首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 39 毫秒
1.

Abstract  

Two series of Cu/Co/Cr modified Fischer–Tropsch catalyst promoted with Zn or Mn and an alkaline metal (Me: Li, Na, K, Rb, Cs) were prepared by co-precipitation method and tested for high alcohol synthesis (HAS) at one hour on-stream and at two temperatures, 300 and 350 °C. The results indicate that the best selectivity toward high alcohols depends on temperature and catalysts composition and is obtained as follows: a) at 300 °C over catalysts without Zn and containing K, Na and Rb; b) at 350 °C over catalysts without Zn and containing K; c) at 350 °C over catalysts containing Zn as well as Li and Cs.  相似文献   

2.

Abstract  

The catalytic decomposition of methane over M–Co–Al (M = Mg, Ni, Zn, Cu) was studied. The samples were prepared by co-precipitation and characterized by SBET, TGA, DTA, TPR and XRD. The carbon produced in the reaction was characterized by SEM and TPO. Activity tests were carried out in a thermobalance between 500 and 750 °C. The results show that the textural properties of the calcined samples did not change significantly with the partial substitution of Co by Mg, Ni, Zn or Cu. On the other hand, there were marked differences in the reduced samples. There was a strong influence on the reducibility of cobalt oxides in the presence of Ni or Cu. Nickel promoted the reduction of Co3O4 at the same temperature as the NiO phase, whereas copper strongly decreased the reduction temperature of both Co3O4 and CoAl2O4 due to a synergistic effect between Cu and Co. The sample containing Cu resulted in low catalytic activity in the whole temperature range because the reduction conditions promoted the formation of a Cu–Co alloy. In the reaction carried out at 700 °C, the observed activity was Co–Al > Mg–Co–Al > Ni–Co–Al. All the samples were deactivated by encapsulation under these conditions due to high rates of carbon deposition. The carbon produced was mainly carbon nanotubes, except for the Cu–Co–Al sample, which produced mostly amorphous carbon.  相似文献   

3.
Copper (Cu) is an essential trace metal that is toxic in excess. It is therefore important to be able to accurately assess Cu deficiency or overload. Cu chaperone for Cu/Zn superoxide dismutase (CCS) protein expression is elevated in tissues of Cu-deficient animals. Increased CCS content in erythrocytes is particularly sensitive to decreased Cu status. Given the lack of a non-invasive, sensitive and specific biomarker for the assessment of Cu excess, we investigated whether CCS expression in erythrocytes reflects Cu overload. Rats were fed diets containing normal or high levels of Cu for 13 weeks. Diets contained 6.3 ± 0.6 (Cu-N), 985 ± 14 (Cu-1000) or 1944 ± 19 (Cu-2000) mg Cu/kg diet. Rats showed a variable response to the high Cu diets. Some rats showed severe Cu toxicity, while other rats showed no visible signs of toxicity and grew normally. Also, some rats had high levels of Cu in liver, whereas others had liver Cu concentrations within the normal range. Erythrocyte CCS protein expression was 30% lower in Cu-2000 rats compared to Cu-N rats (P < 0.05). Notably, only rats that accumulated high levels of Cu in liver had lower erythrocyte CCS (47% reduction, P < 0.05) compared to rats fed normal levels of Cu. Together, these data indicate that decreased erythrocyte CCS content is associated with Cu overload in rats and should be evaluated further as a potential biomarker for assessing Cu excess in humans.  相似文献   

4.
Heavy metal uptake by wheat from a sewage sludge-amended calcareous soil   总被引:1,自引:0,他引:1  
The objective of this 4-year study was to determine single and repetitive effects of sewage sludge applications on the accumulation of lead (Pb), cadmium (Cd), zinc (Zn) and copper (Cu) in soil and wheat (Triticum aestivum). A single sludge application at a rate of 100 Mg ha−1 (for all the metals) and at a rate of 50 Mg ha−1 (for Cu) significantly increased DTPA-extractable metal concentrations 4 years later. DTPA-extractable concentrations of Pb, Zn and Cu were closely correlated with the total concentrations in soil. Their relationships between metal uptake in stalks and DTPA-extractable metal concentrations in soil were approximately linear for Pb, Cd and Cu, but better described by a quadratic equation for Cd and Zn. TF for Pb, Zn and Cu, BF for all metals and BCF for Pb, Cd and Zn were lower in wheat grown on sludge-treated than control plots.  相似文献   

5.
Cobalt(II), copper(II) and zinc(II) complexes of 2-(o-aminophenyl)benzimidazole (AmPhBzlH) encapsulated in the super cages of zeolite-Y and ZSM-5 have been synthesized and characterized by spectroscopic studies (IR, UV/visible, EPR), elemental analyses, thermal studies and X-ray diffraction patterns. The catalytic activity of encapsulated complexes was investigated for the hydroxylation of phenol using 30% H2O2 as an oxidant. Under optimized reaction conditions, the hydroxylation of phenol yielded catechol and hydroquinone as the major products. All catalysts show good selectivity for diphenol products. A maximum conversion of phenol was obtained with [Cu(AmPhBzlH)]-Y as the catalyst. The results showed that conversion of phenol varies in the order [Cu(AmPhBzlH)]-Y > [Cu(AmPhBzlH)]-ZSM-5 > [Zn(AmPhBzlH)]-Y > [Co(AmPhBzlH)]-Y > [Zn(AmPhBzlH)]-ZSM-5 > [Co(AmPhBzlH)]-ZSM-5 after 6 h of reaction time. Test for the recyclability of the reaction was also carried out and the results indicate their recyclability.  相似文献   

6.

Abstract  

In the present study we introduce a copper-catalyzed protocol for the dehydration of primary amides to their corresponding nitriles applying N-methyl-N-(trimethylsilyl)trifluoroacetamide (MSTFA) as silylation reagent. For that purpose investigations of various reaction parameters (copper source, solvent, temperature, MSTFA and copper loading) have been carried out to find suitable reaction conditions. Simple copper(I) chloride (2.5 mol%) and MSTFA (2.0 equiv) in toluene allow for the straightforward synthesis of a variety of nitriles (15 examples).  相似文献   

7.

Abstract  

Metal acetylacetonates were found to be efficient and cost effective catalysts for the formation of cyclic carbonates by cycloaddition of carbon dioxide with epoxides, providing high to excellent yields of the corresponding carbonates. Among the various catalysts such as acetylacetonates of Co, Ni, Cu, Zn, Fe, Cr and VO studied, Ni(acac)2 was found to be promising catalyst for this reaction. The present methodology was found to be superior due to the easy accessibility and comparatively inexpensive nature of metal acetylacetonates than salen complexes.  相似文献   

8.
《Applied Clay Science》2008,38(3-4):221-225
This paper studied the influence of copper concentration, pH, temperature, and the ratio of solid to solution on desorption of Zn in the kaolin from Suzhou, China in a background solution of 0.01 M CaCl2 by batch extraction experiments. At 0, 5, 50, 100 mg/l Cu concentration, for each 0.5 increase in pH between about 1.80 and 3.04% desorption decreases 3.80, 13.87, 9.97, and 7.65%, respectively. The pH50 (pH at 50% Zn desorption) is found to follow the sequence: Cu (5 mg/l, pH50 = 2.60) < Cu (50 mg/l, pH50 = 2.70) < Cu (100 mg/l, pH50 = 2.95) < Cu (0 mg/l, pH50 = 10.65). The free energy change (ΔG) values, the values of enthalpy change (ΔH), and entropy change (ΔS) have been calculated. There were no large differences in the desorption of Zn from 25 to 50 °C. The concentration of Zn in solution after desorption equilibrium increases and percent desorption decreases when the solid to liquid ratio increases from 0.025 to 0.2. The kaolin possibly cannot be used for the landfill clay liner.  相似文献   

9.
A new synthesis method of low-temperature methanol proceeded on Cu/ZnO/Al2O3 catalysts from CO/CO2/H2 using 2-butanol as promoters. The Cu/ZnO/Al2O3 catalysts were prepared by co-impregnation of r-Al2O3 with an aqueous solution of copper nitrate and zinc nitrate. The total carbon turnover frequency (TOF), the yield and selectivity of methanol were the highest by using the Cu/ZnO/Al2O3 catalyst with copper loading of 5% and the Zn/Cu molar ratio of 1/1, which precursor were not calcined, and reduced at 493 K. The activity of the catalysts increased due to the presence of the CuO/ZnO phase in the oxidized form of impregnation Cu/ZnO/Al2O3 catalysts. The active sites of the Cu/ZnO/Al2O3 catalyst for methanol synthesis are not only metallic Cu but also special sites such as the Cu–Zn site, i.e. metallic Cu and the Cu–Zn site work cooperatively to catalyze the methanol synthesis reaction.  相似文献   

10.

Abstact  

Cu-SBA-16 has been prepared by one-pot synthesis method, and Characterized by XRD, TEM, and N2 adsorption measurements. An extended study about the nature of copper species in the Cu-SBA-16 has been performed by FT-IR, UV-DRS, H2-TPR and XPS. The copper species is mainly present on the mesoporous SBA-16 in the form of isolated mononuclear Cu2+ ions and highly dispersive CuO nanoclusters. The excellent catalytic activity has been obtained for phenol hydroxylation due to the presence of high amount of highly dispersive Cu species. The conversion to phenol and selectivity to diphenol are 29.4 and 91.5%, respectively.  相似文献   

11.
The CuO dispersed on ZnCr2O4 catalysts derived from Cu–Zn–Cr hydrotalcite like layered double hydroxide precursors with varying Zn/Cr ratios have been synthesized, characterized by BET—Surface area, X-ray diffraction (XRD), temperature programmed reduction (TPR), electron spin resonance (ESR), N2O titrations and the activities were evaluated for single step dimethyl ether (STD) synthesis from syngas. It is observed that the copper species were in highly dispersed state over Cu–ZnO–Cr2O3 at high Zn/Cr ratios while the copper cluster were present at low Zn/Cr ratios. The ESR analysis revealed signals due to isolated Cu2+ at high Zn/Cr ratios and clustered Cu2+ at low Zn/Cr ratio in fresh catalysts and only Cr3+ species in used catalysts. The TPR results indicated that the reduction peak shifted to high temperatures with an increase in chromium content due to large copper crystallites, which was supported by XRD analysis. The conversion of syngas to DME was well correlated with the copper metal surface areas, indicating that STD synthesis can be controlled by methanol synthesis rate.  相似文献   

12.
Two new complexes, [M2(L)2(bpy)2](ClO4)2 [L = methyl salicylate, bpy = 2,2′-bipyridine, M = Cu (1) and Zn (2)] have been synthesized and structurally characterized by X-ray structure analyses. The centrosymmetric dimeric structure consists of a binuclear unit, in which M (M = Cu or Zn) atoms are bridged by two phenol oxygen atoms as a μ 2-bridged. The neighboring binuclear units interact with each other by two kinds of weak contacts: one kind is π–π stacking by π–σ attraction with an edge-to-face C–H···π interaction, and the second type is a H-bonding interaction, which extends the binuclear unit into a 3D network. Magnetic measurements confirm that 1 presents a very strong intradinuclear ferromagnetic coupling between the copper(II) ions.  相似文献   

13.
Cu2O grass-like and ZnO flower-like nanoarchitectures were fabricated directly on Cu powders and Zn powders using a novel thermal oxidation stress-induced (TOS) method based on catalyst assistance at a low temperature of 150°C under moderate humid atmosphere. The experiments of Al powder were also carried out based on TOS method. Overlapping migration (OLM) of Cu and Zn atoms and toothpaste squeezing migration (TSM) of Al atoms caused by different atom densities in metal oxide materials were studied.

PACS

81. Materials science; 81.07.-b Nanoscale materials and structures: fabrication and characterization; 81.16.Hc Catalytic methods  相似文献   

14.
Cu–Zn–Ti catalysts were prepared by coprecipitation method. The calcined and reduced Cu–Zn–Ti catalysts were characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction (TPR), and N2 adsorption. The calcined Cu–Zn–Ti catalysts were composed of CuO, ZnO, and amorphous TiO2. There were two kinds of CuO species present in the calcined Cu–Zn–Ti catalyst. At a lower copper content, CuO species interacted with ZnO and TiO2; at a higher copper content, both the surface-anchored and bulk CuO species were present. After reduction, metallic copper (Cuo) appeared in all Cu–Zn–Ti catalysts. Cuo produced by reduction of the surface-anchored CuO favored the deep hydrogenation of maleic anhydride. ZnO and TiO2 had synergistic effect on the catalytic activity of Cu–Zn–Ti catalysts in hydrogenation of maleic anhydride.  相似文献   

15.
The TiO2/SiO2/Ni–Cu–Zn ferrite composite for magnetic photocatalysts with high photocatalytic activity is successfully prepared in this study. The composite are composed of spherical or elliptical Ni–Cu–Zn ferrite nanoparticles about 20–60 nm as magnetic cores, silica as barrier layers with thickness of 15 nm between the magnetic cores and titania shells with thickness approximately 1.5 nm. Photodegradation examination of TiO2/SiO2/ Ni–Cu–Zn ferrite composite was carried out in methylene blue (MB) solutions illuminated under a Xe arc lamp with 35 W and color temperature of 6000 K. The results indicated that about 47.1% of MB molecules adsorbed on the TiO2/SiO2/Ni–Cu–Zn ferrite composite within 30 min mixing due to it higher pore volume of 0.034 cm3/g, and after 6 h Xe lamp irradiation, 83.9% of MB 16.1% was photodegraded. Compared with the TiO2 /Ni–Cu–Zn ferrite composite, the TiO2/SiO2/Ni–Cu–Zn ferrite composite with silica barrier layer prohibited the photodissolution and enhanced the photocatalytic ability. The magnetic photocatalyst shows high photocatalytic efficiency that the apparent first‐order rate constant kobs is 0.18427 h?1, and good magnetic property that the saturation magnetization (Ms) of is 37.45 emu/g, suggesting the magnetic photocatalyst can be easily recovered by the application of an external magnetic field.  相似文献   

16.

Abstract  

The synthesis, X-ray structure, spectroscopic and catalytic properties of sterically hindered Schiff-base ligands (L1H = N-[allylamine]-3,5-di-tert-butyl salicylaldimine, L2H=N-[2-amino-5-methyl pyridine]-3,5-di-tert-butyl salicylaldimine and L3H=N-[2-amino-6-methyl pyridine]-3,5-di-tert-butyl salicylaldimine), and their mononuclear Cu(II) complex for L1H with multinuclear Cu(II) complexes for L2H and L3H, were described. The copper(II) complexes of these ligands were synthesized by treating an methanolic solution of the appropriate ligand with an appropriate amount of CuCl2·2H2O. The ligands and their copper(II) complexes were characterized by FT-IR, UV–Vis, 1H-NMR, elemental analysis, measurement of room temperature magnetic moment, and X-ray structural determination. The reaction of the L2H and L3H ligands in a 1:1 mol ratio with CuCl2·2H2O afforded ionic copper metal(II) complexes in the presence of NEt3. The Cu(II) metal complexes tested as catalysts for the formation of cyclic organic carbonates from carbon dioxide and liquid epoxides which served as both reactant and solvent. [Cu3(L2)4]Cl2·CuCl2 complex which has 5-methyl substituent on the pyridine ring showed high catalytic activity for chemical coupling carbon dioxide with epoxides (propylene oxide (PO), epichlorohydrine (EC) and 1,2-epoxy butane (EB)) selectively.  相似文献   

17.
Comparison is made between Cu–ZnO and alumina-supported Cu–ZnO as catalysts for the reverse water-gas shift (RWGS) reaction. For both types of catalyst the Cu/Zn ratio has been varied between Cu-rich and Zn-rich compositions. By applying X-ray diffractometry, X-ray line broadening, optical reflectance spectroscopy and other techniques the effects on the structural and physical properties of the hydroxycarbonate precursors, the calcined products and the ultimately derived catalysts are determined. The presence of alumina decreases the crystallite size of the CuO and ZnO particles produced on calcination and at high Cu/Zn ratios increases the dispersion of copper in the final catalyst. The activities of the catalysts for the RWGS reaction at 513K are compared and the most active are shown to be those which are Cu rich (Cu/Zn > 3) and contain alumina as support. The activities of all the catalysts can be rationalized by referring the activity to unit surface area of copper metal.  相似文献   

18.
K.C. Waugh 《Catalysis Letters》1999,58(2-3):163-165
Fujitani and Nakamura recently reported on the effect of ZnO on Cu/ZnO methanol synthesis catalysts (Catal. Lett. 56 (1998) 119). Having measured the methanol synthesis activity of a series of Cu/ZnO catalysts of different Cu/ZnO ratios, they reported a linear relationship between the copper metal area and the methanol yield (implying a fixed value of the copper specific activity) and paradoxically they also reported a volcano-type relationship between the copper specific activity in methanol synthesis and the ZnO content. This paradox is resolved by showing that their Cu/ZnO catalysts fall into two groups: (i) the low-surface-area copper catalysts which have a specific activity of 10 mg CH3OH/m2-Cu h and (ii) the high-surface-area copper catalysts which have specific activity of 14.8 mg CH3OH/m2-Cu h. These different specific activities derive from different surface morphologies of the copper in these catalysts. This revised version was published online in November 2006 with corrections to the Cover Date.  相似文献   

19.
In present study, selective extraction of cadmium from acidic leach solutions, containing various heavy metal ions, by emulsion liquid membrane (ELM) is studied. For this reason, the zinc plant copper cake was leached with sulfuric acid and main acidic leach solution containing Zn(II), Cu(II), Fe(II), Cd(II), Co(II) and Ni(II) ions was obtained. After Zn(II), Cu(II), Fe(II) and Cd(II) ions in the acidic leach solution were separated, the important parameters influencing the extent of cadmium extraction were investigated and optimum conditions were determined. Cadmium extraction was influenced by number of parameters like initial metal ion concentration, mixing speed, phase ratio, extractant concentration, surfactant concentration, the stripping solution type and concentration, and the feed solution acid concentration. The optimum values of parameter above mentioned were used and cadmium in the acidic leach solution containing 650 mg Cd/L, 365 mg Co/L, 535 mg Ni/L, and 1260 mg Zn/L was almost completely extracted within 10 min. The results showed that it is possible to extract 99% of cadmium after 10 min contact time by using ELM from aqueous solutions, containing Fe(II), Al(III), Cu(II), Zn(II), Pb(II), Co(II) and Ni(II) ions, at the optimum operating conditions.  相似文献   

20.
The selective production of hydrogen via steam reforming of methanol (SRM) was performed using prepared catalysts at atmospheric pressure over a temperature range 200–260°C. Reverse water gas shift reaction and methanol decomposition reactions also take place simultaneously with the steam reforming reaction producing carbon monoxide which is highly poisonous to the platinum anode of PEM fuel cell, therefore the detailed study of effect of catalyst preparation method and of different promoters on SRM has been carried out for the minimization of carbon monoxide formation and maximization of hydrogen production. Wet impregnation and co-precipitation methods have been comparatively examined for the preparation of precursors to Cu(Zn)(Al2O3) and Cu(Zn)(Zr)(Al2O3). The catalyst preparation method affected the methanol conversion, hydrogen yield and carbon monoxide formation significantly. Incorporation of zirconia in Cu(Zn)(Al2O3) catalyst enhanced the catalytic activity, hydrogen selectivity and also lower the CO formation. Catalyst Cu(Zn)(Zr)(Al2O3) with composition Cu/Zn/Zr/Al:12/4/4/80 prepared by co-precipitation method was the most active catalyst giving methanol conversion up to 97% and CO concentration up to 400 ppm. Catalysts were characterized by atomic absorption spectroscopy (AAS), Brunauer-Emett-Teller (BET) surface area, pore volume, pore size and X-ray powder diffraction (XRPD). The XRPD patterns revealed that the addition of zirconia improves the dispersion of copper which resulted in the better catalytic performance of Cu(Zn)(Zr)(Al2O3). The time-on-stream (TOS) catalysts stability test was also conducted for which the Cu(Zn)(Zr)(Al2O3) catalyst gave the consistent performance for a long time compared to other catalysts.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号