Ozonation of alachlor catalyzed by Cu/Al2O3 in water

The Cu/Al₂O₃ catalyzed ozonation for degrading an endocrine disruptor—alachlor in water was investigated. The Cu/Al₂O₃ powders were coated on a cordierite honeycomb column, which was taken as the reactor of catalytic ozonation of alachlor. Additional uncatalyzed experiments were carried out and the results were compared to those of the catalytic runs.

The experimental results demonstrated that Cu/Al₂O₃ was a very effective catalyst for ozonation of alachlor. The removal rate of alachlor in total organic carbon (TOC) with ozonation in the absence of Cu/Al₂O₃ was only above 20% in 180 min, while the reduction of totle organic carbon (TOC) in the presence of Cu/Al₂O₃ was more than 60%. Correspondingly, more inorganic ions created and less by-products produced in the Cu/Al₂O₃ catalyzed ozonation than in the unanalyzed process. These results indicated that the use of Cu/Al₂O₃ substantially enhanced the mineralization of alachlor in ozonation. The EPR experiments verified that more √OH radicals generated in the Cu/Al₂O₃ catalyzed ozonation could bring on a higher alachlor removal rate.     

Vector Presentation of Liquid Immiscibility in Alkali-Free CaO-FeO-MgO-A12O3-TiO2 Melts

Problems with graphical display of immiscible liquids containing >3 components are overcome by recasting tie lines and reference compositional sections into vectors. The technique is demonstrated for experimental work and a theoretical model of liquid immiscibility in the system CaO-FeO-MgO-A1₂O₃-SiO₂-TiO₂. Both experimental and theoretical work indicate that tie lines simply project radially to SiO₂, so that network-forming components are partitioned like cation-modifying components in these melts. The addition of alkali oxides destroys this simple radial partitioning.     

The Dominant Type of Atomic Disorder in α-Al2O3

Comparison of the energy of formation per defect, as deduced from experimental results on α-Al₂O₃ doped with donors and acceptors on the basis of various models, with theoretical values calculated by Dienes et al . for various disorder models shows closest correspondence of the exFrimentd values with the smallest theoretical values (obtained for Schottky disorder). This indicates that the theoretical results are reliable and that Schottky disorder is the major type of atomic disorder in α-Al₂O₃. Creep data on Al₂O₃:Fe by Hollenberg and Gordon make it possible to determine the enthalpy of Frenkel disorder of Al.     

Oxidation-Reduction and the Major Type of Ionic Disorder in α=AI2O3

The oxidation-reduction constants of AI₂O₃:Ti and AI₂O₃ are derived from experimental data on the basis of models with aluminum vacancies or oxygen interstitials as dominant species. Reasonable agreement between the experimental values of the enthalpies involved and published theoretical values are found in both cases. Combination with the enthalpies of oxidation determined from acceptor-doped AI₂O₃ leads to values of the enthalpy of disorder for the four possible mechanisms. All agree equally well with computed values. Published microstructure studies point to Frenkel disorder of oxygen as the dominant ionic disorder mechanism. Empirical potentials used in theoretical computations appear to be preferable to nonempirical ones, at least for computations related to oxygen defects.     

The Effect of Microstructure and Microcracking on the Thermal Conductivity of UO2-U4O9

Several microstructures were produced in dense polycrystalline UO₂-U₄O₉ specimens by cooling UO_2+x, solid solutions at different rates. Void formation (intragranular pores, grain-boundary microcracks) was observed in specimens which had a nonuniform distribution of the U₄O₉ precipitate; such formation was probably caused by the relief of stresses generated by differential thermal contraction. The microstructures were assessed quantitatively and used to calculate thermal conductivities from theoretical models. The effect of microcracking was calculated. Thermal conductivities were also determined from thermal diffusivity values measured by the laser-flash method. The thermal conductivity was primarily influenced by the amount of U₄O₉, present and the occurrence of voids, whereas the effect of U₄O₉, distribution was minor. Good agreement was obtained between theoretical predictions of thermal conductivity based on microstructure and experimental values.     

Epoxidation of propylene by using [π-C5H5NC16H33]3[PW4O16] as catalyst and with hydrogen peroxide generated by 2-ethylanthrahydroquinone and molecular oxygen

The epoxidation of propylene catalyzed by a reaction-controlled phase transfer catalyst [π-C₅H₅NC₁₆H₃₃]₃[PW₄O₁₆] is investigated. The H₂O₂ is generated by the oxidation of 2-ethylanthrahydroquinone (EAHQ) with molecular oxygen in the organic solvent. Under mild conditions, the selectivity for propylene oxide, based on propylene, is 95%, and the yield, based on 2-ethylanthrahydroquinone, is 85%. During the epoxidation, the catalytic system is homogeneous. However, after the H₂O₂ is used up, the catalyst can be recovered as a precipitate and can be reused. After the epoxidation reaction, 2-ethylanthraquinone can be regenerated to 2-ethylanthrahydroquinone by catalytic hydrogenation, and no coproduct is produced.     

Formation of NiAl2O4 by Solid State Reaction

The growth of nickel-aluminum spinel, NiAl₂O₄, in diffusion couples of polycrystalline Al₂O₃ and NiO was investigated between 1200° and 1500°C. The growth kinetics for the spinel layer obeyed a parabolic rate law in this temperature range. Marker experiments showed that the spinel layer formed by counterdiffusion of nickel and aluminum ions. Comparison of experimental and theoretical values of the parabolic rate constants suggests that the diffusion of aluminum ions through the spinel layer is rate controlling.     

Faceted Grain Boundaries in Al2O3

Different types of faceted grain boundaries in commercial poly-crystalline Al₂O₃ were examined. Three distinct cases, namely the basal twin, the rhombohedral twin, and other special high-angle grain boundaries, are discussed, comparing theoretical models and experimental observations. It is shown that the faceting of the boundaries can be associated with their migration. A mechanism for the separation of a σ= 13 grain houndary from a pinning void, small grain, or second-phase particle is illustrated. It is also shown experimentally that faceting of high-angle boundaries can occur on a scale of Σ 5 nm, and that, theoretically, faceting most likely also occurs on an atomistic scale. Throughout the theoretical analysis the basal plane is predicted to be a favored facet plane, which is confirmed by experimental observation.     

Transient kinetics investigations of reaction intermediates involved in CF2Cl2 hydrodechlorination

The reaction intermediates formed during hydrodechlorination of CF₂Cl₂ catalyzed by Pd supported on AlF₃ have been investigated using steady state and transient kinetics experiments. The formation of the coupling product C₂H₆ and its dependence on H₂ partial pressure have been used to investigate the pathways by which possible surface carbene species react. Reactions of surface species formed during the CF₂Cl₂ hydrodechlorination with scavenging agent C₂H₄ yielded addition products typical of metal-carbenes. Information from these experiments suggests that for carbene and fluorocarbene species formed on the surface of a Pd/AlF₃ catalyst the rates of hydrogenation vs. coupling reactions are different.     

DTA and X-Ray Analysis Study of Nucleation and Crystallization of MgO-Al2O3-SiO2 Glasses Containing ZrO2, TiO2, and CeO2

Crystallization sequences of glasses with compositions in the tridymite primary phase field of the MgO-Al₂O₃-SiO₂ system were studied by DTA, X-ray diffraction, and other techniques. Crystallization was catalyzed by the addition of 7 wt% of either ZrO₂ or TiO₂. Up to 10 wt% CeO₂ was also added to some glasses. Metastable solid solutions with the high-quartz structure exhibiting varying lattice parameters commonly occurred at low temperatures, transforming into a high cordierite at higher temperatures. Depending on the composition and heat treatment, other phases also appeared, e.g. Ce₂Ti₂O₄ (Si₂O₇). The rate of crystallization was markedly dependent on the catalyst. Colloidal precipitation of the catalyst accompanied by bulk crystallization of the glass was observed with ZrO₂, but no crystalline TiO₂ was detected. In the presence of CeO₂, TiO₂ was a more effective catalyst than ZrO₂. Although CeO₂ lowered the melting temperatures of the glass-ceramics, it increased the stability of the glasses and inhibited volume nucleation, causing coarse structures to form on crystallization.     

Al–Al2O3 Composites with Interpenetrating Network Structures: Composite Modulus Estimation

The effective Young's moduli of co-continuous Al–Al₂O₃ composites over the 5–97 vol% Al₂O₃ composition range were experimentally measured and compared with theoretical composite modulus values predicted using the methods of Ravichandran, Tuchinskii, Hashin-Shtrikman, and the effective medium approximation (EMA). The influence of phase morphology and the modulus ratio ( E ₁/ E ₂) of the constituent phases on the resulting experimental and calculated Young's modulus is discussed. For two-phased co-continuous composites with a modulus ratio greater than 5, the EMA, with an appropriate microstructural shape factor, was the most consistent method for approximating the composite Young's modulus over the entire composition range.     

Phase Equilibria in the System HfO2–Y2O3–CaO

Phase equilibria in the system HfO₂–Y₂O₃–CaO were studied in the temperature range 1250° to 2850°C by both experimental methods (X-ray phase analysis at 20° to 2000°C, petrography, annealing and quenching, differential thermal analysis in He at temperatures to 2500°C, thermal analysis in air using a solar furnace at temperatures to 3000°C, and electron microprobe X-ray analysis) and theoretical means (development of a mathematical model for the liquidus surface by means of the reduced polynomial method). Phase equilibria were determined by the structure of the restricting binary systems. No ternary compounds were found. The liquidus was characterized by the presence of six four-phase, invariant equilibria. Solid solutions were based on monoclinic (M), tetragonal (T), and cubic (F) modifications of HfO₂; C and H forms of Y₂O₃; CaO; and CaHfO₃ that crystallized in two polymorphous modifications, namely, the cubic and rhombic perovskite-type structure.     

Preparation of High-Density Si3N4 by a Gas-Pressure Sintering Process

Si₃N₄ compacts, containing ≅7 wt% of both BeSiN₂ and SiO₂ as densification aids, can be reproducibly sintered to relative densities >99% by a gas-pressure sintering process. Nearly all densification takes place via liquid-phase sintering of transformed β-Si₃N₄ grains at T =1800° to 2000°C. Compacts with high density are produced by first sintering to the closed-pore stage (≅92% relative density) in 2.1 MPa (20 atm) of N₂ pressure at 2000°C and then increasing the N₂ pressure to 7.1 MPa (70 atm) where rapid densification proceeds at T = 1800° to 2000°C. The experimental density results are interpreted in terms of theoretical arguments concerning the growth (coalescence) of gas-filled pores and gas solubility effects. Complex chemical reactions apparently occur at high temperatures and are probably responsible for incomplete understanding of some of the experimental data.     

Probing the basicity of zeolite frameworks with N2O4: A DFT approach

The basicity of alkali exchanged faujasite type zeolites is estimated on the basis of DFT calculations of the NO⁺ stretching frequencies of adsorbed N₂O₄. N₂O₄ is allowed to interact with the alkali cations and a range of molecules covering a wide basicity scale. An alkali nitrate salt is formed and NO⁺ interacts with the basic molecules. The resulting NO⁺ stretching frequencies decrease with increasing proton affinity and basicity of the basic molecules for each alkali cation. If experimental proton affinities and basicities of the model molecules are used, the data fall on two straight lines, which are almost parallel. The zeolitic basicities and proton affinities are obtained by interpolation of the experimental NO⁺ frequencies of alkali exchanged faujasites on the linear plots of NO⁺ frequencies against the experimental proton affinities and basicities. With theoretical proton affinities and basicities two non-parallel straight lines are obtained and three molecules are offset. The reason for this is unclear and needs more investigation. The NO⁺ stretching frequency is linearly correlated with the hardness of the alkali cations in zeolite X. For zeolite Y the same trend is observed, but the scatter of the data is too large to define it as linear.     

High-Temperature Elastic Properties of Polycrystalline MgO and Al2O3

Adiabatic bulk modulus, B_s , of polycrystalline MgO and Al₂O₃ was measured from 298° to 1473°K using the resonance technique. The Grüneisen constant, calculated from the measured bulk modulus, was constant over the whole temperature range (1.53 for MgO and 1.34 for Al₂O₃). Another important parameter,     , is constant at high temperature and is 3.1 for MgO and 3.6 for Al₂O₃. The Poisson's ratio increases linearly with temperature for MgO and Al₂O₃. To describe the change of bulk modulus with temperature a theoretical equation was verified by using the foregoing constants. A practical form of this theoretical equation is where B_s⁰ is the adiabatic bulk modulus at 0°K, δ is the quantity     , γ is the Grüneisen constant, H is the enthalpy. The experimental data are described very well by this equation, which is equivalent to the empirical equation suggested by Wachtman et al., B_s^T= B_s⁰ - CT exp (-T_c/T) , where C and T_c are empirical constants.     

Relationship between Doping and Ordering (1/3<111> and 1/2<111> Types) in A(B2+B5+)O3 and A(B3+B6+)O3 Systems

The Madelung energies of A²⁺ (B_1/3²⁺ B_2/3⁵⁺) O₃^2- and A²⁺ (B_2/3³⁺ B_1/3⁶⁺) O₃^2- systems were calculated for different dopants on the A-site. The theoretical results show that the higher-valence dopant enhances the 1/2<111>-type (1:1) ordered arrangement of B-site cations in A²⁺ (B_1/3²⁺ B_2/3²⁺)O₃^2-, whereas the lower-valence dopant promotes the 1:1 ordering in A²⁺ (B_2/3³⁺ B_1/3⁶⁺)O₃^2-, and no doping promotes the 1/3<111>-type (1:2) ordering in the both systems. These calculation results are in agreement with the experimental observations of donor- and acceptor-doped PMN systems.     

Para-to-Ortho H2 Conversion on Gd, Y, Gd2O3, and Y2O3

The mechanism of parahydrogen conversion was studied on Gd₂O₃ and Y₂O₃ powders and on Gd and Y evaporated metal films at low and high temperatures (77° to 90°K and 298° to 418°K). Absolute rates of conversion are compared to theoretical values for 3 possible reaction mechanisms, and it is concluded that a paramagnetic vibrational mechanism is operative on Gd₂O₃, Gd, and Y. On Y₂O₃ the reaction rate is enhanced by additional surface paramagnetic sites. The portion of the surface which is active is ∼1 for the metals and ∼0.01 for the oxides.     

V2O5/HZSM-5催化剂制备及其催化苯羟化合成苯酚性能

采用离子交换法制备一系列不同钒含量的HZSM-5负载钒催化剂x％V2 O5/HZSM-5,采用XRD、FT-IR、SEM、TEM、EDS、Mapping、N2物理吸脱附和XPS等对催化剂物化性能进行表征.结果表明,在最优条件下,以V元素的质量分数为基准,5％V2 O5/HZSM-5催化剂在苯羟基化制苯酚反应中凸显最佳催...     

Synthesis of C2H4 by partial oxidation of CH4 over LiCl/NiO

Alkali halide added transition metal oxides produced ethylene selectively in oxidative coupling of methane. The role of alkali halides has been investigated for LiCl-added NiO (LiCl/NiO). In the absence of LiCl the reaction over NiO produced only carbon oxides (CO₂ + CO). However, addition of LiCl drastically improved the yield of C₂ compounds (C₂H₆ + C₂H₄). One of the roles of LiCl is to inhibit the catalytic activity of the host NiO for deep oxidation of CH₄. The reaction catalyzed by the LiCl/NiO proceeds stepwise from CH₄ to C₂H₄ through C₂H₆ (2CH₄ → C₂H₆ → C₂H₄). The study on the oxidation of C₂H₆ over the LiCl/NiO showed that the oxidative dehydrogenation of C₂H₆ to C₂H₄ occurs very selectively, which is the main reason why partial oxidation of CH₄ over LiCl/NiO gives C₂H₄ quite selectively. The other role of LiCl is to prevent the host oxide (NiO) from being reduced by CH₄. The catalyst model under working conditions was suggested to be the NiO covered with molten LiCl. XPS studies suggested that the catalytically active species on the LiCl/NiO is a surface compound oxide which has higher valent nickel cations (Ni^(2+δ)+ or Ni³⁺). The catalyst was deactivated at the temperatures>973 K due to vaporization of LiCl and consumption of chlorine during reaction. The kinetic and CH₄---CD₄ exchange studies suggested that the rate-determining step of the reaction is the abstraction of H from the vibrationally excited methane by the molecular oxygen adsorbed on the surface compound oxide.     

The System HfO2-Y2O3-Er2O3

A mathematical model of the liquidus surface based on a reduced polynomial method was proposed for the system HfO₂-Y₂O₃-Er₂O₃. The results of calculations according to this model agree fairly well with the experimental data. Phase equilibria in the system HfO₂-Y₂O₃-Er₂O₃ were studied on melted (as-cast) and annealed samples using X-ray diffraction (at room and high temperatures) and micro-structural and petrographic analyses. The crystallization paths in the system HfO₂-Y₂O₃-Er₂O₃ were established. The system HfO₂-Y₂O₃-Er₂O₃ is characterized by the formation of extended solid solutions based on the fluorite-type (F) form of HfO₂ and cubic (C) and hexagonal (H) forms of Y₂O₃ and Er₂O₃. The boundary curves of these solid solutions have the minima at 2370°C (15. 5 mol% HfO₂, 49. 5 mol% Y₂O₃) and 2360°C (10. 5 mol% HfO₂, 45. 5 mol% Y₂O₃). No compounds were found to exist in the system investigated.