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1.
Cr/MgO(x)–CeO2(100?x) nanocatalysts were synthesized by a coprecipitation method and characterized by X-ray diffraction (XRD) analysis, field-emission scanning electron microscopy (FESEM), energy-dispersive x-ray (EDX) spectroscopy, diffuse reflectance spectroscopy (DRS), and Brunauer–Emmett–Teller (BET) analysis. The effect of ceria addition on their physicochemical characteristics was investigated, and the results were correlated with their catalytic performance in oxidative dehydrogenation of ethane. A decrease in the size of the metal particles was found when adding a suitable content of ceria to the support. Crystalline Cr2O3 was not found in the calcined samples, indicating good dispersion of Cr species on the support. All samples showed nanosized particles with uniform morphology, with the best surface morphology for the Cr/MgO(50)–CeO2(50) sample, on which the particle distribution mainly lay in the range of 40–60 nm. Variation of the amount of Ce in the support led to an enhancement of the Cr6+/Cr3+ ratio, with the highest value for the Cr/MgO(50)–CeO2(50) sample. This catalyst effectively dehydrogenated ethane to ethylene with CO2 at 700 °C even after 5 h on-stream, giving 42.76 % ethylene yield. 相似文献
3.
Catalytic decomposition of methane has been studied extensively as the production of hydrogen and formation of carbon nanotube is proven crucial from the scientific and technological point of view. In that context, variation of catalyst preparation procedure, calcination temperature and use of promoters could significantly alter the methane conversion, hydrogen yield and morphology of carbon nanotubes formed after the reaction. In this work, Ni promoted and unpromoted Fe/Al 2O 3 catalysts have been prepared by impregnation, sol–gel and co-precipitation method with calcination at two different temperatures. The catalysts were characterized by X-ray diffraction (XRD), N 2 physisorption, temperature programmed reduction (TPR) and thermogravimetric analysis (TGA) techniques. The catalytic activity was tested for methane decomposition reaction. The catalytic activity was high when calcined at 500 °C temperature irrespective of the preparation method. However while calcined at high temperature the catalyst prepared by impregnation method showed a high activity. It is found from XRD and TPR characterization that disordered iron oxides supported on alumina play an important role for dissociative chemisorptions of methane generating molecular hydrogen. The transmission electron microscope technique results of the spent catalysts showed the formation of carbon nanotube which is having length of 32–34 nm. The Fe nanoparticles are present on the tip of the carbon nanotube and nanotube grows by contraction–elongation mechanism. Among three different methodologies impregnation method was more effective to generate adequate active sites in the catalyst surface. The Ni promotion enhances the reducibility of Fe/Al 2O 3 oxides showing a higher catalytic activity. The catalyst is stable up to six hours on stream as observed in the activity results. 相似文献
4.
Research on Chemical Intermediates - Herein, we investigated the NOx reduction performance of Sb–V–CeO2/TiO2 (SbVCT) catalyst subjected to hydrothermal aging, where 6 vol% of H2O was... 相似文献
5.
In this investigation, Zr 1−x
Ce
x
O 2 coatings were fabricated on quartz fiber reinforced polyimide matrix composites via sol–gel process at 400 °C. The phase
evolution, structural and morphological characteristic of specimens were investigated by differential scanning calorimetric,
Fourier transform infrared spectroscopy, powder X-ray diffraction and scanning electron microscopy. The significant phase
evolution of final powders with the decreasing Zr/Ce molar ratio could be observed as follows: tetragonal ( t′) → cubic + tetragonal ( t′) → tetragonal ( t″). BET specific surface areas of powders exhibited a decreased tendency with the increasing calcination temperature as well
as the decreasing Zr/Ce molar ratio. The average crystallite size and the mean particle size increased with the elevated calcination
temperature, while the particle size also increased with the increase in Ce content. The progressive addition of Ce could
promote the sintering process and the densification of coating. Morphologies of coatings changed with the variation of the
Zr/Ce molar ratio. The results indicate that Zr 0.75Ce 0.25O 2 coating with the Zr/Ce molar ratio of 3 is a stable uniform coating with excellent adhesion. 相似文献
6.
In the present work, Fe 3O 4@L-Tyrosine-Pd heterogeneous nanocatalyst was prepared by a simple and inexpensive procedure. The prepared nanocatalyst was characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray Diffraction (XRD), energy-dispersive X-ray spectroscopy (EDS), inductively coupled plasma optical emission spectroscopy (ICP-OES), scanning electron microscopy (SEM), Transmission electron microscopy)TEM(, X-ray mapping, thermal gravimetric analysis (TGA), N 2 adsorption and desorption (BET) and vibrating sample magnetometer (VSM) techniques. Besides, it was employed as an efficent catalyst for C-C cross coupling and S-arylation reactions under green conditions. The optimized conditions for these reactions are described. The heterogeneous catalyst can be easily separated by applying a simple magnet and can also be reused in several consecutive runs without appreciable change in its catalytic activity. 相似文献
7.
The morphological manipulation and structural characterisation of TiO 2?CMgO binary system by an aqueous particulate sol?Cgel route were reported. Different crystal structures including pure MgTiO 3, mixtures of MgTiO 3 and TiO 2 and mixtures of MgTiO 3 and Mg 2TiO 4 were tailored by controlling Mg:Ti molar ratio and annealing temperatures as the processing parameters. X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR) revealed that all compounds crystallised at the low temperature of 500?°C. Furthermore, it was found that the average crystallite size of the compounds depends upon the Mg:Ti molar ratio as well as the annealing temperature, being in the range 3?C5?nm at 500?°C and around 6?nm at 700?°C. Field emission scanning electron microscope (FE-SEM) analysis revealed that the deposited thin films had nanocrystalline structure with the average grain size of 25?C30?nm at 500?°C depending upon the Mg:Ti molar ratio. Moreover, atomic force microscope (AFM) images presented that the thin films had a hill-valley like morphology made up of small grains. 相似文献
8.
The reduction of monometallic Pd/Al 2O 3 and bimetallic PdFe/Al 2O 3 catalysts produced by co-impregnation or sequential impregnation of the support with metal salts was possible not only under high temperature hydrogen treatment but also at 30 °C under the action of aqueous phenol solution and hydrogen. According to the XPS data, both reduction routes provided sufficient degrees of Pd reduction required for fast hydrodehalogenation of 4-chlorophenol and 4-bromophenol to phenol in aqueous solutions. The degree of Pd reduction was higher in the co-impregnated bimetallic PdFe catalyst, which was more efficient in transformation of 4-bromophenol; the bimetallic catalysts were more stable than the monometallic Pd one in the conversion of 4-chlorophenol. 相似文献
9.
Kinetics of oxidation of propylene to propylene glycol and its acetates in acetic acid solutions of lithium nitrate over Pd/C and Pd–Pt/C catalysts has been studied. Catalysts were investigated using X-ray phase analysis and electron microscopy. Platinum introduction into catalyst increases the metal dispersity and the catalyst stability but produces no effect on the nature of surface sites active in propylene oxidation.
Pd/C Pd–Pt/C. . , , , . 相似文献
10.
Journal of Solid State Electrochemistry - CdSe@CdS@TiO2 microsheet array (MSA) ternary core–shell heterojunctions were prepared by successive electrodeposition of CdS and CdSe onto TiO2... 相似文献
11.
A hybrid catalyst has been prepared by incorporating sulfonic acid onto cobalt ferrite magnetic nanoparticles. The catalyst was successfully applied for rapid (20?min) synthesis of α, α-dibromoketones directly from alkynes and NBS. The reaction works well in the presence of 10?wt% of the catalyst at room temperature to produce the desired products in high yield. The catalyst could be recovered using an external magnet and reused without appreciable change in activity. 相似文献
13.
Pd-MoO3/SiO2 catalyst has been prepared using the method of incipient wetness impregnation. The photo absorbing behaviors and chemisorbing properties of the catalyst have been characterized by UV-vis spectra and TPD-MS experiments. The results indicated that metal Pd loaded on MoOe/SiO2 has a significant effect on the photo absorbing performance of MoO3/SiO2, and an obvious blue shift of the absorption edge is produced. Under UV irradiation, the chemisorption state of CO2 undergoes decomposing process to form CO at 481 K, and a two-site adsorption state of ethane can be formed at around 496 K. Photo-oxidation of ethane using carbon dioxide can mainly produce propanal, ethanol and acetaldehyde in the temperature range of 353-423 K. The presence of metal Pd improves the catalytic activity remarkably. 相似文献
14.
The mechanism and kinetics of energy transfer from Xe(6s[3/2] 1) resonance state ( E=8.44 eV) to selected hydrocarbon molecules have been investigated by XeCl(B–X) ( λmax=308 nm) fluorescence intensity measurements at stationary conditions in Xe–CCl 4–M systems. Steady-state analysis of the fluorescence intensity dependence on the xenon and M pressure at constant CCl 4 concentration shows that these process occur in the two- and three-body reactions: Xe(6s[3/2] 10)+M→products, Xe(6s[3/2] 10+M+Xe→products. The two- and three-body rate constants for these reactions have been found (see Table 1Table 1. Experimental parameters of Eq. (8)found by least square method in Xe–CCl 4–C 2H 2 and Xe–CCl 4–C 2H 4 systems for chosen xenon pressures in the range 25–150 Torr. Linear correlation coefficients ( R) are also shown P(Xe) (Torr) | C2H4 | C2H2 |
---|
Empty Cell | a | b×1016 cm3/molec. | R | a | b×1016 cm3/molec. | R |
---|
25 | 0.92 | 3.26 | 0.98 | 1.00 | 2.78 | 0.95 | 40 | 0.86 | 3.29 | 0.97 | 1.00 | 2.91 | 0.98 | 50 | 0.87 | 3.33 | 0.97 | 0.99 | 3.05 | 0.98 | 60 | 0.85 | 3.33 | 0.97 | 1.02 | 2.99 | 0.98 | 75 | 0.86 | 3.39 | 0.97 | 1.03 | 2.95 | 0.98 | 90 | 0.92 | 3.30 | 0.97 | 1.03 | 2.85 | 0.98 | 100 | 0.92 | 3.21 | 0.98 | 1.0 | 2.77 | 0.98 | 110 | 0.88 | 3.19 | 0.96 | 1.02 | 2.71 | 0.99 | 125 | 0.86 | 3.12 | 0.95 | — | — | — | 140 | 0.92 | 2.90 | 0.95 | — | — | — | 150 | 0.95 | 2.77 | 0.94 | — | — | — | 相似文献
15.
An ideal adsorbent for separation requires optimizing both storage capacity and selectivity, but maximizing both or achieving a desired balance remain challenging. Herein, a de-linker strategy is proposed to address this issue for metal–organic frameworks (MOFs). Broadly speaking, the de-linker idea targets a class of materials that may be viewed as being intermediate between zeolites and MOFs. Its feasibility is shown here by a series of ultra-microporous MOFs (SNNU-98-M, M=Mn, Co, Ni, Zn). SNNU-98 exhibit high volumetric C 2H 2 uptake capacity under low and ambient pressures (175.3 cm 3 cm −3 @ 0.1 bar, 222.9 cm 3 cm −3 @ 1 bar, 298 K), as well as extraordinary selectivity (2405.7 for C 2H 2/C 2H 4, 22.7 for C 2H 2/CO 2). Remarkably, SNNU-98-Mn can efficiently separate C 2H 2 from C 2H 2/CO 2 and C 2H 2/C 2H 4 mixtures with a benchmark C 2H 2/C 2H 4 (1/99) breakthrough time of 2325 min g −1, and produce 99.9999 % C 2H 4 with a productivity up to 64.6 mmol g −1, surpassing values of reported MOF adsorbents. 相似文献
16.
A simple method is developed to estimate mixture critical temperatures ( Tc), pressures ( Pc), and densities ( ρc) as a function of overall composition ( X) from near critical region experimental coexistence data. This three-step method is applied to four mixtures, CO 2–C 3H 8, CO 2– nC 4H 10, C 2H 6–C 3H 8, and C 3H 8– nC 4H 10. Isothermal liquid–vapor coexistence data, which includes temperature, vapor pressure, coexisting densities ( ρℓ and ρv), and coexisting compositions for the more volatile component ( x1v and x1ℓ) are used. In the first step, the difference of the saturated liquid and vapor densities ( ρℓ− ρv) is fitted to an empirical function in (( Pc− P)/ Pc) to obtain Pc. Then P/ Pc and (( ρℓ+ ρv)/2 ρc) are simultaneously fitted to functions of a polynomial in ( X1−( x1v+ x1ℓ)/2) yielding estimates of ρc and X1. Finally, the discrete estimated critical data points are fitted with an equation to provide a continuous representation of the critical lines. The method is successfully tested for the mixtures, CO 2–C 3H 8 and CO 2– nC 4H 10, for which there is a reasonable amount of isothermal data. The procedure is then applied to the mixtures, C 2H 6–C 3H 8 and C 3H 8– nC 4H 10, for which there are sparse data. For all four mixtures, the critical temperature line, Tc vs. X1, matches literature values within ±0.5%. The critical pressure line, Pc vs. X1, and critical density line, ρc vs. X1, match literature values, in general, within ±2%. 相似文献
18.
Titanium dioxide thin films have been synthesized by sol–gel spin coating technique on glass and silicon substrates with and without surfactant polyethylene glycol (PEG). XRD and SEM results confirm the presence of nano-crystalline (anatase) phase at an annealing temperature of 300 °C. The influence of surfactant and annealing temperature on optical properties of TiO 2 thin films has been studied. Optical constants and film thickness were estimated by Swanepoel's (envelope) method and by ellipsometric measurements in the visible spectral range. The optical transmittance and reflectance were found to decrease with an increase in PEG percentage. Refractive index of the films decreased and film thickness increased with the increase in percentage of surfactant. The refractive index of the un-doped TiO 2 films was estimated at different annealing temperatures and it has increased with the increasing annealing temperature. The optical band gap of pure TiO 2 films was estimated by Tauc's method at different annealing temperature. 相似文献
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