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1.
Activated carbon‐supported Mo‐Co‐K sulfide catalysts, prepared by stepwise impregnation, were used in the synthesis of higher alcohols via CO2 hydrogenation. The catalysts with varying Mo contents and defined K/Mo and Co/Mo molar ratios exhibited relatively high CO2 conversions and high selectivity to total alcohols and C2+ alcohols. Moreover, the influence of calcination conditions on the sulfidation states and catalytic performance was studied. The surface sulfur runoff of the supported catalysts can be effectively suppressed by online calcination. As a result, the selectivity to total alcohols and C2+ alcohols can be improved.  相似文献   

2.
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   

3.
For hydrogen generation from alkaline sodium borohydride (NaBH4) solution, Co–Fe–B catalysts with different Co/(Co + Fe) molar ratios (χCo) were prepared by the chemical reduction of CoCl2 and FeCl3 ethanol solution with KBH4 solution. The X‐ray diffraction (XRD) and scanning electron microscopy (SEM) analyses revealed that the as‐prepared Co–Fe–B catalysts were in amorphous form and ultrafine. The hydrogen generation measurements showed that as‐prepared Co–B and Co–Fe–B catalysts exhibited excellent catalytic activity. Co–Fe–B with the Co/(Co + Fe) molar ratio (χCo) of 0.85 was the best. Its maximum hydrogen generation rate at 298 K was 4,310 mL min–1 g–1, while the Co–B was 2,773 mL min–1 g–1. The enhanced activity could be attributed to large active surface area, electron transfer from B and Fe to active Co sites, and improvement in the dispersion of Co–B with Fe2O3. The activation energy of Co–Fe–B catalyst with the molar ratio χCo = 0.85 was decreased to 29.09 kJ mol–1 as compared to 30.85 kJ mol–1 obtained with Co–B.  相似文献   

4.
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   

5.
Results of the characterization of six Co-based Fischer–Tropsch (FT) catalysts, with 15% Co loading and supported on SiO2 and Al2O3, are presented. Room temperature X-ray diffraction (XRD), temperature and magnetic field (H) variation of the magnetization (M), and low-temperature (5 K) electron magnetic resonance (EMR) are used for determining the electronic states (Co0, CoO, Co3O4, Co2+) of cobalt. Performance of these catalysts for FT synthesis is tested at reaction temperature of 240 °C and pressure of 20 bars. Under these conditions, 15% Co/SiO2 catalysts yield higher CO and syngas conversions with higher methane selectivity than 15% Co/Al2O3 catalysts. Conversely the Al2O3 supported catalysts gave much higher selectivity towards olefins than Co/SiO2. These results yield the correlation that the presence of Co3O4 yield higher methane selectivity whereas the presence of Co2+ species yields lower methane selectivity but higher olefin selectivity. The activities and selectivities are found to be stable for 55 h on-stream.  相似文献   

6.
This research is aimed to improve the activity and stability of ternary alloy Pt–Ru–Ni/C catalyst. A novel anodic catalyst for direct methanol fuel cell (DMFC), carbon supported Pt–Ru–Ni–P nanoparticles, has been prepared by chemical reduction method by using NaH2PO2 as a reducing agent. One glassy carbon disc working electrode is used to test the catalytic performances of the homemade catalysts by cyclic voltammetric (CV), chronoamperometric (CA) and amperometric it measurements in a solution of 0.5 mol L–1 H2SO4 and 0.5 mol L–1 CH3OH. The compositions, particle sizes and morphology of home‐made catalysts are evaluated by means of energy dispersive analysis of X‐ray (EDAX), X‐ray diffraction (XRD) and transmission electron micrographs (TEM), respectively. TEM images show that Pt–Ru–Ni–P nanoparticles have an even size distribution with an average diameter of less than 2 nm. The results of CV, CA and it curves indicate that the Pt–Ru–Ni–P/C catalyst shows significantly higher activity and stability for methanol electrooxidation due to the presence of non‐metal phosphorus in comparison to Pt–Ru–Ni/C one. All experimental results indicate that the addition of non‐metallic phosphorus into the Pt–Ru–Ni/C catalyst has definite value of research and practical application for enhancing the performance of DMFC.  相似文献   

7.
Junhua Li  Yao Xu  Dong Wu  Yuhan Sun   《Catalysis Today》2009,148(1-2):148
High dispersion Co3O4 nano-particles supported on hollow mesoporous silica spheres (HMSS) with bimodal pore distribution were prepared by “two-solvent” technique. As-synthesized catalysts were characterized by XRD, N2 adsorption–desorption, XPS, SEM, TEM, and H2-TPR. The results showed that Co3O4 nano-particles were present inside the pore system of HMSS and the particles sizes increased with the increasing loaded cobalt content. The catalysts show good performance and high selectivity of C5–C18 hydrocarbon in F–T synthesis, which should attribute to the unique bimodal pore distribution facilitating reactants to access the active sites and to transport higher hydrocarbon products.  相似文献   

8.
G. Kaur  S. Basu 《Fuel Cells》2014,14(6):1006-1013
Electro‐catalytic activity of Cu–Co/CeO2–YSZ anodes towards oxidation of H2 and n‐C4H10 fuels and carbon depositions are investigated using different Cu–Co loadings. Cu–Co/CeO2–YSZ anode based SOFCs with YSZ as electrolyte and LSM/YSZ as cathode were prepared by tape casting and wet impregnation methods and performance was analyzed using IV characteristics and impedance spectroscopy. The Cu–Co/CeO2–YSZ anodes with Cu–Co loading of 10, 15, and 25 wt.% produced power density of 60, 197, and 400 mW cm–2 in H2 and 190, 225, and 275 mW cm–2 in n‐C4H10 at 800 °C. The power density is increased with the increase in Cu–Co loading in Cu–Co/CeO2–YSZ anodes. The electrochemical impedance spectra shows less ohmic and polarization resistance for 25 wt.% Cu–Co loading in comparison to 10 and 15 wt.% Cu–Co. Scanning electron microscopy and high resolution transmission electron microscopy shows that the carbon fibers formed are hollow in nature with 70 nm size, whereas, thermal gravimetric analysis and X‐ray diffraction points out that they are amorphous in nature. The performance degradation of Cu–Co/CeO2–YSZ anodes in n‐C4H10 in 16 h is attributed to increasing amount of carbon deposition with time, which is contrary to our earlier observation in Cu‐Fe/CeO2–YSZ anode.  相似文献   

9.
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   

10.
The effect of the ruthenium promotion of Fischer–Tropsch (FT) cobalt–alumina catalysts on the temperature of catalyst activation reduction and catalytic properties in the FT process is studied. The addition of 0.2–1 wt % of ruthenium reduces the temperature of reduction activation from 500 to 330–350°C while preserving the catalytic activity and selectivity toward C5+ products in FT synthesis. FT ruthenium-promoted Co–Al catalysts are more selective toward higher hydrocarbons; the experimental value of parameter αASF of the distribution of paraffinic products for ruthenium-promoted catalysts is 0.93–0.94, allowing us to estimate the selectivity toward C20+ synthetic waxes to be 48 wt %, and the selectivity toward C35+ waxes to be 23 wt %. Ruthenium-promoted catalysts also exhibit high selectivity toward olefins.  相似文献   

11.
The effect of the porosity of Ziegler–Natta catalyst particles on early fragmentation, nascent polymer morphology, and activity were studied. The bulk polymerization of propylene was carried out with three different heterogeneous Ziegler–Natta catalysts under industrial conditions at low temperatures, that is, with a novel self‐supported catalyst (A), a SiO2‐supported catalyst (B), and a MgCl2‐supported catalyst (C), with triethyl aluminum as a cocatalyst and dicyclopentyl dimethoxy silane as an external donor. The compact catalyst A exhibited no measurable porosity and a very low surface area (<5 m2/g) by Brunauer–Emmet–Teller analysis, whereas catalysts B and C showed surface areas of 63 and 250 m2/g, respectively. The surface and cross‐sectional morphologies of the resulting polymer particles at different stages of particle growth were analyzed by scanning electron microscopy and transmission electron microscopy. The compact catalyst A showed homogeneous and instantaneous fragmentation already in the very early stages of polymerization, which is typically observed for porous MgCl2‐supported Ziegler–Natta catalysts. Moreover, the compact catalyst particles gave rise to almost perfectly spherical polymer particles with a smooth surface. In contrast, the silica‐supported catalyst B gave rise to particles having a cauliflower morphology, and the second reference catalyst C produced fairly spherical polymer particles with a rough surface. All of the three catalysts exhibited similar activities of 450 g of polypropylene/g of catalyst after 30 min of polymerization, and most interestingly, the comparative kinetic data presented indicated that the reaction rates were not influenced by the porosity of the catalyst. © 2008 Wiley Periodicals, Inc. J Appl Polym Sci, 2008.  相似文献   

12.
Cobalt catalysts supported on silica aerogel have been prepared using sol–gel chemistry followed by drying under supercritical ethanol conditions. Three different loadings of cobalt were synthesized: 2, 6, and 10% by weight. Transmission electron micrographs indicate that the metallic cobalt exists as discrete particles 50–70 nm in diameter for the 2 and 6% loadings. The 10% catalyst shows long needles of cobalt. BET and BJH measurements indicate that the catalysts retain the silica aerogel properties of high surface area (∼800 m2/g), large pore volume (∼5 cm3/g), and an average pore diameter in the mesoporous regime (∼25 nm). The catalysts were evaluated for Fischer–Tropsch activity in a laboratory-scale packed bed reactor. All three catalysts were active with the 10% Co catalyst achieving more than 20% CO conversion which corresponds to a rate of 1.53 g CO per g-cat per hour. The catalysts were selective for the C10+ hydrocarbons with more than 50% of the carbon contained within this fraction. A significant portion of the C9–C15 hydrocarbon product was observed as 1-olefins which reflects the enhanced mass transport within the very porous aerogel support.  相似文献   

13.
Platelet and fishbone carbon nanofibers (CNFs) have been used as supports for cobalt Fischer–Tropsch catalysts. The activity and selectivity of the CNF supported catalysts have been studied at 483 K, 20 bar, and H2/CO = 2.1, and compared with corresponding activity and selectivity for α-Al2O3 and γ-Al2O3 supported cobalt catalysts. The platelet CNF supported catalyst has demonstrated high activity and high selectivity to C5+ hydrocarbons, with activity comparable with Co/γ-Al2O3 and selectivity comparable with Co/α-Al2O3.  相似文献   

14.
CaO–La2O3–MgO and BaO–La2O3–MgO catalysts with different compositions have been studied for their bulk and surface properties (viz. crystal phases, surface area, acidity/acid strength distribution, basicity/base strength distribution, etc.) and catalytic activity/selectivity in the oxidative coupling of methane (OCM) at different processing conditions (reaction temperature, 700–850°C; CH4/O2 ratio in feed, 3·0, 4·0 and 8·0 and GHSV, 102000 and 204000 cm3 g−1 h−1). The surface acidity and strong basicity of La2O3–MgO are found to be increased due to the addition of a third component (CaO or BaO), depending upon its concentration in the catalyst. The addition of CaO or BaO to La2O3–MgO OCM catalyst causes a significant improvement in its performance. Both the CaO- and BaO-containing catalysts show a high activity and selectivity at 800°C, whereas, the activity and selectivity of BaO-containing catalysts at 700°C is lower than that of CaO-containing catalysts. © 1997 SCI.  相似文献   

15.
The performance of Co/Nb2O5 was compared to that of Co/γ-Al2O3 for the Fischer–Tropsch synthesis at 20 bar and over the temperature range of 220–260 °C. The C5+ selectivity of Nb2O5-supported cobalt catalysts was found to be very high, i.e. up to 90 wt% C5+ at 220 °C. The activity per unit weight cobalt was found to be similar for Nb2O5 and γ-Al2O3-supported catalysts at identical reaction temperature. However, due to the low porosity of crystalline Nb2O5, the cobalt loading was limited to 5 wt% and consequently the activity per unit weight of catalyst was lower than of Co/γ-Al2O3 catalysts with higher cobalt loadings. This low activity was largely compensated by increasing the reaction temperature, although the C5+ selectivity decreased upon increasing reaction temperature. Due to the high intrinsic C5+ selectivity, Nb2O5-supported catalysts could be operated up to ~250 °C at a target C5+ selectivity of 80 wt%, whereas γ-Al2O3-supported catalysts called for an operation temperature of ~210 °C. At this target C5+ selectivity, the activity per unit weight of catalyst was found to be identical for 5 wt% Co/Nb2O5 and 25 wt% Co/Al2O3, while the activity per unit weight of cobalt was a factor of four higher for the niobia-supported catalyst.  相似文献   

16.
The Pd/ZrC–C and Pd/ZrO2–C catalysts with zirconium compounds ZrC or ZrO2 and carbon hybrids as novel supports for direct formic acid fuel cell (DFAFC) have been synthesized by microwave‐assisted polyol process. The Pd/ZrC–C and Pd/ZrO2–C catalysts have been characterized by X‐ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS), energy dispersive analysis of X‐ray (EDAX), transmission electron microscopy (TEM), and electrochemical measurements. The physical characteristics present that the zirconium compounds ZrC and ZrO2 may promote the dispersion of Pd nanoparticles. The results of electrochemical tests show that the activity and stability of Pd/ZrC–C and Pd/ZrO2–C catalysts show higher than that of Pd/C catalyst for formic acid electrooxidation due to anti‐corrosion property of zirconium compounds ZrC, ZrO2, and metal–support interaction between Pd nanoparticles and ZrC, ZrO2. The Pd/ZrC–C catalyst displays the best performance among the three catalysts. The peak current density of formic acid electrooxidation on Pd/ZrC–C electrode is nearly 1.63 times of that on Pd/C. The optimal mass ratio of ZrC to XC‐72 carbon is 1:1 in Pd/ZrC–C catalyst with narrower particle size distribution and better dispersion on surface of the mixture support, which exhibits the best activity and stability for formic acid electrooxidation among all the samples.  相似文献   

17.
The synthesis of higher alcohols from syngas has been studied over different types of Cu-based catalysts. In order to provide control over the catalyst composition at the scale of a few nanometers, we have synthesized two sets of Co–Cu nanoparticles with novel structures by wet chemical methods, namely, (a) cobalt core–copper shell (Co@Cu) and (b) cobalt–copper mixed (synthesized by simultaneous reduction of metal precursors) nanoparticles. These catalysts were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and temperature programmed reduction (TPR). The catalysts were tested for CO hydrogenation at temperatures ranging from 230 °C to 300 °C, 20 bar and 18,000 scc/(hr.gcat). It was observed that the Co–Cu mixed nanoparticles with higher Cu concentration exhibit a greater selectivity towards ethanol and C2+ oxygenates. The highest ethanol selectivity achieved was 11.4% with corresponding methane selectivity of 17.2% at 270 °C and 20 bar.  相似文献   

18.
Co/Rh heterobimetallic nanoparticles were prepared from cobalt‐rhodium carbonyl clusters [Co2Rh2(CO)12 and Co3Rh(CO)12] and immobilized on charcoal. HR‐TEM revealed that the size of the heterobimetallic nanoparticles was ca. 2 nm and ICP‐AES analysis showed a 2 : 2 and a 3 : 1 cobalt‐rhodium stoichiometry (Co2Rh2 and Co3Rh1) in the heterobimetallic nanoparticles. The Co/Rh heterobimetallic nanoparticles immobilized on charcoal were used as a catalyst in the Pauson–Khand‐type reaction under 1 atm of CO. The catalytic reactivity was highly dependent upon the ratio of Co : Rh with the highest reactivity being observed when the ratio was 2 : 2 (Co2Rh2). The Co2Rh2 immobilized catalyst is quite an effective catalyst for intra‐ and intermolecular Pauson–Khand‐type reactions. When the immobilized Co2Rh2 catalyst was used as a catalyst in the Pauson–Khand‐type reaction in the presence of an aldehyde instead of carbon monoxide, the catalytic system was highly efficient. When the reaction was carried out in the presence of chiral diphosphines, ee values up to 87% were observed. The catalytic system can be reused at least five times in the presence of chiral diphosphines without loss of catalytic activity and enantioselectivity. The addition of Hg(0), a known heterogeneous catalyst poison, completely inhibits further catalysis. Thus, an environmentally friendly and sustainable process was developed.  相似文献   

19.
This work is aimed at evaluating the performance of several catalysts in the partial hydrogenation of sunflower oil. The catalysts are composed of noble (Pd and Pt) and base metals (Ni, Co and Cu), supported on both silica and alumina. The following order can be proposed for the effect of the metal on the hydrogenation activity: Pd > Pt > Ni > Co > Cu. At a target iodine value of 70 (a typical value for oleomargarine), the production of trans isomers is minimum for supported nickel catalysts (25.7–32.4 %, depending on the operating conditions). Regarding the effect of the support, Al2O3 allows for more active catalysts based on noble metals (Pd and Pt) and Co, the effect being much more pronounced for Pt. Binary mixtures of catalysts have been studied, in order to strike a balance between catalyst activity and product distribution. The results evidence that Pd/Al2O3–Co/SiO2 mixture has a good balance between activity and selectivity, and leads to a very low production of trans isomers (11.8 %) and a moderate amount of saturated stearic acid (13.5 %). Consequently, the utilization of cobalt‐based catalysts (or the addition of cobalt to other metallic catalysts) could be considered a promising alternative for the hydrogenation of edible oil.  相似文献   

20.
Microporous poly(ether sulfone) (PES) supported hybrid polymer–inorganic membranes were prepared by the crosslinking of poly(vinyl alcohol) (PVA), maleic acid (MA), and SiO2 via an aqueous sol–gel route and a solution‐casting method. The membrane performance was tested for the pervaporation separation of ethanol–water mixtures from 20 to 60 °C with a feed ethanol concentration of 96 wt %. The membrane characterization results reveal that different SiO2 loadings affected the crystallinity and roughness of the membranes. The PVA–MA–SiO2 membrane containing 10 wt % SiO2 showed that SiO2 nanoparticles were well dispersed within the polymer matrix; this resulted in significant enhancements in both the flux and selectivity. The membrane achieved a high water permeability of 1202 g·μm·m?2 h?1 kPa?1 and a selectivity of 1027 for the separation of a 96 wt % ethanol‐containing aqueous solution. This enhanced membrane performance might have been due to the dense crosslinking membrane network, increased free volume, and uniform distribution of SiO2 nanoparticles. Both the water and ethanol fluxes increased with the feed water concentration and temperature. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44839.  相似文献   

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