负载型Co基F-T合成催化剂中贵金属助剂促进作用的研究进展

在负载型Co基催化剂中添加少量贵金属助剂能显著影响催化剂活性、选择性与稳定性。贵金属助剂的添加提高了Co活性组分的还原度与分散度,增加了催化剂表面的活性位数目,改变了催化剂的几何结构和电子结构,影响CO、H₂或中间产物的吸附活化行为,抑制催化剂积炭和金属Co小粒子的再氧化。综述贵金属助剂对催化剂活性中心性质、反应物的吸附活化行为和催化剂反应稳定性的影响。     

氧化物助剂对费托合成钴基催化剂的促进作用

氧化物助剂促进的钴基催化剂具有费托合成反应活性和长链烃选择性高等特点,是高选择性地获得馏分油的关键,具有良好的应用和研究价值。本文针对氧化物助剂对钴基催化剂的促进作用,综述了氧化物助剂对钴基催化剂的结构、稳定性以及费托合成反应性能的影响,详细分析了氧化物助剂对钴基催化剂的还原性能和分散度的影响, 同时介绍了影响氧化物助剂促进作用的因素,重点讨论了氧化物助剂的促进作用机理。并对如何更好地发挥氧化物助剂在钴基催化剂中的促进作用进行了展望：应加强氧化物助剂对钴基催化剂促进作用机理的基础研究,并且重视影响氧化物助剂促进作用的因素。     

Fischer-Tropsch synthesis on supported cobalt catalysts promoted by platinum and rhenium

An investigation of the CO hydrogenation of Pt- or Re-promoted 8.7 wt% Co/Al₂O₃ (1.0 wt% Pt or 1.0 wt% Re) has been carried out at two different conditions: 473 K, 5 bar, H₂/CO = 2 and 493 K, 1 bar, H₂/CO = 7.3. The addition of Pt or Re significantly increases the CO hydrogenation rate (based on weight of Co), but the selectivity was not changed by the presence of Pt or Re. The results show that the observed increases in the reaction rates are caused by increased reducibility and increased number of surface exposed Co-atoms. Steadystate isotopic transient kinetic analysis (SSITKA) with carbon tracing was used to decouple the effects of the concentration of active surface intermediates and the average site reactivity of intermediates during steady-state CO hydrogenation. The SSITKA results show that the concentration of active surface intermediates leading to CH₄ increased as a result of the addition of a noble metal promoter. However, the average site activity was not significantly affected upon Re or Pt addition.     

费托合成钴催化剂的失活与再生研究进展

为降低费托合成钴催化剂成本,提高费托合成钴催化剂的稳定性和寿命,分析了费托合成钴催化剂的失活与再生机理,论述了费托合成钴催化剂的再生方法。结果表明,中毒、烧结长大、积碳、氧化及固相反应是造成费托合成钴催化剂失活的主要原因。通过净化原料气、调节钴与载体相互作用、调整催化剂配方及工艺条件、控制钴颗粒尺寸及体系中水和H2的分压比等措施可以提高催化剂稳定性和寿命。通过脱蜡、氧化、还原可实现催化剂再生,氧化是再生的关键步骤,要注意氧化过程中升温速率、热量移除等问题;多次的氧化和还原过程可增加再生催化剂中金属钴与还原助剂的均匀性,提高再生催化剂的活性。     

Dynamics of the fischer-tropsch synthesis over a supported cobalt catalyst

Step-change experiments between H₂, CO, and syngas mixtures with time resolution of ca. 0.3 s were undertaken to critically test mechanisms proposed in the literature for the Fischer-Tropsch synthesis. A silica-supported cobalt catalyst was used. Results suggest C₂₊ olefins and branched paraffins form from a carbon deposit on the catalyst surface. Two pathways appear to exist for methane formation. The first of these is from the carbon deposit through direct hydrogenation and through hydrogenolysis of the long-chain materials formed. The second pathway is hydrogenation of strongly adsorbed CO.     

Composition modulation of the fischer-tropsch synthesis over a supported cobalt catalyst

Different cycling strategies are explored to see if carbon chain growth can be enhanced and methane formation suppressed. Of the strategies considered, bang-bang cycling between H₂ and CO feeds substantially increased the consumption of CO and H₂, but the formation of higher hydrocarbons and olefins was reduced. The best strategy for longer chain hydrocarbons suitable for jet or diesel fuels was found to be cycling between syngas mixtures. None of the cycling strategies was able to produce C₈₊ or low-molar mass olefin yields that matched yields found in steady-state operation.     

助剂对活性炭负载钴催化剂氨合成活性的影响

采用四槽高压连续流动反应器研究了添加助剂Ba、K和Sm对活性炭负载钴催化剂氨合成活性的影响,结果发现,添加助剂Ba、K和Sm可以提高催化剂的氨合成活性,其中,Ba的促进效果最好,Ba与Co物质的量比为0.3时,催化活性最高。在Ba-Co/AC催化剂中,助剂Sm的加入降低了催化剂的氨合成活性,而少量K助剂(K与Co物质的量比为0.25～0.5)可以提高其催化性能,在10 MPa、10 000 h^-1和450 ℃条件下,双助剂催化剂的氨合成活性可达120 mmol·(g·h）^-1,进一步增加K的量,其氨合成活性下降。     

Synthesis and catalytic properties of eggshell cobalt catalysts for the Fischer-Tropsch synthesis

CO diffusional restrictions decrease C₅₊ synthesis rates and selectivity within large (1–3 mm) catalyst pellets often required in Fischer-Tropsch (FT) synthesis reactors. Eggshell catalysts, where Co is located preferentially near outer pellet surfaces, reduce the severity of these transport restrictions and lead to higher synthesis rates and C₅₊ selectivity. Maximum C₅₊ selectivities occur on catalysts with intermediate shell thickness, within which transport restrictions limit the removal of reactive olefins but not the arrival of reactants at catalytic sites. A new synthetic technique leads to sharp distributions of active sites near outer pellet surfaces by controlling the rate of imbibition of cobalt nitrate melts. Also, slow reduction of the impregnated salt leads to moderate Co dispersions (0.05–0.10) even at high local Co loadings present within shell regions.     

载体焙烧温度对Co/Al2O3催化剂F-T合成反应催化性能的影响

采用等体积浸渍法,以不同温度焙烧的Al2O3为载体制备Co/Al₂O₃催化剂,通过N₂物理吸附、X射线衍射和程序升温还原等方法对催化剂进行表征,并在固定床反应器中评价催化剂的F-T合成反应性能。结果表明,低温焙烧可获得较大比表面积的Al₂O₃载体,有利于提高活性组分的分散度,但增强了钴与载体之间的相互作用,降低催化剂活性和选择性。高温焙烧的Al2O3载体有利于提高C⁺₅选择性,尤其是柴油组分的选择性。     

Effect of hierarchical meso-macroporous silica supports on Fischer-Tropsch synthesis using cobalt catalyst

Hierarchical meso-macroporous (HS-X) silica with different mesopore diameters synthesized by using rice husk ash as a silica source and chitosan as a natural template were applied for the first time as the cobalt support for Fischer-Tropsch synthesis. Unimodal mesoporous silica (MS-X) supports with equivalent mesopore diameters to HS-X supports have also been prepared for comparison. Effects of diffusion in MS-X and HS-X supports of different particle sizes on the catalytic activity and hydrocarbon selectivity were investigated. The cobalt crystallite sizes were increased with increasing mesopore diameters, whereas the highest amount of H₂ chemisorbed was found for the catalyst with the medium mesopore diameter. The HS-X supports revealed lower surface area and higher macroporosity which led to the formation of larger cobalt crystallite size and less chemisorbed H₂. However, the catalytic activity was much higher for cobalt supported on HS-X silica of both small and large catalyst particle sizes. Moreover, with the large catalyst particle size, the C₅₊ selectivity of cobalt supported on HS-X silica was much higher than that on MS-X silica, indicating the influence of mass transfer of reactants and products in macropores of HS-X supports.     

干燥温度对Co/SiO2费托合成催化剂结构和性能的影响

采用浸渍法制备了钴负载质量分数15％的Co/SiO2催化剂,考察干燥温度对催化剂性能的影响.随着干燥温度升高,催化剂活性先增大后减小,但对产物选择性没有明显影响.BET、SEM、XRD和H2 - TPR测定结果表明,改变干燥温度可以影响钴在催化剂中的分布状态,从而使催化剂结构、晶粒度和还原性能发生相应变化,这些效应的叠...     

载体碱性对Fe基催化剂费-托合成反应的影响

低碳烃类化合物是化学工业中重要的有机原料,通过非石油路线由费-托反应(Fischer-Tropsch)制备低碳烃类具有巨大前景,载体对于费-托合成催化剂的反应产物分布具有重要影响。探究了载体碱性对负载型Fe 基催化剂在费-托合成反应中反应性能的影响。通过浸渍法制备了Fe₂₀/AlPO₄、Fe₂₀/γ-Al₂O₃、Fe₂₀/MgAl₂O₄ 催化剂,考评结果表明,载体碱性越强,碳链增长概率(α值)越大,C₅₊选择性上升,烯烷比(O/P)增加。通过Raman 光谱和TPH 实验对由柠檬酸铁铵为前体煅烧后的催化剂表层碳物种进行分析表明,载体碱性越强,催化剂表面碳石墨化程度越高,吸附碳数量越少。并依托XRD、H₂-TPR、CO₂-TPR 表征信息构建了不同碱性载体负载的Fe 基催化剂的构效关系,表明载体给电子能力的强弱引起催化剂表面碳物质含量和金属载体相互作用的差异,最终导致了催化活性和选择性的不同。     

氧化石墨烯复合金属催化剂催化碳酸二甲酯合成反应性能

针对甲醇气相氧化羰基化直接合成碳酸二甲酯（DMC）反应中催化剂活性低和稳定性差的问题，制备了一系列氧化石墨烯复合金属催化剂，并对其进行活性评价。结果表明：催化剂PdCl₂-CuCl₂-KOAc/AC@GO-HCl表现出最佳的催化活性和稳定性：DMC的空时收率（STY）为800~900 g·(L cat)^-1·h^-1，且反应16 h内活性无明显下降；甲醇选择性保持在95%以上，CO选择性为35%~40%。结合XRD和XPS表征发现，活性物种Cu₂Cl(OH)₃的生成，提高了催化剂催化活性，而CuO和KCl均可导致催化剂的失活。     

Studies of the fischer-tropsch synthesis on a colbalt catalyst. III. mechanistic formulation of the kinetics of selectivity for higher hydrocarbon formation

Mechanistic models are derived to quantify selectivity in the Fischer-Tropsch synthesis. The models are fitted to experimental selectivity data obtained on a cobalt catalyst and are found to give a satisfactory fit. Results show that branching reactions can be explained by assuming a rate limiting 1-2 hydrogen shift. For small molecules the 1-2 shift takes place on one site, whereas larger molecules need an adjacent sit for the shift to take place. The “break” arises from the sum of two Anderson-Schulz-Flory distributions arising on two different locations.     

Microfluidic synthesis of ultrasmall Co nanoparticles over reduced graphene oxide and their catalytic properties

We prepared a one-stage microfluidic-based method for continuous synthesis of cobalt (Co) nanoparticles over reduced graphene oxide (rGO) to produce Co/rGO composites. These were generated by the coreduction of Co²⁺ ions and GO with NaBH₄ which was confined within discrete aqueous plugs segmented by octane as continuous phase. Owing to the excellent transfer properties from recirculation in these plugs, ultrasmall Co nanoparticles were distributed homogeneously on the GO sheets without using any surfactants. As compared to batch methods, the average size of Co nanoparticles and the relative standard deviation decreased from 4.0 ± 1.42 nm and 35.9% to 2.0 ± 0.45 nm and 22.6%, respectively. The as-prepared Co/rGO composites exhibited superior activity towards the catalytic reduction of p-nitrophenol to p-aminophenol with NaBH₄ compared with Co nanoparticles and rGO; this enhanced activity could be attributed to the synergistic effect between Co nanoparticles and rGO.     

合成气费托合成制重质烃Ru-Co/SiC催化剂的制备及性能

费托合成是以合成气生产清洁燃料和其他化学品的重要途径。传统费托合成产物遵循A-S-F分布,只有甲烷和重质烃的选择性没有极限值。因此,费托合成研究以最大程度地合成重质烃,提高合成产物中重质烃的选择性为目标。基于此,首先详细探究了Al₂O₃、SiO₂和SiC载体对费托反应性能的影响。结果表明 Co/SiC催化剂具有最高的CO转化率（83.5%）和C₅₊选择性（80.3%）。与浸渍法相比,原位还原法更为有效地引入Ru到Co/SiC催化剂,将C₅₊选择性提高至90.1%。Ru助剂能在保持较高催化活性不变的前提下,有效提高Co/SiC催化剂C₅₊选择性。催化剂表征（XRD、H₂-TPR、XPS、H₂-化学吸附和TEM）结果表明,Ru能与Co发生相互作用,提高了催化剂的可还原性和活性组分的分散性,进而改善了Co/SiC催化剂重质烃的选择性。     

Fischer-Tropsch synthesis: Support and cobalt cluster size effects on kinetics over Co/Al2O3 and Co/SiO2 catalysts

The influence of support type and cobalt cluster size (i.e., with average diameters falling within the range of 8-40 nm) on the kinetics of Fischer-Tropsch synthesis (FT) were investigated by kinetic tests employing a CSTR and two Co/γ-Al₂O₃ catalysts having different average pore sizes, and two Co/SiO₂ catalysts prepared on the same support but having different loadings. A kinetic model that contains a water effect constant “m” was used to fit the experimental data obtained with all four catalysts. Kinetic parameters suggest that both support type and average Co particle size impact FT behavior. Cobalt cluster size influenced kinetic parameters such as reaction order, rate constant, and the water effect parameter. In the cluster size range studied, decreasing the average Co cluster diameter by about 30% led to an increase in the intrinsic reaction rate constant k, defined on a per g of catalyst basis, by 62-102% for the γ-Al₂O₃ and SiO₂-supported cobalt catalysts. This increase was due to the higher active Co⁰ surface site density as measured by hydrogen chemisorption. Moreover, less inhibition by adsorbed CO and greater H₂ dissociation on catalysts having smaller Co particles was suggested by the higher a and lower b values obtained for the measured reaction orders. Interestingly, irrespective of support type, the catalysts having smaller average Co particles were more sensitive to water. Comparing the catalysts having strong interactions between cobalt and support (Co/Al₂O₃) to the ones with weak interactions (Co/SiO₂), the water effect parameters were found to be positive (indicating a negative influence on CO conversion) and negative (denoting a positive effect on CO conversion), respectively. No clear trend was observed for b values among the different supports, but greater a and a/b values were observed for both Al₂O₃-supported Co catalysts, implying greater inhibition of the FT rate by strongly adsorbed CO on Co/Al₂O₃ relative to Co/SiO₂. For both supports, the order on P_CO was always found to be negative (i.e., suggesting an inhibiting effect) and positive for P_H2 for all four catalysts. The order of the reaction on P_H2 was close to 0.5, suggesting that dissociated H₂ is likely involved in the catalytic cycle. Finally, in the limited range of average pore diameters studied (13.5 and 18.2 nm), the average pore size of the Al₂O₃-supported Co catalysts displayed no observable impact on the reaction rate or water effect, suggesting either that the reaction is kinetically controlled, or that the pore size difference was not significant enough to elicit a measurable response.     

Selective synthesis of alcohols from syngas and hydroformylation of ethylene over supported cluster-derived cobalt catalysts

Hydroformylation of ethylene and CO hydrogenation were studied over cobalt-based catalysts derived from reaction of Co₂(CO)₈ with ZnO, MgO and La₂O₃ supports. At 433 K a similar activity sequence was reached for both reactions: Co/ ZnO > Co/La₂O₃ > Co/MgO. This confirms the deep analogy between hydroformylation and CO hydrogenation into alcohols. In the CO hydrogenation the selectivity towards alcohol mixture (C₁-C₃) was found to be near 100% at 433 K for a conversion of 6% over the Co/ZnO catalyst; this catalyst showed oxo selectivity higher than 98% in the hydroformylation of ethylene. Magnetic experiments showed that no metallic cobalt particles were formed at 433 K. It is suggested that the active site for the step that is common to both reactions is related to the surface homonuclear Co²⁺/[Co(CO)₄]^– ion-pairing species.     

Production of hydrocarbons in Fischer-Tropsch synthesis with Fe-based catalyst: Investigations of primary kerosene yield and carbon mass balance

The Fischer-Tropsch synthesis (FTS) of syngas was carried out using Fe-based catalysts in order to produce hydrocarbons (HCs) equivalent to kerosene, which is used as an alternative aviation fuel. The FTS was conducted in a downdraft continuous-flow-type fixed-bed reactor under a temperature of 533-573 K and a pressure of 3.0 MPa. The effects of reduction gases and time of the Fe-based catalyst, reaction temperature and the chemical species included in the Fe-based catalyst on the FTS were studied by focusing on primary kerosene yield and the carbon mass balance. The carbon mass balances in the study were almost 100%. In C6 + HCs, the selectivity of CO to the C11−C14 HCs equivalent to kerosene was found to be the second highest, the highest being its selectivity to C20 + HCs equivalent to wax. The amount of primary kerosene produced was maximum under the following conditions: the prepared Fe catalyst did not contain other chemical species, the feed ratio of the reduction gases H₂:CO:N₂ was 2:1:3, the catalyst reduction time was 8 h, and the FTS reaction temperature was 553 K.     

Studies on cobalt catalyst supported on silica with different pore size for Fischer–Tropsch synthesis

The adsorption and surface reactions of acetonitrile and acetonitrile-oxygen gas mixture were studied on TiO₂-supported Au catalysts at 300–673 K. FTIR spectra show different kinds of molecularly adsorbed CH₃CN:acetonitrile can be bonded to weak Lewis acid sites (2295 cm⁻¹), to strong Lewis acid sites (2337 cm⁻¹) of titania; it can be coordinated linearly through the lone electron pair of the N atom on Au sites and η² (C,N) CH₃CN species can be formed on Au particles. CH₃CN dissociates on Au sites, the resulting CN_(a) can be oxidized in small extent by lattice oxygen and in a greater extent by gaseous oxygen into NCO surface species. The formation of other products (CH₃NH₂, H₂, CO₂, CH₄, C₂H₄ and CO) was demonstrated and discussed.