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1.
A series of Ce xPr 1−xO 2−δ mixed oxides were synthesized by a sol–gel method and characterized by Raman, XRD and TPR techniques. The oxidation activity for CO, CH 3OH and CH 4 on these mixed oxides was investigated. When the value x was changed from 1.0 to 0.8, only a cubic phase CeO 2 was observed. The samples were greatly crystallized in the range of the value x from 0.99 to 0.80, which is due to the formation of solid solutions caused by the complete insertion of Pr into the CeO 2 crystal lattices. Raman bands at 465 and 1150 cm −1 in Ce xPr 1−xO 2−δ samples are attributed to the Raman active F 2g mode of CeO 2. The broad band at around 570 cm −1 in the region of 0.3 ≤ x ≤ 0.99 can be linked to oxygen vacancies. The new band at 195 cm −1 may be ascribed to the asymmetric vibration caused by the formation of oxygen vacancies. The TPR profile of Pr 6O 11 shows two reduction peaks and the reduction process is followed: . The reduction temperature of Ce xPr 1−xO 2−δ mixed oxides is lower than those of Pr 6O 11 or CeO 2. TPR results indicate that Ce xPr 1−xO 2−δ mixed oxides have higher redox properties because of the formation of Ce xPr 1−xO 2−δ solid solutions. The presence of the oxygen vacancies favors CO and CH 3OH oxidation, while the activity of CH 4 oxidation is mostly related to reduction temperatures and redox properties. 相似文献
2.
The catalytic activity of MV 2O 6 and M 2V 2O 7 type oxides prepared by the molten method (MM) for anaerobic oxidation of isobutane was studied in order to construct a system for the selective oxidation of isobutene using a thin layer reactor. Isobutene, CO and CO 2 were formed by every catalyst tested. The activities for isobutene formation were CuV 2O 6 > ZnV 2O 6, NiV 2O 6, CoV 2O 6 > MgV 2O 6 > MnV 2O 6 CaV 2O 6. Isobutene was a major product over M 2V 2O 7 (MM). Co 2V 2O 7 showed the highest activity and high isobutene selectivity exceeded 90%, demonstrating that Co 2V 2O 7 is a suitable oxide for a thin layer reactor for anaerobic oxidation of isobutane. Partial substitution of Mg by Cu in Mg 2V 2O 7 (MM) improved the activity. It is shown by the oxidation at low O 2 concentration as 2–3% that two types of oxidations occurred simultaneously: isobutene formation by the lattice oxygen ions diffused from the bulk, and CO and CO 2 formation by the oxygen species derived from molecular oxygen in the gas phase. 相似文献
3.
The heat capacities of the tungsten oxides WO 3, W 20O 58, W 18O 49 and WO 2 have been measured over the temperature range 340–999 K using differential scanning calorimetry. The lower oxides were prepared by controlled reduction of WO 3 in H 2/H 2O gas atmospheres. Previous calorimetric work on WO 3 is confirmed in the temperature range 340–800 K, however, significant increases in heat capacity were observed in the range 800–999 K prior to the orthorhombic—tetragonal phase transition. W 20O 58 is shown to behave similarly to WO 3. A high temperture phase change is evident, however, this appears to be complete by 970–990 K. The measured values of heat capacity for W 18O 49 are in close agreement with estimated data for W 18O 49. There is no evidence of any phase transitions for this oxide in the temperature range studied. The heat capacity data for WO 2 confirm previous drop calorimetry measurements and give no evidence of any phase changes for WO 2 in the temperature range 340–990 K. 相似文献
4.
In a specimen of 70V 2O 5-30P 2O 5glass, EPR lineshapes of the vanadium 3d 1 polaron have been studied between 4 and 77 K. At the lowest temperature the unpaired electron is localized at a single 51V site, and values of g=1.959, g= 1.989, A = 156.6 × 10 −4 cm −1 and A=53.8 × 10 −4 cm −1 have been measured. A Markovian small-step rotational diffusion model consistent with the random structure of the glass network is proposed for the polaron dynamics at the higher temperatures up to 77 K. This motion has a small activation energy barrier of 114 μeV. 相似文献
5.
Aerosol flame pyrolysis deposition method was applied to deposit the oxide glass electrolyte film and LiCoO 2 cathode for thin film type Li-ion secondary battery. The thicknesses of as-deposited porous LiCoO 2 and Li 2O–B 2O 3–P 2O 5 electrolyte film were about 6 μm and 15 μm, respectively. The deposited LiCoO 2 was sintered for 2 min at 700 °C to make partially densified cathode layer, and the deposited Li 2O–P 2O 5–B 2O 3 glass film completely densified by the sintering at 700 °C for 1 h. After solid state sintering process the thicknesses were reduced to approximately 4 μm and 6 μm, respectively. The cathode and electrolyte layers were deposited by continuous deposition process and integrated into a layer by co-sintering. It was demonstrated that Aerosol flame deposition is one of the good candidates for the fabrication of thin film battery. 相似文献
6.
The perovskite transition-metal oxide ABO 3 has been extensively studied in various areas in solids. While the B ion determines the electronic properties, e.g., ferroelectricity, ferromagnetism, and superconductivity, the A site has been regarded as a “back-seat player” to change the doping level or the bandwidth. However, in the ordered perovskite oxide AA′ 3B 4O 12, the A site order is closely related to the peculiar electronic states. In CaMn 3Mn 4O 12, the unusually small bandwidth justifies to extrapolate the transport data to the high-temperature limit, and in CaCu 3Ru 4O 12, a novel heavy-fermion state is realized through the Cu–O–Ru interaction. 相似文献
7.
The hydrothermal reactions of vanadium oxide starting materials with divalent transition metal cations in the presence of nitrogen donor chelating ligands yield the bimetallic cluster complexes with the formulae [{Cd(phen 2) 2V 4O 12]·5H 2O (1) and [Ni(phen) 3] 2[V 4O 12]·17.5H 2O (2). Crystal data: C 48H 52Cd 2N 8O 22V 4 (1), triclinic.
a=10.3366(10), b=11.320(3), c=13.268(3) Å, =103.888(17)°, β=92.256(15)°, γ=107.444(14)°, Z=1; C 72H 131N 12Ni 2O 29.5V 4 (2), triclinic.
a=12.305(3), b=13.172(6), c=15.133(4), =79.05(3)°, β=76.09(2)°, γ=74.66(3)°, Z=1. Data were collected on a Siemens P4 four-circle diffractometer at 293 K in the range 1.59° <θ<26.02° and 2.01°<θ<25.01° using the ω-scan technique, respectively. The structure of 1 consists of a [V 4O 12] 4− cluster covalently attached to two {Cd(phen) 2} 2+ fragments, in which the [V 4O 12] 4− cluster adopts a chair-like configuration. In the structure of 2, the [V 4O 12] 4− cluster is isolated. And the complex formed a layer structure via hydrogen bonds between the [V 4O 12] 4− unit and crystallization water molecules. 相似文献
8.
搜集并统计了世界129种典型煤种、城市污水污泥及污泥/煤混烧灰样的灰成分及灰熔融特征温度等相关数据,研究灰中酸性成分SiO2、Al2O3、TiO2和P2O5对灰熔融特性的影响。结果表明,Al2O3是决定灰熔点的主要因素,酸性金属氧化物SiO2、Al2O3和TiO2形成的耐熔矿物质石英、偏高岭石、莫来石、金红石等可提高灰熔点。非金属氧化物P2O5与污泥和污泥/煤的灰熔点FT二次拟合很好且明显降低熔点,污泥灰中P2O5含量显著高于煤灰是导致其熔点明显低于煤的重要原因。 相似文献
9.
The thermal decomposition of CaOsO 3 by differential thermal analyses, thermogravimetry and X-ray powder diffraction has been studied. In nitrogen CaOsO 3 decomposes at 880 ± 10°C into CaO, osmium metal and oxygen due to the reaction CaOsO 3 → CaO + Os + O 2. In static air the decomposition occurs in three stages: 2CaOsO 3 + 1/2O 2 → Ca 2Os 2O 7 (in region 775–808°C), Ca 2Os 2O 7 → Ca 2Os 2O 6,5 + 1/4O 2 (at a temperature interval of 850–1000°C) and in the third stage Ca 2Os 2O 6,5 → 2CaO + OsO 4 ÷ 1/4 O 2 (at 1005 ± 5°C). The first intermediate Ca 2Os 2O 7 is isostructural with orthorhombic Ca 2Nb 2O 7 and its cell parameters are: a0 = 3.745 Å, b0 = 25.1 Å, c0 = 5.492 Å, Z = 4, space group Cmcm or Cmc2. Ca 2Os 2O 7 exhibits metallic conductivity and its electrical resistivity is 4.6 × 10 −2 ohm-cm at 296K. 相似文献
10.
The arsenic oxide pressure of As 2O 5 has been studied using mass spectrometry and a transportation method. Mass spectrometry revealed the presence of the species As 4O +6, As 4O +7, and As 4O +8 in the vapour. The existence of volatile species up to As 4O 10(g) as a result of the reaction As 4O 10(g) As 4O (10−y) (g) +1/2 yO 2(g) has been assumed. The oxygen pressure of this equilibrium builds up very slowly. The equilibrium pressure can be expressed by log(pO2/atm) (880−952 K) = −(13940±930)/T + (14.53 ± 1.01) A stationary arsenic oxide pressure has been measured using the transportation method. Since the oxygen pressure in the transportation gas did not influence the arsenic oxide pressure, it is assumed that only the As4O10(g) pressure has been measured. The results can be expressed by the linear function log(pAs4O10/atm) (865−1009 K) = −(15741 ± 410)/T + (13.87 ± 0.42). 相似文献
11.
The reaction between transition metal alkoxides and benzyl alcohol provides a novel soft chemistry route to metal oxide nanoparticles. The method allows the preparation of nanocrystals of two important transition metal oxides, namely V 2O 3 and Nb 2O 5. Although the reaction temperatures of 200–220 °C are comparably low, the obtained particles are highly crystalline. According to TEM investigations, the V 2O 3 crystals exhibit particle sizes between 20 and 50 nm, and the Nb 2O 5 crystals display platelet-like particle shapes with sizes of 50–80 nm, without any indications of amorphous character. 相似文献
12.
Nanoparticles of Cu 2L 2O 5 (L=Ho, Er) (15–25 nm in size) were synthesised by the intermediate use of W/O microemulsions. In this process the aqueous cores of water/cetyltrimethylammonium bromide/n-octane/1 -butanol microemulsions were used as microreactors for the precipitation of Cu 2Ho 2(CO 3) 4(OH) 2 (25–30 nm) and Cu 2Er 2(CO 3) 4(OH) 2 (10–40 nm) as precursors. These mixed salts were separated and further decomposed to the corresponding mixed oxides at 900°C for 16 h. All solids were characterised by scanning and transmission electron microscopy, IR, XRPD, ICP-OES, TGA, XPS measurements and elemental analyses. 相似文献
13.
The solid–solid interactions between pure and alumina-doped cobalt and ferric oxides have been investigated using DTA, IR and XRD techniques. Equimolar proportions of basic cobalt carbonate and ferric oxide and different amounts of aluminum nitrate were added as dopant substrate. The amounts of dopant were 0.75, 1.5, 3.0 and 4.5 mol% Al 2O 3. The results obtained revealed that solid–solid interaction between Fe2O3 and Co3O4 takes place at temperatures starting from 700°C to produce cobalt ferrite. The degree of propagation of this reaction increases progressively as a function of precalcination temperature and Al2O3-doping of the reacting solids. However, the heating of pure mixed solids at 1000°C for 6 h. was not sufficient to effect the complete conversion of the reacting solids into CoFe2O4, while the addition of a small amount of Al2O3 (1.5 mol%) to ferric/cobalt mixed solids followed by precalcination at 1000°C for 6 h conducted the complete conversion of the reacting solids into cobalt ferrite. The heat treatment of pure and the 0.75 mol%-doped solids at 900 and 1000°C effected the disappearance of most of IR transmission bands of the free oxides with subsequent appearance of new bands characteristic for the CoFe2O4 structure. An increase in the amount of Al2O3 added from 1.5–4.5 mol% to the mixed solids precalcined at 1000°C led to the disappearance of all bands of free oxides and appearance of all bands of cobalt ferrite. The promotion effect of Al2O3 in cobalt ferrite formation was attributed to an effective increase in the mobility of the various reacting cations. The activation energy of formation (ΔE) of CoFe2O4 phase was determined for pure and doped solids. The computed values of ΔE were, respectively, 99.6, 87.8, 71.9, 64.7 and 48.7 kJ mol−1 for the pure solid and those treated with 0.75, 1.5, 3 and 4.5 mol% Al2O3. 相似文献
14.
The effects of calcination temperature and doping with K 2O on solid–solid interactions and physicochemical properties of NiO/Fe 2O 3 system were investigated using TG, DTA and XRD techniques. The amounts of potassium, expressed as mol% K 2O were 0.62, 1.23, 2.44 and 4.26. The pure and variously doped mixed solids were thermally treated at 300, 500, 750, 900 and 1000 °C. The catalytic activity was determined for each solid in H 2O 2 decomposition reaction at 30–50 °C. The results obtained showed that the doping process much affected the degree of crystallinity of both NiO and Fe 2O 3 phases detected for all solids calcined at 300 and 500 °C. Fe 2O 3 interacted readily with NiO at temperature starting from 700 °C producing crystalline NiFe 2O 4 phase. The degree of reaction propagation increased with increasing calcination temperature. The completion of this reaction required a prolonged heating at temperature >900 °C. K 2O-doping stimulates the ferrite formation to an extent proportional to its amount added. The stimulation effect of potassium was evidenced by following up the change in the peak height of certain diffraction lines characteristic NiO, Fe 2O 3, NiFe 2O 4 phases located at “d” spacing 2.08, 2.69 and 2.95 Å, respectively. The change of peak height of the diffraction lines at 2.95 Å as a function of firing temperature of pure and doped mixed solids enabled the calculation of the activation energy (Δ E) of the ferrite formation. The computed Δ E values were 120, 80, 49, 36 and 25 kJ mol −1 for pure and variously doped solids, respectively. The decrease in Δ E value of NiFe 2O 4 formation as a function of dopant added was not only attributed to an effective increase in the mobility of reacting cations but also to the formation of potassium ferrite. The calcination temperature and doping with K 2O much affected the catalytic activity of the system under investigation. 相似文献
15.
The energy-localized CNDO/2 molecular orbitais have been calculated for the clusters containing molybdenum, > {Mo 3S 42Mo} 8+ and> Mo 3S 4]CuI> 4+, versus the prototype arene-metal sandwich (C 6H 6) 2Cr and half-sandwich complexes C 6H 6Cr(CO) 3. The bonding characteristics of these compounds are described from a localization bonding viewpoint. There are two typical M-arene and M-[Mo 3S 4] bondings. One is formed by electron donation from the three-center two-electron π-bonds in the arene or [Mo 3S 4] 4+ ligands into the vacant hybrid orbitais of the “stranger” metal atom. In the other M-arene or M-[Mo 3S 4] bond there is very little donation by the lone electron pair occupying the d AOs of the “stranger” metal atom to the arene or [Mo 3S 4] 4+ ligands. The analogy of the ligand [Mo 3S 4] 4+ in the clusters studied with the ligand benzene is also briefly discussed. 相似文献
16.
Ir(H) 2(OR f)P 2 (P = P tBu 2Ph, R f = CH 2CF 3) reacts with ethylene at 25°C to give R fOH, ethane and Ir(P C)P(C 2H 4) (2) then Ir(P C)(C 2H 4) 2 (1) and Ir(P C)H(OR f)P (3) (P C = η 2-C 6H 4P tBu 2). It is shown that 2 and 1 are in equilibrium by P and C 2H 4 addition/dissociation. Compound 3 is a product “late” in the reaction sequence, and results from H---OR f oxidative addition to 2. Since 3 reacts with ethylene to give 2, 2 and 3 are in thermal equilibrium. Compound 3 reacts readily with H 2 to give IrH 5P 2 and R fOH. The reason why OR f and ethylene ligands seem to be mutually incompatible is discussed. 相似文献
17.
The effects of doping of Co 3O 4with MgO (0.4–6 mol%) and V 2O 5 (0.20–0.75 mol%) on its surface and catalytic properties were investigated using nitrogen adsorption at −196°C and decomposition of H 2O 2 at 30–50°C. Pure and doped samples were prepared by thermal decomposition in air at 500–900°C, of pure basic cobalt carbonate and basic carbonate treated with different proportions of magnesium nitrate and ammonium vanadate. The results revealed that, V 2O 5 doping followed by precalcination at 500–900°C did not much modify the specific surface area of the treated Co 3O 4 solid. Treatment of Co 3O 4 with MgO at 500–900°C resulted in a significant increase in the specific surface area of cobaltic oxide. The catalytic activity in H 2O 2 decomposition, of Co 3O 4 was found to suffer a considerable increase by treatment with MgO. The maximum increase in the catalytic reaction rate constant ( k) measured at 40°C on Co 3O 4 due to doping with 3 mol% MgO attained 218, 590 and 275% for the catalysts precalcined at 500, 700 and 900°C, respectively. V 2O 5-doping of Co 3O 4 brought about a significant progressive decrease in its catalytic activity. The maximum decrease in the reaction rate constant measured at 40°C over the 0.75 mol% V 2O 5-doped Co 3O 4 solid attained 68 and 93% for the catalyst samples precalcined at 500 and 900°C, respectively. The doping process did not modify the activation energy of the catalyzed reaction but much modified the concentration of catalytically active constituents without changing their energetic nature. MgO-doping increased the concentration of CO 3+–CO 2+ ion pairs and created Mg 2+–CO 3+ ion pairs increasing thus the number of active constituents involved in the catalytic decomposition of H 2O 2. V 2O 5-doping exerted an opposite effect via decreasing the number of CO 3+–CO 2+ ion pairs besides the possible formation of cobalt vanadate. 相似文献
18.
采用灰熔点仪、X射线荧光仪(XRF)研究了无机非金属P2O5对城市污水污泥与烟煤的混烧灰熔融特性的影响,利用X射线衍射仪(XRD)、X射线光电子能谱仪(XPS)研究在各混烧温度下灰中含磷矿物在晶体和非晶体间的演变。结果表明,对于Al_2O_3含量较多且熔点较高的灰样,磷含量的增加可显著降低其灰熔点,P2O5含量在0-4%时影响最大,使其灰熔点降低126℃;但对碱性含量高的灰样的影响较小。低温灰中主要以磷酸铝(AlPO_4)晶体为主,温度升高后,与硬石膏(CaSO_4)等含钙矿物和赤铁矿(Fe_2O_3)反应生成晶体Ca_3(PO_4)_2和玻璃相(Fe_2O_3)_(0.252)(P_2O_5)_(0.748),磷含量增加可使灰中玻璃相(Fe_2O_3)_(0.252)(P_2O_5)_(0.748)增加,是磷降低灰熔点的主要原因。 相似文献
19.
The H 2O 2-based epoxidation of bridged cyclic alkenes in a monophasic system containing low concentrations (<2 mM) of [Bu 4nN] 4[Pr 2iNH 3] 2H[P{Ti(O 2)} 2W 10O 38]·H 2O (1) (with two η 2-peroxotitanium sites in the anion) has been studied in search of the catalytically active species involved. 31P NMR spectra of 1, measured under a variety of conditions, revealed that the active species was not hydroperoxotitanium complex [P{Ti(OOH)} 2W 10O 38] 7−or [P{Ti(OOH)}Ti(O 2)W 10O 38] 7−. The reaction pathways for the alkene epoxidation are discussed to understand the kinetics (especially the initial [H 2O 2] dependence). It was concluded that the net catalytic reaction for the epoxidation occurred through the two-electron oxidation at the hydroperoxotitanium site in the catalyst. 相似文献
20.
Calculations on linear and bent structures of N 3 and P 3 show that these species are quite different. N 3 is linear, P 3 is bent almost to a D 3h geometry. The symmetry of P 3 in D 3h is 2E″ but the Jahn-Teller distortion is very small, ≈4°. The many-body expansion of the energy of P n clusters appears to be only slowly convergent. 相似文献
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