Structure and redox properties of CexPr1−xO2−δ mixed oxides and their catalytic activities for CO, CH3OH and CH4 combustion

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, CH₃OH and CH₄ on these mixed oxides was investigated. When the value x was changed from 1.0 to 0.8, only a cubic phase CeO₂ 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 CeO₂ 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 CeO₂. 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 Pr₆O₁₁ 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 Pr₆O₁₁ or CeO₂. 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 CH₃OH oxidation, while the activity of CH₄ oxidation is mostly related to reduction temperatures and redox properties.     

Anaerobic oxidation of isobutane: Catalytic properties of MgV2O6 and Mg2V2O7 prepared by the molten method

The catalytic activity of MV₂O₆ and M₂V₂O₇ 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 CO₂ were formed by every catalyst tested. The activities for isobutene formation were CuV₂O₆ > ZnV₂O₆, NiV₂O₆, CoV₂O₆ > MgV₂O₆ > MnV₂O₆  CaV₂O₆. Isobutene was a major product over M₂V₂O₇ (MM). Co₂V₂O₇ showed the highest activity and high isobutene selectivity exceeded 90%, demonstrating that Co₂V₂O₇ is a suitable oxide for a thin layer reactor for anaerobic oxidation of isobutane. Partial substitution of Mg by Cu in Mg₂V₂O₇ (MM) improved the activity. It is shown by the oxidation at low O₂ 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 CO₂ formation by the oxygen species derived from molecular oxygen in the gas phase.     

Heat capacities of the tungsten oxides WO3, W20O58, W18O49 and WO2

The heat capacities of the tungsten oxides WO₃, W₂₀O₅₈, W₁₈O₄₉ and WO₂ have been measured over the temperature range 340–999 K using differential scanning calorimetry. The lower oxides were prepared by controlled reduction of WO₃ in H₂/H₂O gas atmospheres. Previous calorimetric work on WO₃ 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. W₂₀O₅₈ is shown to behave similarly to WO₃. A high temperture phase change is evident, however, this appears to be complete by 970–990 K. The measured values of heat capacity for W₁₈O₄₉ are in close agreement with estimated data for W₁₈O₄₉. There is no evidence of any phase transitions for this oxide in the temperature range studied. The heat capacity data for WO₂ confirm previous drop calorimetry measurements and give no evidence of any phase changes for WO₂ in the temperature range 340–990 K.     

EPR lineshape studies of low-temperature vanadium 3d polaron dynamics in the 70V2O5-30P2O5 binary glass

In a specimen of 70V₂O₅-30P₂O₅glass, EPR lineshapes of the vanadium 3d¹ 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.     

Fabrication of solid thin film electrolyte and LiCoO2 by aerosol flame pyrolysis deposition

Aerosol flame pyrolysis deposition method was applied to deposit the oxide glass electrolyte film and LiCoO₂ cathode for thin film type Li-ion secondary battery. The thicknesses of as-deposited porous LiCoO₂ and Li₂O–B₂O₃–P₂O₅ electrolyte film were about 6 μm and 15 μm, respectively. The deposited LiCoO₂ was sintered for 2 min at 700 °C to make partially densified cathode layer, and the deposited Li₂O–P₂O₅–B₂O₃ 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.     

Thermoelectric properties of the AA′3B4O12-type ordered perovskite oxides

The perovskite transition-metal oxide ABO₃ 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′₃B₄O₁₂, the A site order is closely related to the peculiar electronic states. In CaMn₃Mn₄O₁₂, the unusually small bandwidth justifies to extrapolate the transport data to the high-temperature limit, and in CaCu₃Ru₄O₁₂, a novel heavy-fermion state is realized through the Cu–O–Ru interaction.     

Hydrothermal syntheses and crystal structures of bimetallic cluster complexes [{Cd(phen)2}2V4O12]·5H2O and [Ni(phen)3]2[V4O12]·17.5H2O

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(phen₂)₂V₄O₁₂]·5H₂O (1) and [Ni(phen)₃]₂[V₄O₁₂]·17.5H₂O (2). Crystal data: C₄₈H₅₂Cd₂N₈O₂₂V₄ (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; C₇₂H₁₃₁N₁₂Ni₂O_29.5V₄ (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 [V₄O₁₂]⁴⁻ cluster covalently attached to two {Cd(phen)₂}²⁺ fragments, in which the [V₄O₁₂]⁴⁻ cluster adopts a chair-like configuration. In the structure of 2, the [V₄O₁₂]⁴⁻ cluster is isolated. And the complex formed a layer structure via hydrogen bonds between the [V₄O₁₂]⁴⁻ unit and crystallization water molecules.     

灰中酸性成分对灰熔融温度的影响

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。     

Thermal stability of osmium mixed oxides I. CaOsO3 decomposition products: A new orthorhombic phase Ca2Os2O7

The thermal decomposition of CaOsO₃ by differential thermal analyses, thermogravimetry and X-ray powder diffraction has been studied. In nitrogen CaOsO₃ decomposes at 880 ± 10°C into CaO, osmium metal and oxygen due to the reaction CaOsO₃ → CaO + Os + O₂. In static air the decomposition occurs in three stages: 2CaOsO₃ + 1/2O₂ → Ca₂Os₂O₇ (in region 775–808°C), Ca₂Os₂O₇ → Ca₂Os₂O_6,5 + 1/4O₂ (at a temperature interval of 850–1000°C) and in the third stage Ca₂Os₂O_6,5 → 2CaO + OsO₄ ÷ 1/4 O₂ (at 1005 ± 5°C). The first intermediate Ca₂Os₂O₇ is isostructural with orthorhombic Ca₂Nb₂O₇ and its cell parameters are: a₀ = 3.745 Å, b₀ = 25.1 Å, c₀ = 5.492 Å, Z = 4, space group Cmcm or Cmc2. Ca₂Os₂O₇ exhibits metallic conductivity and its electrical resistivity is 4.6 × 10⁻² ohm-cm at 296K.     

The vapour pressure of di-arsenic pentoxide (As2O5)

The arsenic oxide pressure of As₂O₅ has been studied using mass spectrometry and a transportation method. Mass spectrometry revealed the presence of the species As₄O⁺₆, As₄O⁺₇, and As₄O⁺₈ in the vapour. The existence of volatile species up to As₄O₁₀(g) as a result of the reaction As₄O₁₀(g) As₄O_(10−y) (g) +1/2yO₂(g) has been assumed.

The oxygen pressure of this equilibrium builds up very slowly. The equilibrium pressure can be expressed by log(p_O2/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(p_As4O10/atm) (865−1009 K) = −(15741 ± 410)/T + (13.87 ± 0.42).     

A novel nonaqueous route to V2O3 and Nb2O5 nanocrystals

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 V₂O₃ and Nb₂O₅. Although the reaction temperatures of 200–220 °C are comparably low, the obtained particles are highly crystalline. According to TEM investigations, the V₂O₃ crystals exhibit particle sizes between 20 and 50 nm, and the Nb₂O₅ crystals display platelet-like particle shapes with sizes of 50–80 nm, without any indications of amorphous character.     

Synthesis of spherical nanoparticles of Cu2L2O5 (L=Ho, Er) from W/O microemulsions

Nanoparticles of Cu₂L₂O₅ (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 Cu₂Ho₂(CO₃)₄(OH)₂ (25–30 nm) and Cu₂Er₂(CO₃)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.     

Solid–solid interactions between ferric and cobalt oxides as influenced by Al2O3-doping

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% Al₂O₃.

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.     

Thermal solid–solid interactions and physicochemical properties of NiO/Fe2O3 system doped with K2O

The effects of calcination temperature and doping with K₂O on solid–solid interactions and physicochemical properties of NiO/Fe₂O₃ system were investigated using TG, DTA and XRD techniques. The amounts of potassium, expressed as mol% K₂O 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 H₂O₂ decomposition reaction at 30–50 °C. The results obtained showed that the doping process much affected the degree of crystallinity of both NiO and Fe₂O₃ phases detected for all solids calcined at 300 and 500 °C. Fe₂O₃ interacted readily with NiO at temperature starting from 700 °C producing crystalline NiFe₂O₄ phase. The degree of reaction propagation increased with increasing calcination temperature. The completion of this reaction required a prolonged heating at temperature >900 °C. K₂O-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, Fe₂O₃, NiFe₂O₄ 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 (ΔE) of the ferrite formation. The computed ΔE values were 120, 80, 49, 36 and 25 kJ mol⁻¹ for pure and variously doped solids, respectively. The decrease in ΔE value of NiFe₂O₄ 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 K₂O much affected the catalytic activity of the system under investigation.     

A localized molecular orbital study on the bonding of> Mo3S4]2Mo> and> Mo3S4]CuI> versus (C6H6)2Cr and C6H6Cr(CO)3

The energy-localized CNDO/2 molecular orbitais have been calculated for the clusters containing molybdenum, > {Mo₃S₄₂Mo}⁸⁺ and> Mo₃S₄]CuI> ⁴⁺, versus the prototype arene-metal sandwich (C₆H₆)₂Cr and half-sandwich complexes C₆H₆Cr(CO)₃. The bonding characteristics of these compounds are described from a localization bonding viewpoint. There are two typical M-arene and M-[Mo₃S₄] bondings. One is formed by electron donation from the three-center two-electron π-bonds in the arene or [Mo₃S₄]⁴⁺ ligands into the vacant hybrid orbitais of the “stranger” metal atom. In the other M-arene or M-[Mo₃S₄] bond there is very little donation by the lone electron pair occupying the d AOs of the “stranger” metal atom to the arene or [Mo₃S₄]⁴⁺ ligands. The analogy of the ligand [Mo₃S₄]⁴⁺ in the clusters studied with the ligand benzene is also briefly discussed.     

Ethylene hydrogenation by the hydride alkoxide species Ir(H)2(OCH2CF3)(PBu2Ph)2. Ethylene-induced reductive elimination of alcohol from Ir

Ir(H)₂(OR_f)P₂ (P = P^tBu₂Ph, R_f = CH₂CF₃) reacts with ethylene at 25°C to give R_fOH, ethane and Ir(P C)P(C₂H₄) (2) then Ir(P C)(C₂H₄)₂ (1) and Ir(P C)H(OR_f)P (3) (P C = η²-C₆H₄P^tBu₂). It is shown that 2 and 1 are in equilibrium by P and C₂H₄ 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 H₂ to give IrH₅P₂ and R_fOH. The reason why OR_f and ethylene ligands seem to be mutually incompatible is discussed.     

Catalytic decomposition of H2O2 on Co3O4 doped with MgO and V2O5

The effects of doping of Co₃O₄with MgO (0.4–6 mol%) and V₂O₅ (0.20–0.75 mol%) on its surface and catalytic properties were investigated using nitrogen adsorption at −196°C and decomposition of H₂O₂ 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, V₂O₅ doping followed by precalcination at 500–900°C did not much modify the specific surface area of the treated Co₃O₄ solid. Treatment of Co₃O₄ with MgO at 500–900°C resulted in a significant increase in the specific surface area of cobaltic oxide. The catalytic activity in H₂O₂ decomposition, of Co₃O₄ 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 Co₃O₄ due to doping with 3 mol% MgO attained 218, 590 and 275% for the catalysts precalcined at 500, 700 and 900°C, respectively. V₂O₅-doping of Co₃O₄ 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% V₂O₅-doped Co₃O₄ 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 CO³⁺–CO²⁺ ion pairs and created Mg²⁺–CO³⁺ ion pairs increasing thus the number of active constituents involved in the catalytic decomposition of H₂O₂. V₂O₅-doping exerted an opposite effect via decreasing the number of CO³⁺–CO²⁺ ion pairs besides the possible formation of cobalt vanadate.     

磷对泥/煤混燃灰熔融特性的影响及矿物相演变规律

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。     

H2O2-based epoxidation of bridged cyclic alkenes with [P{Ti(O2)}2W10O38] in monophasic systems: active site and kinetics

The H₂O₂-based epoxidation of bridged cyclic alkenes in a monophasic system containing low concentrations (<2 mM) of [Bu₄ⁿN]₄[Pr₂ⁱNH₃]₂H[P{Ti(O₂)}₂W₁₀O₃₈]·H₂O (1) (with two η²-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)}₂W₁₀O₃₈]⁷⁻or [P{Ti(OOH)}Ti(O₂)W₁₀O₃₈]⁷⁻. The reaction pathways for the alkene epoxidation are discussed to understand the kinetics (especially the initial [H₂O₂] 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.     

A comparative study of species N3 and P3

Calculations on linear and bent structures of N₃ and P₃ show that these species are quite different. N₃ is linear, P₃ is bent almost to a D_3h geometry. The symmetry of P₃ 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.