Spectroellipsometric Characterization of Multilayer Sol-Gel Fe2O3 Films

Multilayer Fe₂O₃ films were deposited by the sol-gel method on glass substrates using three successive deposition procedures. The films were thermally treated for 1 h at 300°C.The optical and microstructural properties of these films were investigated by spectroscopic ellipsometry (SE) in the 500–1000 nm range. The optical gap was found by fitting the dispersion of the film refractive index (n) with the Wemple-DiDomenico (WDD) formula.The ellipsometric measurements showed also that the Fe₂O₃ films are anisotropic. The birefringence values (n) of the sol-gel films (0.05–0.08) are smaller than the large values of the Fe₂O₃ (which are around 0.28) but increase with the crystalization of the films. AFM mesurements showed that the films treated at 300°C start to crystallize.     

Effect of Thermal Activation of Supported Catalysts Pt/MeOx,Where MOx = Al2O3, CeO2, La2O3, and ZrO2, for Complete Oxidation

A sharp increase in the atomic catalytic activity (ACA) of supported platinum catalysts in the model reaction of n-pentane complete oxidation is found on going from the preliminary calcination temperature of 500–600°C to a temperature of 700°C. ACA increases by an order of magnitude for the Pt/-Al₂O₃ system, 3 times for Pt/ZrO₂, and 1.5 times for Pt/CeO₂. The per-gram activities of all catalysts decrease because of a decrease in the dispersion of supported platinum with an increase in the temperature of preliminary calcination.     

Preparation and characterization of silicate gel glasses containing Cr2O3

The effect of thermal treatment on the structural incorporation of Cr₂O₃ in xCr₂O₃·(100 – x)SiO₂ and 5R _n O·xCr₂O₃·(95 – x)SiO₂ (where x=0.01–1 mol.% and R=Li, Na and Ca) gel glasses was studied by optical absorption spectrophotometry, DTA-TG, XRD and electron microscopy.Samples heat treated at 60°C have green color due to the presence of Cr³⁺ in octahedral coordination. The optical transmission, and color (yellow, orange or ambar), of the samples heat treated between 200 and 700°C prove that Cr³⁺ (octahedrally coordinated) and Cr⁶⁺ (tetrahedrally coordinated) are both present. Segregation of Cr₂O₃ take place at temperatures above 800°C.In reducing conditions the gel glasses were green due to the presence of a high content of Cr³⁺ ions. Samples containing Li or Na show crystalline phases at temperatures below 850°C.     

The effect of Fe2O3 dopants on electrophysical and sorption properties of ZnO

The effect of Fe₂O₃ dopants (0–0.8 mol.%) on ZnO conductivity and its chlorine chemisorption ability has been studied in the temperature range of 20–250 °C. Introduction of dopants increases the activation energy of ZnO conductivity and decreases the conductivity. The effective charge of the chemisorbed chlorine species as well as the strength of their bonding to the surface in samples containing Fe₂O₃ are considerably lower than in initial ZnO, which leads to a decrease of reactivity of the doped catalysts in chlorination.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1196–1199, July, 1993.     

Cyclohexane transformations over metal oxide catalysts. 1. Effect of the nature of metal and support on the catalytic activity in cyclohexane ring opening

The activities of monometallic Pt-, Ru-, and Rh-containing catalysts supported on Al₂O₃, Al₂O₃—F, SiO₂, WO₃/ZrO₂, and La₂Î₃/ZrO₂, in cyclohexane ring opening to form n-hexane were studied. The most active catalyst is Rh/Al₂O₃. Cyclohexane hydrogenolysis to n-hexane also occurs over the Pt/Al_;>2O₃ and Pt/La₂Î₃/ZrO₂ catalysts. Ring opening over the Ru catalysts proceeds at significantly lower temperatures (210—230 °C) than over the Pt and Rh catalysts (350—400 °C), but the ruthenium systems are less selective for n-hexane formation than Rh/Al₂O₃ catalysts. The effects of acid-basic properties of the support and the reaction conditions on the activities of the catalytic systems in cyclohexane ring opening was studied.     

Oxidation by a “H2O2-vanadium complex-pyrazine-2-carboxylic acid” reagent

Lower alkanes (ethane, propane,n-butane,n-pentane) are readily oxidized in acetonitrile solvent by H₂O₂ with vanadate anion — pyrazine-2-carboxylic acid (PCA), as the catalyst at 75 °C and pressures of –3 atm to produce predominantly or exclusively ketones (aldehydes). Isobutane is transformed selectively intotert-butyl alcohol. The oxidation of cyclohexane at 26 °C in acetone or acetic acid is less efficient than in acetonitrile. The reaction does not occur intert-butyl alcohol.For Part 4, see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2514–2517, October, 1996.     

Formation of Carbon Filaments from 1,3-Butadiene on Fe/Al2O3 Catalysts

The formation of carbon filaments with different crystallographic and morphological characteristics in the course of 1,3-butadiene decomposition on Fe/Al₂O₃ catalysts at low (500–600°C) and high (700–800°C) temperatures was considered in terms of a carbide cycle mechanism. The conditions of formation and decomposition of an iron carbide phase in the course of formation of graphite nanotubes in the low-temperature region were studied.     

Catalytic Performance of Re/Ga2O3/WO3/ZrO2 Catalyst for n-Hexane Isomerization

A series of Re/Ga₂O₃/WO₃/ZrO₂ catalysts were prepared by the impregnation method. The crystalline structure, redox, and acid site distribution of the catalysts were characterized by X-ray powder diffraction, temperature-programmed reduction of H₂, and temperature-programmed desorption of NH₃. Their catalytic performance for n-hexane isomerization was studied. The results showed that the addition of Re greatly affected the redox properties and the acid site distribution of the catalysts. Owing to the presence of Re, n-hexane isomerization was catalyzed by metal and acid sites, and thus the conversion of n-hexane and the selectivity for 2,2-dimethylbutane were significantly increased. Under the conditions of 195 °C, 1.0 MPa, LHSV = 1.0 h⁻¹, and n(H₂)/n(C₆) = 2.0, the conversion of n-hexane over 1.0%Re/1.0%Ga₂O₃/WO₃/ZrO₂ is 84.8%, and the selectivities for 2,2-dimethylbutane, i-hexane, and cracking products (C_5-) are 20%, 97.7%, and 2.1%, respectively. The catalyst is stable during 150 h operation.     

n-Octane Dehydrocyclization on Cr2O3/La2O3/ZrO2 Catalyst Elucidated by H–D-Tracer Experiments

H–D tracer experiments during n-octane aromatization on Cr₂O₃/La₂O₃/ZrO₂ catalysts allow conclusions to be drawn on the reaction mechanism. The rate-determining step is the dissociative adsorption of the paraffin molecule. The following dehydrogenation steps seem to proceed predominantly reversibly.     

Spektroskopische Untersuchungen und Phasenbeziehungen im System Li2O−Al2O3−Cr2O3

Zusammenfassung Aus Li₂CO₃ und (Al_1–x Cr _x )₂O₃ wurde durch Festkörperreaktionen die Mischkristallreihe LiAl_1–x Cr _x O₂ hergestellt. Die thermische Stabilität der mikrokristallinen Substanzen (-NaFeO₂-Typ, Raumgruppe R3m) wurde röntgenographisch verfolgt. Die diffusen Reflexionsspektren (12 bis 30 kK, 25°C) wurden mit dem Modell der erweiterten Kristallfeldtheorie ausgewertet. Die durch Multiphononen-Struktur charakterisierten spin-erlaubten Banden ergeben für kubische MikrosymmetrieDq- undRacah-B-Werte, die im Gegensatz zur Rubinreihe nur wenig von Cr-Gehalt abhängen.Dq beruht zum Teil auf dem Einfluß von zweitnächsten Li⁺-Nachbarn, wodurch die effektive Ladung der Sauerstoff-Liganden in der Bindung größer ist. Die breite spin-verbotene Bande bei 15 kK deutet auf eine Magnon-Satellitenstruktur durch antiferromagnetische Ordnung hin.

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Optical studies and phase relations in the system Li₂O–Al₂O₃–Cr₂O₃

The series LiAl_1–x Cr _x O₂ was prepared by solid state reactions with Li₂CO₃ and (Al_1–x Cr _x )₂O₃. The thermal stability of the microcrystalline samples (-NaFeO₂ type, space group R3m) was controlled by X-ray methods. The diffuse reflectance spectra at 25 °C in the region from 12 to 30 kK were analyzed by the extended crystal field theory. From the spin-allowed peaks characterized by a multiphonon structureDq-andRacah-B-values were obtained for cubic site symmetry (neglecting trigonal distortions and spin-orbit effects) that are only slightly dependent on the Cr-content, in contrast to the ruby series.Dq is partly due to the influence of the secondnearest Li⁺-neighbours leading to a greater effective charge of the oxygen ligands in the bond. The broad spin-forbidden peak at 15 kK points to a magnon satellite structure caused by antiferromagnetic ordering.

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Mit 1 Abbildung     

Studies on hydrolyzable carbides. XXII: The carbothermal reduction of scandium oxide Sc2O3

The composition of the products of carbothermal reduction of Sc₂O₃ is examined by X-ray diffraction and chemical analysis and by the hydrolysis method. At pressures of 10^–2-1 Pa, the reaction starts in the temperature region of 1 000–1 200°C. The first product is Sc₂OC of NaCl type; at 1 Pa and 1 400–1 500°C this substance is formed quantitatively (according to stoichiometry) within 50–100 h, repeated homogenization, however, is necessary, or else Sc₂OC reacts locally with Sc₂O₃ giving Sc₂O_1+x C_1–x . The lattice parameter of Sc₂OC in the presence of Sc₁₅C₁₉ is 457.6₃pm. At temperatures above 1 500°C, Sc₁₅C₁₉ is incompletely formed by subsequent reaction with carbon. The product melts at cca. 1 800°C; carbon dissolves and the final composition approaches ScC₂. Carbon separates during solidification. The phase fractions in the products are affected by evaporation, the vapour pressures above both Sc₂OC and Sc₁₅C₁₉ being comparable with the pressure requisite for the carboreduction process. The results are discussed with respect to the often ambiguous published data.

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Untersuchung hydrolysierbarer Carbide, XXII. Die karbothermische Reduktion von Scandiumoxid

Zusammenfassung Zur Untersuchung von Produkten der karbothermischen Reduktion von Scandiumoxid wurden sowohl röntgenographische und chemische Analyse als auch die hydrolytische Methode verwendet. Bei 10^–2 bis 1 Pa beginnt die Reaktion im Temperaturintervall von 1 000–1 200°C. Das erste Reaktionsprodukt ist das Scandiumoxidcarbid Sc₂OC von NaCl-Typ, das quantitativ (der Stöchiometrie entsprechend) bei 1 400–1 500°C und 1 Pa in 50–100 Stunden entsteht. Eine wiederholte Homogenisierung ist allerdings notwendig, damit es zu keiner lokalen Reaktion zwischen Sc₂OC und Sc₂O₃ kommt, bei der dann die Phase Sc₂O_1+x C_1–x entsteht. In Gegenwart von Sc₁₅C₁₉ ist der Gitterparameter von Sc₂OCa=457.6₃pm. Über 1 500°C führt eine weitere Reaktion mit Kohlenstoff zu einer nicht ganz vollendeten Bildung von Sc₁₅C₁₉. Bei cca. 1 800°C schmilzt das Reaktionsprodukt bei gleichzeitiger Auflösung von weiterem Kohlenstoff und die Zusammensetzung nähert sich der Formel ScC₂, beim Erstarren fällt der Kohlenstoff wieder aus. Die Verteilung der Phasen im Produkt wird von der Verdampfung beeinflußt, da die Dampfdrucke von Sc₂OC und Sc₁₅C₁₉ mit dem zum Karboreduktionverlauf notwendigen Druck vergleichbar sind. Die erhaltenen Ergebnisse werden in Relation mit den nicht eindeutigen Angaben in der Literatur diskutiert.

     

Gas-Sensing Properties of Doped In2O3 Films as Sensors for NO2 in Air

A number of sensing systems based on indium oxide doped with various metal oxides (In₂O₃ · WO₃, In₂O₃ · ZnO, In₂O₃ · RuO₂, In₂O₃ · Gd₂O₃, and In₂O₃ · Sm₂O₃) in amounts of no more than 3–5 mol % and also Au · In₂O₃ films were studied as sensors for detecting NO₂ in air. The working temperature of sensors was 250°C (except for In₂O₃ · RuO₂, for which T = 150–190°C). In₂O₃ · WO₃-based sensors reach a high sensitivity especially at a concentration of NO₂ in air higher than 10 ppm (the relative sensor conductivity changes by 2.5 orders of magnitude). However, a shortcoming of this system is an increased response time (7–9 min) as compared to the other studied systems, for which the response time does not exceed 15–20 s. In₂O₃ · Gd₂O₃ and In₂O₃ · Sm₂O₃ films exhibit the best sensing properties in sensitivity, selectivity, and stability. Various NO₂ species adsorbed on the surface of dispersed indium oxide were detected by Fourier-transform IR spectroscopy. The mechanism of changing the conductivity of In₂O₃ · Gd₂O₃ films upon detecting NO₂ in air is discussed.     

Effects of gamma-irradiation and Li2O-doping on surface and catalytic properties of unloaded Co3O4 solid

The effects of -irradiation (20–160 Mrad) and lithium oxide doping (0.75–6 mol%) on the surface and catalytic properties of unloaded Co₃O₄ solid have been investigated. The surface characteristics of various solids were determined from nitrogen adsorption isothems taken at –196 °C and their catalytic activities were measured by following the kinetics of CO-oxidation by O₂ at 100–150 °C using a static method. The results showed that -rays brough about a decrease of 21% inS _BET of Co₃O₄ due to widening of its pores and led also to a considerable increase in its catalytic activity. A maximum increase of 91% was observed upon exposure to a dose of 80 Mrad. Lithium oxide-doping at at 500 °C resulted in an increase of 150% inS _BET of treated solid without changing its mean pore radius. This treatment was also accompanied by an increase of about 50% in its catalytic activity measured at 150 °C. Gamma-irradiation and Li₂O-doping of unloaded Co₃O₄ did not change the magnitude of apparent activation energy of catalysis of CO-oxidation by O₂ but increased the concentration of catalytically active sites contributing in the catalytic process. In other words, -rays and lithium oxide doping did not alter the mechanism of catalytic oxidation of CO by O₂ over unloaded cobaltic oxide solid.     

Physicochemical properties of Ti-grafted SBA-15

Partial oxidation of n-heptane to syngas at 400–450°C was investigated over Rh and Rh-Ni based catalysts. The Rh/-Al₂O₃ catalyst exhibited much better catalytic activity than the Rh-Ni/-Al₂O₃ catalyst. A combination of the Rh-based catalyst with the WGS reaction catalyst (Fe₃O₄—Cr₂O₃) increases the hydrogen selectivity but has no distinct effect on shifting the balance of the partial oxidation of n-heptane.This revised version was published online in December 2005 with corrections to the Cover Date.     

Structural and Catalytic Activity of V2O5-Supported on AlPO4 Catalysts

Summary. A series of AlPO₄-V₂O₅ (APV) systems with various vanadia amounts 1–30mol% were prepared by the impregnation method and calcinated at 400 and 600°C for 4h. The catalysts were characterized by TG/DTG, DSC, IR spectroscopy, XRD, N₂ adsorption, and electrical conductivity measurements. The surface acidity and basicity of the catalysts were studied by the dehydration-dehydrogenation of isopropyl alcohol and the adsorption of pyridine. The catalytic gas phase esterification of acetic acid with ethyl alcohol was carried out at 210°C in a flow system at 1atm using air as a carrier gas. The results showed that the catalysts calcinated at 400°C were active and selective towards the formation of ethyl acetate whereas the calcination of samples at 600°C led to a drastic reduction in both activity and selectivity. Good correlations were obtained between catalytic activities towards ester formation and acidity of the prepared catalysts.     

Selective oxidation of methanol on V2O5 and V2O5?MoO3 supported on montrmorillonite

Methanol oxidation on V₂O₅ and V₂O₅–MoO₃ catalysts supported on montmorillonite has been studied in the temperature range of 250–500°C. The V₂O₅–MoO₃ containing sample shows higher selectivity towards formaldehyde formation than the V₂O₅ catalyst.     

Phasenänderungen im System Er2O3—TiO2

Zusammenfassung Röntgenographische und Gefügeuntersuchungen werden im System Er₂O₃–TiO₂ durchgeführt und ein Phasendiagramm im Solidusbereich ermittelt. Der Homogenitätsbereich der Pyrochlor-(von 33,3 Molprozent bis 50 Molprozent Er₂O₃) und der Fluoritphase (von 50 Molprozent bis 57 Molprozent Er₂O₃) wird bei 1550°C bestimmt.

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Phase transformations in the system Er₂O₃—TiO₂

The system Er₂O₃–TiO₂ has been investigated by microscopic and X-ray procedures. A phase diagram for the solidus range has been proposed. The pyrochlore phase is homogeneous from 33.3 to 50 mole% Er₂O₃ at 1550°C. Beyond 50 and up to 57 mole% Er₂O₃, the fluorite phase is homogeneous.

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Mit 2 Abbildungen     

Autothermal Reforming of Methane over Ni Catalysts Supported on CuO-ZrO2-CeO2-Al2O3

Ni catalysts supported on various mixed oxides of Al2O3 with rare earth oxide and transitional metal oxides were synthesized. The studies focused on the measurement of the autothermal reforming of methane to hydrogen over Ni catalysts supported on the mixed oxide ZrxCe30-xAl70Oδ (x=5, 10, 15). The catalytic performance of Ni/Zr10Ce20Al70Oδ was better than that of other catalysts. XRD results showed that the addition of Zr to Ni/Ce30Al70Oδ prevented the formation of NiAl2O4 and facilitated the dispersion of NiO. Effects of CuO addition to Zr10Ce20Al70Oδ were also investigated. The activity of Ni catalyst supported on CuO-ZrO2-CeO2-Al2O3 was somewhat affected and the Ni/Cu5Zr10Ce20Al65Oδ showed the best catalytic performance with the highest CH4 conversion, yield of H2, selectivity for H2 and H2/CO production ratio in operation temperatures ranging from 650 to 750℃.     

Natural product chemistry,part 100: The structure of carissone,C15H24O2

Summary C₁₅H₂₄O₂,M=236.2, monoclinic, P 2₁,a=7.229(7),b=14.925 (9),c=6.235 (9) Å, =92.40 (9)°,V=672.1 ų,T=–133 °C,Z=2,D _x=1.17 g cm^–3. The X-ray diffraction analysis of this sesquiterpenoid fromCarissa opaca confirmed the previously proposed constitution of the isolate and, furthermore, allowed precise NMR assignment.

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Naturstoffchemie, 100. Mitt.: Die Struktur des Carissons, C₁₅H₂₄O₂

Zusammenfassung C₁₅H₂₄O₂,M=236.2, monoklin, P 2₁,a=7.229 (7),b=14.925 (9),c=6.235 (9) Å, =92.40 (9)°,V=672.1 ų,T=–133 °C,Z=2,D _x=1.17 g cm^–3. Die Röntgenstrukturanalyse dieses Sesquiterpenoids ausCarissa opaca bestätigte die bereits vorgeschlagene Struktur und erlaubte ferner eine genaue NMR-Zuordnung.

     

Cyclization of diols with ammonia over CuO-ZnO-Al2O3 catalyst in the presence of H2

Cyclization of diols with ammonia in an H₂ atmosphere over an industrial CuO-ZnO-Al₂O₃ catalyst for the synthesis of methanol (SNM-1) gives nitrogen-containing five-, six-, or seven-membered heterocyclic compounds. The yields of cyclic amines in the 180–230 °C temperature range are 46 to 97 %.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2046–2048, October, 1995.