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1.
Selective synthesis of gasoline-range hydrocarbons (C5-C12) was investigated in a fixed-bed micro reactor using two series of CO2-containing syngas with various mole CO2/(CO + CO2) and H2/(CO + CO2) ratios, where Fischer-Tropsch synthesis(FTS) and in situ hydrocracking/hydroisomerization were performed over bifunctional Co/SiO2/HZSM-5 catalyst. CO2 was converted at 0.15-0.55 of CO2/(CO + CO2) ratio under H2-rich condition (H2/(CO + CO2) = 2.0), highest conversion of 20.3% at 0.42. Further increasing CO2 content decreased CO2 conversion and quite amount of CO2 acted as diluting component. For the syngas with low H2 content or H2/(CO + CO2) ratio(< 1.85, H2/CO = 2.0), the competitive adsorption of CO, H2 and CO2 resulted in low CO, CO2 and total carbon conversion, which was 57.9%, 12.7% and 31.4% respectively at 0.74 of H2/(CO + CO2) ratio(H2/CO/CO2/N2 = 40.8/20.4/34.8/4). FTS results indicated that high H2 content and proper H2/(CO + CO2) ratio were favorable for the conversion of CO2-containing syngas. More than 45% selectivity to gasoline-range hydrocarbons including isoparaffins was obtained under the two series of syngas. It was also tested that the catalytic activity of Co/SiO2/HZSM-5 kept stable under CO2-containing syngas(< 7.5%). And the quick catalytic deactivation under high CO2 containing syngas(H2/CO/CO2/N2 = 45.3/23.2/27.1/3.06) was due to carbon deposition and pore blockage by heavy hydrocarbon, tested by thermal gravimetry, N2 physisorption and scanning electron microscopy(SEM).  相似文献   

2.
3.
Nowadays, the syngas which is obtained from the reforming of coal, biomass or natural gas contain significantly amounts of CO2 that cannot be separated and consequently, it can take part into the Fischer–Tropsch (FTS) catalytic activity. Therefore, the presence of CO2 in the syngas flow should be taken into account. In the present study, the FTS CO hydrogenation process was compared to that of CO2 on a carbon nanofibers supported Co catalyst. The influence of CO2 content in the feed stream (H2/CO/CO2 ratio) on the reaction performance in terms of conversion and selectivity to the different products was described. Both the support and the prepared catalyst were characterized by nitrogen adsorption–desorption, temperature-programmed reduction (TPR) and X-ray diffraction (XRD). Results showed that CO hydrogenation was controlled by a Fischer–Tropsch regime, whereas CO2 hydrogenation was controlled by a methanation process. When feed was composed of CO and CO2 mixtures, the catalytic activity decreased with respect to that obtained with a CO2-free feed stream. Moreover, the presence of CO2 in feed stream favored the formation of lighter hydrocarbons and could block the production of further CO2 via Water-Gas-Shift (WGS) reaction.  相似文献   

4.
In this work, 3% Ru-Al2O3 and 2% Rh-CeO2 catalysts were synthesized and tested for CH4-CO2 reforming activity using either CO2-rich or CO2-lean model biogas feed. Low carbon deposition was observed on both catalysts, which negligibly influenced catalytic activity. Catalyst deactivation during temperature programmed reaction was observed only with Ru-Al2O3, which was caused by metallic cluster sintering. Both catalysts exhibited good stability during the 70 h exposure to undiluted equimolar CH4/CO2 gas stream at 750 °C. By varying residence time in the reactor during CH4-CO2 reforming, very similar quantities of H2 were consumed for water formation. Reverse water-gas shift (RWGS) reaction occurred to a very similar extent either with low or high WHSV values over both catalysts, revealing that product gas mixture contained near RWGS equilibrium composition, confirming the dominance of WGS reaction and showing that shortening the contact time would actually decrease the H2/CO ratio in the syngas produced by CH4-CO2 reforming, as long as RWGS is quasi equilibrated. H2/CO molar ratio in the produced syngas can be increased either by operating at higher temperatures, or by using a feed stream with CH4/CO2 ratio well above 1.  相似文献   

5.
Activation with three different gases (H2, CO and synthesis gas) over an Fe100/K1.4/Si4.6/Cu2.0 catalyst was conducted to investigate the effects of pretreatment gas on Fischer-Tropsch Synthesis (FTS) activity and selectivity. Catalyst slurry was withdrawn from the reactor at increasing time intervals of FTS for Mössbauer spectroscopic analysis. Activation with CO produced the highest syngas conversion while H2 generated the lowest; syngas activation produced a slightly lower conversion than CO activation. CO activation transformed the majority of the iron into χ-Fe5C2 and Magnetite with only 12% -Fe2.2C being detected. Unlike the CO activated catalyst, the syngas activated iron catalyst resulted in a lower amount of χ-Fe5C2 than -Fe2.2C. The initial high (64%) content of -Fe2.2C decreased gradually to below 30% while CO conversion decreased from 83% to 55%. During this period, χ-Fe5C2 increased from initial 10% to 33%. Magnetite changed little during the process while the form of carbides interchanged. Hydrogen activation yielded a low CO conversion of 50% and only 8% χ-Fe5C2 and 16% -Fe2.2C was formed while Magnetite was as high as 75% after the FTS reaction rate became constant. Although activation gas type had a significant effect on syngas conversion, hydrogen, syngas and CO activations produced similar H2 to CO usage ratio, hydrocarbon product distribution, olefin fraction, alpha value and CO2 selectivity.  相似文献   

6.
在浆态床反应器中详细考察了合成气还原空速对微球状工业铁基催化剂还原和反应后的物相以及F-T合成反应性能的影响. 研究结果表明:空速能够影响铁基催化剂还原反应进程,催化剂在较高的空速下易被还原,还原后催化剂的比表面积降低,平均孔径增大. 在较低空速下还原时,还原形成的高的CO2分压对铁物相有一定的氧化作用,使得还原态催化剂中的Fe3+(spm)含量增大. 还原空速对F-T合成烃产物分布影响不明显,但对催化剂的反应活性和运行稳定性影响较大,较低和较高空速还原后的催化剂失活速率均较高,适宜的还原空速为1.0~2.0 L&#8226;(g cat)-1&#8226;h-1.  相似文献   

7.
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.  相似文献   

8.
The production of liquid hydrocarbons based on CO2 and renewable H2 is a multi‐step process consisting of water electrolysis, reverse water‐gas shift, and Fischer‐Tropsch synthesis (FTS). The syngas will then also contain CO2 and probably sometimes H2O, too. Therefore, the kinetics of FTS on a commercial cobalt catalyst was studied with syngas containing CO, CO2, H2, and H2O. The intrinsic kinetic parameters as well as the influence of pore diffusion (technical particles) were determined. CO2 and H2O showed only negligible or minor influence on the reaction rate. The intrinsic kinetic parameters of the rate of CO consumption were evaluated using a Langmuir‐Hinshelwood (LH) approach. The effectiveness factor describing diffusion limitations was calculated by two different Thiele moduli. The first one was derived by a simplified pseudo first‐order approach, the second one by the LH approach. Only the latter, more complex model is in good agreement with the experimental results.  相似文献   

9.
《Catalysis communications》2007,8(10):1538-1545
Two model spherical iron catalysts (100Fe/0Al2O3 and 100Fe/15Al2O3) with free Cu and K promoters were prepared by the combination of co-precipitation and spray drying method for the application of slurry Fischer–Tropsch synthesis (FTS). The effect of Fe–Al2O3 interaction on the reduction/carburization behavior in H2/CO/syngas, surface basicity and the change of phase structure were comparatively studied by means of H2 or CO temperature-programmed reduction (TPR), CO2 temperature-programmed desorption (TPD) and Mössbauer effect spectroscopy (MES). The results showed that the catalyst incorporated with Al2O3 exhibits a strong Fe–Al2O3 interaction, which obviously weakens the surface basicity, stabilizes the FeO phase and inhibits the reduction of iron catalyst in H2 or syngas. Furthermore, Fe–Al2O3 interaction also restrains the carburization of iron catalyst in CO or syngas. In slurry FTS process, it was found that the strong Fe–Al2O3 interaction decreases the FTS activity and suppresses the water gas shift (WGS) reaction, but can stabilize the active sites of iron catalyst and improve its run stability. Due to the strong Fe–Al2O3 interaction, the weak surface basicity on the catalyst incorporated with Al2O3 greatly decreases the selectivity of heavy hydrocarbon products.  相似文献   

10.
Fischer-Tropsch synthesis has been experiencing a strong revival in recent years, due to the resource utilization considerations and environmental concerns. Cobalt supported catalysts represent the optimal choice for the synthesis of long-chained hydrocarbons from syngas with high H2/CO ratio. This paper reviews the state of the art related to the influence of cobalt particle size and cobalt phase composition, catalyst support and support texture, and promotion with noble metals on Fischer-Tropsch reaction rates, hydrocarbon selectivity and catalyst stability. Possible mechanisms of catalyst deactivation and modification of cobalt active sites during the reaction are also discussed. Several requirements to the design of cobalt Fischer-Tropsch catalysts have been specified.  相似文献   

11.
Effects of CO2 on low-temperature Fischer–Tropsch synthesis were investigated with four different cobalt catalysts in an experimental study. CO2 was found to behave as an inert gas component with three catalysts, however, a negative effect on Fischer–Tropsch reaction rate and catalyst deactivation was observed in one case (Co-La-Ru-SiO2). CO2 effects in a large-scale FTS slurry reactor were simulated by means of a mathematical reactor model using the kinetic information gained in the experiments. The reactor volume required for achieving a desired CO conversion must be higher if the syngas contains CO2, more strongly in cases where the catalyst exhibits a deactivation behavior in the presence of CO2. These model calculations can contribute to process optimization with respect to CO2 removal before synthesis.  相似文献   

12.
The effects of manganese promoter on the reduction–carburization behavior, surface basicity, bulk phase structure and their correlation with Fischer-Tropsch synthesis (FTS) performances have been emphatically studied over a series of spray-dried Fe–Mn–K catalysts with a wide range of Mn incorporation amount. The catalysts were characterized by means of H2 and CO temperature-programmed reduction (TPR), CO2 temperature-programmed desorption (TPD), Mössbauer spectroscopy etc.. The results indicated that small amount of Mn promoter can promote the reduction of the catalyst in H2. However, FeO phase formed during reduction is stabilized by MnO phase with the further increase of Mn content, making FeO phase difficult to be reduced in H2. The addition of Mn promoter can stabilize the Fe2+ and Fe3+ ions, and suppresses the reduction and carburization of the catalyst in syngas and CO. Mn promoter can also enhance the amount of the basic sites and weaken the strength of the basic sites, which possibly come from the reason that the Mn–K interaction is strengthened with the addition of Mn promoter. The change of surface basicity can modify the selectivity of hydrocarbons and olefins, and the change of bulk structure phase derived from the addition of Mn promoter will affect the catalyst activity and run stability. The synergetic effects of the two main factors result in an optimized amount of Mn promoter for the highest catalyst activity and heavy hydrocarbon selectivity in slurry FTS reaction of Fe–Mn–K catalysts.  相似文献   

13.
Carbon-coated Ni/SiO2 prepared by dry reforming of CH4 with CO2 was applied for the preparation of the cobalt-based Fischer-Tropsch synthesis (FTS) catalyst with 20 wt%Co to elucidate the metal-support interaction to FTS activity after carbon depositions on the Ni/SiO2. The deposited carbons on the reforming catalyst of Ni/SiO2, which were mainly in the form of filamentous or encapsulated carbons, largely increased CO conversion compared with the fresh Ni/SiO2 without a significant variation of hydrocarbon distributions. The deposited carbons on the Ni/SiO2 play an important role in increasing the reducibility of cobalt oxides due to a mitigated metal-support interaction. The enhanced catalytic activity during FTS reaction is mainly attributed to the proper modification of the Ni/SiO2 surfaces with encapsulated carbons on the exposed nickel surfaces, which largely alters the reducibility of cobalt oxides by reducing the interaction of cobalt particles with the carbon-coated Ni/SiO2 surfaces.  相似文献   

14.
By simultaneous reactions of methane with CO2 and O2 over NiO-CaO catalyst under certain reaction conditions, it is possible to convert methane into syngas with low H2/CO ratio (1 2/CO <2) at above 95% conversion, with 100% CO selectivity and above 90% H2 selectivity and also with very high CO productivity without catalyst deactivation due to coking for a long period, in a most energy efficient and safe manner, requiring little or no external energy.  相似文献   

15.
Accelerated deactivation of 15 wt.% Co/Al2O3 catalyst in Fischer–Tropsch synthesis (FTS) in a single-bed and a dual-bed reactor is reported. Water was found to have a remarkable effect on the deactivation of Co/Al2O3 catalyst during FTS. Synthesis at higher temperatures and lower space velocities resulted in higher values of PH2O/(PCO + PH2) and PH2O/PCO and higher catalyst deactivation rates. Water-induced back-oxidation of cobalt, cobalt–alumina interactions, irreducible cobalt aluminates formation and refractory coke formation are the main sources of deactivation. When the water to carbon monoxide plus hydrogen ratio PH2O/(PCO + PH2) is greater than about 0.55 or water to carbon monoxide ratio PH2O/PCO is greater than about 1.5, it is not uncommon to find rapid catalyst deactivation. Separation of water and heavy hydrocarbons between the two catalytic beds of the dual-bed reactor, resulted in 62% lower catalyst deactivation rate than that of the single-bed reactor. The amount of refractory coke formation on the catalysts of the dual-bed reactor is 34% lower than that of the single-bed reactor. It was revealed that activity recovery of the used catalysts of the dual-bed is higher than that of the single-bed reactor.  相似文献   

16.
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.  相似文献   

17.
The effect of the support nature on the performance of Pd catalysts during partial oxidation of ethanol was studied. H2, CO2 and acetaldehyde formation was favored on Pd/CeO2, whereas CO production was facilitated over Pd/Y2O3 catalyst. According to the reaction mechanism, determined by DRIFTS analyses, some reaction pathways are favored depending on the support nature, which can explain the differences observed on products distribution. On Pd/Y2O3 catalyst, the production of acetate species was promoted, which explain the higher CO formation, since acetate species can be decomposed to CH4 and CO at high temperatures. On Pd/CeO2 catalyst, the acetaldehyde preferentially desorbs and/or decomposes to H2, CH4 and CO. The CO formed is further oxidized to CO2, which seems to be promoted on Pd/CeO2 catalyst.  相似文献   

18.
Temperature-programmed methanations of CO in both He-diluted and reformate-simulated CO–CO2–H2 mixtures over a commercially available 0.5% Ru/Al2O3 catalyst have revealed that CO methanation always occurred earlier than that of CO2 at lower temperatures and the temperature where CO2 started methanating and the corresponding remaining CO decreased with decreasing initial CO content in the feed. This, while confirming the prior methanation of CO over CO2, indicates that the fully selective CO methanation is possible. Thus, a novel method called thermally differential methanation was proposed and a totally 820 h long term, simplified thermally differential methanation was conducted to verify the effectiveness of the method on realizing simultaneously the full selectivity and a satisfactorily deep removal of CO from H2-rich reformates for PEFC application.  相似文献   

19.
《Fuel》2007,86(7-8):921-928
The effects of manganese on the textural properties, bulk and surface phase compositions, reduction/carburization behaviors and surface basicity of an Fe–Mn–K/SiO2 catalyst prepared from ferrous sulfate were investigated by N2 physisorption, Mössbauer spectroscopy, X-ray photoelectron spectroscopy (XPS), H2 (or CO) temperature-programmed reduction (TPR) and CO2 temperature-programmed desorption (TPD). The Fischer–Tropsch synthesis (FTS) performance of the catalysts with different contents of manganese was studied in a slurry-phase continuously stirred tank reactor. The characterization results suggested that the added manganese suppressed the crystal growth of hematite and the catalyst reduction from FeO to Fe in H2. An appropriate amount of manganese improved the FTS activity, increased the surface basicity and enhanced the carburization of the catalyst. However, the excessive addition of manganese retarded the catalyst carburization in CO and syngas due to the high enrichment of manganese on the catalyst surface. At the same time, the addition of manganese suppressed the formation of CH4 and shifted the selectivity to heavy hydrocarbons (C12+).  相似文献   

20.
In this research, Ni/SiO2 catalyst was modified with different amount of Gd2O3 and characterized with temperature-programmed desorption of CO2 (CO2-TPD) and NH3 (NH3-TPD), temperature-programmed reduction with H2 (H2-TPR) and X-ray diffraction (XRD). It was found that Gd2O3-modified Ni/SiO2 catalysts possessed higher CO2 adsorption and activation ability due to the formation of surface carbonate species. H2-TPR and XRD characterizations found that the strong interaction among nickel, Gd2O3 and SiO2 took place, which improved the dispersion of Ni. Gd2O3-modified Ni/SiO2 catalysts exhibited higher activity and stability for the combined oxy-CO2 reforming of methane in fluidized-bed reactor. The H2/CO ratio in produced syngas could be controlled via controlling reaction temperature and CO2/O2 ratio in feed.  相似文献   

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