、La助剂促进了Ni物种在载体表面的分散,减小了Ni的晶粒尺寸,降低了催化剂的还原温度;掺杂Mg助剂则导致催化剂的还原温度升高。浆态床活性评价结果表明,掺杂Zr、Co、Ce、Zn、La助剂提高了催化剂的甲烷化性能,其中以La助剂的效果最明显,通过对La负载量进一步优化后发现,当La负载量为8%时,催化剂的甲烷化催化性能最优,CO转化率、CH4选择性和时空收率分别达到96.3%、87.1%和179.6 g·kg-1·h-1;掺杂Mg助剂则降低了催化剂的甲烷化活性。     

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).     

Ce-Cu-Co/CNTs催化剂催化合成气制低碳醇及乙醇的研究

采用共浸渍法制备了不同Ce含量的Ce-Cu-Co/CNTs 催化剂, 考察了其在合成气制低碳醇反应中的催化性能, 借助X射线衍射(XRD)、程序升温还原(H₂-TPR)、N₂吸脱附实验(BET)、透射电镜(TEM)和CO程序升温脱附(CO-TPD)对这些催化剂进行了表征. 结果表明, 当Ce的质量分数为3%时, 低碳醇的时空收率和选择性达到最高, 分别为696.4 mg·g^-1·h^-1和59.7%, 其中乙醇占总醇的46.8%, 适量Ce的添加能提高Cu物种在催化剂上的分散度和催化剂的还原性能, 能显著地增加催化剂吸附CO的能力, 促进合成醇活性位的形成, 进而明显提高催化剂的活性和总醇的选择性. 研究表明, 将具有高活性和高碳链增长能力的CuCo基催化剂与碳纳米管的限域效应结合, 可实现缩窄产物分布、大幅度提高乙醇选择性的目的.     

特定碱性MgO纳米晶暴露晶面上铁基催化剂及其费-托合成反应的研究

本研究采用等量浸渍法、化学沉淀法和超声浸渍法合成了一系列具有良好外露晶面的Fe/MgO催化剂。采用X射线粉末衍射、高分辨透射电子显微镜、CO₂程序升温脱附、H₂程序升温还原、X射线光谱学和N₂物理吸附等物理化学方法对催化剂进行了表征。MgO纳米晶载体的碱性会影响费-托合成产物的选择性。在超声浸渍过程中,MgO纳米晶载体的碱性得到了保持。研究结果显示,Fe/MgO催化剂的碱性会提高CO解离速率和产物中烯烃的选择性。此外,相比于MgO（100）晶面,MgO（111）晶面负载铁基催化剂具有更高的活性（TOF）和烯烃选择性。MgO（111）晶面上更有利于CO的吸附,抑制二次加氢反应,提高产物中烯烃的收率。     

硅对铁基费-托合成催化剂的影响

用共沉淀法制备了一系列不同硅含量的铁基催化剂,采用N2吸附和原位X射线衍射对催化剂进行了表征,在固定床反应器中考察了催化剂的费-托合成反应活性、选择性和稳定性.结果表明,含硅的催化剂具有较大的比表面积和较小的平均孔径,在CO还原及费-托合成反应中生成的碳化铁物种的稳定性比不含硅的催化剂高.在费-托合成反应中,不含硅的催化剂具有较高的初始活性,但易失活;含硅的催化剂具有较低的初始活性,但稳定性较高.Fe7C3是活性最高的碳化铁物种.随着硅含量的增加,催化剂的费-托合成反应更易生成低碳数产物.     

Water–gas shift kinetics over lanthanum-promoted iron catalyst in Fischer–Tropsch synthesis: thermodynamic analysis of nanoparticle size effect

The kinetic parameters of water–gas shift (WGS) reaction in the Fischer–Tropsch synthesis (FTS) on lanthanum-promoted iron catalyst are analyzed by size-dependent thermodynamic method. A Langmuir–Hinshelwood kinetic equation is considered for the catalysts activity evaluation. A series of unsupported iron catalysts with different particle sizes are prepared via microemulsion method. These results show that the iron particle size has considerable effects on reactants adsorption and WGS kinetic parameters and WGS activity pass from a maximum by increasing the catalyst particle size. Finally, the analysis of data showed that by increasing the iron particle from 14 to 41 nm, the WGS activation energies and heats of adsorption of carbon monoxide and water on catalysts increased from 68 to 83, 22 to 28 and 75 to 94 kJ/mol, respectively.     

含骨架铁ZSM-5的合成及其负载Pt催化剂在正十二烷脱氢反应中的催化性能

采用水热合成法使铁进入分子筛MFI骨架结构,成功合成出含骨架铁的分子筛Na-[Fe]-ZSM-5,并通过离子交换法负载Pt制备脱氢催化剂Pt/Na-[Fe]-ZSM-5。通过正十二烷脱氢反应,研究了该催化剂对长链烷烃脱氢制单烯烃反应的催化性能。采用N2吸附-脱附测试、X射线衍射(XRD)、傅立叶变换红外光谱(FT-IR)、氨气程序升温脱附(NH3-TPD)、吡啶吸附的红外光谱(Py-IR)、CO化学吸附、透射电子显微镜(TEM)等不同方法对催化剂进行了表征。结果表明,通过控制骨架铁含量可调控催化剂表面酸性;含骨架铁的ZSM-5分子筛载体具有抑制负载金属晶粒长大,保持金属高分散度的作用;其负载铂催化剂Pt/Na-[Fe]ZSM-5-50具有表面弱酸中心(0.69 mmol·g^-1)和高分散Pt中心,因而具有良好的长链烷烃脱氢活性、稳定性和单烯烃选择;在转化率稳定在~20%时,TOF为4.56 s^-1,单烯烃选择性为92.7%;在实验范围内,Pt/Na-[Fe]ZSM-5催化剂表面弱酸量和脱氢反应的本征活性(TOF)均随催化剂铁含量的增加而增加。     

Formation of Co-Ru/MgO/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts for the Fischer-Tropsch synthesis: A magnetic method for the estimation of cobalt particle size

The physicochemical properties of Co-supported catalysts were studied, and the particle size of Co in Co/MgO/Al₂O₃ and Co-0.2% Ru/MgO/Al₂O₃ catalysts for the Fischer-Tropsch synthesis (FTS) was estimated using a magnetic method. It was found that a considerable fraction of superparamagnetic Co particles, which increase selectivity for C₅₊ hydrocarbons and decrease the yield of methane in the FTS, was present in a ruthenium-containing catalyst along with single-domain ferromagnetic particles. In this case, the catalyst activity increased by a factor of 10.     

Efficient Ni-based catalysts for low-temperature reverse water-gas shift (RWGS) reaction

CO₂ hydrogenation for syngas can alleviate the pressure of un-controlled emissions of CO₂ and bring enormous economic benefits. Advantageous Ni-catalysts have good CO₂ hydrogenation activity and high CO selectivity merely over 700 °C. Herein, we introduced Cu into Ni catalysts, which were evaluated by H₂-TPR, XRD, BET, in-situ XPS and CO₂-TPD, and their CO₂ hydrogenation activity and CO selectivity were significantly affected by the Ni/Cu ratios, which was rationalized by the synergistic effect of bimetallic catalysts. In addition, the reduction temperatures of studied catalysts apparently affected the CO₂ hydrogenation, which were caused by the number and dispersion of the active species. It's found that the Ni₁Cu₁-400 had good stability, high CO selectivity (up to 90%), and fast formation rate (1.81×10⁻⁵ mol/g_cat/s) at 400 °C, which demonstrated a good potential as a superior catalyst for reverse water-gas shift (RWGS) reaction.     

Steam reforming of dimethyl ether to hydrogen-rich gas

The steam reforming of dimethyl ether (DME) (SR) to a hydrogen-rich gas over a mechanical mixture of WO_x/ZrO₂ (the DME hydration catalyst) and CuZnAlO_x (the methanol SR catalyst) was studied. The mechanically mixed catalyst was shown to provide almost complete conversion of DME to the hydrogen-rich gas containing <0.5 vol.% of CO at 300°C, atmospheric pressure, gas hourly space velocity (GHSV) of 10000 h⁻¹ and molar ratio H₂O/DME = 3. The hydrogen production rate in DME SR was found to reach 180–250 mmol H₂/(g_cat·h) at 250–300°C.     

溶液燃烧法制备的Ni基催化剂及其浆态床甲烷化催化性能

分别以硝酸铝、硝酸氧锆、硝酸镧和硝酸铈为载体前驱体,与硝酸镍和尿素配制水溶液,采用溶液燃烧法制备了Ni-Al₂O₃、Ni-ZrO₂、Ni-La₂O₃和Ni-CeO₂催化剂,研究了浆态床CO甲烷化催化性能,并进行了低温N₂吸附-脱附、XRD、SEM、TEM、H₂-TPR和H2化学吸附等表征分析.结果表明,以硝酸铝为前驱体制备Ni-Al₂O₃催化剂时燃烧火焰稳定且持续时间长,达23 s,样品比表面积(468 m²·g^-1)和金属Ni表面积(10 m²·g^-1)均较大、Ni粒径小(3~5 nm)且分散度高,CO甲烷化催化活性和稳定性好,CO转化率和CH₄选择性分别达到94%和95%,在100 h的甲烷化反应中未出现明显失活;以硝酸氧锆和硝酸镧为前驱体制备样品时未出现明显的燃烧火焰,持续时间仅为12 s和5 s,催化剂比表面积、金属表面积及催化活性均较低;以硝酸铈为前驱体制备样品时燃烧过程迅速而剧烈,样品比表面积(22 m²·g^-1)和金属Ni表面积(5 m²·g^-1)小、Ni粒径大且分散性差,甲烷化催化性能最差,CO转化率仅为41%,CH₄选择性仅为89%.     

Nanosized cobalt-based catalyst prepared by supercritical phase condition for Fischer-Tropsch synthesis

A series of nanosized Co/Zn/Mn/K composite catalysts for Fischer-Tropsch synthesis (FTS) were prepared by supercritical fluid drying (SCFD) method and common drying (CD) method. The nanosized cobalt-based catalysts were characterized by XRD, TEM and BET techniques. Their catalytic performances were tested in a slurry-bed reactor under FTS reaction conditions. The drying and crystallization were carried out simultaneously during SCFD, therefore, the catalysts prepared by SCFD method have ideal structure and show the FTS performance superior to the others prepared by CD method. The FTS activity and selectivity were improved via adding Zn, Mn and K promoters, and less CH₄ and CO₂ as well as higher yield of C₅₊ products were achieved. The optimal performance of a 92% CO conversion and a 65% C₅₊ product yield was obtained over a catalyst with the component of Co/Zn/Mn/K = 100/50/10/7. Furthermore, the catalytic performance was studied under the conditions of liquid-phase and supercritical phase slurry-bed, and C₅₊ product yield were 57.4% and 65.4%, respectively. In summary, better catalytic performance was obtained using the nanosized catalyst prepared by SCFD method under supercritical reaction conditions, resulting in higher conversion of CO, less CO₂ byproduct, and higher yield of C₅₊ products.