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1.
The oxygen reduction reaction (ORR) was studied at carbon supported MoOx-Pt/C and TiOx-Pt nanocatalysts in 0.5 mol dm−3 HClO4 solution, at 25 °C. The MoOx-Pt/C and TiOx-Pt/C catalysts were prepared by the polyole method combined by MoOx or TiOx post-deposition. Home made catalysts were characterized by TEM and EDX techniques. It was found that catalyst nanoparticles were homogenously distributed over the carbon support with a mean particle size about 2.5 nm. Quite similar distribution and particle size was previously obtained for Pt/C catalyst. Results confirmed that MoOx and TiOx post-deposition did not lead to a significant growth of the Pt nanoparticles.The ORR kinetics was investigated by cyclic voltammetry and linear sweep voltammetry at the rotating disc electrode. These results showed the existence of two E − log j regions, usually observed with polycrystalline Pt in acid solution. It was proposed that the main path in the ORR mechanism on MoOx-Pt/C and TiOx-Pt/C catalysts was the direct four-electron process with the transfer of the first electron as the rate-determining step. The increase in catalytic activity for ORR on MoOx-Pt/C and TiOx-Pt/C catalysts, in comparison with Pt/C catalyst, was explained by synergetic effects due to the formation of the interface between the platinum and oxide materials and by spillover due to the surface diffusion of oxygen reaction intermediates.  相似文献   

2.
Ethylene decomposition was performed over supported Pt catalysts to fabricate composites of Pt metal nanoparticles and carbon nanotubes (CNTs). All supported Pt catalysts (Pt/carbon black, Pt/CNT, Pt/MgO, Pt/Al2O3 and Pt/SiO2) showed catalytic activity for ethylene decomposition at 973 K to form CNTs. Pt metal particles were found at tips of CNTs. These results indicate that Pt metal particles have catalytic activity for growth of CNTs through hydrocarbon decomposition. A broad range (5-50 nm) of CNT diameters were formed from the use of supported Pt metal catalysts although Pt metal particles in the catalysts before ethylene decomposition were relatively uniform in size (2-5 nm). These results imply that Pt metal particles in the catalysts aggregated during ethylene decomposition at 973 K. Aggregation of Pt metal particles in catalysts during ethylene decomposition could be suppressed by covering catalysts with silica layers that were a few nanometers thick. Silica-coated Pt catalysts showed high activity for ethylene decomposition to form CNTs with uniform diameters (8-10 nm) despite the uniform coverage of Pt metal particles with silica layers.  相似文献   

3.
L Xiong 《Electrochimica acta》2004,49(24):4163-4170
Pt/TiOx/C nanocomposites have been synthesized by depositing hydrated titanium oxide on carbon-supported Pt (Pt/C), reducing H2PtCl6 with sodium formate on carbon-supported hydrated titanium oxide (TiO2/C), and simultaneously depositing hydrated titanium oxide and reducing H2PtCl6 with formate on carbon support, followed by heat treatment at 500 and 900 °C in 90% Ar-10% H2 mixture. The catalytic activity for oxygen reduction was evaluated in half cells with sulfuric acid electrolyte and in single direct methanol fuel cells (DMFC). Tolerance to methanol was studied with half cells containing sulfuric acid mixed with methanol. Charge transfer resistance and electrochemical active surface area of the Pt/TiOx/C catalysts were studied with impedance and cyclic voltammetry measurements. Both the synthesis methods and heat treatments influence the catalytic activity, and some of the Pt/TiOx/C composites exhibit higher catalytic activity than Pt/C. The Pt/TiOx/C catalysts also exhibit better methanol tolerance than Pt/C. The mechanism for the enhanced catalytic activity of Pt/TiOx/C is discussed.  相似文献   

4.
Mn-Ce-OX catalysts loaded on TiO2-carbonaceous materials were prepared by sol-gel method. Selective catalytic reduction of NOX was conducted in a fixed-bed flow-reactor over catalysts coated on aluminum plates. A de-NOX efficiency of more than 90% was obtained over the Mn-Ce-OX/TiO2-carbon nanotubes (CNTs) catalyst between 75 °C and 225 °C under a gas hourly space velocity (GHSV) of ~ 36,000 h−1. This activity improvement is attributed to the increase of the BET surface area, and the occurrence of reaction between adsorbed NOX and NH3. Moreover, the de-NOX efficiency was increased to 99.6% by adding 250 ppm SO2 between 100 °C and 250 °C.  相似文献   

5.
Li Li 《Carbon》2006,44(14):2973-2983
Characteristics of nanosized Pt electro-catalyst deposited on carbon nanotubes (CNTs) were studied with CO-stripping voltammogram and chronoamperometry measurements. The CNTs were pretreated by oxidation in HNO3, mixed HNO3 + H2SO4 and H2SO4 + K2Cr2O7 solution, respectively, to enable surface modification. Well-homogenized Pt particles (average size: ≈3 nm) were loaded onto the pretreated CNT samples by a modified colloidal method. TEM, BET, FTIR and XRD techniques were used to characterize the physicochemical properties of the pretreated CNT samples. In the electro-oxidation of CO, all the Pt/CNT samples showed lower on-set as well as peak potentials than the conventional Pt/XC-72 electro-catalyst, indicating that the Pt/CNT samples were more resistant to CO poisoning and could be superior anode electro-catalyst for the proton exchange membrane fuel cells (PEMFCs). Moreover, we found that the pretreatment of CNTs in mixed HNO3 + H2SO4 solution was very beneficial for the performance enhancement of Pt/CNT electro-catalyst; the catalyst obtained as such gave the lowest peak potential and the highest catalytic activity for the electro-oxidation of CO. Larger amount of oxygen-containing functional groups, higher percentage of mesopores, and higher graphitic crystallinity of the pretreated CNTs were considered crucial for the performance enhancement, e.g., by strengthening the interaction between Pt nanoparticles and the CNT support and enhancing the mass diffusion in the electro-chemical reaction.  相似文献   

6.
The kinetics of carbon nanotube (CNT) synthesis by decomposition of CH4 over Mo/Co/MgO and Co/MgO catalysts was studied to clarify the role of catalyst component. In the absence of the Mo component, Co/MgO catalysts are active in the synthesis of thick CNT (outer diameter of 7-27 nm) at lower reaction temperatures, 823-923 K, but no CNTs of thin outer diameter are produced. Co/MgO catalysts are significantly deactivated by carbon deposition at temperatures above 923 K. For Mo-including catalysts (Mo/Co/MgO), thin CNT (2-5 walls) formation starts at above 1000 K without deactivation. The significant effects of the addition of Mo are ascribed to the reduction in catalytic activity for dissociation of CH4, as well as to the formation of Mo2C during CNT synthesis at high temperatures. On both Co/MgO and Mo/Co/MgO catalysts, the rate of CNT synthesis is proportional to the CH4 pressure, indicating that the dissociation of CH4 is the rate-determining step for a catalyst working without deactivation. The deactivation of catalysts by carbon deposition takes place kinetically when the formation rate of the graphene network is smaller than the carbon deposition rate by decomposition of CH4.  相似文献   

7.
Sulfated TiO2 nanotubes and a series of iron oxide loaded sulfated TiO2 nanotubes catalysts with different iron oxide loadings (1 wt%, 3 wt%, 5 wt% and 7 wt%) were prepared and calcined at 400 °C. The physico-chemical properties of the catalysts were studied by using XRD, N2-physisorption, Raman spectroscopy, SEM-EDX, TEM, XPS, and pyridine adsorption using FTIR and H2-TPR techniques. It was observed that iron oxide was highly dispersed on the sulfated TiO2 nanotube support due to its strong interaction. The activity of these catalysts in the catalytic removal of NO with propane was also studied in the temperature range of 300–500 °C. Highest activity (90% NO conversion) was observed with 5 wt% iron oxide supported on sulfated TiO2 catalyst at 450 °C. Selective catalytic reduction of NO activity of the catalysts was correlated with iron oxide loading, reducibility, and the Brönsted and Lewis acid sites of the catalysts. The catalyst also showed good stability under studied reaction conditions that no deactivation was observed during the 50 h of reaction.  相似文献   

8.
This paper presents the growth evolutions in terms of the structure, growth direction and density of rapid grown carbon nanotube (CNT) forests observed by scanning and transmission electron microcopies (SEM/TEM). A thermal CVD system at around 700 °C was used with a catalyst of Fe films deposited on thin alumina (Al2O3) supporting layers, a very fast raising time to the growth temperature below 25 °C/s, and a carbon source gas of acetylene diluted with hydrogen and nitrogen without water vapor. Activity of Fe catalyst nanoparticles was maintained for 5 min during CVD process, and it results in CNT forests with heights up to 0.6 mm. SEM images suggest that the disorder in CNT alignment at the initial stage of CNTs plays a critical role in the formation of continuous CNT growth. Also, the prolonged heating process leads to increased disorder in CNT alignment that may be due to the oxidation process occurring at the Fe nanoparticles. TEM images revealed that both double- and few-walled CNTs with diameters of 5-7 nm were obtained and the CNT density was controlled by thickness of Fe catalytic layer. The number of experiments at the same conditions showed a very good repeatability and reproducibility of rapid grown CNT forests.  相似文献   

9.
Nanostructures consisting of TiO2 particles as a core and carbon as a shell (TiO2@C) were prepared by heat treatment of TiO2 nanoparticles at 700 or 900 °C in a methane atmosphere. X-ray diffraction and transmission electron microscopy showed that a carbon shell layer was formed whose thickness increased with increasing reaction temperature. These structures were used as supports for platinum nanoparticles and the hybrid particles exhibit improved catalytic activity and stability toward methanol electrooxidation compared to Pt on a carbon black (Vulcan XC-72R). It is likely that enhanced catalytic properties of the Pt on TiO2@C could be due to the stability of the core-shell support in comparison with carbon black support.  相似文献   

10.
Hollow carbon spheres (HCSs) were prepared through a simple hydrothermal method using silica particles and glucose as the template and carbon precursor, respectively. HCSs used as supports for platinum catalysts deposited with cerium oxide (CeO2) were prepared for application as anode catalysts in direct methanol fuel cells. The composition and structure of the samples were investigated by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), energy dispersive spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS). The electrocatalytic properties of the as-prepared catalysts for methanol oxidation were investigated by cyclic voltammetry (CV). The Pt/CeO2/HCSs catalyst heated at 550 °C for 1 h exhibited the best catalytic activity for methanol oxidation.  相似文献   

11.
Guodong Jiang  Lihua Zhu  Yaobin Ding 《Carbon》2010,48(12):3369-798
Composite films of TiO2 and carbon nanotubes (CNTs) were prepared on titanium sheets by liquid phase deposition and the photoelectrocatalytic (PEC) properties of the films were investigated through the degradation of methyl orange (MO) in 0.1 M solutions. It was demonstrated that CNTs in the TiO2 film significantly decreased the charge transfer resistance and increased the anodic photocurrent response of the film under UV light irradiation when the bias was above −0.1 V. The PEC performance of the CNT-based composite film could be tuned by controlling the preparation parameters including the deposition time and calcination temperature. The deposition time and calcination temperature were optimized at 1 h and 450 °C, respectively. On the TiO2/CNT film prepared under the optimized conditions, 95% of the added MO (10 mg L−1) was degraded within 90 min, which was much higher than the 60% removal seen on the pure TiO2 films.  相似文献   

12.
Carbon nanotubes (CNTs) were synthesized using CH4/H2 plasmas and plasmas simulated using a one-dimensional fluid model. The thinnest and longest CNTs with the highest number density were obtained using CH4/H2 = 27/3 sccm at 10 Torr. These conditions allowed CNTs to grow for 90 min without any meaningful loss of catalyst activity. However, an excess H2 supply to the CH4/H2 mixture plasma made the diameter distribution of the CNTs wider and the yield lower. Hydrogen concentration is considered to affect catalyst particle size and activity during the time interval before starting CNT growth (=incubation period). With CH4/H2 = 27/3 sccm for a growth time of 10 min efficient CNT growth was achieved because the amount of carbon atoms in the CNTs and that calculated from simulation showed good agreement. The effect of hydrogen etching on CNTs was analyzed by scanning electron microscopy and X-ray photoelectron spectroscopy by observing CNTs treated by H2 plasma after CNT growth. It was confirmed that (a) multi-walled CNTs were not etched by the H2 plasma, (b) the C 1s XPS spectra of the CNTs showed no chemical shift after the treatment, and (c) C-H bonds were produced in CNTs during their growth.  相似文献   

13.
The influence of heat treatment on the improvement of the catalytic activity of CoTETA/C catalysts is investigated. These non-precious metal oxygen reduction catalysts are prepared from carbon-supported cobalt triethylenetetramine (CoTETA/C) and heat treated in the temperature interval from 500 to 1000 °C in Ar atmosphere. Electrochemical characteristics are demonstrated in oxygen-saturated acid electrolyte by rotating disk electrode, cyclic voltammetry, as well as single fuel cell tests. The results show that the effect of heat treatment is important on the catalytic activity of CoTETA/C catalysts for the ORR and a maximum catalytic activity is obtained after heat treatment at 800 °C. The ORR reaction mechanism on the catalysts heat treated at 700, 800 and 900 °C is mainly through a 4e reaction path, while a 2e reaction is dominant on the catalysts heat treated at 500, 600 and 1000 °C. Tafel slopes of the CoTETA/C catalysts are all around −200 mV/dec. X-ray absorption measurements reveal that the CoN4 centers are no longer detected after heat treatment. XRD results clearly confirm the formation of nanometallic α-Co with different sizes aggregated. A possible interpretation of the catalytic active sites is also discussed.  相似文献   

14.
Jiangying Qu  Zhiyu Wang  Jieshan Qiu 《Carbon》2010,48(5):1465-889
Hierarchical three-dimensional (3D) tubular micropatterns made of carbon nanotubes (CNTs) are fabricated on silicon substrates by catalytic decomposition of a ferrocene-cyclohexane mixture at 850 °C in the presence of CO2. It is found that the catalyst concentration, temperature and the presence of CO2 are key factors that govern the assembly and growth of CNTs. The self-assembled patterns of catalysts in the initial stage are responsible for the formation of CNT patterns in which a multi-level self-assembly is involved. The potential use of the tubular CNT micropatterns as electrode in the electroanalysis of biomolecules (dopamine) has been demonstrated.  相似文献   

15.
A non-platinum cathode electrocatalyst must have the stability and catalytic activity for the oxygen reduction reaction (ORR) in order to be used in polymer electrolyte fuel cells (PEFCs). Titanium oxide catalysts as the non-platinum catalyst were prepared by the heat treatment of titanium sheets in the temperature range from 600 to 1000 °C. The prepared catalysts were chemically and electrochemically stable in 0.1 mol dm−3 H2SO4. The titanium oxide catalysts showed different catalytic activities for the ORR. The ORR of the catalysts heat-treated at around 900 °C occurred at the potential of about 0.65 V versus RHE. It is considered that the deference in the catalytic activity for the ORR of the heat-treated titanium oxide catalysts was due to the fact that the heat-treatment condition changed the material property of the catalyst surface. In particular, it was found that the catalytic activity for the ORR of the Ti oxide catalysts increased with the increase in the specific crystalline structure, such as the TiO2 (rutile) (1 1 0) plane and the work function. It is considered that a surface state change, such as the crystalline structure and work function, might affect the catalytic activity for the ORR.  相似文献   

16.
Pt/C nanocatalysts were prepared by the reduction of chloroplatinic acid with sodium borohydride, with citric acid as a stabilizing agent in ammonium hydroxide solution. These nanocatalysts were obtained by altering the molar ratio of citric acid to chloroplatinic acid (CA/Pt) from 1:1, 2:1, 3:1 to 4:1. Transmission electron microscopy and X-ray diffraction analyses indicated that the well-dispersed Pt nanoparticles of around 3.82 nm in size were obtained when the CA/Pt ratio was maintained at 2:1. X-ray photoelectron spectroscopy measurements revealed that the 2:1, 3:1 and 4:1 molar ratio catalysts had a relatively higher amount of Pt in their metallic state than did the 1:1 molar ratio catalyst. Cyclic voltammetry results demonstrated that the Pt/C nanocatalysts annealed at 400 °C in an N2 atm provided higher electrocatalytic activity. Among all the molar ratio catalysts, the 2:1 molar ratio catalyst exhibited the largest electrochemical active surface (EAS) area, and its methanol oxidation reaction current was superior to the E-TEK catalyst. The oxygen reduction reaction of the catalysts studied by linear sweep voltammetry and tested in a fuel cell indicated that the catalytic activity of the 2:1 molar ratio catalyst was comparable to that of an E-TEK catalyst.  相似文献   

17.
We report the synthesis of multi-walled carbon nanotubes coated with sulfated TiO2 (S-TiO2/MWCNTs) as a promising support for Pt catalyst in a direct ethanol fuel cell. Highly dispersed Pt nanoparticles were supported on the S-TiO2/MWCNT composites by NaBH4 reduction procedure (Pt-S-TiO2/MWCNTs). The presence and nature of the catalyst were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, high-resolution transmission electron microscopy. The size of the sulfated TiO2 product was about 8 nm, and that of the Pt nanoparticle on the S-TiO2/MWCNT composites was about 5 nm. The Pt-S-TiO2/MWCNTs were used to study the electrochemical ethanol oxidation reaction using cyclic voltammetry, chronoamperometry and impedance spectroscopy. The results show that Pt-S-TiO2/MWCNT catalysts show higher catalytic activity for ethanol oxidation compared with Pt supported on non-sulfated TiO2/MWCNT composites and commercial Pt/C catalysts.  相似文献   

18.
L. Xiong 《Electrochimica acta》2005,50(11):2323-2329
Nanostructured Pt-M/C (M = Fe and Co) catalysts have been synthesized by a microemulsion method and a high-temperature route. They have been characterized by cyclic voltammetry in 1 M H2SO4 and for oxygen reduction in proton exchange membrane fuel cells (PEMFC). The Pt-M alloy catalysts synthesized by the microemulsion method show higher electrochemical active surface area than those prepared by the high-temperature route, and some of them exhibit improved catalytic activity towards oxygen reduction compared to pure Pt. Among the various alloy catalysts investigated, the Pt-Co/C catalyst prepared by the microemulsion method shows the best performance with the maximum catalytic activity and minimum polarization loss. Mild heat treatment of the catalysts prepared by the microemulsion method at moderate temperatures (200 °C) in reducing atmosphere is found to improve the catalytic activity due to a cleaning of the surface and an increase in the electrochemical surface area.  相似文献   

19.
Se-Jin Kyung 《Carbon》2006,44(8):1530-1534
Carbon nanotubes (CNTs) were grown using a modified atmospheric pressure plasma with NH3(210 sccm)/N2(100 sccm)/C2H2(150 sccm)/He(8 slm) at low substrate temperatures (?500 °C) and their physical and electrical characteristics were investigated as the application to field emission devices. The grown CNTs were multi-wall CNTs (at 450 °C, 15-25 layers of carbon sheets, inner diameter: 10-15 nm, outer diameter: 30-50 nm) and the increase of substrate temperature increased the CNT length and decreased the CNT diameter. The length and diameter of the CNTs grown for 8 min at 500 °C were 8 μm and 40 ± 5 nm, respectively. Also, the defects in the grown CNTs were also decreased with increasing the substrate temperature (The ratio of defect to graphite (ID/IG) measured by FT-Raman at 500 °C was 0.882). The turn-on electric field of the CNTs grown at 450 °C was 2.6 V/μm and the electric field at 1 mA/cm2 was 3.5 V/μm.  相似文献   

20.
A Co/Fe catalyst was prepared using the sol/gel technique in order to study its catalytic activity and selectivity in the Fischer-Tropsch synthesis. The effect of a range of operation variables such as pressure, temperature and H2/CO molar feed ratio on the catalytic performance of 40%Fe/60%Co/15 wt.%SiO2/1.5 wt.%K catalyst was investigated. It was found that the optimum operating conditions is a H2/CO = 2/1 molar feed ratio at 350 °C temperature and 3 bar pressure. Characterization of both precursor and calcined catalysts was carried out using XRD, SEM, EDS, TPR, BET surface area measurements and thermal analysis methods such as TGA and DSC. It was observed that all of the different operation variables influenced the structure, morphology and catalytic performance of the catalysts.  相似文献   

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