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1.
Monometallic (Co) and bimetallic (Co-Ni and Co-Cu) oxides catalysts supported on the almond based activated carbon (AC) were prepared by the heterogeneous deposition-precipitation method. The activity of these catalysts was evaluated as a function of reaction temperature, NaOH, and NaBH4 concentration. Several analysis methods including XRD, XPS, FTIR, TEM, FESEM, ICP-OES, and BET were applied to characterize the structure of prepared samples. Well-dispersed supported bimetallic nano-catalysts with the size of particles below 20 nm were formed by using nickel and copper oxides as a promoter which was confirmed by XRD and TEM techniques. Surface composition of alloy and core-shell cobalt-nickel oxides catalysts was analyzed by ICP-OES which was in a good agreement with nominal content during catalyst preparation. The performance of bimetallic cobalt-nickel oxides catalysts indicated the synergic effect between cobalt and nickel in comparison with monometallic and bimetallic cobalt-copper samples for hydrogen production. Maximum hydrogen generation rate was measured for the supported core-shell catalyst as named Ni1/Co3/AC. The reaction rate increased with increasing the temperature of the alkaline solution as a significant parameter while other operating conditions were kept constant. The optimal values for NaOH and NaBH4 content were calculated to be 10 wt % for both variables at 30 °C. Hydrogen production rates were calculated to be 252.0, 310.8 and 658.8 mL min?1.g?1 by applying Co3/Ni1/AC, Co3-Ni1/AC (alloy) and Ni1/Co3/AC at 30 °C in 5 wt % NaBH4 and 5 wt % NaOH solutions, respectively. Obtained activation energy (50 kJ mol?1) illustrated that the suitable catalysts were synthesized for hydrogen generation. The experimental study showed that the hydrolysis of NaBH4 was a zero-order type reaction with the respect to the sodium borohydride concentration. A semi empirical kinetic model was derived at the various temperatures and NaOH concentrations.  相似文献   

2.
The aim of this work is to prepare CoB catalysts supported on raw bentonite (CoB/bentonite) and Na-exchanged bentonite (CoB/Na-bentonite) by the impregnation and chemical reduction method. The prepared catalysts were characterized using X-ray diffractometry (XRD), X-ray fluorescence spectroscopy (XRF), scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and Fourier transform infrared spectroscopy (FTIR) techniques. The activities of the catalysts were tested in the hydrolysis reaction of sodium borohydride (NaBH4) in a semi-batch system. The volume of the evolved hydrogen gas was determined by a water displacement method. The effects of catalyst amount, NaOH (a base stabilizer) concentration, NaBH4 concentration and solution temperature on the hydrogen generation rate were investigated. The maximum hydrogen generation rates were determined as 921.94 mL/min.gcat for CoB/bentonite and 1601.45 mL/min.gcat for CoB/Na-bentonite when the 5 wt % NaBH4 and 10 wt % NaOH solutions were used at 50 °C. The activation energies (Ea) of the hydrolysis reaction over CoB/bentonite and CoB/Na-bentonite were determined as 55.76 and 56.61 kJ/mol, respectively.  相似文献   

3.
Amorphous Co-W-P catalysts, which were prepared on carbon cloth (CC) by electrodeposition, have been investigated as bifunctional non-noble catalysts for the hydrogen generation from alkaline NaBH4 solution and the reduction of 4-nitrophenol by NaBH4. Scanning electron microscopes (SEM), energy dispersive X-ray spectrometer (EDX), and X-ray diffraction (XRD) were used to characterize the Co-W-P/CC catalysts. The hydrogen generated catalytic properties of as-prepared catalysts with different content of P and the stability were investigated in the alkaline NaBH4 solution of 5 wt% NaBH4 and 2 wt% NaOH. The activation energy for hydrolysis of NaBH4 by the Co-W-P catalyst was also probed at different temperature, and the results show that the obtained Co-W-P/CC catalysts exhibit very low apparent active energy (Ea = 27.18 kJ mol?1). Finally, we detect the catalytic activity of Co-W-P/CC in the reduction of 4-nitrophenol for the first time, and it also presents outstanding catalytic capability with the apparent rate constant (kapp) of 11.91 × 10?3 s?1. These characteristics indicate that the Co-W-P/CC catalysts possess a potential application on both the sodium borohydride hydrolysis and reduction of 4-nitrophenol.  相似文献   

4.
Effective Co/Cu, CoB/Cu, and CoBM (M = Mo,Zn,Fe)/Cu catalysts were prepared on the copper surface by a simple electroless deposition method using a morpholine borane as a reducing agent in the glycine solution. The activity of the deposited catalysts was investigated for hydrogen generation from an alkaline sodium borohydride solution. It was determined that these synthesized catalysts demonstrated the catalytic activity for the hydrolysis reaction of NaBH4. The lowest obtained activation energy (EA) of the hydrolysis reaction of NaBH4was 27 kJ mol?1 for the CoBMo/Cu catalyst. The hydrogen generation rate of 15.30 ml min?1 was achieved using CoBMo/Cu catalysts at 313 K and it increased ~3.5 times with the increase of temperature to 343 K. The highest hydrogen generation rate obtained by CoBMo/Cu films may be related to the hierarchical cauliflower-shaped 3D structures and the high roughness surface area. Moreover, the CoBMo/Cu catalyst showed an excellent reusability.  相似文献   

5.
CoB/ZIF-8 supported catalysts were successfully prepared using Co/Zn-ZIF-8 as the precursor by single-step reduction, which was applied in hydrogen release from the hydrolysis of NaBH4. Reducible Co ions of Co/Zn-ZIF-8 can be partially in-situ transformed into CoB by direct reduction, whereas ZIF-8 framework structure can be well preserved due to the resistance of Zn to reducing ambiences. Accordingly, CoB active components can be highly loaded onto ZIF-8 support to produce CoB/ZIF-8 catalysts. The texture evolution of Co/Zn-ZIF-8 during reduction was investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscope and nitrogen adsorption–desorption isotherms. Compared with the reduction of Co-ZIF-67, the framework structure of Co/Zn-ZIF-8 can be effectively preserved although Co ions of Co/Zn-ZIF-8 were partially reduced into cobalt-based alloy. In the hydrogen release from hydrolysis of NaBH4, CoB/ZIF-8 supported catalyst exhibits excellent catalytic activity. The effect of NaOH concentration, NaBH4 concentration and reaction temperature on hydrolysis reaction of NaBH4 was deeply studied based on this catalyst. Compared with other published catalysts, this catalyst exhibits relatively low activation energy of about 57.72 kJ mol?1.  相似文献   

6.
Sodium borohydride (NaBH4) is one of promising hydrogen storage materials for practical application, and the development of high-efficient catalysts for NaBH4 hydrolysis to generate hydrogen is of critical importance. In this communication, Co3O4 hollow fiber composed of nanoparticles array was served as catalyst precursor and facilely prepared by combustion method with template of the absorbent cotton. For characterization, FE-SEM, HRTEM, EDS, XRD, FTIR and ICP were applied, respectively, and typical water-displacement method was performed to evaluate the catalytic activity. Using a solution composed of 10 wt% NaBH4 and 2 wt% NaOH, hydrogen generation rate was up to 11.12 L min?1 g?1 (25 °C), which is much higher than that of the commercial cobalt oxides and similar catalyst precursors reported in literature.  相似文献   

7.
Hydrogen production through the reaction between sodium borohydride (NaBH4) and water in presence of three different catalysts including; NiB, CoB and NiCoB is studied. The catalysts are synthesized by chemical reduction method at room and 0 °C temperature. The products are characterized by X-Ray Diffraction (XRD), High-Resolution Scanning Electron Microscopy (HRSEM) and Inductively Coupled Plasma-optical emission spectroscopy (ICP). The results showed that carrying out synthesizing process at low temperature, causes decreasing the nuclei size and reducing driving force for the growth stage, and results in a meaningful reduction in size of the produced catalysts particles. Furthermore, it leads to a recognizable change in particles shape to fine spherical with definite boundaries and slightly increase in boron content of each catalyst. These changes, especially in size and shape of the produced catalysts, results in an improvement in catalytic activity of the synthesized catalysts and the rate of hydrogen generation through using them. This achievement were successfully proved for all three NiB, CoB and NiCoB catalysts, although it was more pronounced for CoB so that it was possible to produce 1.4 lit hydrogen in less than 13 s (12,923 ml·min?1.g?1catalyst) by using 0.5 g of CoB catalyst synthesized at 0 °C.  相似文献   

8.
With the aim of designing an efficient hydrogen generator for portable fuel cell applications nickel–cobalt–boride (Ni–Co–B) catalysts were prepared by a chemical reduction method and their catalytic hydrolysis reaction with alkaline NaBH4 solution was studied. The performance of the catalysts prepared from NaBH4 solution with NaOH, and without NaOH show different hydrogen generation kinetics. The rate of hydrogen generation was measured using Ni–Co–B catalyst as a function of the concentrations of NaOH and NaBH4, as well as the reaction temperature, in the hydrolysis of alkaline NaBH4 solution. The hydrogen generation rate increases for lower NaOH concentrations in the alkaline NaBH4 solution and decreases after reaching a maximum at 15 wt.% of NaOH. The hydrogen generation rate is found to be constant with respect to the concentration of NaBH4 in the alkaline NaBH4 solution. The activation energy for hydrogen generation is found to be 62 kJ mol−1, which is comparable with that of hydrogen generation by a ruthenium catalyst.  相似文献   

9.
Micrometer sized carbon spheres (CSs) are prepared in a single step using lactose precursor via hydrothermal method. These CSs are chemically modified with 3-chloro-2-hydroxypropyl ammonium chloride (CHPACl) and triethylenetetramine (TETA) to generate amine groups on the particle surface. Modified CSs with TETA was protonated with HCl as CSs-TETA-HCl that the zeta potential is increased to +40.3 ± 0.70 from ?51.4 ± 4.66 mV. The catalytic performance of CSs are tested as catalysts in the methanolysis of NaBH4, and the best catalytic performance as 2586 mL min?1 g?1 hydrogen generation rate (HGR) was obtained by CSs-TETA-HCl catalyst at 298 K as metal free catalyst. Furthermore, various parameters such as the amount of NaBH4, the reaction temperature, and the reusability of CSs-TETA-HCl particles are investigated. More importantly, relatively low activation energy, 23.82 kJ mol?1 for CSs-TETA-HCl catalyzed NaBH4 methanolysis reaction is obtained in comparison to metal nanoparticle and metal free catalysts reported for the same purpose in the literature.  相似文献   

10.
Cyclic life of catalyst for hydrolysis of sodium borohydride is one of the key issues, which hinder commercialization of hydrogen generation from sodium borohydride (NaBH4) solution. This paper is aimed at promoting the cyclic life of Ru/Ni foam catalysts by employing an electro-deposition method. The effect of hydrolysis parameters on hydrolysis of sodium borohydride was studied for improving the catalytic performance. It is found that the hydrogen generation rate (HGR) of the hydrolysis reaction catalyzed by Ru/Ni foam catalyst can reach as high as 23.03 L min?1 g?1 (Ru). The Ru/Ni foam catalyst shows good catalytic activity after a cycleability test of 100 cycles by rinsing with HCl, which is considered as more effective method than rinsing with water for recovering the performance of Ru/Ni foam catalyst.  相似文献   

11.
Agglomeration of CoB catalysts is a severe problem in hydrogen generation from NaBH4 hydrolysis. Herein, highly dispersed carbon nanofiber immobilized CoB catalysts (CoB/CN) were synthesized by a combined prereduction and carbonization method, which is used in hydrogen generation from NaBH4 hydrolysis. Morphological evolution of carbon nanofibers, phase structure and elemental distribution of CoB/CN catalysts are explored by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Compared to Co/carbon nanofiber catalysts (Co/CN) without prereduction, CoB/CN catalysts can afford higher CoB dispersity and specific surface area because the migration rate of cobalt species during carbonization is effectively retarded by prereduction. Hence the agglomeration of magnetic CoB nanoparticles can be effectively inhibited. The hydrogen generation experiment shows that CoB/CN catalysts process higher catalytic activity and lower activation energy than Co/CN.  相似文献   

12.
Generation of hydrogen by hydrolysis of alkali metal hydrides has attracted attention. Unsupported CoB catalyst demonstrated high activity for the catalytic hydrolysis of NaBH4 solution. However, unsupported CoB nanoparticles were easy to aggregate and difficult to reuse. To overcome these drawbacks, CoB/SiO2 was prepared and tested for this reaction. Cobalt (II) acetate precursor was loaded onto the SiO2 support by incipient-wetness impregnation method. After drying at 100 °C, Co cations were deposited on the support. The dried sample was then dispersed in methanol/water solution and then fully reduced by NaBH4 at room temperature. The catalyst was characterized by N2 sorption, XRD and XPS. The results indicated that the CoB on SiO2 possessed amorphous structure. B and Co existed both in elemental and oxidized states. SiO2 not only affected the surface compositions of CoB, but also affected the electronic states of Co and B. B0 could donate partial electron to Co0. The structure effect caused by the SiO2 support helped to prevent CoB nanocluster from aggregation and therefore the activity increased significantly on hydrolysis of alkaline NaBH4 solution. The CoB/SiO2 catalyst showed much higher activity than the unsupported CoB catalyst. At 298 K, the hydrogen generation rate on CoB/SiO2 catalyst was 4 times more than that on the unsupported CoB catalyst. The hydrogen generation rate was as high as 10,586 mL min−1 g−1 catalyst at 298 K. CoB/SiO2 is a very promising catalyst for this reaction.  相似文献   

13.
Highly dispersed Co–Ce–B nanoparticles supported on chitosan-derived carbon (Co–Ce–B/Chi–C) were synthesized through chemical reduction and carbonization. The morphology and microstructure of the Co–Ce–B/Chi–C nanocomposite were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, and Brunauer–Emmett–Teller adsorption analysis. This nanocomposite had uniform morphology and large surface area, and it showed high catalytic activity for NaBH4 hydrolysis and good cycle stability. Compared with unsupported Co–Ce–B particles, this nanocomposite showed greatly increased catalytic activity for NaBH4 hydrolysis. A remarkably high hydrogen generation rate of 4760 mL?1 min?1 g?1 at 30 °C was achieved with low activation energy of 33.1 kJ mol?1. These results indicate that the Co–Ce–B/Chi–C nanocomposite is a promising catalyst for on-demand hydrogen generation via NaBH4 hydrolysis.  相似文献   

14.
A novel recyclable cobalt nanocatalyst, supported on magnetic carbon with core-shell structure, was successfully synthesized by using wetness impregnation-chemical reduction method for hydrogen generation from hydrolysis of NaBH4. The resultant nanocomposite was characterized to determine the structural and physical-chemical properties by a series of analytical techniques such as FT-IR (Fourier transform infrared spectroscopy), XRD (X-ray diffraction), SEM (scanning electron microscope), EDX (energy-dispersive X-ray spectroscopy), TEM (transmission electron microscopy), etc. The results demonstrated that amorphous cobalt nanoparticles were homogeneously surrounded on the surface of the support due to having abundant hydrophilic groups (such as aldehyde and hydroxyl groups) on the surface of carbon layer for the effective immobilization of metal ions. The supported catalyst showed superior catalytic performance towards the hydrolysis reaction of NaBH4 at room temperature. The total rate of hydrogen generation and activation energy were calculated to be 1403 ml H2 gcat?1 min?1 and 49.2 kJ mol?1, respectively, which were comparable to the values of most cobalt-based catalyst reported for hydrogen production from hydrolysis of NaBH4. Additionally, reusability test revealed that the hydrogen in NaBH4 substrate could be completely released within 25 min with a minimum hydrogen generation rate of 832 ml H2 gcat?1 min?1 even after five runs of hydrolytic reaction, implying the as-prepared Co/Fe3O4@C composite could be considered as a promising candidate catalyst for portable hydrogen fuel system such as PEMFC (proton exchange membrane fuel cells).  相似文献   

15.
Magnetic nickel–ruthenium based catalysts on resin beads for hydrogen generation from alkaline NaBH4 solutions were synthesized with combined methods of chemical reduction and electroless deposition. Factors, such as solution temperature, NaBH4 loadings, and NaOH concentration, on performance of these catalysts on hydrogen production from alkaline NaBH4 solutions were investigated. Furthermore, characteristics of these nickel–ruthenium based catalysts were carried out by using various instruments, such as SEM/EDS, XPS, SQUID VSM and BET. These catalysts can be easily recycled from spent NaBH4 solution with permanent magnets owing to their intrinsic soft ferromagnetism and, therefore, reducing the operation cost of the hydrogen generation process. A rate of hydrogen evolution as high as ca. 400 mL min−1 g−1 could be reached at 35 °C in 10 wt% NaBH4 solution containing 5 wt% NaOH using Ni–Ru/50WX8 catalysts. Activation energy of hydrogen generation using such catalysts is estimated at 52.73 kJ mol−1.  相似文献   

16.
Cobalt–phosphorous (Co–P) catalysts with a high hydrogen generation rate in alkaline sodium borohydride (NaBH4) solution are developed by electroless deposition. The microstructures of the Co–P catalysts and their catalytic activities for hydrolysis of NaBH4 are analyzed as a function of the electroless deposition conditions such as the pH and temperature of the Co–P bath. The electroless-deposited Co–P catalysts are composed of nano-crystalline Co and amorphous Co–P. The size of the nano-crystalline Co particles dispersed in amorphous Co–P matrix depends largely on the electroless deposition conditions. Moreover, Co–P catalysts with finer crystalline Co exhibit a higher hydrogen generation rate. In particular, the Co–P catalysts formed in a pH 12.5 bath at 60–70 °C exhibit the best hydrogen generation rate of 3300 ml min−1 g−1-catalyst in 1 wt.% NaOH + 10 wt.% NaBH4 solution at 30 °C, which is 60 times faster than that obtained with a Co catalyst.  相似文献   

17.
Low cost transition metal catalysts with high performance are attractive for the development of on-board hydrogen generation systems by catalytic hydrolysis of sodium borohydride (NaBH4) in fuel cell fields. In this study, hydrogen production from alkaline NaBH4 via hydrolysis process over carbon-supported cobalt catalysts was studied. The catalytic activity of the supported cobalt catalyst was found to be highly dependent on the calcination temperatures. The hydrogen generation rate increases with calcination temperatures in the range of 200–400 °C, but a high calcination temperature above 500 °C led to markedly decreased activity. X-ray diffraction patterns reveal that the catalysts experience phase transition from amorphous Co–B to crystalline cobalt hydroxide with increase in calcination temperatures. The reaction performance is also dependent on the concentration of NaBH4, and the hydrogen generation rate increases for lower NaBH4 concentrations and decreases after reaching a maximum at 10 wt.% of NaBH4.  相似文献   

18.
In this study, a dandelion-like Co–Mo–B catalyst was prepared on carbon cloth (CC) by two-step electrodeposition method for the first time. The composition and microscopy are characterized by XRD and SEM technology. The results revealed that the as-synthesized Co–Mo–B catalyst exhibited high hydrogen generation rate (1280.80 mL min?1 g?1) and low activation energy (51.0 kJ mol?1) for the hydrolysis of alkaline NaBH4 solution. The results reveal that the reason might be due to high specific surface of the novel dandelion-like nanostructure and the synergistic effect of Co, Mo and B. Moreover, the catalytic activity was closely related to NaOH concentration, and OH anions were competitive with BH4 anions in alkaline NaBH4 solution to transfer to the catalyst surface.  相似文献   

19.
Solution combustion synthesis (SCS) has recently been explored as one method to synthesize metal oxides (e.g. Co3O4) that can serve as catalytic precursors for the hydrolysis of sodium borohydride (NaBH4). In this work, SCS is used to produce the mixed metal oxide lithium cobalt oxide (LiCoO2) from a solution of cobalt nitrate, lithium acetate, and glycine. Its subsequent use as an effective catalyst precursor for NaBH4 hydrolysis is characterized and compared to commercially available LiCoO2. To remove residual impurities from the SCS material the materials were heated at a rate of 10 °C min?1 and held for 2 h at temperatures ranging from 500 to 800 °C and subsequently characterized. It was found that the layered phase of LiCoO2 results at heat treat temperatures above 700 °C. Using a 0.6 wt.% aqueous solution of NaBH4 at 25 °C and a 1 wt.% catalyst precursor loading, an optimized HGR of 2.09 L min?1 gcat?1 was achieved for the solution combustion synthesized LiCoO2. In contrast, at the same conditions, a HGR of 0.29 L min?1 gcat?1 was obtained for commercial materials even though the specific surface area was much higher.  相似文献   

20.
The catalyst with high activity and durability plays a crucial role in the hydrogen generation systems for the portable fuel cell generators. In the present study, a ruthenium supported on graphite catalyst (Ru/G) for hydrogen generation from sodium borohydride (NaBH4) solution is prepared by a modified impregnation method. This is done by surface pretreatment with NH2 functionalization via silanization, followed by adsorption of Ru (III) ion onto the surface, and then reduced by a reducing agent. The obtained catalyst is characterized by transmission electron microscope (TEM) and X-ray photoelectron spectroscopy (XPS). Very uniform Ru nanoparticles with sizes of about 10 nm are chemically bonded on the graphite surface. The hydrolysis kinetics measurements show that the concentrations of NaBH4 and NaOH all exert considerable influence on the catalytic activity of Ru/G catalyst towards the hydrolysis reaction of NaBH4. A hydrogen generation rate of 32.3 L min−1 g−1 (Ru) in a 10 wt.% NaBH4 + 5 wt.% NaOH solution has been achieved, which is comparable to other noble catalysts that have been reported.  相似文献   

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