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1.
The cyclodehydration of 1,4‐butanediol over cobalt catalysts in the liquid phase is used for the production of 2,3‐dihydrofuran. The catalyst preparation parameters considered were the metal loading, precipitation pH and reduction temperature of cobalt salt. It was found that the use of Co(NO3)2 together with Na2CO3 in a 1:1 ratio yielded better catalysts. Under the conditions used in this study the optimum cobalt loading for the selective production of 2,3‐dihydrofuran is in the range 15–50 wt%. The optimum reduction temperature of Co/porcelain catalyst depends on cobalt loading. The optimum reduction temperatures for 15 and 50 wt% cobalt loading are 773 and 723 K (reduction time 20 min), respectively. © 2001 Society of Chemical Industry  相似文献   

2.
Perovskite oxide structured YBa2Cu3O7-x(YBCO) has been first prepared by carbonate precipitation and then modified with palladium or ruthenium by impregnation on the perovskite oxide, while cobalt was co-precipitated simultaneously in the same pH range with perovskite oxide. After characterization the catalysts were used in the temperature range 300–450°C, in the pressure range 1–9 atmospheres and for H2/CO ratios in the range 1–4 in a differential plug flow reactor for the hydrogenation of carbon monoxide to give hydrocarbons. The perovskite oxide (YBCO) 20% (w/w) and doped 2% (w/w) cobalt oxide catalyst were prepared by the wet chemical method from their nitrate solutions and oxidized at 950°C. Perovskite oxide (Dursun, G. & Winterbottom, J. M., J. Chem. Technol Biotechnol. 63 (1995) 113–16) was also doped with palladium and ruthenium metal by impregnation followed by oxidation at 250°C. The catalysts prepared were characterized by using TemperatureProgrammed Reduction (TPR) to observe the reduction temperature and also to measure total and metal surface area. The modified perovskite oxide on alumina, ruthenium- and cobalt-doped catalysts, has been shown to give a better conversion and also selectivity towards saturated hydrocarbons compared with palladium-doped catalyst. The temperature effect of these catalysts is more consistent, giving a steady increase of conversion with increasing temperature. Although increase of pressure increases the conversion, it causes very little change in product distribution. The activation energy of palladium- and ruthenium-doped, and cobalt co-precipitated catalysts for the reaction has been measured to be 55 kJ mol−1, 75 kJ mol−1 and 50 kJ mol−1 respectively. A general rate equation of the form r=k[H2]m[CO]n has been observed and found to be applicable at the pressures and temperatures used for the catalytic system studied and found to be m≌1·0 for palladium-doped, m≌1·2 for ruthenium-doped and m≌0·95 for cobalt co-precipitated catalysts as n becomes zero or negligibly less than zero. The mechanism of reaction to produce hydrocarbons from syngas has been deduced from the results. It appeared that the carbon monoxide insertion mechanism has been more evident for palladium-doped catalysts whereas the carbide mechanism plays the main role for the ruthenium-doped and cobalt co-precipitated catalysts. © 1998 Society of Chemical Industry  相似文献   

3.
Co/Al2O3 and Co/Al2O3–BaO catalysts with low cobalt loading (0.1, 0.3 and 1 wt%) for the selective catalytic reduction (SCR) of NO x by C3H6 were prepared. The distribution of cobalt species was investigated by UV–vis diffuse reflectance spectroscopy and by H2-TPR in order to identify the active cobalt species in hydrocarbons (HC)-selective catalytic reduction (SCR). It was found that the nature of cobalt species strongly depends on the cobalt loading as well as on the properties of the support. The barium addition to the alumina slows down solid state diffusion processes, improving the thermal stability of the support and preventing diffusion of cobalt into the bulk. Highly dispersed surface Co2+ species over alumina were identified as active sites in the NO-SCR process. Accordingly, a high concentration of surface Co2+ sites in Co 1 wt%/Al2O3 improves the catalytic performance in NO-SCR, the long term stability as well as the water tolerance. On the contrary, the formation of Co3O4 particles in Co 1 wt%/Al2O3–BaO promotes the propylene oxidation by oxygen, decreasing the activity and selectivity of the catalyst in NO reduction.  相似文献   

4.
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   

5.
Alkali metal (viz. Li, Na, K, Rb and Cs) promoted MgO catalysts (with an alkali metal/Mg ratio of 0·1) calcined at 750°C have been compared for their surface properties (viz. surface area, morphology, acidity and acid strength distribution, basicity and base strength distribution, etc.) and catalytic activity/selectivity in the oxidative coupling of methane (OCM) to C2-hydrocarbons at different temperatures (700–750°C), CH4/O2 ratios (4·0 and 8·0) in feed, and space velocities (10320 cm3 g−1 h−1). The surface and catalytic properties of alkali metal promoted MgO catalysts are found to be strongly influenced by the alkali metal promoter and the calcination temperature of the catalysts. A close relationship between the surface density of strong basic sites and the rate of C2-hydrocarbons formation per unit surface area of the catalysts has been observed. Among the catalysts calcined at 750°C, the best performance in the OCM is shown by Li–MgO (at 750°C). © 1997 SCI.  相似文献   

6.
Cobalt silicate formation reduces the activity of the catalyst in Fischer–Tropsch synthesis (FTS). In this article, the effects of calcination temperature and support surface area on the formation of cobalt silicate are explored. FTS catalysts were prepared by incipient wetness impregnation of cobalt nitrate precursor into various silica supports. Deionized water was used as preparation medium. The properties of catalysts were characterized at different stages using FTIR, XRD and BET techniques. FTIR-ATR analysis of the synthesized catalyst samples before and after 48 h reaction identified cobalt species formed during the impregnation/calcination stage and after the reduction/reaction stage. It was found that in the reduction/reaction stage, metal-support interaction (MSI) added to the formation of irreducible cobalt silicate phase. Co/silica catalysts with lower surface area (300 m2/g) exhibited higher C5+ selectivity which can be attributed to less MSI and higher reducibility and dispersion. The prepared catalysts with different drying and calcination temperatures were also compared. Catalysts dried and calcined at lower temperatures exhibited higher activity and lower cobalt silicate formation. The catalyst sample calcined at 573 K showed the highest CO conversion and the lowest CH4 selectivity.  相似文献   

7.
Cobalt-based catalysts were prepared by precipitation method. This research investigated the effects of different supports cobalt loading, promoters, loading of promoters and calcination conditions on the catalytic performance of cobalt catalysts for Fisher-Tropsch synthesis (FTS). It was found that the catalyst containing 40 wt.% Co/TiO2 promoted with 6 wt.% Zn was an optimal catalyst for the conversion of synthesis gas to hydrocarbons especially light olefins. The activity and selectivity of optimal catalyst were studied in different operational conditions. The results showed that the best operational conditions were the H2/CO = 2/1 molar feed ratio at 240 °C and GHSV = 1100 h−1 under atmospheric pressure. Characterization of catalysts were carried out by using X-ray diffraction (XRD), thermal gravimetric analysis (TGA), hydrogen temperature program reduction (H2-TPR), N2 physisorption measurements such as Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods.  相似文献   

8.
The design of supported Co‐based Fischer–Tropsch (F–T) catalysts with suitable reducibility, dispersion, loading, and nanoparticle structure is necessary so that high catalytic activity and selectivity for C5+ hydrocarbons can be achieved. Herein, we report that pyrolyzing a Co‐metal–organic framework‐71 precursor can provide porous carbon‐supported Co catalysts with completely reduced, well‐dispersed face‐centered cubic (FCC) Co nanoparticles (~10 nm in average size). The catalysts can be further tailored dimensionally by doping with Si species, and the FCC Co nanoparticles can be partially transformed into hexagonal close‐packed Co via a Co2C intermediate. All the as‐prepared catalysts had extremely high Co site density (>3.5 × 10?4 mol/g‐cat.) because they had a high number of Co active sites and low mass. Aside from having high F–T activity and C5+ selectivity, with diesel fuels being the main constituents, they showed unprecedentedly high C5+ space time yields (up to 1.45 g/(g‐cat. h)) as compared to conventional Co catalysts. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2935–2944, 2017  相似文献   

9.
This paper reports on notable promotion of C2 + hydrocarbons formation from CO2 hydrogenation induced by combining Fe and a small amount of selected transition metals. Al2O3-supported bimetallic Fe–M (M = Co, Ni, Cu, Pd) catalysts as well as the corresponding monometallic catalysts were prepared, and examined for CO2 hydrogenation at 573 K and 1.1 MPa. Among the monometallic catalysts, C2 + hydrocarbons were obtained only with Fe catalyst, while Co and Ni catalysts yielded higher CH4 selectively than other catalysts. The combination of Fe and Cu or Pd led to significant bimetallic promotion of C2 + hydrocarbons formation from CO2 hydrogenation, in addition to Fe–Co formulation discovered in our previous work. CO2 conversion on Ni catalyst nearly reached equilibrium for CO2 methanation which makes this catalyst suitable for making synthetic natural gas. Fe–Ni bimetallic catalyst was also capable of catalyzing CO2 hydrogenation to C2 + hydrocarbons, but with much lower Ni/(Ni+Fe) atomic ratio compared to other bimetallic catalysts. The addition of a small amount of K to these bimetallic catalysts further enhanced CO2 hydrogenation activity to C2 + hydrocarbons. K-promoted Fe–Co and Fe–Cu catalysts showed better performance for synthesizing C2 + hydrocarbons than Fe/K/Al2O3 catalyst which has been known as a promising catalyst so far.  相似文献   

10.
Controlling preparation variables in supported cobalt Fischer–Tropsch catalysts has a dramatic effect on the dispersion and distribution of cobalt, and determines how active and selective the resulting catalyst will be. We detail specific examples of catalyst synthesis strategies for modifying interactions between the support and the cobalt precursor, promoting reduction, stabilizing catalysts to high-temperature treatments, minimizing deleterious support metal interactions, and controlling the distribution of cobalt on large support particles. It is important to optimize the support and precursor interaction strength, so that it is strong enough to obtain good dispersion but not too strong to prevent low temperature reduction. We show examples in which formation of surface complexes and epitaxial matching of precursor and support structures improves dispersion dramatically. Reduction promoters can help in those cases where support–precursor interactions are too strong. We show how substitutions of silicon into a titania lattice stabilizes surface area and retards formation at high oxidation temperatures of cobalt ternary oxides that reduce only at very high temperatures—an important consideration if oxidative coke removal is necessary. In addition, surface treatment of TiO2 with an irreducible oxide like ZrO2 can inhibit deleterious support interactions that can block surface cobalt sites. Selectivity can also be dramatically altered by catalyst synthesis. We illustrate a case of large (2 mm) SiO2 particles onto which cobalt can be added either uniformly or in discrete eggshells, with the eggshell catalysts having substantially higher C5+ selectivity. These approaches can lead to optimal Fischer–Tropsch catalysts with high activity and C5+ selectivity, good physical integrity, and a long life.  相似文献   

11.
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   

12.
《Journal of Catalysis》2007,245(1):11-24
Chloride-free Cu/zeolite Y catalysts with Cu loading of 2–14% were prepared by precipitation from aqueous copper(II) acetate solutions and inert activation with an Ar flow at 700–750 °C for 15 h. This inert activation resulted in a considerable activity of the catalyst for the oxidative carbonylation of methanol (MeOH) to dimethyl carbonate (DMC) under normal pressure at 140–160 °C at 10–12 wt% Cu loading. Space-time yields (STY) of DMC up to 100 gDMC l−1Cat h−1 were achieved with a feed composed of 36% MeOH, 48% CO, 6% O2, and balance He at a gaseous hourly space velocity (GHSV) of 3000 h−1. A threshold of copper loading (5–6 wt%) was found to exist before catalysts became active. This is associated with the preferential location of copper at ion-exchange positions of the zeolite structure Y not accessible for the reactants. After saturation of these sites, the placement of copper ions within the supercage led to active catalysts. Characterization of samples at various stages of preparation by N2 adsorption, XRD, XPS, ESR, 27Al-MAS-NMR, and TPR analysis revealed that the solid-state ion exchange during inert activation is accompanied by reduction of Cu2+ to Cu+. Copper ions exert a stabilizing effect on the crystallinity of the zeolite (in situ XRD, 27Al-MAS-NMR). No crystalline metallic copper, cuprous oxide, or cupric oxide were formed (XRD), but melting occurred at 750 °C for catalysts with 14% copper loading, resulting in the formation of a glassy amorphous copper silicate/aluminate phase. The latter effect can be prevented by applying lower activation temperatures. The catalysts were prepared without using chloride, and the reaction did not require co-feeding of HCl for maintaining activity, as is needed for CuCl/zeolite catalyst formulations.  相似文献   

13.
《Applied Catalysis A: General》2001,205(1-2):183-193
Dynamic hydroformylation of ethylene at atmospheric pressure and 150°C has been studied in a fixed bed reactor over ruthenium- and cobalt-containing SiO2-supported catalysts (1% Ru loading). Any combination of ruthenium and cobalt precursors leads to significant improvement of hydroformylation activity with respect to those of monometallic catalysts. The optimal atomic ratio of Co:Ru is estimated to be 3:1 for ideal catalytic activity. A catalyst derived from Ru3(CO)12 and Co2(CO)8 is most active. A catalyst derived from metal carbonyls is generally more active than a catalyst prepared from metal salts. Metal chlorides retard the preparation of active catalysts in most cases. The catalysts studied exhibit fairly good catalytic stability. The determined rate enhancement of ethylene hydroformylation suggests a synergy of ruthenium and cobalt, which is understood as catalysis by bimetallic particles or ruthenium and cobalt monometallic particles in intimate contact. The synergy causes high ethylene hydrogenation activity while giving enhanced ethylene hydroformylation activity. Meanwhile, the potential of the ruthenium-based catalysts is evaluated from both catalytic performances and cost by comparison with the corresponding rhodium-based ones.  相似文献   

14.
Au/CeLaOx mixed oxide catalysts containing 0.6–1.0 wt% Au were prepared by co-precipitation with Na2CO3. BET surface areas ranged from 15 to 45 m2/g depending on aging time (precipitation time) and calcination conditions. The differences in the activity of the catalysts for preferential oxidation (PROX) of CO are ascribed to the differences in the metal loading, Ce/La ratio and support crystallinity, chloride content, and the resultant effect on the reduction properties of the catalysts. The catalysts did not require activation in H2 prior to reaction. The temperature at which the catalysts exhibit significant activity correlates with the temperature of reduction, indicating that reduction of the metal and support is important for high activity.  相似文献   

15.
Co/SiO2 catalysts were prepared by sol-gel method with varied en (ethylenediamine)/Co molar ratios under the same pH. Their physical-chemical properties were compared with those prepared with similar en/Co molar ratios at natural pH or without adding ethylenediamine. Regardless of pH, the catalysts prepared using ethylenediamine possessed high microporosity, which led to a better selectivity to C5–18 hydrocarbons, versus the catalyst possessing higher mesoporosity which showed slightly higher C18+ selectivity. As enough positions in the coordination sphere were blocked by ethanediamine ligands, the formation of cobalt silicate disfavored for (en/Co=2) catalysts, which resulted in the higher activity in FT reaction. Whereas the catalysts prepared with lower or higher en/Co molar ratio both showed lower activity due to the formation of [(SiO)Co(en)(EtOH)3] species or the electronic adsorption of cobalt complexes in the negatively charged silica surface, respectively. However, for the catalyst without using ethylenediamine, the lowest activity and the highest CH4 selectivity obtained due to its much lower reducibility. This work was presented at the 7 th China-Korea Workshop on Clean Energy Technology held at Taiyuan, Shanxi, China, June 26–28, 2008.  相似文献   

16.
The oxidized and weakly reducible perovskite oxide YBa2Cu3O7 − x (YBCO) has been prepared as a catalyst, supported on γ‐Al2O3. It was further modified by (i) impregnation with Ru and Pd and (ii) cobalt incorporation via co‐precipitation. All the catalysts were either 20% (w/w) YBCO/γ‐Al2O3 or 2% (w/w) Ru, Pd or Co/20% (w/w) YBCO/γ‐Al2O3. The catalysts were characterized using temperature programmed reduction (TPR), surface area measurements and X‐ray diffraction (XRD) studies before and after various treatments. They were studied as catalysts in the pressure range 20–50 atmospheres and in the temperature range 523–573 K in an autoclave equipped with a spinning basket catalyst container. The Pd‐, Ru‐ and Co‐modified catalysts gave predominantly methanation products, along with some C2–C4 hydrocarbons. However the YBCO/γ‐Al2O3 catalyst exhibited significant methanol selectivity at 50 atmospheres and at 523 K X‐ray diffraction studies revealed the presence of Cu(0), Cu(I) and Cu(II) after reduction and the species Cu(0) and Cu(I) are probably essential to CH3OH production. © 2000 Society of Chemical Industry  相似文献   

17.
The Fischer-Tropsch synthesis in the presence of composite materials prepared by the IR pyrolysis of polyacrylonitrile (PAN) with cobalt salts immobilized on it was studied. The catalysts were small granules containing PAN carbonization products and to 80% cobalt metal particles of size 10–17 nm. The synthesis was performed in flow reactors with a fixed bed and a catalyst bed suspended in a liquid at 2–3 MPa and 200–310°C. It was established that the activity of the catalyst depends on the nature of the cobalt salt used, the temperature of IR pyrolysis, and the synthesis conditions. The catalyst prepared with the use of cobalt carbonate exhibited the greatest activity. The yield of liquid hydrocarbons on it reached ~70 g/m3 at ~60% selectivity. It was found that the test composite materials were characterized by an extremely high productivity of 2–5 kg (kg Co)?1 h?1.  相似文献   

18.
The reduction of NO with octane under lean conditions was examined over gold supported on alumina and titania and over alumina supported bimetallic gold–silver catalysts. The silver loading was either 1.2 or 1.9 wt% whereas 0.3, 1 or 5 wt% gold was used. The catalysts were characterized by means of EDXS, N2-adsortion, UV–Vis and TEM to correlate recorded results with different preparation methods. UV–Vis measurements indicated that gold was present in the form of fine Au particles, single Au ions and small (Au)n δ+ clusters on the catalysts and silver was mainly present in the form of single Ag ions. The highest NO to N2 reduction activity was recorded over the 0.3Au–Al2O3 catalyst. The Au–TiO2 catalysts did not result in significant NO to N2 reduction.  相似文献   

19.
Sr-promoted rare earth (viz. La, Ce, Pr, Nd, Sm, Eu, Gd, Dy, Er and Yb) oxide catalysts (Sr/rare earth ratio = 0·1) are compared for their performance in the oxidative coupling of methane (OCM) to C2 hydrocarbons and oxidative dehydrogenation of ethane (ODE) to ethylene at different temperatures (700 and 800°C) and CH4 (or C2H6)/O2 ratios (4–8), at low contact time (space velocity = 102000 cm3 g−1 h−1). For the OCM process, the Sr–La2O3 catalyst shows the best performance. The Sr-promoted Nd2O3, Sm2O3, Eu2O3 and Er2O3 catalysts also show good methane conversion and selectivity for C2 hydrocarbons but the Sr–CeO2 and Sr–Dy2O3 catalysts show very poor performance. However, for the ODE process, the best performance is shown by the Sr–Nd2O3 catalyst. The other catalysts also show good ethane conversion and selectivity for ethylene; their performance is comparable at higher temperatures (≥800°C), but at lower temperature (700°C) the Sr–CeO2 and Sr–Pr6O11 catalysts show poor selectivity. © 1998 SCI.  相似文献   

20.
In this paper, the preparation of vanadium phosphate catalysts was shown to be improved by (1) using V2O5 and ethylene glycol as starting and reducing agent material, respectively for VOPO4 · 2H2O, (2) subsequent water treatment and (3) microwave irradiation. In particular, the preparation route, based on the reduction of VOPO4 · 2H2O with various alcohols, is described in detail and contrasted with other three established methods performed by using ethylene glycol and isobutyl alcohol as reductant and solvent for V2O5 or distilled water as a solvent material. The preparation of catalyst precursor is carried out by two different methods, namely conventional heating and microwave irradiation. With this new technique, catalysts derived from the reduction of VOPO4 · 2H2O by ethylene glycol exhibit substantially higher surface area (typically >40 m2 g?1) and activity. In fact, the surface area of the catalyst is significantly enhanced when the precursor is refluxed by distilled water and dried by microwave heating. The characterization of catalysts was carried out using X-ray diffraction (XRD), Brunauer–Emmer–Teller (BET) surface area measurement, temperature programmed reduction (H2-TPR), temperature-programmed reaction (TPRn) and scanning electron microscopy (SEM). This study shows that employing ethylene glycol as reducing agent, followed by adding the water treatment step to catalyst synthesis procedure, and using microwave irradiation would give rise to enhanced surface area, activity and selectivity of the catalyst. Moreover, it introduces a more energy efficient procedure for preparation of vanadium phosphate catalyst used in selective oxidation of n-butane process.  相似文献   

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