共查询到20条相似文献,搜索用时 31 毫秒
1.
The effects of promotion with ruthenium on the structure of cobalt catalysts and their performance in Fischer–Tropsch synthesis were studied using MCM-41 and SBA-15 as catalytic supports. The catalysts were characterized by N2 physisorption, H2-temperature programmed reduction, in situ magnetic measurements, X-ray diffraction and X-ray photoelectron spectroscopy. It was found that monometallic cobalt catalysts supported by smaller pore mesoporous silicas (dp = 3–4 nm) had much lower activity in Fischer–Tropsch synthesis than their larger pore counterparts (dp = 5–6 nm). Promotion with ruthenium of smaller pore cobalt catalysts led to a considerable increase in Fischer–Tropsch reaction rate, while the effect of the promotion with ruthenium was less significant with the catalysts supported by larger pore silicas.Characterizations of smaller pore cobalt catalysts revealed strong impact of ruthenium promotion on the repartition of cobalt between reducible Co3O4 phase and barely reducible amorphous cobalt silicate in the calcined catalyst precursors. Smaller pore monometallic cobalt catalysts showed high fraction of barely reducible cobalt silicate. Promotion with ruthenium led to a significant increase in the fraction of reducible Co3O4 and in decrease in the amount of cobalt silicate. In both calcined monometallic and Ru-promoted cobalt catalysts supported by larger pore silicas, easy reducible Co3O4 was the dominant phase. Promotion with ruthenium of larger pore catalysts had smaller influence on cobalt dispersion, fraction of reducible cobalt phases and thus on catalytic performance. 相似文献
2.
The rate of Fischer–Tropsch synthesis over an industrial well-characterized Co–Ru/γ-Al2O3 catalyst was studied in a laboratory well mixed, continuous flow, slurry reactor under the conditions relevant to industrial operations as follows: temperature of 200–240 °C, pressure of 20–35 bar, H2/CO feed ratio of 1.0–2.5, gas hourly space velocity of 500–1500 N cm3 gcat− 1 h− 1 and conversions of 10–84% of carbon monoxide and 13–89% of hydrogen. The ranges of partial pressures of CO and H2 have been chosen as 5–15 and 10–25 bar respectively. Five kinetic models are considered: one empirical power law model and four variations of the Langmuir–Hinshelwood–Hougen–Watson representation. All models considered incorporate a strong inhibition due to CO adsorption. The data of this study are fitted fairly well by a simple LHHW form − RH2 + CO = apH20.988pCO0.508 / (1 + bpCO0.508)2 in comparison to fits of the same data by several other representative LHHW rate forms proposed in other works. The apparent activation energy was 94–103 kJ/mol. Kinetic parameters are determined using the genetic algorithm approach (GA), followed by the Levenberg–Marquardt (LM) method to make refined optimization, and are validated by means of statistical analysis. Also, the performance of the catalyst for Fischer–Tropsch synthesis and the hydrocarbon product distributions were investigated under different reaction conditions. 相似文献
3.
Anatoly S. Lermontov Jean-Sébastien Girardon Anne Griboval-Constant Stanislas Pietrzyk Andrei Y. Khodakov 《Catalysis Letters》2005,101(1-2):117-126
Chemisorption of propene and propane was studied in a pulse reactor over a series of cobalt silica-supported Fischer–Tropsch catalysts. It was shown that interaction of propene with cobalt metal particles resulted in its rapid autohydrogenation. The reaction consists in a part of the propene being dehydrogenated to surface carbon and CHx chemisorbed species; hydrogen atoms released in the course of propene dehydrogenation are then involved in hydrogenation of remaining propene molecules to propane at 323–423 K or in propene hydrogenolysis to methane and ethane at temperatures higher than 423 K. The catalyst characterization suggests that propene chemisorption over cobalt catalysts is primarily a function of the density of cobalt surface metal sites. A correlation between propene chemisorption and Fischer–Tropsch reaction rate was observed over a series of cobalt silica-supported catalysts. No propane chemisorption was observed at 323–373 K over cobalt silica-supported catalysts. Propane autohydrogenolysis was found to proceed at higher temperatures, with methane being the major product of this reaction over cobalt catalysts. Hydrogen for propane autohydrogenolysis is probably provided by adsorbed CHx species formed via propane dehydrogenation. Propene and propane chemisorption is dramatically reduced upon the catalyst exposure to synthesis gas (H2/CO = 2) at 323–473 K. Our results suggest that cobalt metal particles are probably completely covered by carbon monoxide molecules under the conditions similar to Fischer–Tropsch synthesis and thus, most of cobalt surface sites are not available for propene and propane chemisorption. 相似文献
4.
This paper reports recent research results about the impact of different catalyst bed configurations on Fischer–Tropsch (FT) synthesis product distributions. A powdered CoRe/γ-alumina catalyst with a particle size ranging from 60 to 100 mesh was prepared and tested in a packed bed reactor. The same catalyst was ball milled and coated on a ceramic monolith support structure of channel size about 1 mm. The monolith catalyst module was tested in two different ways, as a whole piece and as well-defined channels. Steady-state reaction conversion was measured at various temperatures under a constant H2/CO feed ratio of 2 and a reactor pressure of 25 bar. Detailed product analysis was performed. Significant formation of wax was evident with the packed particle bed and with the monolith catalyst that was improperly packed. By contrast, wax formation was not detected in the liquid product by confining the reactions inside the monolith channel. This study presents an important finding about the structured catalyst/reactor system, in that the product distribution highly depends on how the structured reactor is set up. Even if a catalyst is tested under identical reaction conditions (T, P, H2/CO ratio), hydrodynamics (or flow conditions) inside a structured channel may have a significant impact on the product distribution. 相似文献
5.
Zhichao Tao Yong Yang Chenghua Zhang Tingzhen Li Jianhua Wang Haijun Wan Hongwei Xiang Yongwang Li 《Catalysis communications》2006,7(12):1061-1066
A series of precipitated Fe/Mn Fischer–Tropsch synthesis (FTS) catalysts incorporated with calcium promoter were prepared by the combination of co-precipitation and spray-drying technology. The catalysts were characterized by using N2 physisorption, CO2 temperature-programmed desorption and Mössbauer spectroscopy methods. FTS performances of the catalysts were tested in a 1 dm3 continuous stirred tank reactor. It is found that calcium promoter has negligible effect on the textural properties, and the addition of calcium promoter can enhance the surface basicity of the catalyst. An appropriate amount of calcium promoter can promote the reduction and carburization of the catalysts during the reduction and Fischer–Tropsch synthesis (FTS) reaction in syngas, but the excessive addition of calcium promoter will decrease the extent of reduction and carburization. The reaction results indicated that the activities of both FTS and water-gas shift (WGS) decrease with the incorporation of calcium promoter. Calcium promoter can inhibit the hydrogenation ability, suppress the formation of methane, and enhance the selectivities to olefin and higher molecular weight products. 相似文献
6.
A microchannel catalytic reactor with improved heat and mass transport has been used for Fischer–Tropsch synthesis. It was demonstrated that this microchannel reactor based process can be carried out at gas hourly space velocity (GHSV) as high as 60,000 h−1 to achieve greater than 60% of single-pass CO conversion while maintaining relatively low methane selectivity (<10%) and high chain growth probability (>0.9). In this study, performance data were obtained over a wide range of pressure (10–35 atm) and hydrogen-to-carbon monoxide ratio (1–2.5). The catalytic materials were characterized using BET, scanning electron microcopy (SEM), transmission electron microcopy (TEM), and H2 chemisorption. A three-dimensional pseudo-homogeneous model was used to simulate temperature profiles in the exothermic reaction system in order to optimize the reactor design. Intraparticle non-isothermal characteristics are also analyzed for the FT synthesis catalyst. 相似文献
7.
30 wt.%Co/SBA-15 catalysts with different ruthenium contents (0.05–0.5 wt.%) were prepared by incipient wetness impregnation and characterized by diffuse reflectance infrared fourier transform spectroscopy, N2 adsorption-desorption, X-ray diffractometry, temperature-programmed reduction and H2 desorption, oxygen titration as well as X-ray photoelectron spectroscopy. The addition of a small amount of Ru promoter to Co/SBA-15 shifted the reduction temperature of both steps (Co3O4 → CoO and CoO → Co0) to lower temperatures and suppressed the formation of Co2+ species. After reduction, ruthenium atoms were encapsulated partially with cobalt cluster. There was no strong electronic interaction between metal cobalt and ruthenium, however, hydrogen spillover from ruthenium to cobalt oxide clusters occurred. With increasing ruthenium content, catalyst reducibility increased and the surface was enriched in cobalt atoms. Moreover, the peak intensities of both the linear and bridge types CO adsorption increased with the increase of ruthenium content, enhancing the catalytic activity on Fischer–Tropsch synthesis. 相似文献
8.
Ali Nakhaei Pour Yahya Zamani Ahmad Tavasoli Seyyed Mehdi Kamali Shahri Sayyed Ali Taheri 《Fuel》2008,87(10-11):2004-2012
The dependencies of hydrocarbon product distributions of iron and physical mixture of iron–zeolite catalyzed Fischer–Tropsch synthesis on reaction conditions include: reaction temperature, reaction pressure, H2/CO feed ratios; space velocity and effect of zeolite presence have been investigated. The concept of two superimposed Anderson–Schulz–Flory distributions has been applied for the representation of the product distribution for both iron and iron–zeolite catalysts. Zeolite presence increased secondary reactions that include cracking of heavier products and light olefins oligomerization. Product distribution of iron–zeolite catalyst was comparable with iron catalyst at high space velocity, because the role of the zeolite on overall reaction declined.The results of the product distribution dependency on the reaction conditions over both iron and iron–zeolite catalysts showed that the average number of carbon decreases with H2/CO ratio increasing and the reaction temperature in product. 相似文献
9.
Carbon nanotubes (CNTs) and the ones grown on MgO and alumina are used as supports for cobalt catalyst in Fischer–Tropsch (FT) synthesis. Carbon nanotubes were synthesized by chemical vapor deposition of methane on 5.0 wt.% iron on MgO or alumina at 950 °C. The carbon nanotubes were characterized by SEM and TEM microscopy and Raman spectroscopy. Cobalt nitrate was impregnated onto the supports by impregnation, and the samples were dried and reduced in-situ at 400 °C for 12 h, and then FT synthesis was carried out in a fixed-bed reactor. The catalysts were characterized by BET surface area measurement, TPR and TPD. The effect of carbon nanotubes as cobalt support on CO conversion, product selectivity, and olefin to paraffin ratio of FT synthesis was investigated and compared with activated carbon as well as Al2O3, as a traditional support. The results revealed that the activity of the Co/CNT catalyst was improved by 22%, compared to the conventional Co/alumina catalysts. Also the cobalt supported on CNTs grown on MgO (Co/CNT–MgO) shows the highest selectivity to C5+ as the most desired FTS products. The C5+ selectivity enhancement was about 37, 34, 17, and 77% as compared to the Co/CNT, Co/alumina, Co/CNTs-alumina, and Co/activated carbon, respectively. Also the olefin/paraffin ratio on the Co/CNTs-MgO catalyst is about 7.7 times higher than the conventional cobalt catalysts. It seems that the degree of reduction of cobalt is higher when supported on CNTs than on alumina. This leads to higher FTS activity. Also, the particle size distribution of the cobalt is affected by the CNT–MgO support leading to higher C5+ selectivity. 相似文献
10.
Tingzhen Li Yong Yang Zhichao Tao Chenghua Zhang Hongwei Xiang Yongwang Li 《Fuel Processing Technology》2009,90(10):1247-1251
A systematic study was undertaken to investigate the effects of the initial oxidation degree of iron on the bulk phase composition and reduction/carburization behaviors of a Fe–Mn–K/SiO2 catalyst prepared from ferrous sulfate. The catalyst samples were characterized by powder X-ray diffraction (XRD), Mössbauer spectroscopy, X-ray photoelectron spectroscopy (XPS) and H2 (or CO) temperature-programmed reduction (TPR). The Fischer–Tropsch synthesis (FTS) performance of the catalysts was studied in a slurry-phase continuously stirred tank reactor (CSTR). The characterization results indicated that the fresh catalysts are mainly composed of α-Fe2O3 and Fe3O4, and the crystallite size of iron oxides is decreased with the increase of the initial oxidation degree of iron. The catalyst with high content of α-Fe2O3 in its as-prepared state has high content of iron carbides after being reduced in syngas. However, the catalyst with high content of Fe3O4 in its as-prepared state cannot be easily carburized in CO and syngas. FTS reaction study indicates that Fe-05 (Fe3+/Fetotal = 1.0) has the highest CO conversion, whereas Fe-03 (Fe3+/Fetotal = 0.55) has the lowest activity. The catalyst with high CO conversion has a high selectivity to gaseous hydrocarbons (C1–C4) and low selectivity to heavy hydrocarbons (C5+). 相似文献
11.
The influence of CO2 on the deactivation of Co/γ-Al2O3 Fischer–Tropsch (FT) catalyst in CO hydrogenation has been investigated. The presence of CO2 in the feed stream reveals a negative effect on catalyst stability and in the formation of heavy hydrocarbons. The CO2 acts as a mild oxidizing agent on cobalt metal during Fischer–Tropsch synthesis. During FT synthesis on Co/γ-Al2O3 of 70 h, the CO conversion and C5+ selectivity in the presence of CO2 decreased more significantly than in the absence of CO2. CO2 is found to be responsible for the partial oxidation of surface cobalt metal at FT synthesis environment with the co-existence of generated water. 相似文献
12.
A series of noble metal (Pt, Ru or Pd) promoted Co/Al2O3 catalysts were prepared by sequential impregnation method. The catalysts were characterized by XRD, TPR, H2-TPD and TPSR techniques, and their catalytic performance in Fischer–Tropsch synthesis was investigated in a fixed-bed reactor. The results of activity measurements show that the addition of small amounts of noble metal greatly improved the activity of the Co/Al2O3 catalyst. TPR experimental results demonstrate that hydrogen spillover from the noble metal to cobalt oxide clusters facilitated the reduction of cobalt oxide and, thus significantly increased the reducibility of Co/Al2O3 catalyst. The presence of noble metal increased the amount of chemisorbed hydrogen and weakened the bond strength of Co–H. TPSR results indicate that CO was adsorbed in a more reactive state on the promoted catalysts. 相似文献
13.
Yong Heon Kim Ki-Won Jun Hyunku Joo Chonghun Han In Kyu Song 《Chemical engineering journal (Lausanne, Switzerland : 1996)》2009,155(1-2):427-432
A simulation study on gas-to-liquid (natural gas to Fischer–Tropsch synthetic fuel) process was carried out in order to find optimum reaction conditions for maximum production of synthetic fuel. Optimum operating condition for GTL (gas-to-liquid) process was determined by changing reaction variable such as temperature. During the simulation, overall synthetic process was assumed to proceed under steady-state conditions. It was also assumed that physical properties of reaction medium were governed by RKS (Redlich–Kwong–Soave) equation. ATR (auto-thermal reforming) in synthesis gas production unit and slurry phase reaction over Co-based catalyst in FTS (Fischer–Tropsch synthesis) unit were considered as reaction models for GTL process. The effect of reaction temperature on CO conversion and C5–C20 hydrocarbon yield in FTS unit was mainly examined. Simulation and experimental results showed that optimum reaction temperature in FTS unit was 255 °C. Simulation results were also compared to experimental results to confirm the reliability of simulation model. Simulation results were reasonably well matched with experimental results. 相似文献
14.
Yu-Ping Li Tie-Jun Wang Chuang-Zhi Wu Xin-Xin Qin Noritatsu Tsubaki 《Catalysis communications》2009,10(14):1868-1874
Microporous HZSM-5 zeolite and mesoporous SiO2 supported Ru–Co catalysts of various Ru adding amounts were prepared and evaluated for Fischer–Tropsch synthesis (FTS) of gasoline-range hydrocarbons (C5–C12). The tailor-made Ru–Co/SiO2/HZSM-5 catalysts possessed both micro- and mesopores, which accelerated hydrocracking/hydroisomerization of long-chain products and provided quick mass transfer channels respectively during FTS. In the same time, Ru increased Co reduction degree by hydrogen spillover, thus CO conversion of 62.8% and gasoline-range hydrocarbon selectivity of 47%, including more than 14% isoparaffins, were achieved simultaneously when Ru content was optimized at 1 wt% in Ru–Co/SiO2/HZSM-5 catalyst. 相似文献
15.
It has been suggested that the behavior of Group VIII metal catalysts supported on transition metal oxides can be significantly affected by pretreatment conditions due to strong metal–oxide interactions (SMOI). However, the origins for the SMOI effect are still in debate. In this research, SMOI of Rh and vanadium oxide (as a promoter) supported on SiO2 were studied at the site level for the first time, which provides an insight into the modification of surface properties after high temperature reduction. H2 chemisorption, Fischer–Tropsch synthesis (FTS), and SSITKA (steady-state isotopic transient kinetic analysis) were used to probe the SMOI effects. The catalytic properties of the catalysts for CO hydrogenation were investigated using a differential fixed bed reactor at 230 °C and 1.8 atm, while for SSITKA, a reaction temperature of 280 °C and an excess of H2 was used to maximize methane production. The addition of V to Rh/SiO2 suppresses H2 chemisorption, and high reduction temperature further decreases H2 chemisorption on Rh/V/SiO2 but has little effect on Rh/SiO2. As reduction temperature increases, the activity for CO hydrogenation on Rh/SiO2 remains essentially unchanged, but the activity of Rh/V/SiO2 decreases significantly. SSITKA shows that the concentration of surface reaction intermediates decreases on Rh/V/SiO2 as the reduction temperature increases, but the activities of the reaction sites increase. The results suggest that Rh being covered by VOx species is probably the main reason for the decreased overall activity induced by high reduction temperature, but more active sites appear to be formed probably at the Rh–VOx interface. 相似文献
16.
The effects of the addition of Ag, Au, or Rh to a 15 wt% Co/SiO2 catalyst on the Fischer–Tropsch (FT) synthesis were studied. Both Au and Rh showed a promoting effect on the FT activity, whereas the addition of Ag decreased the activity. The addition of a small amount of Rh (0.1–0.5 wt%) increased the CO conversion by 50% without affecting the selectivity. It was found that Rh catalyzed the reduction of cobalt oxides, but it did not change the number of surface cobalt atoms. It is proposed that the higher activity of Rh-promoted catalysts is due to the hydrogen spillover from Rh to Co during FT synthesis. 相似文献
17.
Sang-Hoon Song Sang-Bong Lee Jong Wook Bae P.S. Sai Prasad Ki-Won Jun 《Catalysis communications》2008,9(13):2282-2286
γ-Al2O3 and SiO2 supported Co catalysts, with varying amounts of Ru, were prepared and evaluated for Fischer–Tropsch synthesis (FTS). The composition of Ru for optimum activity was found to be support-dependent. The reducible Co3O4 was high in the region of 0–1.64 wt.% of Ru in Co/SiO2 catalysts. Co/γ-Al2O3 displayed a maximum for reducible Co species at 0.42 wt.% Ru. Segregation of Ru occurred beyond this composition decreasing the extent of reduction. Co/γ-Al2O3 catalysts showed lower activity and olefin selectivity, in spite of higher Co dispersion, than Co/SiO2 catalysts. The catalytic performance depends on the amount of reducible Co species, which again depends upon the optimum content of Ru. 相似文献
18.
Wei Chu Petr A. Chernavskii Lon Gengembre Galina A. Pankina Pascal Fongarland Andrei Y. Khodakov 《Journal of Catalysis》2007,252(2):215-230
The structure of cobalt species at different stages of the genesis of monometallic and Pt-promoted cobalt alumina-supported Fischer–Tropsch catalysts was studied using X-ray diffraction, UV–visible spectroscopy, in situ X-ray absorption, in situ magnetic method, X-ray photoelectron spectroscopy, and DSC–TGA thermal analysis. The catalysts were prepared by incipient wetness impregnation using solutions of cobalt nitrate and dihydrogen hexachloroplatinate. Both variation of catalyst calcination temperature between 473 and 773 K and promotion with 0.1 wt% of Pt had no significant affect on the size of supported Co3O4 crystallites. The size of cobalt oxide particles in the calcined catalysts seems to be influenced primarily by the pore diameter of the support. Cobalt reducibility was relatively low in monometallic cobalt alumina-supported catalysts and decreased as a function of catalyst calcination temperature. The effect was probably due to the formation of mixed surface compounds between Co3O4 and Al2O3 at higher calcination temperatures, which hinder cobalt reduction. Promotion with platinum spectacularly increased the rate of cobalt reduction; the promotion seemed to reduce the activation energy of the formation of cobalt metallic phases. Analysis of the magnetization data suggests that the presence of Pt led to the reduction of smaller cobalt oxide particles, which could not be reduced at the same conditions in the cobalt monometallic catalysts. Promotion of cobalt alumina-supported catalysts with small amounts of Pt resulted in a significant increase in Fischer–Tropsch cobalt time yield. The efficient control of cobalt reducibility through catalyst calcination and promotion seems to be one of the key issues in the design of efficient cobalt alumina-supported Fischer–Tropsch catalysts. 相似文献
19.
Haojian Zhang Hongfang Ma Haitao Zhang Weiyong Ying Dingye Fang 《Catalysis Letters》2012,142(1):131-137
Abstract
The effects of Zr and K promoters on the structure, adsorption, reduction, carburization and catalytic behavior of precipitated iron-based Fischer–Tropsch synthesis (FTS) catalysts were investigated. The catalysts were characterized by N2 physisorption, temperature-programmed reduction/desorption (TPR/TPD) and M?ssbauer effect spectroscopy (MES) techniques. As revealed by N2 physisorption, Zr and/or K promoted catalysts showed lower surface area than Fe/SiO2 catalyst. Zr promoter inhibited the reduction and carburization because of the interaction between Fe and Zr in Fe–Zr/SiO2 catalysts. K promoter enhanced the reduction in CO and apparently facilitated the CO adsorption, thus promoted the carburization, but it retarded the reduction in H2 and severely suppressed the H2 adsorption. Compared with the singly promoted catalysts, the doubly promoted catalyst had the highest FTS activity. In addition, both Zr and K promoters suppressed the formation of methane and shifted the production distribution to heavy hydrocarbons. 相似文献20.
Suk-Hwan Kang Jae-Hong Ryu Jin-Ho Kim P. S. Sai Prasad Jong Wook Bae Joo-Young Cheon Ki-Won Jun 《Catalysis Letters》2011,141(10):1464-1471