共查询到20条相似文献,搜索用时 15 毫秒
1.
Ki Woong Kim Sun-Woo Lee Kyoo-Seung Han Hyun Jin Chung Seong Ihl Woo 《Electrochimica acta》2003,48(28):4937-4231
A novel process called Liquid Source Misted Chemical Deposition (LSMCD) was used to synthesize Al-doped LiMn2O4 cathode films for Lithium microbatteries. The cathode films were characterized by XRD, SEM, cyclic volatmmetry, and charge/discharge test. LiMn1.8Al0.2O4 film crystallized at 800 °C in rapid thermal annealing (RTA) for 5 min under oxygen atmosphere exhibited more improved electrochemical rechargeability than spinel LiMn2O4 film because the substitution of Al3+ for Mn3+ increased Mn---O bonding strength in the spinel framework and suppressed the two-phase behavior of the unsubstituted spinel during the intercalation/deintercalation that is the origin of the failure mechanism in the 4 V region. As a result, LiMn1.8Al0.2O4 film showed an initial discharge capacity of 52 μAh/cm2 μm and no capacity fade over 100 cycles. 相似文献
2.
With an aim to improve the 5 V capacity and cyclability of the LiMn1.5Ni0.5O4 spinel oxide, three series of Cr substitutions have been pursued with y ≤ 0.2: LiMn1.5Ni0.5−yCryO4, LiMn1.5−0.5yNi0.5−0.5yCryO4, and LiMn1.5−0.33yLi0.33yNi0.5−yCryO4. While the first series involves an increase in the Mn3+ content, the second and third series are designed to maintain charge neutrality (Mn4+, Ni2+, Cr3+, and Li+) without introducing Mn3+ ions. The LiMn1.5Ni0.5−yCryO4 series experiences a widening of the 4 V plateau and a decrease in the 5 V capacity compared to LiMn1.5Ni0.5O4 due to an increase in the Mn3+ content. On the other hand, the LiMn1.5−0.5yNi0.5−0.5yCryO4 series shows a suppression of the 4 V plateau and an increase in the 5 V capacity due to the elimination of the Mn3+ions. The LiMn1.5−0.33yLi0.33yNi0.5−yCryO4 series shows a suppression of the 4 V plateau at low Cr contents, but an increase in the 4 V plateau as the Cr content increases above 0.1. Among the various compositions investigated, LiMn1.45Ni0.45Cr0.1O4 exhibits the best combination of high 5 V capacity (128 mAh/g at 5–4.2 V) and excellent capacity retention (98% in 50 cycles) compared to 118 mAh/g and 92% for LiMn1.5Ni0.5O4. 相似文献
3.
The surface of as-prepared LiMn2O4 was modified with Al2O3 by a melting impregnation method. X-ray diffraction, field emission scanning electron microscopy (FESEM) and transmission electron microscopy (TEM) studies indicated that Al2O3 nano-particles are distributed around the spinel. X ray absorption fine structure analysis (XAFS) further demonstrated that Al atoms were also doped to the surface of LiMn2O4 particles. The nano-Al2O3 particle coating improves the capacity retention of spinel LiMn2O4 efficiently at both room temperature and 55 °C. The mechanism of improvement for surface modified LiMn2O4 can be attributed to the inhibition of a surface Jahn-Teller distortion and the decrease of manganese dissolution, leading to good electric contact among particles. 相似文献
4.
Ha Heon Phil Maddigapu Pratap Reddy Pullur Anil Kumar Lee Kyung Ju Jung Soon Hyo 《Applied catalysis. B, Environmental》2008,78(3-4):301-308
To get the low temperature sulfur resistant V2O5/TiO2 catalysts quantum chemical calculation study was carried out. After selecting suitable promoters (Se, Sb, Cu, S, B, Bi, Pb and P), respective metal promoted V2O5/TiO2 catalysts were prepared by impregnation method and characterized by X-ray diffraction (XRD) and Brunner Emmett Teller surface area (BET-SA). Se, Sb, Cu, S promoted V2O5/TiO2 catalysts showed high catalytic activity for NH3 selective catalytic reduction (NH3-SCR) of NOx carried at temperatures between 150 and 400 °C. The conversion efficiency followed in the order of Se > Sb > S > V2O5/TiO2 > Cu but Se was excluded because of its high vapor pressure. An optimal 2 wt% ‘Sb’ loading was found over V2O5/TiO2 for maximum NOx conversion, which also showed high resistance to SO2 in presence of water when compared to other metal promoters. In situ electrical conductivity measurement was carried out for Sb(2%)/V2O5/TiO2 and compared with commercial W(10%)V2O5/TiO2 catalyst. High electrical conductivity difference (ΔG) for Sb(2%)/V2O5/TiO2 catalyst with temperature was observed. SO2 deactivation experiments were carried out for Sb(2%)/V2O5/TiO2 and W(10%)/V2O5/TiO2 at a temperature of 230 °C for 90 h, resulted Sb(2%)/V2O5/TiO2 was efficient catalyst. BET-SA, X-ray photoelectron spectroscopy (XPS) and carbon, hydrogen, nitrogen and sulfur (CHNS) elemental analysis of spent catalysts well proved the presence of high ammonium sulfate salts over W(10%)/V2O5/TiO2 than Sb(2%)/V2O5/TiO2 catalyst. 相似文献
5.
Effect of promoters including tungsten and barium on the thermal stability of V2O5/sulfated TiO2 catalyst for NO reduction by NH3 总被引:2,自引:0,他引:2
The effect of tungsten and barium on the thermal stability of V2O5/TiO2 catalyst for NO reduction by NH3 was examined over a fixed bed flow reactor system. The activity of V2O5/sulfated TiO2 catalyst gradually decreased with respect to the thermal aging time at 600 °C. The addition of tungsten to the catalyst surface significantly enhanced the thermal stability of V2O5 catalyst supported on sulfated TiO2. On the basis of Raman and XRD measurements, the tungsten on the catalyst surface was identified as suppressing the progressive transformation of monomeric vanadyl species into crystalline V2O5 and of anatase into rutile phase of TiO2. However, the NO removal activity of V2O5/sulfated TiO2 catalyst including barium markedly decreased after a short aging time, 6 h at 600 °C. This may be due to the transformation of vanadium species to inactive V–O–Ba compound by the interaction with BaO which was formed by the decomposition of BaSO4 on the catalyst surface at high reaction temperature of 600 °C. The addition of SO2 to the feed gas stream could partly restore the NO removal activity of thermally aged V2O5/sulfated TiO2 catalyst containing barium. 相似文献
6.
The surface structure analysis of a model catalyst MoOx/TiO2(110) was for the first time performed by polarization-dependent total-reflection fluorescence X-ray absorption fine structure (PTRF-XAFS) in three different directions of the crystal surface. Two samples of MoOx/TiO2(110) were prepared by an impregnation of (NH4)6Mo7O24·4H2O using ultra high purity water and normal distilled water. The PTRF-XAFS analysis revealed that anisotropic Mo dimer species was preferentially formed on the TiO2(110) surface, with Mo–Mo bond (0.335 nm) parallel to the
direction when the ultra high purity water was used as the solvent. On the other hand, the Mo oxide on the surface prepared using normal distilled water had a symmetric tetrahedral structure (MoO4) with Mo–O of 0.176 nm, which was due to the coexistence of alkaline metals at the surface. 相似文献
7.
Shihong Xu Wenfeng Shangguan Jian Yuan Mingxia Chen Jianwei Shi 《Applied catalysis. B, Environmental》2007,71(3-4):177-184
A magnetically separable nitrogen-doped photocatalyst TiO2−xNx/SiO2/NiFe2O4 (TSN) with a typical ferromagnetic hysteresis was prepared by a simple process: the magnetic SiO2/NiFe2O4 (SN) dispersion prepared by a liquid catalytic phase transformation method and the visible-light-active photocatalyst TiO2−xNx were mixed, sonificated, dried, and calcined at 400 °C. The prepared photocatalyst is photoactive under visible light irradiation and easy to be separated from a slurry-type photoreactor under the application of an external magnetic field, being one of promising photocatalysts for wastewater treatment. Transmission electron microscope (TEM) and X-ray diffractometer (XRD) were used to characterize the structure of the TSN photocatalyst. The results indicate that the magnetic SiO2/NiFe2O4 (SN) nanoparticles adhere to the surface of TiO2−xNx congeries. The magnetic photocatalyst TSN shows high catalytic activity for the degradation of methyl orange in water under UV and visible light irradiation (λ > 400 nm). SiO2 coating round the surface of NiFe2O4 nanoparticles prevents effectively the injection of charges from TiO2 particles to NiFe2O4, which gives rise to the increase in photocatalytic activity. Moreover, the recycled TSN exhibits a good repeatability of the photocatalytic activity. 相似文献
8.
Cu2O/TiO2, Bi2O3/TiO2 and ZnMn2O4/TiO2 heterojunctions were studied for potential applications in water decontamination technology and their capacity to induce an oxidation process under VIS light. UV–vis spectroscopy analysis showed that the junctions-based Cu2O, Bi2O3 and ZnMn2O4 are able to absorb a large part of visible light (respectively, up to 650, 460 and 1000 nm). This fact was confirmed in the case of Cu2O/TiO2 and Bi2O3/TiO2 by photocatalytic experiments performed under visible light. A part of the charge recombination that can take place when both semiconductors are excited was observed when a photocatalytic experiment was performed under UV–vis illumination. Orange II, 4-hydroxybenzoic and benzamide were used as pollutants in the experiment. Photoactivity of the junctions was found to be strongly dependent on the substrate. The different phenomena that were observed in each case are discussed. 相似文献
9.
Photocatalytic performance of nanometer-sized FexOy/TiO2 particle synthesized by hydrothermal method
The nanometer particles of two FexOy/TiO2’s with high photocatalytic activities were obtained through hydrothermal treatment and impregnation method. The XRD result did not show the peaks assigned to the Fe components (for example Fe2O3, Fe3O4, FeO3, and Fe metal) on the external surface of the anatase structure in the FexOy/TiO2 attained through hydrothermal treatment. This meant that Fe components were well incorporated into the TiO2 anatase structure. In addition, it exhibited uniform anatase structure with particle size of below 50 nm. The FeO3 component on the external surface of the TiO2 anatase structure was identified in the Fe-loaded TiO2 prepared through the impregnation method. In particular, the FT-IR spectroscopy revealed that the FexOy/TiO2 particle attained through hydrothermal treatment had higher hydrophilic property compared to the other catalysts. Together with the Fe component, they absorbed wavelength of above 370 nm. The band slightly shifted to the right without tail broadness, which was the UV absorption of Fe oxide in the FexOy/TiO2 particle attained through hydrothermal method. This meant that Fe components were well inserted into the framework of the TiO2 anatase structure. Despite the red shift in UV-Vis absorption, however, CHCl3 decomposition on the FexOy/TiO2 catalyst was not largely enhanced compared to pure TiO2. 相似文献
10.
TiO2/epoxy composite thick films containing the TiO2 powders doped with 4 and 10 vol% Nb2O5 heat treated under vacuum at 1050 and 1150 °C, were prepared by the screen printing and curing steps. The Nb2O5-doped TiO2 ceramic bulks demonstrated a higher effective dielectric constant at different densification environments, as compared with pure TiO2. The dielectric properties of the TiO2/epoxy thick films were improved if the heat-treated 4 vol% Nb2O5-doped TiO2 powder was incorporated instead of the un-doped and heat-treated 10 vol% Nb2O5-doped TiO2 powders. The disadvantage of the doped TiO2 having higher dielectric loss tangent could be minimized after its powder was properly treated and mixed with epoxy to form the TiO2/epoxy composite. A best result with the dielectric constant of 23 and the loss tangent of 0.046 was obtained for the 40 vol% TiO2/epoxy composite thick films, where the TiO2 powder was doped with 4 vol% Nb2O5 followed by calcination at 1000 °C in air and heat treatment at 1150 °C under vacuum. 相似文献
11.
The effect of TiO2 on the grain growth of the ZnO–Bi2O3–CoO–MnO ceramic system prepared by chemical coprecipitation, was studied between 1150 and 1300 °C in air. Bi2O3 melts during firing, and then TiO2 dissolves into Bi2O3-rich liquid. TiO2 initially reacts with Bi2O3 to form Bi4Ti3O12. Above ≈1050 °C, Bi4Ti3O12 reacts with ZnO to form Zn2TiO4 spinel phase. The kinetic study of grain growth carried out using the expression Gn–Gon=Ko·t·exp(−Q/RT) gave grain exponent (n) value as 6 and the apparent activation energy (Q) as 226.46 kJ/mol. 1.00 mol% TiO2 addition increased the grain growth exponent value from 6 to 7 and apparent activation energy with 1.00 mol% TiO2 addition was found to be 197.10 kJ/mol. The ZnO grain size gradually increases with increasing TiO2 content. Addition of TiO2 may increase the reactivity of the Bi2O3-rich liquid towards the ZnO grain, thus affecting the ZnO grain growth. 相似文献
12.
Spinel LiMn2O4 films were obtained by spin-coating the lithium/manganese acetates-containing precursor solution on a Pt-coated silicon substrate. The effect of chitosan addition in the acetates-containing precursor solution on the formation of the LiMn2O4 films was investigated by TG/DTA, FT-IR spectroscopy, glancing-angle XRD and cyclic voltammetry. It was demonstrated that the addition of chitosan is very beneficial to the deposition of a single-phase LiMn2O4 film due to the fact that chitosan is able to chelate with lithium/manganese ions and form a stable complex compound. Moreover, the electrochemical measurements also showed that the deposited LiMn2O4 film from the chitosan-added precursor solution exhibits a higher discharge capacity of 134 mAh/g at 1 C and a better rate performance (86.4% of the discharge capacity at 1 C can be maintained when the discharge rate increases from 1 up to 8 C) in comparison with one from the chitosan-free solution. 相似文献
13.
Characterization by XPS–UPS and XRD of commercial bulk WO2 enabled us to identify the presence of four to five layers of WO3 on the sample surface with an equal amount of W5+, possibly W20O58 in the interface. The presence of these WO3 and W20O58 on the WO2 surface were not detected by XRD. Exposure of commercial bulk WO2 to hydrogen at temperatures higher than 673 K results in the reduction of surface WO3 to WO2 and the formation of the bifunctional WO2(Hx)ac phase on its surface. A complete conversion of surface WO3 to WO2(Hx)ac has been obtained following the exposure of the sample to hydrogen for at least 6 h at 773 K. A conversion of 52% of n-heptane at 573 K reaction temperature and a selectivity of 90% in isomerization products, mainly 2,3-MH and multibranched molecules were obtained. The isomerization products distribution is in agreement with the statistical and thermodynamic equilibrium of the methyl-shift mechanism. The stability of the active WO2(Hx)ac phase has been tested under prolonged exposure to hydrogen and the reaction mixture. Similar results were obtained in the case of bulk WO3 and WO3/TiO2 systems. Dehydration and dehydrogenation of 2-propanol were studied on these systems at 393 K reaction temperature. 相似文献
14.
Motonobu Kobayashi Ryoji Kuma Sinyuki Masaki Noboru Sugishima 《Applied catalysis. B, Environmental》2005,60(3-4):173-179
TiO2-SiO2 with various compositions prepared by the coprecipitation method and vanadia loaded on TiO2-SiO2 were investigated with respect to their physico-chemical characteristics and catalytic behavior in SCR of NO by NH3 and in the undesired oxidation of SO2 to SO3, using BET, XRD, XPS, NH3-TPD, acidity measurement by the titration method and activity test. TiO2-SiO2, compared with pure TiO2, exhibits a remarkably stronger acidity, a higher BET surface area, a lower crystallinity of anatase titania and results in allowing a good thermal stability and a higher vanadia dispersion on the support up to high loadings of 15 wt% V2O5. The SCR activity and N2 selectivity are found to be more excellent over vanadia loaded on TiO2-SiO2 with 10–20 mol% of SiO2 than over that on pure TiO2, and this is considered to be associated with highly dispersed vanadia on the supports and large amounts of NH3 adsorbed on the catalysts. With increasing SiO2 content, the remarkable activity decrease in the oxidation of SO2 to SO3, favorable for industrial SCR catalysts, was also observed, strongly depending on the existence of vanadium species of the oxidation state close to V4+ on TiO2-SiO2, while V5+ exists on TiO2, according to XPS. It is concluded that vanadia loaded on Ti-rich TiO2-SiO2 with low SiO2 content is suitable as SCR catalysts for sulfur-containing exhaust gases due to showing not only the excellent de-NOx activity but also the low SO2 oxidation performance. 相似文献
15.
Operating the SCR DeNOx reactor at temperatures below 200 °C results in a considerable saving in operating costs. Plant experience shows that on the catalysts in these second generation DeNOx plants, even for flue gases with SO2 concentration below 10 mg/m3, over 1–2 years operating time sizeable quantities of ammonium sulfates accumulate. Ammonium sulfates deposited on V2O5–WO3/TiO2 catalysts react with NOx to nitrogen and sulfuric acid. Second-order rate constants of this reaction for temperatures of 170 °C have been derived. It could be shown that the sulfuric acid formed on the catalyst is displaced by water vapour and desorbs resulting in gas phase concentrations of up to 6.5 mg acid/m3 flue gas. Plant equipment downstream of the ammonium sulfate containing low temperature DeNOx catalysts has to be protected against the corrosive action of the sulfuric acid in the flue gases leaving the DeNOx reactor. 相似文献
16.
Yuko Habuta Naoaki Narishige Kazu Okumura Naonobu Katada Miki Niwa 《Catalysis Today》2003,78(1-4):131-138
Vanadium oxide spread highly on TiO2 (anatase, A) and SnO2, and rather densely on TiO2 (rutile, R) and ZrO2 to make the monolayer in less than 4–5 V nm−2. Profile of acid site of the monolayer was measured by temperature programmed desorption of ammonia, and its relation with the surface oxidation state was studied. The acid site density was high on the V2O5/TiO2 (A) independent of the degree of oxidation. On the other hand, that of V2O5/TiO2 (R) and V2O5/ZrO2 depended on the oxidation state, and the high value of the concentration was observed on the oxidized one. The strength of acid site generated on the V2O5 monolayer on TiO2 was as high as on the HZSM-5 zeolite. Turnover frequency (TOF) of propane conversion, and product selectivity were measured in propane oxidation. Among tested oxides, the V2O5/TiO2 (A) showed the high TOF and selectivity to form propylene, while those loaded on TiO2 (R) and ZrO2 the small TOF and poor selectivity. Therefore, the reaction profile of activity and selectivity could be related with the extent of spreading and solid acidity. An idea of limit of the acid site density ca. 1.5 nm−2 on the monolayer was elucidated. 相似文献
17.
Zheng Xu Yumin Li Jiyan Zhang Liu Chang Rongqi Zhou Zhanting Duan 《Applied Catalysis A: General》2001,210(1-2):45-53
The effects of nickel loading, calcination temperature, support, and basic additives on Ni-based catalyst structure and reactivity for CH4 reforming with CO2 were investigated. The results show that the structure of the nickel active phase strongly depends on the interactions of the metal and the support, which are related to the support properties, the additives and the preparation conditions. “Free” Ni species can be formed when the interaction is weak and their mobility makes them easily deactivated by coking and sintering. The effect of strong metal-support interaction (SMSI effect) is different for various supports. The formation of solid solution of Ni–Mg–O2 and the blocking of TiOx by the partially reduced TiO2 can both decrease the availability of Ni active sites in Ni/MgO and Ni/TiO2. The spinel NiAl2O4 formed in Ni/γ-Al2O3 might be responsible for its high activity and resistance to coking and sintering because it can produce a highly dispersed active phase and a large active surface area as bound-state Ni species when the catalyst is prepared at high calcined temperatures or with low nickel loading. The addition of La2O3 or MgO as alumina modifiers can also be beneficial for the performance of the Ni/γ-Al2O3 catalyst. 相似文献
18.
Manfred Nacken Steffen Heidenreich Marius Hackel Georg Schaub 《Applied catalysis. B, Environmental》2007,70(1-4):370-376
The development of a catalytically active filter element for combined particle separation and NOx removal or VOC total oxidation, respectively, is presented. For NOx removal by selective catalytic reduction (SCR) a catalytic coating based on a TiO2–V2O5–WO3 catalyst system was developed on a ceramic filter element. Different TiO2 sols of tailor-made mean particle size between 40 and 190 nm were prepared by the sol–gel process and used for the impregnation of filter element cylinders by the incipient wetness technique. The obtained TiO2-impregnated sintered filter element cylinders exhibit BET surface areas in the range between 0.5 and 1.3 m2/g. Selected TiO2-impregnated filter element cylinders of high BET surface area were catalytically activated by impregnation with a V2O5 and WO3 precursor solution. The obtained catalytic filter element cylinders show high SCR activity leading to 96% NO conversion at 300 °C, a filtration velocity of 2 cm/s and an NO inlet concentration of 500 vol.-ppm. The corresponding differential pressures fulfill the requirements for typical hot gas filtration applications. For VOC total oxidation, a TiO2-impregnated filter element support was catalytically activated with a Pt/V2O5 system. Complete oxidation of propene with 100% selectivity to CO2 was achieved at 300 °C, a filtration velocity of 2 cm/s and a propene inlet concentration of 300 vol.-ppm. 相似文献
19.
A 5 wt% CoOx/TiO2 catalyst has been used to study the effect of calcination temperature on the activity of this catalyst for CO oxidation at 100 °C under a net oxidizing condition in a continuous flow type fixed-bed reactor system, and the catalyst samples have been characterized using TPD, XPS and XRD measurements. The catalyst after calcination at 450 °C gave highest activity for this low-temperature CO oxidation, and XPS measurements yielded that a 780.2-eV Co 2p3/2 main peak appeared with this catalyst sample and this binding energy was similar to that measured with pure Co3O4. After calcination at 570 °C, the catalyst, which had possessed practically no activity in the oxidation reaction, gave a Co 2p3/2 main structure peak at 781.3 eV which was very similar to those obtained for synthesized ConTiOn+2 compounds (CoTiO3 and Co2TiO4), and this catalyst sample had relatively negligible CO chemisorption as observed by TPD spectra. XRD peaks indicating only the formation of Co3O4 particles on titania surface were developed in the catalyst samples after calcination at temperatures ≥350 °C. Based on these characterization results, five types of Co species could be modeled to exist with the catalyst calcined at different temperatures. Among these surface Co species, the Type A clean Co3O4 particles were predominant on a sample of the catalyst after calcination at 450 °C and highly active for CO oxidation at 100 °C, and the calcination at 570 °C gave the Type B Co3O4 particles with complete ConTiOn+2 overlayers inactive for this oxidation reaction. 相似文献
20.
We reported an asymmetric supercapacitor technology where RuO2/TiO2 nanotube composite was used as positive electrode and the activated carbon as negative electrode in 1 mol/L KOH electrolyte solution. The electrochemical capacitance performance of the asymmetric supercapacitor was tested by cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge-discharge tests. The results show that the asymmetric supercapacitor has electrochemical capacitance performance within potential range 0–1.4 V. A power density 1207 W/kg was obtained with an energy density of 5.7 W h/kg at a charge–discharge current density of 120 mA/cm2. The supercapacitor also exhibits a good cycling performance and keep 90% of initial capacity over 1000 cycles. 相似文献