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1.
Xiankuan Zhang Arden B. Walters M. Albert Vannice 《Applied catalysis. B, Environmental》1996,7(3-4):321-336
Both NO decomposition and NO reduction by CH4 over 4%Sr/La2O3 in the absence and presence of O2 were examined between 773 and 973 K, and N2O decomposition was also studied. The presence of CH4 greatly increased the conversion of NO to N2 and this activity was further enhanced by co-fed O2. For example, at 773 K and 15 Torr NO the specific activities of NO decomposition, reduction by CH4 in the absence of O2, and reduction with 1% O2 in the feed were 8.3·10−4, 4.6·10−3, and 1.3·10−2 μmol N2/s m2, respectively. This oxygen-enhanced activity for NO reduction is attributed to the formation of methyl (and/or methylene) species on the oxide surface. NO decomposition on this catalyst occurred with an activation energy of 28 kcal/mol and the reaction order at 923 K with respect to NO was 1.1. The rate of N2 formation by decomposition was inhibited by O2 in the feed even though the reaction order in NO remained the same. The rate of NO reduction by CH4 continuously increased with temperature to 973 K with no bend-over in either the absence or the presence of O2 with equal activation energies of 26 kcal/mol. The addition of O2 increased the reaction order in CH4 at 923 K from 0.19 to 0.87, while it decreased the reaction order in NO from 0.73 to 0.55. The reaction order in O2 was 0.26 up to 0.5% O2 during which time the CH4 concentration was not decreased significantly. N2O decomposition occurs rapidly on this catalyst with a specific activity of 1.6·10−4 μmol N2/s m2 at 623 K and 1220 ppm N2O and an activation energy of 24 kcal/mol. The addition of CH4 inhibits this decomposition reaction. Finally, the use of either CO or H2 as the reductant (no O2) produced specific activities at 773 K that were almost 5 times greater than that with CH4 and gave activation energies of 21–26 kcal/mol, thus demonstrating the potential of using CO/H2 to reduce NO to N2 over these REO catalysts. 相似文献
2.
This work deals with poly(ethylene oxide), PEO–MX (M=Li, K and Cs) amorphous electrolytes with −X–X−, [CF3SO2NCH2(CH2OCH2)2CH2NSO2CF3]2− (EDSA) and [CF3SO2NCH2CH2(CH2OCH2)3CH2CH2NSO2CF3]2− (TTSA) disulfonamide anions. These dianions have X− end-groups identical to anions [CF3SO2N(CH2)2OCH3]− (MESA) and [CF3SO2N(CH2)3OCH3]− (MPSA), one of which (MPSA) was reported to yield chelate-like associated species (presumably LiX2− triplets) at concentrations above EO/Li=20 in PEO. This feature of LiMPSA, evidenced through glass transition temperature (Tg) measurements, does not apply to Li2EDSA and Li2TTSA. Though none of these lithium salts form crystalline intermediate compounds with PEO, the limit of solubility of LiMESA (EO/Li=16) does not allow a clarification of this point for this salt. At lower concentrations, however, a conductivity comparison with the potassium and caesium salts shows that the apparent degree of dissociation (=CLi+/CLi) of LiMESA is comparable to that of LiMPSA. As opposed to both these salts and to some extent to Li2EDSA, a much greater dissociation takes place for Li2TTSA, the anion of which contains an inner, third ether group in its structure. 相似文献
3.
Jian Guo Li Fang Jiao HuaTang Yuan Li Qin Wang Hai Xia Li Ming Zhang Yong Mei Wang 《Electrochimica acta》2006,51(28):6275-6280
Layered Li[Ni(1−x)/3Mn(1−x)/3Co(1−x)/3Crx]O2 materials with x = 0, 0.01, 0.02, 0.03, 0.05 are prepared by a solid-state pyrolysis method. The oxide compounds were calcined with various Cr-doped contents, which result in greater difference in morphological (shape, particle size and specific surface area) and the electrochemical (first charge profile, reversible capacity and rate capability) differences. The Li[Ni(1−x)/3Mn(1−x)/3Co(1−x)/3Crx]O2 powders were characterized by means of X-ray diffraction (XRD), charge/discharge cycling, cyclic voltammetry, and SEM. XRD experiment revealed that the Li[Ni(1−x)/3Mn(1−x)/3Co(1−x)/3Crx]O2 (x = 0, 0.01, 0.02, 0.03, 0.05) were crystallized to well layered -NaFeO2 structure. The first specific discharge capacity and coulombic efficiency of the electrode of Cr-doped materials were higher than that of pristine material. When x = 0.02, the sample showed the highest first discharge capacity of 241.9 mAh g−1 at a current density of 30 mA g−1 in the voltage range 2.3–4.6 V, and the Cr-doped samples exhibited higher discharge capacity and better cycleability under medium and high current densities at room temperature. 相似文献
4.
Complete Ni2+ exchange of a single crystal of zeolite X of composition Na92Si100Al92O384 per unit cell was attempted at 73°C with flowing aqueous 0.05 M NiCl2 (pH=4.3 at 23°C). After partial dehydration at 23°C and ≈10−3 Torr for two days, its structure, now of composition Ni2(NiOH)35(Ni4AlO4)2(H3O)46Si101Al91O384 per unit cell, was determined by X-ray diffraction techniques at 23°C (space group Fd
, a0=24.788(5) Å). It was refined using all intensities; R1=0.080 for the 236 reflections for which Fo>4σ(Fo), and wR2=0.187 using all 1138 unique reflections measured. At four crystallographic sites, 45 Ni2+ ions were found per unit cell. Thirty of these are at two different site III′ positions. Twenty of those are close to the sides of 12-rings near O–Si–O sequences, where each coordinates octahedrally to two framework oxygens, to three water molecules which hydrogen bond to the zeolite framework, and to an OH− ion. The remaining 10 are near O–Al–O sequences; only three members of a likely octahedral coordination sphere could be found. In addition, two Ni2+ ions are at site I, eight are at site I′, and five are at site II. Forty six H3O+ ions per unit cell, 24 at site II′ and 22 at site II, each hydrogen bond triply to six rings of the zeolite framework. Each of the 22 H3O+ ions also hydrogen bonds to a H2O molecule that coordinates to a site III′ Ni2+ ion. Six of the eight sodalite cages each contain four H3O+ ions at site II′; the remaining two each contains a tetrahedral orthoaluminate anion at its center. Each tetrahedral face of each orthoaluminate ion is centered by a site I′ Ni2+ ion to give two Ni4AlO4 clusters. The five site II Ni2+ ions each coordinate to a OH− ion. With 46 H3O+ ions per unit cell, the great tendency of hydrated Ni2+ to hydrolyze within zeolite X is demonstrated. With a relatively weak single-crystal diffraction pattern, with dealumination of the zeolite framework, and with an apparent decrease in long-range Si/Al ordering likely due to the formation of antidomains, this crystal like others treated with hydrolyzing cations appears to have been damaged by Ni2+ exchange and partial dehydration. 相似文献
5.
Sbastien Gentil Eulalia Crespo Isabel Rojo Aurlie Friang Clara Vias Francesc Teixidor Bohumír Grüner Detlef Gabel 《Polymer》2005,46(26):12218-12225
The influence of weakly coordinating anions with different shapes and substituents has been studied to get the overoxidation resistance limit of the material, ORL. The anions utilized are derivatives of [Co(C2B9H11)2]−, [B12H12]2− and [B12H11NH3]−. The following tendencies have been established (1) boron cluster monoanions are to date the anions that offer the highest stability to overoxidation of PPy doped materials (2) the ORL stability of the material can not be attributed only to the shape of the cluster (3) monoanionic clusters are far superior than dianionic to get an ORL rise (4) cluster charge density reduction results in ORL rise as has been observed in [Co(C2B9H11)2]− after incorporation of electron-withdrawing substituents with no electron back-donation (5) globular, rigid and large monoanions are less suitable for enhanced ORL values than elongated and non-rigid species (6) adequate anion's substitution produce a rise in the ORL of the material, thus polyether side-arms are beneficial with [Co(C2B9H11)2]−, whereas, T-shaped methylaryl groups are appealing in [B12H11NH3]− based materials, respectively, (7) substituents on the anions usually imply higher difficulty in the materials' growth. The high boron contents in these materials has permitted to learn on the fate of the doping anions during the overoxidation process. There is a built-up of the concentration of the doping anion in the electrolyte near surface area, whereas, a depletion is observed in the nearest inner layers. 相似文献
6.
Catalytic oxidation of methane over hexaaluminates and hexaaluminate-supported Pd catalysts 总被引:4,自引:0,他引:4
Ben W. -L. Jang R. M. Nelson James J. Spivey Meltem Ocal R. Oukaci George Marcelin 《Catalysis Today》1999,47(1-4):103-113
An aqueous (NH4)2CO3 coprecipitation method, based on that of Groppi et al. [Appl. Catal. A 104 (1993) 101–108] was used to synthesize Sr1−xLaxMnAl11O19− hexaaluminates. These materials were first synthesized by alkoxide hydrolysis. This synthesis route requires special handling of the starting materials and is not likely to be commercially practical. The materials prepared by (NH4)2CO3 coprecipitation have similar surface areas as those prepared by the alkoxide hydrolysis method. Their CH4 oxidation activity, measured as the temperature needed for 10% conversion of methane, is higher than those prepared by alkoxide hydrolysis. The La-substantiated material, LaMnAl11O19−, shows high surface area with 19.3 m2/g after calcination at 1400°C for 2 h. It is active for CH4 oxidation with T10% at 450°C using 1% CH4 in air and 70 000 cm3/h g space velocity. The stability and activity of LaMnAl11O19− prepared by (NH4)2CO3 coprecipitation method is a simple and important step forward for the application of CH4 catalytic combustion for gas turbines. 相似文献
7.
Polycrystalline (PbS)1.14(TaS2)2, a misfit layer sulfide, was used as cathodic material for lithium secondary battery. One molar LiClO4 in propylene carbonate (PC) was used as electrolyte. The cell could be galvanostatic discharged down to x = 4.6 [Lix(PbS)1.14(TaS2)2] when the current density was 65 μA cm−2 and the cell was cycled more than 100 times between 3.5 and 1.5 V at a current density of 260 μA cm−2. Lattice expansion increased linearly with lithium content and was less than that reported for the Li/TaS2 system. Chemical diffusion coefficients were determined by a modified version of the galvanostatic intermittent titration technique and they were fairly constant in the composition range 0.2 < x < 1, and an average value of 8.1 × 10−11 cm2 s−1 was calculated. Sodium intercalation was also accomplished, but the uptake of this ion resulting in a significant lattice expansion compared with that observed for lithium ions. Moreover, a similar dependence of the sodium chemical diffusion coefficient on the composition was observed with an average value of 1.4 × 10−10 cm2 s−1, somewhat higher than that of lithium ion. We believe that differences in lattice expansion may be responsible for the differences found in the chemical diffusivity values. 相似文献
8.
Shuiying Gao Rong Cao Wenhua Bi Xing Li Zhengzhong Lin 《Microporous and mesoporous materials》2005,80(1-3):139-145
Three compounds, K2(H2O)4H2SiMo12O40 · 7H2O (1), K2Na2(H2O)4SiW12O40 · 4H2O (2), and Na4(H2O)8SiMo12O40 · 6H2O (3) have been synthesized and structurally characterized by single-crystal X-ray analysis, IR, and thermogravimetry. Compounds 1 and 2 both show the high symmetry trigonal space group P3221 and a novel 3D network structure. The Keggin anions [SiM12O40]4−(M = Mo, W) are linked by potassium or sodium cations to generate hexagon-shaped channels along the c-axis, in which water molecules are accommodated. Compound 3 is tetragonal, space group P4/mnc constructed from [SiMo12O40]4− anions and Na ions. 相似文献
9.
The synthesis and structure of (CH3CH[NH3]CH2NH3)1/2·ZnPO4, an organically templated zincophosphate (ZnPO) analogue of aluminosilicate zeolite thomsonite (THO), are described. The ZnPO framework is built up from an alternating, vertex-sharing, network of ZnO4 and PO4 groups (dav(Zn–O)=1.944 (8) Å, dav(P–O)=1.535 (9) Å, θav(Zn–O–P)=130.5°) involving distinctive 4=1 secondary building units. The 1,2-diammonium propane cations are highly disordered in the [0 0 1] 8-ring channels. Crystal data: (CH3CH[NH3]CH2NH3)1/2·ZnPO4, Mr=198.42, orthorhombic, space group Pncn (no. 52), a=14.119 (6) Å, b=14.136 (5) Å, c=12.985 (5) Å, V=2591 (3) Å3, Z=10, R(F)=0.057, Rw(F)=0.061 (for a twinned crystal). 相似文献
10.
Layered -titanate materials, NaxMx/2Ti1−x/2O2 (M=Co, Ni and Fe, x=0.2–0.4), were synthesized by flux reactions, and electrical properties of polycrystalline products were measured at 300–800 °C. After sintering at 1250 °C in Ar, all products show n-type thermoelectric behavior. The values of both d.c. conductivity and Seebeck coefficient of polycrystalline Na0.4Ni0.2Ti0.8O2 were ca. 7×103 S/m and ca. −193 μV/K around 700 °C, respectively. The measured thermal conductivity of layered -titanate materials has lower value than conductive oxide materials. It was ca. 1.5 Wm−1 K−1 at 800 °C. The estimated thermoelectric figure-of-merit, Z, of Na0.4Ni0.2Ti0.8O2 and Na0.4Co0.2Ti0.8O2 was about 1.9×10−4 and 1.2×10−4 K−1 around 700 °C, respectively. 相似文献
11.
The electrodeposition and dissolution of yttrium-hexacyanoferrate [YHCNFe(II)] were investigated by electrochemical quartz crystal microbalance technique (EQCM). The electrodeposition was carried out by potential cycling or stepping from solutions of Y(NO3)3 and K3[FeIII(CN)6] of different concentrations. The ratio of the reactants was also varied. No deposition was found in dilute solutions (c < 10−3 mol dm−3). The increase of concentrations led to an intense deposition of YHCNFe(II) in the course of reduction of [FeIII(CN)6]3−. At high concentrations of the reactants a coagulation deposition of YHCNFe(III) at open-circuit has also been detected. During the reduction the first phase is the nucleation which requires saturation or oversaturation in respect to the reacting species near the gold surface. The growth phase is much faster than the formation of nuclei, and its rate depends on the concentration and the concentration ratio of the species. The composition of the deposits has been determined by total reflection X-ray fluorescence (TXRF) spectrometry. From the molar ratio of atomic constituents (K, Y and Fe) of the slightly soluble deposit (solubility: 5 × 10−5 mol dm−3) formed after reduction of Fe(III) a formula K0.46Y1.18[FeII(CN)6] can be derived. This value is in good accordance with the molar mass calculated from the results of EQCM experiments which also revealed that the deposit contains ca. 2 mol H2O/mol YHCNFe(II). The solubility of YHCNFe(III) is substantially higher (s = 2 × 10−3 mol dm−3), and according to the results of TXRF measurements, its composition is Y[FeIII(CN)6]. The reoxidation of YHCNFe(II) takes place in two steps. The first one is a partial oxidation which is accompanied by the desorption of K+ ions from the layer. During further oxidation a fast dissolution occurs due to the high solubility of YHCNFe(III). 相似文献
12.
Kjell Ove Kongshaug Helmer Fjellv g Karl Petter Lillerud 《Microporous and mesoporous materials》2000,40(1-3):313-322
The synthesis of a novel 3D aluminophosphate is described. The thermal properties of the material were investigated, and the existence of three high-temperature variants was revealed. The crystal structures of the as-synthesized material (UiO-26-as) and the material existing around 250°C (UiO-26-250) were solved from powder X-ray diffraction data. UiO-26-as with the composition [Al4O(PO4)4(H2O)]2−[NH3(CH2)3NH3]2+ crystallizes in the monoclinic space group P21/c (no. 14) with a=19.1912(5), b=9.3470(2), c=9.6375(2) Å and β=92.709(2)°. It exhibits a 3D open framework consisting of connections by PO4 tetrahedra with AlO4 tetrahedra, AlO5 trigonal bipyramids and AlO5(H2O) octahedra forming two types of layers stacked along [1 0 0] and connected by Al–O–P bondings. The structure possesses a 1D 10-ring channel system running along [0 0 1], in which doubly protonated 1,3-diaminopropane molecules are located. UiO-26-250 with the composition [Al4O(PO4)4]2−[NH3(CH2)3NH3]2+ crystallizes in the monoclinic space group P21/c with a=19.2491(4), b=9.27497(20), c=9.70189(20) Å and β=93.7929(17)°. The transformation to UiO-26-250 involves removal of the water molecule which originally is coordinated to aluminum. The rest of the structure remains virtually unchanged. The crystal structures of the two other variants existing around 400 (UiO-26-400) and 600°C (UiO-26-600) remain unknown. 相似文献
13.
Influence of time-on-stream (0.5–15 h), CH4/O2 ratio in feed (1.8–8.0), space velocity (6000–510,000 cm3 g−1 h−1), catalyst particle size (22–70 mesh), and catalyst dilution by inert solid particles (diluent/catalyst weight ratio=4) on the performance at different temperatures (600–900°C) of the NiO/MgO solid solution deposited on SA-5205 [which is a low surface area macroporous silica-alumina catalyst carrier] in the oxidative conversion of methane to syngas (a mixture of CO and H2) has been investigated. The dependence of conversion and selectivity on the space velocity is strongly influenced by the temperature. Both the conversion and selectivity for H2 and CO are decreased markedly by increasing the CH4/O2 ratio in the feed. The catalyst dilution resulted in a small but significant decrease in both the conversion and selectivity for H2 and CO. The increase in the catalyst particle size had also a small but significant effect on both the conversion and selectivity in the oxidative conversion process. Both the heat and mass transfer processes seem to play significant roles in the oxidative conversion of methane to syngas at a very low contact time or very high space velocity (5.1×105 cm3 g−1 h−1). 相似文献
14.
Au/Pb(ad) electrodes were prepared by the underpotential deposition of lead ions at various potentials in 1 M HClO4 solution containing Pb(CH3COO)2 at concentrations of about 1 × 10−2, 1 × 10−4 and 1 × 10−6 M, respectively. The best preparation condition was selected. These electrodes, modified by foreign metal atom were used to catalyze the reduction of nitrate in concentrated alkaline solution, and exhibited efficient electrocatalytic activity for this system. 相似文献
15.
The preparation of silica-supported osmium catalysts obtained by thermal decomposition of physisorbed Os3(CO)12 has been studied in situ by FTIR, XPS and TPD. Under our experimental conditions, the formation of oxidised Os(II) surface species has been confirmed, either in Ar or in O2 atmosphere. The occurrence of high nuclearity clusters under thermal treatment has been ruled out also by the study of the surface reactivity of adsorbed [Os10(CO)24C]2−. The original Os3 framework is restored from the Os(II) surface species by prolonged treatments at 523 K under CO. 相似文献
16.
The oxidation of CH4 over Pt–NiO/δ-Al2O3 has been studied in a fluidised bed reactor as part of a major project on an autothermal (combined oxidation–steam reforming) system for CH4 conversion. The kinetic data were collected between 773 and 893 K and 101 kPa total pressure using CH4 and O2 compositions of 10–35% and 8–30%, respectively. Rate–temperature data were also obtained over alumina-supported monometallic catalysts, Pt and NiO. The bimetallic Pt–NiO system has a lower activation energy (80.8 kJ mol−1) than either Pt (86.45 kJ mol−1) and NiO (103.73 kJ mol−1). The superior performance of the bimetallic catalyst was attributed to chemical synergy. The reaction rate over the Pt–NiO catalyst increased monotonically with CH4 partial pressure but was inhibited by O2. At low partial pressures (<30 kPa), H2O has a detrimental effect on CH4 conversion, whilst above 30 kPa, the rate increased dramatically with water content. 相似文献
17.
The germanate KF·2[Ca6(SO4) (GeO4)2O] was synthesized by solid state reactions; comparison of the observed and calculated powder pattern, assuming an isostructural relationship with the silicate phase, gives good agreement. Sulphate groups may also be substituted by CrO42− to give the isostructural KF·2[Ca6(CrO4)(SiO4)2O]. 相似文献
18.
The activities of perovskites depend on compositions and preparation methods. Various perovskites, La1−xMxMnO3 (M=Ag, Sr, Ce, La), have been prepared by two different methods (co-precipitation and spray decomposition). The new preparation method, spray decomposition, produced perovskites of a high surface area of over 10 m2/g. The catalytic activities for CH4 and CO oxidation have been studied on a series of catalysts, La1−xMxMnO3. The perovskite-type oxide, La0.7Ag0.3MnO3, shows the highest catalytic activity: the complete conversion of CO and CH4 at 370 and 825 K, respectively. 相似文献
19.
Preparations and physico-chemical characterizations of NASICON-type compounds in the system Li1+xAlxA2−xIV(PO4)3 (AIV=Ti or Ge) are described. Ceramics have been fabricated by sol-gel and co-grinding processes for use as ionosensitive membrane for Li+ selective electrodes. The structural and electrical characteristics of the pellets have been examined. Solid solutions are obtained with Al/Ti and Al/Ge substitutions in the range 0≤x≤0·6. A minimum of the rhombohedral c parameter appears for x about 0·1 for both solutions. The grain ionic conductivity has been characterized only in the case of Ge-based compounds. It is related to the carrier concentration and the structural properties of the NASICON covalent skeleton. The results confirm that the Ti-based framework is more calibrated to Li+ migration than the Ge-based one. A grain conductivity of 10−3 S cm−1 is obtained at 25°C in the case of Li1·3Al0·3Ti1·7(PO4)3. A total conductivity of about 6×10−5 S cm−1 is measured on sintered pellets because of grain boundary effects. The use of such ceramics in ISE devices has shown that the most confined unit cell (i.e. in Ge-based materials) is more appropriate for selectivity effect, although it is less conductive.© 相似文献
20.
Tris complex of FeII with 2,2′ bipyridine (bpy) ligand, has been encapsulated in the supercages of zeolite Y and characterized by powder X-ray diffraction, Infrared spectroscopy, 57Fe Mössbauer, effect measurements and multinuclear NMR spectroscopy. The complex was prepared in the supercages of Zeolite Y by exchanging the cations of zeolite Y with FeII and its subsequent complexing with bpy ligand. Based on the comparison of the results obtained for [FeII(bpy)3](ClO4)2 and the [Fe(bpy)3]Y complexes, it has been inferred that there is significant structural distortion for the encapsulated complex and all Fe is present as FeII in low spin state, which is characterized by isomer shift, δ = 0.37 mm s−1 and quadrupole splitting, ΔEq = 0.81 mm s−1 as revealed by 57Fe Mössbauer spectroscopic measurements. 相似文献