Untersuchungen in Systemen: Übergangsmetall (T)-Bor-Aluminium

Zusammenfassung Legierungen in den Dreistoffen Ti(Zr, Hf)–B–Al werden durch Heißpressen und Homogenisieren, teilweise durch Reaktion der kaltgepreßten Ansätze bei 1200°C hergestellt. Der Aufbau bei etwa dieser Temperatur ist im wesentlichen durch die Gleichgewichte zwischen den Diboriden der Übergangsmetalle und AlB₂, Aluminium sowie den Aluminiden gekennzeichnet. Es wird keinerlei Löslichkeit in den binären Phasen beobachtet, doch treten in den Systemen Zr–B–Al und Hf–B–Al die Bor-stabilisierten Phasen Zr₅Al₃B _x und Hf₅Al₃B _x mit teilweise aufgefülltem Mn₅Si₃-Typ sowie eine -Phase Hf_0,45Al_0,50B_0,05 auf.     

Reactions of ZrOCl2·8H2O with carboxylic acids and thionyl chloride: crystal and molecular structures of K4[Zr(mal)4]·2H2O and K4[Zr(dipic)3]2·13.5H2O

Reactions of ZrOCl₂·8H₂O in aqueous solution with a carboxylic acid in the presence of K₂CO₃ have been studied as a route to Zr^IV-carboxylates. With malonic acid (HO₂CCH₂CO₂H) (H₂mal) the product has been identified as K₄[Zr(mal)₄]·2H₂O (1) by X-ray crystallography. The individual eight-coordinate zirconium anions contain four bidentate (OO) malonate anions with the metal geometry approximating to a square antiprism with each chelating ligand spanning the two square faces, Zr—O 2.091(3)–2.288(3) Å. The four potassium cations feature irregular coordination spheres of oxygen atoms [from both H₂O and (mal) ligand molecules] with a 7–9 coordination range. With 2,6-dicarboxypicolinicacid (HO₂CC₅NH₃CO₂H) (H₂dipic) the product has been characterised as K₄[Zr(dipic)₃]₂·13.5H₂O (2) following X-ray diffraction studies. The structure consists of two [Zr(dipic)₃]^2- anions, four potassium cations and lattice solvate (H₂O) molecules. Individual anions feature nine-coordinate zirconium in which each dipic ligand is terdentate, being bonded via one N (pyridine) and two O (carboxylate) atoms. The metal geometry approximates to tricapped trigonal prismatic with each nitrogen atom capping a regular face of four oxygen atoms, Zr—O, 2.216(6)–2.261(6) Å; Zr—N, 2.343(8)–2.361(7) Å. The potassium cations show similar environments to those observed in structure (1). Dehydration of ZrOCl₂·8H₂O using SOCl₂ in the presence of an excess of THF effects removal of coordinated H₂O molecules and hydroxy bridging groups to provide the anhydrous bis-adduct ZrCl₄(thf)₂ in good yield (72%).     

Untersuchungen in den Systemen: Mangan—{Vanadin,Rhenium, Eisen}—silicium

Zusammenfassung Die strukturchemischen Verhältnisse werden in den Dreistoffen: Mn–{V, Re, Fe}–Si für einen Zustand –1000° C homogenisiert und abgeschreckt — untersucht. Die neu aufgefundene Mn–Re--Phase ist hinsichtlich der Ordnung mit der Re–Nb--Phase vergleichbar. Mn₅Si₂ wird durch Mn/Re-Austausch bei 1000° C stabilisiert. Einer ternären Kristallart (X) mit erheblichem Homogenitätsgebiet kommt die ungefähre Formel Mn_2–3Re_2–1Si zu. Der Austausch Mn/Re in Mn₅Si₃ erfolgt nur in der 6g-Lage. MnSi und ReSi sind lückenlos mischbar.Gitterparameter für die Mn–Re–Si- und V–Mn–Si--Phasen werden bestimmt. V₃Si löst etwa 50 Mol% Mn₃Si. Die lückenlose Mischreihe Mn₃Si–Fe₃Si wird bestätigt; gegenüber Literaturbefunden besteht jedoch im ganzen Bereich ein Ordnungszustand (BiF₃-Typ).

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The ternary systems: Mn–{V, Re, Fe}–Si have been studied after anneal at 1000° C followed by a quench by means of X-ray methods. The newly found Mn–Re--phase compares with the Re–Nb--phase as far as the ordering is concerned. Mn₅Si₂ can be stabilized by Re/Mn-substitution up to higher temperatures. A ternary phase X having a large homogeneous region, can roughly be described by a formula Mn_2–3Re_2–1Si. Re substitutes Mn within the Mn₅Si₃-phase occupying the 6g positions only. Lattice parameters of the Mn–Re–Si- and V–Mn–Si--phases have been determined. V₃Si dissolves about 50 mole% Mn₃Si. The solid solutions Mn₃Si–Fe₃Si can be confirmed; however there is an ordering throughout the whole domain (BiF₃-structure type).

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Synthesis,crystal structure and properties of a novel di-μ2-aqua bridged binuclear manganese(III) Schiff base complex [Mn(vanen)(H2O)2]2(ClO4)2 · 2H2O

The preparation and isolation of the binuclear manganese(III) complex, [Mn(vanen)(H₂O)₂]₂(ClO₄)₂ · 2H₂O was accomplished by air oxidation of a solution containing H₂vanen^**, Et₃N, and Mn(ClO₄)₂ · 6H₂O in absolute EtOH. The crystal structure of complex was determined by X-ray crystallography, and consists of two molecules bridged by two water molecules through hydrogen bonding. The manganese atom is six-coordinate and presents a distorted octahedral coordination sphere, which consists of the two imine N atoms and two phenolic O atoms of vanen^2– ligand in the equatorial plane, with Mn–N bond distances of 1.975 and 1.987 Å, and Mn–O distances of 1.867 and 1.876 Å, respectively. The non-bonding interatomic MnMn distance is 4.79 Å. In the axial direction, the elongated Mn–O(H₂O) bond distances of 2.255 and 2.381 Å, respectively, are due to Jahn–Teller distortion at the d⁴ metal center. The presence of lattice and coordinate water molecules were also confirmed by the t.g. study and the i.r. spectra. Upon irradiation using visible light in water in the presence of p-benzoquinone, the complex demonstrates its ability to split water.     

Die Kristallstruktur von Fe12Zr2P7

Zusammenfassung Die Struktur einer ternären Phase im System Fe–Zr–P wurde mit Hilfe von Einkristallaufnahmen bestimmt und verfeinert. Die Kristallart entspricht der vonVogel undDobbener aufgefundenen Phase Fe₄ZrP₂ und hat eine Idealzusammensetzung von Fe₁₂Zr₂P₇. Die Gitterparameter der hexagonalen Kristallart sinda=9,0002 undc=3,5920 Å, die Raumgruppe ist . Die Struktur ist mit jener von Fe₂P verwandt.

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The crystal structure of a ternary phase in the system Fe–Zr–P has been determined and refined by means of singlecrystal X-ray methods. The phase, already described byVogel andDobbener as Fe₄ZrP₂, has the ideal composition Fe₁₂Zr₂P₇. The cell dimensions are found to be:a=9,0002 andc=3,5920 Å, the space group is . The crystal structure of Fe₁₂Zr₂P₇ is related to Fe₂P.

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New Layered Polymer [{Mn(H2O)3}2{Re6Se8(CN)6}] · 3.3H2O: Synthesis and Properties

The [{Mn(H₂O)₃}₂{Re₆Se₈(CN)₆}] · 3.3H₂O complex was produced on slow evaporation of an aqueous solution containing the salt of a cluster complex K₄Re₆Se₈(CN)₆ · 3.5H₂O and a 23-fold excess of Mn²⁺. The cluster complexes [Re₆Se₈(CN)₆]^4– are linked in a crystal into the charged coordination layers [{Mn(H₂O)₃}₄{Re₆Se₈(CN)₆}₃]^4– ₂ through the Mn²⁺ cations. The Mn²⁺ cations are coordinated in a layer by three cyano nitrogen atoms of the cluster complexes; the Mn–N bond lengths are 2.13(4) and 2.21(2) Å. Each [Re₆Se₈(CN)₆]^4– anion is bonded to three manganese cations Mn(1). The anions are bonded additionally to the Mn(2) cations disordered over two close positions.     

Ein Beitrag zur Kenntnis ternärer Phosphorlegierungen

Zusammenfassung Die Schnitte bei 25 und 33,3 At% P in den Dreistoffsystemen Cr–Mn–P, Cr–Fe–P, Cr–Ni–P, Cr–Cu–P, Mn–Fe–P, Mn–Ni–P, Mn–Cr–P, Fe–Ni–P, Fe–Cu–P und Ni–Cu–P werden röntgenographisch untersucht. Es wird das Ergebnis vonVogel und Mitarbeitern hinsichtlich der Mischbarkeit von Fe₃P–Ni₃P bzw. Cr₃P–Fe₃P bestätigt.Eine solche Mischreihe bilden auch Cr₃P und Mn₃P. Dagegen dürften Cr₃P und Ni₃P nur begrenzt mischbar sein; Fe₃P nimmt mindestens 25 Mol% Mn₃P auf. Ni₃P löst rund 50 Mol% des nicht isotypen Cu₃P, während zwischen den isotypen Phasen Mn₃P und Ni₃P sowie zwischen Cr₃P, Mn₃P, Fe₃P einerseits und Cu₃P keine merkliche Löslichkeit beobachtet wurde.Lückenlose Mischreihen bilden auch Mn₂P–Fe₂P, Fe₂P–Ni₂P sowie Ni₂P–Mn₂P. Obwohl keine isotype Cr₂P-Phase gefunden wird, besteht ein praktisch homogener Übergang zwischen Fe₂P–Cr₂P, Ni₂P–Cr₂P. Mn₂P löst rund 50 Mol% Cr₂P; Mn₂P sowie Fe₂P nehmen jeweils etwa 20 Mol% Cu₂P auf.Mit 4 Abbildungen     

Untersuchungen in den Systemen: Zirkonium-Bor-Kohlenstoff und Zirkonium-Bor-Stickstoff

Zusammenfassung Die Dreistoffe: Zr–B–C und Zr–B–N werden auf Grund von heißgepreßten bzw. im Lichtbogen geschmolzenen Proben mittels röntgenographischer Pulveraufnahmen sowie Gefügebeobachtungen untersucht. Die Aufteilung der Phasenfelder ist durch die Kristallarten der Randsysteme gekennzeichnet, d. h. es wird keine ternäre Phase gebildet. Die sehr stabile Diborid-Phase hat einen sehr geringen homogenen Bereich und nimmt praktisch weder Kohlenstoff noch Stickstoff auf. Zweiphasenfelder bestehen bei: Zr–B–C zwischen: ZrB₂–C und ZrB₂–B₄C. Im Falle: Zr–B–N sind die Verhältnisse im Zr-armen Gebiet durch die Felder: ZrB₂–BN und ZrN-Mk–BN unterhalb 1600° C gekennzeichnet. Bei dieser Temperatur reagiert in Übereinstimmung mit einem Befund vonL. Brewer undH. Haraldsen ZrN mit BN zu Diborid und Stickstoff.Die Phase ZrB₁₂ wird als Hochtemperaturphase bestätgt. In Zr-B-Legierungen mit etwa 50 At % B, die bei 1800° C geglüht wurden, tritt die B 1-Struktur mit einem Gitterparameter:a=4,647–4,677 Å auf, der merkwürdigerweise kleiner ist als jener von ZrC. Die meisten Befunde sprechen für eine Zr-reichere Zusammensetzung von ZrB; vor allem aber besteht eine erhebliche Löslichkeit von ZrB in ZrC bzw. ZrN. Man findet, insbesondere bei: Zr–B–N, Gitterparameter, die einen weitgehenden Übergang von ZrN nach ZrB vortäuschen. Die Proben sind jedoch im Mittelgebiet 50 At % Zr, 25 At % B, Rest (C oder N) stets heterogen (-Zr–Mk+ZrB₂+B 1).8 Abbildungen     

Synthesis and Characterisation of Aluminium-Zirconium Based Organic-Inorganic Materials via Sol-Gel Route

Monolithic and transparent hybrid Al-Zr gels were obtained by the reaction of homogeneous mixtures of metal alkoxides: (Al(OBu^s)₃ + Zr(OPr)₄) with Butan-1,3-diol at room temperature, without solvent, catalyst, or water. The products have been characterized by IR spectroscopy, DTA and TGA. The results show that the diol has reacted with the mixture of alkoxides leading to the monolithic transparent gels in which both organic-inorganic (–Al–O–R–O–Zr–) and inorganic (–Al–O–Zr–O–) bridges are formed.Xerogels obtained after the drying of gels were pyrolysed at different temperatures in air. The structure and morphology of the obtained materials were studied by X-ray powder diffraction (XRD) and the Brunauer-Emmett-Teller (BET) method. At 1200°C, the materials were composed of Al₂O₃, t-ZrO₂ and m-ZrO₂.     

Studies on the Hydrolytic Behavior of Zirconium(IV)

The stability constants of zirconium(IV) hydrolysis species have been measured at 15, 25, and 35 °C [in 1.0 mol-dm^–3 (H,Na)ClO₄] using both potentiometry and solvent extraction. In addition, the solubility of [Zr(OH)₄(am)] has been investigated in a 1 mol-dm^–3 (Na,H)(ClO₄,OH) medium at 25 °C over a wide range of –log [H⁺] (0-15). The results indicate the presence of the monomeric species Zr(OH)³⁺, Zr(OH)₂ ²⁺, Zr(OH)₃ ⁺, and Zr(OH)₄ ⁰(aq) as well as the polymeric species Zr₄(OH)₈ ⁸⁺ and Zr₂(OH)₆ ²⁺. The solvent extraction measurements required the use of acetylacetone. As such, the stability constants of zirconium(IV) with acetylacetone were also measured using solvent extraction. All stability constants were found to be linear functions of the reciprocal of temperature (in kelvin) indicating that H ^o and S ^o are both independent of temperature (over the temperature range examined in the study). The results of the solubility experiments have shown four distinctly different solubility regions. In strongly acidic solutions, the solubility is controlled by the formation of polynuclear hydrolysis species in solution whereas in less acidic solution the formation of mononuclear hydrolysis species becomes dominant. The largest portion of the solubility curve is controlled by equilibrium with aqueous Zr(OH)₄ ⁰(aq) where the solubility is independent of the proton concentration. In alkaline solutions, the solubility increases due to formation of the zirconate ion. The middle region was used to determine the solubility constant (log *K _s10) of Zr(OH)₄(s). From the data in the alkaline region, a value of the stability of the zirconate ion has been determined. This is the first time that the possible evidence for the zirconate ion has been identified in aqueous solution that has previously been found only in the solid phase.     

Fuel Combustion Reactions and Catalysts: XXI. Synthesis and Characterization of Modified Mn–Al–O Catalysts for High-Temperature Oxidation

The phase composition of supported Mn–Al–O catalysts and their activity in the reaction of methane oxidation were studied depending on the composition of aluminum oxide supports (-Al₂O₃ with different -Al₂O₃ contents modified with individual Mg, La, and Ce oxides or Mg + La and Mg + Ce oxide mixtures) and calcination temperatures (500, 900, and 1300°C). It was found that the Mn–Al–O catalysts based on -alumina containing -Al₂O₃ and modified with Mg, La, or Ce additives are more active and thermally stable (up to 1300°C) than the samples based on pure -Al₂O₃. A conclusion was drawn that a higher degree of disorder of the structure of -Al₂O₃, compared to that of -Al₂O₃, is favorable for a deeper interaction of manganese and modifying additives with the support at the early stages of the synthesis and for the formation of Mn–Al compounds with complex composition (solid solutions and/or hexaaluminates) at 1300°C. These compounds are responsible for the stability and high activity of the catalysts in methane oxidation.     

Genesis of phase composition of supported Al?Fe?O catalysts

XPS, ESR and ESDR methods have been used for studying Al–Fe–O catalysts calcined at 620–1270 K. -Al₂O₃ interaction with impregnating solutions of iron oxalate complexes was shown to lead to the formation of isolated Fe³⁺ ions, and supported phases of solid solutions and associates at 620–820 K.     

Order–disorder phase transformations in quaternary pyrochlore oxide system: Investigated by X-ray diffraction, transmission electron microscopy and Raman spectroscopic techniques

Order–disorder transformations in a quaternary pyrochlore oxide system, Ca–Y–Zr–Ta–O, were studied by powder X-ray diffraction (XRD) method, transmission electron microscope (TEM) and FT-NIR Raman spectroscopic techniques. The solid solutions in different ratios, 4:1, 2:1, 1:1, 1:2, 1:4, 1:6, of CaTaO_3.5 and YZrO_3.5 were prepared by the conventional high temperature ceramic route. The XRD results and Rietveld analysis revealed that the crystal structure changed from an ordered pyrochlore structure to a disordered defect fluorite structure as the ratios of the solid solutions of CaTaO_3.5 and YZrO_3.5 were changed from 4:1 to 1:4. This structural transformation in the present system is attributed to the lowering of the average cation radius ratio, r_A/r_B as a result of progressive and simultaneous substitution of larger cation Ca²⁺ for Y³⁺ at A sites and smaller cation Ta⁵⁺ for Zr⁴⁺ at B sites. Raman spectroscopy and TEM analysis corroborated the XRD results.     

Kinetics of stepwise oxidation of manganese(II) by peroxodisulphate in phosphoric acid medium

Summary The oxidation of Mn^II by S₂O₈ ^2– to Mn^VII in phosphoric acid medium proceeds via a stable Mn^III and Mn^IV species. The reaction is catalysed by Ag⁺ and exhibits first order dependence on [S₂O₈ ^2–], [Ag⁺] and, is independent of [Mn^II]. The [H⁺] has no significant effect on the reaction. It is observed that the PO₄ ^3– ion stabilises the transient manganese(III) and manganese(IV) species by forming a stable and soluble phosphato-complexes. The activation parameters for the two stages of oxidation, namely Mn^II Mn^IV and Mn^IVMn^VII at 25° C are E_a=52 ±4 kJ mole^–1, S^*=–57±2 JK^–1 mole^–1 and E_a =56±4 kJ mole^–1, S^*=–44±2 JK^–1 mole^–1, respectively. A mechanism consistent with the experimental observations is proposed.Presented at the National Symposium on Reaction Kinetics and Mechanism, Department of Chemistry, University of Jodhpur, Jodhpur, India, Nov. 15–18, 1986.     

Neue K-Boride und verwandte Phasen (Re3B-Typ,aufgefüllt)

Zusammenfassung Mit Hilfe vonWeissenberg-Aufnahmen wird die Kristall-struktur der K(Kappa)-Hf–Mo–B-Phase verfeinert. Die Punktlage 2 a) in P6₃/mmc ist durch Mo-Atome (nicht Boratome) aufgefüllt. Damit entsteht praktisch Strukturgleichheit mit Co₂Al₅ bzw. Mn₃Al₁₀. Die analogen K-Boride Zr₉Mo₄B (mit Hf₉Mo₄B lückenlos mischbar) und Zr₉W₄B bestehen ebenfalls. In Hf₉Mo₄B werden bis 14 At% Al (1400°C) aufgenommen.In den Systemen Zr–Mo–{Fe, Co, Ni} und Hf–Mo(W)–{Fe, Co, Ni} werden weitere Vertreter mit obigem Strukturtyp (K-Phasen) aufgefunden; die Eisenmetall-Atome treten an Stelle von Bor.Phasen vom Typ Zr₃{Fe, Co, Ni} (N, O) _x entstehen beim Sintern in mäßigem Vakuum und gehören zur aufgefüllten Re₃B-Struktur.

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New K-Borides and related phases (filled up Re₃B-phases)

The crystal structure of the K(Kappa)-Hf–Mo–B-phase has been refined by means ofWeissenberg-photographs; the position 2 a) (P6₃/mmc) is occupied by Mo-atoms (not boron atoms). Thus structural identity with Co₂Al₅ and Mn₃Al₁₀ resp. is obvious. The isotypic K-borides Zr₉Mo₄B (it forms complete solid solutions with Hf₉Mo₄B) and Zr₉W₄B also exist. Hf₉Mo₄B dissolves aluminum up to 14 at% (1400°C).Further compounds with the abovementioned structure type (K-phases) have been detected within the systems Zr–Mo–{Fe, Co, Ni} and Hf–Mo(W)–{Fe, Co, Ni}; the iron metal atoms occupy the boron positions.Phases with composition Zr₃{Fe, Co, Ni} (N, O) _x , obtained by sintering, belong to the filled up Re₃B-type structure.

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Herrn Professor Dr.E. Ziegler zum 60. Geburtstag gewidmet.     

Structural Studies on Saturated Aqueous Solutions of Manganese(II), Cobalt(II), and Nickel(II) Chlorides by X-ray Diffraction

As a part of our studies on crystallization processes of electrolytes, the structure of aqueous solutions of MCl₂ (M = Mn, Co, Ni) equilibrated with hydrate crystals, MCl₂ · mH₂O (m = 6, 4, 2), was investigated by means of X-ray diffraction at 25, 40, 55, and 70°C. The complexes formed in MnCl₂ solutions, were found to be mixed–ligand chloroaqua octahedral complexes of M²⁺ ions with the Mn—O and Mn—Cl distances of about 220 and 251 pm, respectively. The average number of Mn—Cl and Mn—O interactions increased from 1.2 to 1.9 and decreased from 4.8 to 4.1, respectively, with changing MnCl₂ solutions from Mn25 (MnCl₂ solution at 25°C) to Mn70 (MnCl₂ solution at 70°C). In the octahedral species of Co²⁺, the Co—O and Co—Cl distances were found to be about 211 and 240 pm, respectively. With an increase in the saturated concentration by changing temperature from 25 to 70°C, the average coordination number of the Co—Cl contact per Co²⁺ increased from 0.5 to 1.2, and the average number of Co—O interactions decreased from 5.5 to 4.8. The structural analysis was carried out by taking into consideration the existence of the tetrahedral species in the solutions saturated at 40, 55, and 70°C, on the assumption of the existence of [CoCl₄]^2–. The Co—Cl distance was found to be 228 pm, while the number of Co—Cl interactions in the [CoCl₄] complex was calculated to be 3.7 by the least-squares calculations. The Ni—O and Ni—Cl distances were estimated to be about 206 and 237 pm, respectively. The frequency factor n of the Ni—O and Ni—Cl interactions decreased monotonously from 5.6 to 5.0 and increased from 0.4 to 1.0, respectively, with increasing NiCl₂ concentration. The n values of the Co—Cl and Ni—Cl interactions of the octahedral complexes increased sharply with concentration at higher concentrations. Comparing structures of the complexes in the saturated solutions and the hydrate crystals of these metal ions, we discussed a role of the complexing species on crystallization of the hydrates.     

Mechanism of the Formation of O2? Radical Anions on CeO2 and (0.5–10)%CeO2/ZrO2 during the Adsorption of an NO-O2 Mixture

It is established by ESR that the adsorption of an NO + O₂ mixture at 20°C on oxidized CeO₂ (O₂, T = 400–700°C) produces radical anions O ₂ ⁻ located both on isolated Ce⁴⁺ cations (O ₂ ⁻ (1)) and in associated anionic vacancies (O ₂ ⁻ (2)). These species differ in thermal stability. For example, O ₂ ⁻ (2) decomposes at 20°C, while O ₂ ⁻ (1) decomposes at 50°C. Only O ₂ ⁻ (1) species are observed at −196°C in ZrO₂-supported CeO₂. In the case of NO + O₂ adsorption at 20°C, O ₂ ⁻ is stabilized on Zr⁴⁺ cations and decomposes at 270°C. Increasing the cerium oxide content of the ZrO₂ surface from 0.5 to 10% only partially inhibits the formation of O ₂ ⁻ -Zr⁴⁺. The Zr⁴⁺ cation is shown to possess a higher Lewis acidity than the Ce⁴⁺ cation, and the ionic bond in O ₂ ⁻ -Zr⁴⁺ complexes is stronger than that in O ₂ ⁻ -Ce⁴⁺ complexes. ESR, temperature-programmed desorption, and IR spectroscopic data for various adsorption complexes of NO on CeO₂ suggest that, in the key step of O ₂ ⁻ formation, free electrons appear on the surface owing to the conversion of adsorbed NO molecules into nitrito chelates on coordinately unsaturated ion pairs Ce⁴⁺-O ₂ ⁻ .__________Translated from Kinetika i Kataliz, Vol. 46, No. 3, 2005, pp. 414–422.Original Russian Text Copyright © 2005 by Il’ichev, Shibanova, Ukharskii, Kuli-zade, Korchak.     

Selective oxidation of CO in excess hydrogen on copper—cerium-containing catalysts

Selective oxidation of CO that is in mixtures enriched in H₂ was studied to investigate catalytic properties of the 0.5—80% CuO/Ce_0.7Zr_0.3O₂ system. The catalysts were prepared by the combined decomposition of copper, cerium, and zirconyl nitrates at 300 °C. The systems studied are active and stable under mild conditions of the process (80—160 °C) and at high space velocities (to 100000 h^–1) of the reaction mixture (2% CO, 1% O₂, 40—50% H₂). With an increase in the CuO content in the catalysts up to 20%, the degree of CO removal achieves 60% (120 °C and V = 35000 h^–1) and further does not change appreciably. The contribution of oxygen participation into CO oxidation is virtually independent of the copper concentration in the sample and ranges from 65 to 75%. The dependences of the Arrhenius equation parameters for CO and H₂ oxidation on the catalyst composition were determined, which makes it possible to calculate the conversion of reactants and selectivity of CO conversion under the specified conditions of the process. The addition of CO₂ and H₂O (12—15%) to the reaction mixture decreases the catalyst activity and simultaneously increases the selectivity of CO oxidation to 100%. It is shown by the TPR and X-ray diffraction methods that the combined decomposition of the starting Cu²⁺, Ce³⁺, and ZrO²⁺ nitrates produces solid solutions of oxides with a high content of CuO. The reductive pre-treatment of fresh samples of the studied catalysts results in the destruction of the solid solution and formation of highly dispersed Cu particles on the surface of Ce—Zr—O. These particles are active in CO oxidation.     

An equilibrium and calorimetric investigation of the hydrolysis of L-tryptophan to (indole + pyruvate + ammonia)

Apparent equilibrium constants and calorimetric enthalpies of reaction have been measured for the reaction L-tryptophan(aq) + H₂O(l) = indole(aq) + pyruvate(aq) + ammonia(aq) which is catalyzed by L-tryptophanase. High-pressure liquid-chromatography and microcalorimetery were used to perform these measurements. The equilibrium measurements were performed as a function of pH, temperature, and ionic strength. The results have been interpreted with a chemical equilibrium model to obtain thermodynamic quantities for the reference reaction: L-tryptophan(aq) + H₂O(l) = indole(aq) + pyruvate^–(aq) + NH ₄ ⁺ (aq). At T=25°C and I_m=O the results for this reaction are: K^o=(1.05±0.13)×10^–4, G°=(22.71±0.33) kJ-mol^–1, H°=(62.0±2.3) kJ-mol^–1, and S°=(132±8) J-K^–1-mol^–1. These results have been used together with thermodynamic results from the literature to calculate standard Gibbs energies of formation, standard enthalpies of formation, standard molar entropies, standard molar heat capacities, and standard transformed formation properties for the substances participating in this reaction.Presented at the Symposium, 76^th CSC Congress, Sherbrooke, Quebec, May 30–June 3, 1993, honoring Professor Donald Patterson on the occasion of his 65^th birthday.     

Synthesis, spectroscopy and redox properties of mononuclear manganese(II) and manganese(IV) complexes with N-(aryl)-pyridine-2-aldimine (L) and its amide derivatives. X-ray structural characterization of [Mn(MeL)2(NCS)2] (MeL = N-(4-methylphenyl)-pyridine-2-aldimine)

A series of mononuclear Mn^II and Mn^IV complexes of general formulae [MnL₂(NCS)₂] (1a–1d) and [Mn(L)₂(NCS)₂] (2a–2c) have been prepared where L are Schiff bases obtained by the condensation of pyridine-2-aldehyde with para-alkyl-substituted aniline, and L are the corresponding amide ligands. The room temperature magnetic susceptibility data of (1a–1d) indicate that Mn^II is in a high spin state. The cyclic voltammograms of (1a–1d) exhibit a one-electron quasi-reversible Mn^IIMn^III oxidation. A linear correlation has been found when E⁰[Mn^III/Mn^II] is plotted against Hammett _p parameters. X-ray crystallographic data of (1b) shows that the central Mn^II ion adopts a distorted octahedral geometry with six different Mn–N distances. Upon oxidation of Mn^II complexes (1b–1d) by H₂O₂, the corresponding Mn^IV complexes (2a–2c) were obtained, and the Schiff base ligands were oxidized to the corresponding amides. The lowest energy LMCT bands of these Mn^IV complexes correlate linearly with Hammett _p parameters. The redox behavior of the Mn^IV complexes has been investigated by cyclic voltammetry. E.p.r. spectra of the Mn^II and Mn^IV complexes are also reported.