甲烷在金属铁及氧化铁表面还原NO的研究

在程序控温电加热水平陶瓷管反应器、N₂气氛和模拟烟气气氛及300~1 100℃时,对甲烷在金属铁及其氧化铁表面还原NO的特性进行了实验研究。为使甲烷在脱硝反应后完全燃尽以及脱硝反应过程生成的CO等中间产物完全燃尽,在第一段加热炉后串联了第二段加热炉,补充氧气,实现燃尽。结果表明,甲烷在金属铁及氧化铁表面能够高效地还原NO。在N₂气氛中,在900℃以上温度范围内甲烷在金属铁表面的脱硝效率超过95%,与甲烷在氧化铁表面的脱硝效率差别很小。在模拟烟气条件下,当过量空气系数小于1.0时,在900℃以上时,甲烷在金属铁和氧化铁表面的脱硝效率都能超过90%,且未燃尽和燃尽两种条件下NO的还原率相差不大。NO同时通过金属铁的直接还原和甲烷的再燃还原两种反应机理脱除。而甲烷则通过还原氧化铁为金属铁,从而使金属铁直接还原NO可持续进行。同时,甲烷再燃反应的中间产物HCN/NH₃等被氧化铁还原,从而使燃尽后的脱硝效率不下降。研究结果表明,甲烷和金属铁或氧化铁在富燃料条件下可有效地还原NO。     

An oxidized surface state model of vanadium oxides and its application to catalysis

The charge distribution around the VO bonds in V₂O₅, V₆O₁₃, and V₂O₄ was calculated by using an empirical formula. The same expression was also used to calculate the oxygen bond strengths on the surface. The surfaces of lower oxides were treated as though they were in an oxidized state which is believed to correspond to the conditions in oxidation and ammoxidation processes. The result is that O^2?, in the form of VO surface groups, is responsible for the catalytic oxidation of hydrocarbons. O^? is hindered by the formation of stable OH^? groups. The positions of lower valent oxygens are considered to be vacant because of a slow reoxidation rate. In V₂O₅ the VO groups are located on the (010) plane, while in V₆O₁₃ they are mainly located on the (001) surface plane. But in this case the (100) and (010) surface planes also have some VO groups. The catalytic activity of the rutile form of V₂O₄ is limited by sterical factors, but the (110) surface plane has oxygens pointing perpendicular out of the surface.     

Polytetrafluoroethylene surface modification by impregnation with iron and manganese oxides

Polytetrafluoroethylene (PTFE) surfaces can be modified by impregnation with Fe and Mn oxides by procedures based on Fe(CO)₅ sorption in the polymer and followed by oxidation with H₂O₂ or KMnO₄. The effect of some variables (reagent concentrations and temperature) on the amount of oxides deposited was examined. The oxides incorporated in PTFE can be only partly removed by acid cleaning. Water–PTFE contact angles and PTFE surface resistivity are altered. Electron and x-ray diffractograms of the oxides were obtained but unambiguous identification was not achieved. Transmission electron microscopy examination of surface replicas showed that impregnation with oxides which covered most of the PTFE surface was fairly uniform.     

Use of ESCA for a convenient and semi-quantitative state analysis of copper-nickel alloy surfaces

Summary A semi-quantitative technique by means of ESCA was applied to the surface state analysis of copper-nickel alloys. With area integrated intensity of peaks at the L₃M_{4, 5}M_{4, 5} region of copper and 2 p 3/2 region of nickel, cuprous state and nickel oxide state on alloys could be semi-quantitatively determined. As to oxygen states on alloy surfaces, interstitial (Cu₂O and NiO states), non-stoichiometric (represents -OH) and molecular states (adsorbed) were estimated. Further, the surface composition of alloys after heating under high vacuum was discussed.

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Einsatz von ESCA für die einfache halbquantitative Zustandsanalyse von Oberflächen von Kupfer-Nickel-Legierungen

Zusammenfassung Das ESCA-Verfahren wurde für die Untersuchung des Oberflächenzustandes von KupferNickel-Legierungen eingesetzt. Mit Hilfe der flächenintegrierten Peakintensitäten (L₃ M_{4, 5} M_{4, 5} für Kupfer, 2 p 3/2 für Nickel) konnten Kupfer(II) und Nickeloxid auf den Legierungen halbquantitativ bestimmt werden. Sauerstoff wurde im interstitiellen (Cu₂O, NiO) nichtstöchiometrischen (-OH) und molekularen (adsorbierten) Zustand gefunden. Weiterhin wurde die Oberflächenzusammensetzung der Legierungen nach Erhitzen im Hochvakuum diskutiert.

     

Desorption of oxygen and nitrogen from iron surfaces Application of X-ray photoelectron spectroscopy to surface analysis

The patterns of desorption of oxygen and nitrogen from metal surfaces were examined and applied in the determination of gaseous elements in metal samples. The abundance of gaseous elements on metal surfaces is controlled by thermal desorption and diffusion to or from the surface. A heat treatment suitable for the separation of adsorbed gases from those in the bulk sample is discussed. Preheating of the metal samples at ca. 300 degrees in a vacuum reduces the residual adsorbates to a minimum and retards the diffusion of the gaseous elements from the bulk to the surface.     

Solid state reactions between nickel(II) sulphide and oxides of manganese and iron

Thermogravimetry and differential thermal analysis have shown that, when nickel(II) sulphide and manganese or iron oxides are heated together, several reactions occur depending on the molar ratio of the reactants. Detailed examinations of these reactions have shown that there are a number of intermediate stages, including the formation of sulphates.

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Zusammenfassung Thermogravimetrie und Differentialthermoanalyse zeigen, daß bei gemeinsamer Erhitzen von Nickel(II)-Sulfid und Manganoder Eisenoxiden, in Abhängigkeit von dem Molarverhältnis der Reaktionspartner verschiedene Reaktionen stattfinden. Das eingehende Studium dieser Reaktionen zeigte das Auftreten einer Anzahl Zwischenstufen, darunter auch die Bildung von Sulfaten.

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Résumé On montre par thermogravimétrie et analyse thermique différentielle que plusieurs réactions peuvent se produire suivant les rapports molaires des constituants lorsque l'on chauffe du sulfure de nickel(II) avec des oxydes de manganèse ou de fer. L'étude détaillée de ces réactions a mis en évidence un certain nombre d'étapes intermédiaires, avec formation de sulfates.

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, (II) , . , , .

     

Relationship between micrometer to submicrometer surface roughness and topography variations of natural iron oxides and trace element concentrations

The surface area and roughness of natural iron oxide precipitations were quantified by 3D optical microscopy in order to get information about fluid-rock interface topography in high-permeability zones. Converged surface roughness data of microscale to submicroscale topography show the predominance of macroporous half-pores (>500 nm) and the occurrence of smaller half-pores (<500 nm) that dominate the BET surface area of iron oxides. A relationship was found between the occurrence of macroporous surface structures (micrometer range) and the uranium content of iron oxide encrustations. Iron-normalized uranium concentrations of an X-ray amorphous iron oxide encrustation correlate linearly with maximum topography heights of 1 to 2 mum on hand specimen subsamples. Our study shows the potential importance of micrometer- to submicrometer-size surface features, whose environmental impact is often ignored.     

Interaction of carbon oxides with the surface of catalysts containing iron and nickel nanoparticles

The interaction of individual carbon oxides and their mixture with the surface of monometallic catalysts that contain iron and nickel nanoparticles was investigated for the first time by thermoprogrammed desorption. It was found that both oxides are adsorbed molecularly and dissociatively. No competition between CO and CO₂ was observed upon the coadsorption of these oxides. It was shown that the preadsoption of hydrogen on the surface leads to a strengthening of the Me-CO bond, raises the activation energy of desorption, assists in the dissociative chemisorption of carbon monoxide, and leads to the appearance of hydrocarbons among the products of desorption.     

XPES and UVPES studies of iron oxides

X-Ray and uv photoelectron spectra of FeO, Fe₂O₃, and Fe₃O₄ have been studied along with those of a few model compounds. It has been possible to assign distinct bands due to Fe²⁺ and Fe³⁺ in the 3d, 3p, 3s, and 2p bands of Fe₃O₄. The spectra of Fe₃O₄ do not show major changes through the Verwey transition.     

Evolved gas analysis for examination of surface oxides on alloys

Temperature programmed reduction in a hydrogen flow with simultaneous evolved gas analysis was employed to determine surface oxides on oxide dispersion strengthened (ODS) nickel containing TiO₂, A1₂O₃ or Cr₂O₃ particles, and on a Ni-2OCr alloy, after exposure to air at elevated temperatures. Oxides on particles of water-atomized (WA) Ni-2OCr powder were analysed similarly. Significant differences in starting temperatures of the reaction between hydrogen and phases present in oxide layers made identification of the phases possible. NiO or NiO doped with Ti, Al or Cr are the major constituents of the scale formed on ODS Ni. NiTiO₃, NiCr₂O₄ and NiAl₂O₄ are formed as a result of a reaction between TiO₂, A1₂O₃ or Cr₂O₃ particles in the scale with NiO. The oxide layer formed on Ni-2OCr alloy consists of Cr₂O₃ and of NiO doped with Cr. Surface oxides on WA Ni-2OCr contain Cr₂O₃ and a small amount of NiO.

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Zusammenfassung Temperaturprogrammierte Reduktion im Wasserstoffstrom wurde zusammen mit gleichzeitiger Analyse des in Freiheit gesetzten Gases dazu benutzt, um Oberflächenoxide an Nickel enthaltenden TiO₂-, A1₂O₃- oder Cr₂O₃-Partikeln mit verstärkter Oxiddispersion (ODS) und an einer Ni-2OCr-Legierung nach Behandlung in Luft bei erhöhten Temperaturen zu bestimmen. Oxide auf Partikeln von wasser-zerstäubtem (WA) Ni-2OCr-Pulver wurden auf ähnliche Weise analysiert. Signifikante Unterschiede in der Starttemperatur der Reaktionen zwischen Wasserstoff und der in den Oxidschichten vorliegenden Phasen ermöglichen die Identifikation der Phasen. NiO oder mit Ti, Al oder Cr gedoptes NiO sind die Hauptbestandteile des auf ODS-Ni gebildeten Belags. NiTiO₃, NiCr₂O₄ und NiAl₂O₄ treten als Produkte der Reaktion von TiO₂-, Al₂O₃- oder Cr₂O₃-Partikeln mit NiO im Belag auf. Die auf der Ni-2OCr-Legierung gebildete Oxidschicht besteht aus Cr₂O₃ und aus mit Cr gedoptem NiO. Oberflächenoxide auf WA-Ni2OCr enthalten Cr₂O₂ und geringe Mengen an NiO.

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- , , , , , , Ni-2r, . Ni-2OCr. , , . , , , , . NiTiO₃, NiCr₂O₄ NiAl₂O₄ , , . , Ni-2r, , . Ni-2r .

     

Nanoscale analysis of surface oxides on ZnMgAl hot-dip-coated steel sheets

In this work, the first few nanometres of the surface of ZnMgAl hot-dip-galvanised steel sheets were analysed by scanning Auger electron spectroscopy, angle-resolved X-ray photoelectron spectroscopy and atomic force microscopy. Although the ZnMgAl coating itself is exhibiting a complex micro-structure composed of several different phases, it is shown that the topmost surface is covered by a smooth, homogeneous oxide layer consisting of a mixture of magnesium oxide and aluminium oxide, exhibiting a higher amount of magnesium than aluminium and a total film thickness of 4.5 to 5 nm. Especially by the combined analytical approach of surface-sensitive methods, it is directly demonstrated for the first time that within surface imprints—created by industrial skin rolling of the steel sheet which ensures a smooth surface appearance as well as reduced yield-point phenomenon—the original, smooth oxide layer is partly removed and that a layer of native oxides, exactly corresponding to the chemical structure of the underlying metal phases, is formed.     

Release of coprecipitated uranium from iron oxides

Summary The removal of uranium (VI) from zerovalent iron permeable reactive barriers and wetlands can be explained by its association with iron oxides. The long term stability of immobilized U is yet to be addressed. The present study investigates the remobilization of U(VI) from iron oxides via diverse reaction pathways (acidification, reduction, complex formation). Prior, uranium coprecipitation experiments were conducted under various conditions. The addition of various amounts of a pH-shifting agents (pyrite), an iron complexing agent (EDTA) or iron (III) reduction agent (TiCl₃) yielded in uranium remobilization, concentrations above the US EPA allowedmaximum contaminant level(MCL=30 μg/l). This study demonstrates that U(VI) release in nature strongly depends on the conditions and the mechanism of its fixation by geological materials.     

Changes in iron oxidation state and surface composition of iron-chromium catalyst reduced by hydrogen

X-ray photoelectron spectroscopic studies of the reduction of iron-chromium catalysts have been carried out to determine changes in the relative surface concentrations of iron(II) and (III) oxides and metallic iron and in its surface composition at 100–500°C.

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(II), (III) 100–500°C. .

     

Sorption of inorganic radiocarbon on iron oxides

Journal of Radioanalytical and Nuclear Chemistry - The sorption of inorganic radiocarbon on goethite, hematite and magnetite was studied as a function of carbon concentration, pH and ionic...     

Arsenic adsorption onto pillared clays and iron oxides

Arsenic adsorption was carried out on simple materials such as goethite and amorphous iron hydroxide, and more complex matrices such as clay pillared with titanium(IV), iron(III), and aluminum(III). These matrices were synthesized from a bentonite whose montmorillonitic fraction was pillared according to optimized parameters. These sorbents were characterized by various methods: XRD, FTIR, BET, DTA/TGA, surface acidity, and zetametry. Elimination of arsenite and arsenate as a function of pH was studied. Arsenate elimination was favored at acidic pH, whereas optimal arsenite elimination was obtained at 4相似文献   

Reactivity with hydrogen of pure iron oxide and of iron oxides doped with oxides of Mn,Co, Ni and Cu

Using dynamic TG in H₂, X-ray powder diffraction and Mössbauer Spectroscopy the reactivities fot hydrogen reduction of Fe₂O₃ prepared at different temperatures, Fe₂O₃ doped with oxides of Mn, Co, Ni and Cu prepared at 300C from nitrate precursors and intermediate spinels derived from above samples during reduction have been explored. The reactivity is higher for finely divided Fe₂O₃ prepared at 250C. The reduction is retarded by Mn, marginally affected by Co and accelerated by Ni and Cu, especially at higher (5 at.%) dopant concentration. These reactivities confirmed also by isothermal experiments, are ascribed to the nature of disorder in the metastable intermediate spinels and to hydrogen spill over effects.

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Zusammenfassung Mittels Debye-Scherrer-Aufnahmen, Mössbauer-Spektroskopie und DTG in WasserstoffatmosphÄre wurde die ReaktivitÄt bezüglich der Reduktion mit Wasserstoff von Fe₂O₃, versetztem Fe₂O₃ und von intermediÄren Spinellen aus der Reduktion obiger Proben untersucht. Die reinen Fe₂O₃-Proben wurden bei verschiedenen Temperaturen hergestellt. Mit Oxiden von Mn, Co, Ni und Cu versetzte Fe₂O₃-Proben wurden bei 300C aus Nitrat-VorlÄufern hergestellt. Eine höhere AktivitÄt besteht für fein zerkleinertes, bei 250C hergestelltes Fe₂)O₃. Die Reduktion wird durch Mn verzögert, durch Co unwesentlich beeinflu\t und durch Ni und Cu beschleunigt, besonders bei höheren Konzentrationen (5 mol%). Diese ReaktivitÄten, die auch durch isotherme Experimente bestÄtigt werden konnten, wurden der Ungeordnetheit in den metastabilen intermediÄren Spinellen sowie Wasserstoff-überschu\-Effekten zugeschrieben.

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The authors thank Dr. Chitra Sankar for her help and useful discussions on the Mössbauer studies carried out. They also thank A. V. Narayan and D. Molliah for their assistance with the figures.     

Thermodynamics of interaction of iron oxides and carbon monoxide

Computations of equilibrium mole fraction of carbon monoxide in the gas phase in an interaction of iron oxides and carbon monoxide were conducted.     

Contribution to the study of an inorganic semi-quantitative method of analysis: analysis of chromium and nickel

The authors propose a new semi-quantitative; method of analysis,simple and very rapid, based on the use of sensitive and specific organic reagents, by determination of the limit of detection of the reaction.Two methods are described. 1. Determination of chromium by use of the following reagents: gum guaiacum, strychnine or diphenylcarbazide. 2. Determination of nickel by means of cyclohexanedionedioxime, rubeanic acid or diammonium tetrathiocyanatomerculate.     

Modulation of cell surface iron transferrin receptors by cellular density and state of activation.

This report describes investigations of plasma membrane transferring receptors on a variety of lymphoid cell lines and normal peripheral blood lymphocytes during activation and cell growth cycles. Transformed lymphoid cell lines have as many as 1,000 times the number of receptors found on normal resting lymphocytes. The number of iron transferrin receptors on continuous cell lines as well as normal human fibroblasts is down-regulated during the transition from log-phase growth to stationary plateau growth. When normal lymphocytes are transformed by mixed lymphocyte culture or mitogens, they rapidly express a 50-fold increase in the number of transferrin binding sites. This appearance of iron transferrin receptors anticipates nuclear changes during cell activation and subsequent mitosis of normal cells.