X-ray photoelectron spectroscopy of nitrogen oxides adsorbed on iron oxides

Adsorption of N₂O, NO, and NO₂ on Fe₂O₃ and Fe₃O₄ was studied by means of X-ray photoelectron spectroscopy (XPS) using an AEI ES 100 spectrometer at temperatures from ?100 to +250 °C. Adsorption isotherms and isobars of NO and NO₂ have been plotted for Fe₃O₄ and Fe₂O₃. Isotherms are Langmuir curves, and the adsorption isobar of nitrogen dioxide adsorbed on Fe₂O₃ shows a maximum at room temperature. No adsorption of nitrogen monoxide is detected with Fe₂O₃ (the detection limit is about 0.1 monolayer). With adsorbed nitrous oxide a simple peak is recorded in contrast to what is observed in the vapor phase. The N 1s binding energy of adsorbed NO is lower than that of the gaseous species, suggesting that significant electron transfer from the iron oxides to the adsorbed nitrogen oxide occurs; however, this back donation is not observed with adsorbed nitrogen dioxide. Adsorption does not cause changes in the binding energies of Fe₂O₃ core electrons, but shifts the Fe 3p line of Fe₃O₄ toward the higher binding energies, suggesting that Fe₃O₄ is oxidized by the adsorption of nitrogen oxides.     

High-entropy fluorite oxides

Eleven fluorite oxides with five principal cations (in addition to a four-principal-cation (Hf_0.25Zr_0.25Ce_0.25Y_0.25)O_2-δ as a start point and baseline) were fabricated via high-energy ball milling, spark plasma sintering, and annealing in air. Eight of the compositions, namely (Hf_0.25Zr_0.25Ce_0.25Y_0.25)O_2-δ, (Hf_0.25Zr_0.25Ce_0.25)(Y_0.125Yb_0.125)O_2-δ, (Hf_0.2Zr_0.2Ce_0.2)(Y_0.2Yb_0.2)O_2-δ, (Hf_0.25Zr_0.25Ce_0.25)(Y_0.125Ca_0.125)O_2-δ, (Hf_0.25Zr_0.25Ce_0.25)(Y_0.125Gd_0.125)O_2-δ, (Hf_0.2Zr_0.2Ce_0.2)(Y_0.2Gd_0.2)O_2-δ, (Hf_0.25Zr_0.25Ce_0.25)(Yb_0.125Gd_0.125)O_2-δ, and (Hf_0.2Zr_0.2Ce_0.2)(Yb_0.2Gd_0.2)O_2-δ, possess single-phase solid solutions of the fluorite crystal structure with high configurational entropies (on the cation sublattices), akin to those high-entropy alloys and ceramics reported in prior studies. Most high-entropy fluorite oxides (HEFOs), except for the two containing both Yb and Gd, can be sintered to high relative densities. These single-phase HEFOs exhibit lower electrical conductivities and comparable hardness (even with higher contents of softer components such as Y₂O₃ and Yb₂O₃), in comparison with 8?mol. % Y₂O₃-stabilized ZrO₂ (8YSZ). Notably, these single-phase HEFOs possess lower thermal conductivities than that of 8YSZ, presumably due to high phonon scattering by multiple cations and strained lattices.     

Fatty acid allene oxides

Presented at the 1989 AOCS Annual Meeting as the acceptance address for the Supelco AOCS Research Award.     

氧化胺的性能研究

考察了不同碳链的脂肪烷基二甲基氧化胺与脂肪烷基酰胺丙基氧化胺的表面活性、泡沫性能和接触角。实验结果表明:氧化胺具有优异的泡沫稳定性,且随着碳链的增加,泡沫性能降低;脂肪烷基酰胺丙基氧化胺的临界胶束浓度随着碳链的增加而降低,而脂肪烷基二甲基氧化胺的临界胶束浓度随着碳链的增加而增加;氧化胺的接触角随着碳链的增加而变大。     

High active alkyldimethylamine oxides

A recently developed, high active, alkyldimethylamine oxide powder now permits the use of this valuable surfactant in water-sensitive formulations such as bar soaps. Study of the various amine oxide homologs in key performance properties of soap bars showed them to be effective foam modifiers, plasticizers, and synergistic lime soap dispersants. The solid amine oxides were found to be a versatile additive which could readily be formulated into a wide variety of personal care bars.     

Simultaneous removal of nitrogen oxides and diesel soot particulates catalyzed by perovskite-type oxides

Perovskite-type oxides (ABO₃) catalyzed the simultaneous removal of NO_x and diesel soot particulates in the presence of oxygen, and were superior to transition metal simple oxides in the selectivity for NO_x reduction. Although the catalytic activity of perovskite-type oxides depended on both A-site and B-site cations, the substitution of potassium at A sites prominently promoted the oxidation of soot and the reduction of NO_x.     

Pyrolysis of coal and iron oxides mixtures. 2. Reduction of iron oxides

The reduction of iron oxides during the pyrolysis of blends of coal and iron oxides on a laboratory scale, has been studied. The pyrolysis of blends of bituminous coal and 30 wt% of magnetite or hematite has been studied by thermogravimetry and analysis of gases, using a heating rate of 3.2 K min^?1. The state of iron in ferrocoke has been established by X-ray diffraction. A primary reduction by hydrogen and carbon monoxide of the hematite has been observed at between 400 °C and 500 °C, but hidden in thermogravimetric measurements by primary volatilization of the coal. At ≈600 °C magnetite is progressively reduced to wustite and then to iron. This reduction starts a little earlier if the heating rate is slow and the coal rank is low and progresses more rapidly when using hematite. Except for higher heating rates in the coal-magnetite blends, the reduction is complete at 1000 °C. The reductants are H₂ and CO, with production of H₂O and CO₂. When the temperature is increased the reduction by CO becomes of increasing importance, being mainly produced from the coke by the Boudouard reaction. The consumption of coke for the reduction of iron oxides is therefore more important at higher temperatures. Lignite is clearly a better reducing agent than the other coals, because of larger quantities of CO produced from the start of its pyrolysis, and the good reactivity of its char towards CO₂ and H₂O.     

Correlation between the electrochemical properties of colloidal oxides and supported oxides on metallic substrates

Mixed oxide electrodes of Ti(IV) and Cr(III) were prepared by calcining Cr(OH)₃ layers deposited on metallic titanium supports. This treatment produced a mixed oxide film of TiO₂–Cr₂O₃ covered with a layer of pure Cr₂O₃. The electrochemical response (cyclic voltammetry) shows the presence of two or three oxidation peaks depending on the electrode preparation conditions. One peak may be interpreted as the oxidation of Cr(III) to Cr(VI) species and the appearance of other peaks is due to the presence of chromium atoms in oxidation states higher than (III). The results of chemical analyses, electrophoretic mobilities and acid-base potentiometric titrations on calcined Cr(OH)₃ powders shows that the calcination step in air produced the decomposition of the Cr(III) hydroxide to the Cr(VI) oxide. Soluble Cr(VI) compounds were found in equilibrium with the suspended powder oxide which markedly affected the shape of the titrations curves. From the amount of Cr(VI) present in solution it was possible to correct the experimental ₀-pH curves. These corrected data indicated that Cr(VI) soluble species adsorbed at the Cr₂O₃/electrolyte interface.     

Mechanical properties of graphene oxides

The mechanical properties, including the Young's modulus and intrinsic strength, of graphene oxides are investigated by first-principles computations. Structural models of both ordered and amorphous graphene oxides are considered and compared. For the ordered graphene oxides, the Young's modulus is found to vary from 380 to 470 GPa as the coverage of oxygen groups changes, respectively. The corresponding variations in the Young's modulus of the amorphous graphene oxides with comparable coverage are smaller at 290-430 GPa. Similarly, the ordered graphene oxides also possess higher intrinsic strength compared with the amorphous ones. As coverage increases, both the Young's modulus and intrinsic strength decrease monotonically due to the breaking of the sp(2) carbon network and lowering of the energetic stability for the ordered and amorphous graphene oxides. In addition, the band gap of the graphene oxide becomes narrower under uniaxial tensile strain, providing an efficient way to tune the electronic properties of graphene oxide-based materials.     

Hidden transformations in entropy-stabilized oxides

Entropy-stabilized oxides (ESO) display a reversible entropy-driven phase transformation that can be leveraged to produce a continuum of metastable phase states, allowing for property optimization and novel functionalities. X-ray absorption spectroscopy reveals that entropic stabilization extends to the electronic structure (valence state and cation coordination) in sintered (Co,Cu,Mg,Ni,Zn)O, manifesting as a tunable lattice distortion in the entropy-stabilized phase. Co, Cu, and Zn ions reversibly transform from six-fold to four-fold coordinated structures and from low to high valence states due to the competition between electronic structures that are equilibrium and enthalpy-driven or metastable and entropy-driven. The segregation of a Cu-rich tenorite phase and a Co-rich spinel phase influences the electronic structure evolution. ESOs can adjust their electronic structures through heat treatment, providing a powerful tool for developing functional properties. These results indicate that the definition of entropy stabilization should include entropy-stabilized electronic structures, providing motivation to reassess previously studied HEO materials.     

Electrochemical synthesis of perovskite oxides

Hydroxide precursors to perovskite oxides of the formula, LnMO₃ (Ln = La, Pr, Nd; M = Al, Mn, Fe) and LaMO₃ (M = Co and Ni) were synthesized by electrogeneration of base by cathodic reduction of the appropriate mixed-metal nitrate solution. The precursors were heat treated at different temperatures to obtain the perovskite oxides. The bath composition for various systems was optimized to get a single-phase oxide product. This method can be adapted as a simple route to the synthesis of perovskite oxide coatings on conducting substrates.     

Oxygen evolution on semiconducting oxides

The oxygen evolution reaction is of particular interest to secondary metal air batteries and water electrolysis plants. However, most of the earlier work has been on precious metals and there are no guidelines for the choice of semiconducting oxides as oxygen evolving electrodes. In this study, the role of the metal/metal oxide or the lower metal oxide/higher metal oxide couple in determining the minimum voltage required for the evolution of oxygen is emphasized, together with other essential requirements such as electrical resistivity, electrode microstructure, corrosion resistance and catalytic properties. A survey of various metal oxides based on the above criterion suggested that NiCo₂O₄ is of particular interest and Teflon bonded electrodes based on this material gave over 13000 A/m² at 1.63 V vs dhe, 70°C, 5 N KOH.     

Twist-boat conformation in graphene oxides

We have investigated the structural, electronic, and vibrational properties of graphene oxide based on first-principles density-functional calculations. A twist-boat conformation is identified as the energetically most favorable nonmetallic configuration for fully oxidized graphene. The calculated Raman G-band blue shift is in very good agreement with experimental observations. Our results provide important insight into structural and electronic characteristics that are useful for further development of graphene-based nanodevices.     

Dielectric relaxation of high-k oxides

Frequency dispersion of high-k dielectrics was observed and classified into two parts: extrinsic cause and intrinsic cause. Frequency dependence of dielectric constant (dielectric relaxation), that is the intrinsic frequency dispersion, could not be characterized before considering the effects of extrinsic frequency dispersion. Several mathematical models were discussed to describe the dielectric relaxation of high-k dielectrics. For the physical mechanism, dielectric relaxation was found to be related to the degree of polarization, which depended on the structure of the high-k material. It was attributed to the enhancement of the correlations among polar nanodomain. The effect of grain size for the high-k materials'' structure mainly originated from higher surface stress in smaller grain due to its higher concentration of grain boundary.     

Obtaining high-purity fused refractory oxides

Conclusions Using yttrium oxide and aluminum oxide as examples we demonstrated the possibility of successfully using the induction heating method in a cold crucible for obtaining fused refractory materials possessing a high purity. The contamination of the charge by the crucible material during melting does not exceed 10^–3%.Translated from Ogneupory, No. 7, pp. 26–29, July, 1973.     

Nanophase catalytic oxides: I. Synthesis of doped cerium oxides as oxygen storage promoters

Doped CeO₂ materials were synthesized with the aim to improve the performance of CeO₂ as oxygen storage promoter in gas catalytic reactions. The coprecipitation method was used for the synthesis of fine oxalate precursors of high homogeneity and well defined composition. The chemical and morphological properties of both the coprecipitated oxalates and the calcined oxides were examined. The influence of doping of different metal cations into the CeO₂ structure on the oxygen storage capacity in particular was investigated. Some of the doped oxides Ce_0.9M_0.1 O_{2 − δ} (M = Ca, Nd, Pb, etc.) give an increased oxygen storage capacity, 20–40% higher than the undoped. Their redox activity also remarkably increased.     

Synthesis of alcohols from carbon oxides and hydrogen on ZnCrTi oxides: preparation and catalytic activity

Ternary systems of composition (1–x)ZnCrO_2.5·xZn₂TiO₄ were tested in the synthesis of higher alcohols from syngas. The catalysts after calcination were found to be solid solutions of Zn, Cr and Ti oxides of spinel like structure, with only a small amount of crystalline ZnO phase segregated. After the catalytic test more important quantities of crystalline ZnO were formed in the catalysts revealing an intrinsic instability of the system. However, a significant maximum in selectivity to higher alcohols was found forx = 0.1 and is associated with an increased rate of isobutanol (2-methylpropanol) formation observed on this system.     

CeO2纳米棒负载Co催化CO脱除NOx的机理

以碱法水热合成径向尺寸6～10 nm的CeO₂纳米棒,采用湿法浸渍在纳米棒上负载不同含量的Co氧化物。通过实验探究Co含量改变对脱硝性能的影响原理,实验结果显示浸渍方案为3 g CeO₂∶30 ml 10%（质量分数） 硝酸钴溶液时,脱硝效率最高,在NO与CO摩尔比为1∶5,体积空速为30000 h^-1,无氧状态下,250℃ 即能达到70%以上的效率。采用氮气吸附、XPS、TEM以及XRD测试不同钴含量催化剂的物化性质,与催化性能结果比对分析后得出Co的添加是通过改变催化剂表面的活性官能团来提高效率,其中Co₂O₃对于催化CO与NO_x进行反应具有较高的效率,提高催化剂中Co₂O₃的比重可以将高效率温度段降低,CoO在一定程度上对CO与NO_x反应具有负面作用,而Co₃O₄对低温阶段N₂O选择性影响较大。