Total chromatographic optimization (TOCO) I. Simultaneous optimization of many variables in liquid chromatography

Summary The following chromatographic variables are totally optimized based on the recently developed information theory of optimization: mobile phase composition, column length, flow rate, wavelength, and the amount of internal standard. The optimal internal standard is selected from among six candidates. Two types of optimal conditions (- and -optimals) are proposed: the -optimal is defined as the most precise analysis (the maximal ) while the -optimal is the most efficient (rapid) analysis (the maximal ). The observation times for the determination of an antipyretics mixture (three components) in liquid chromatography are ca. 50 s for the -optimal and ca. 8 min for the -optimal. The reliability of the - and -optimals is verified by experiments.     

Isotherm of Adsorption at a Solid Electrode Accounting for the Electrode Elasticity: A General Solution

To continue work on the basis of a full electrocapillarity equation, the thermodynamically equilibrium single-component adsorption from a dilute liquid solution on a solid electrode is considered with the effect of its surface deformation . The general case, where the arising new function depends on all the three dimensionless variables: surface concentration of adsorbate , electrode potential, and surface deformation is studied. By expanding all the functions into series by small parameter , a set of equations with respect to linear expansion coefficients of unknown functions is obtained. For the model of two parallel capacitors, the initial equations are reduced to the same common differential first-order equation or to a transcendental equation, where the boundary conditions use the experimental capacitance curves. The unknown constant integration parameter is proposed to be calculated using at least one additional experimental value of a surface concentration. For the same model of non-deformed electrode, the additive component of the full value , which depends only on , is shown to have no effect on the isotherm equation.     

Consecutive hydrogenation of pseudoionon. Application of diffusion kinetic model to predict experimental reactor operation

A method for the calculation of fixed catalyst bed reactors by using a diffusion kinetic model is suggested. Correlation between calculated curves for the time distribution of the reaction mixture composition and experimental data is given.

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=qo . .

     

Influence of excess MoO3 in a non-stoichiometric cadmium-molybdenum catalyst on the catalytic properties in methanol oxidation

By IR and Raman spectroscopy it has been shown that excess MoO₃ is bound molecularly on the surface of CdMoO₄, presumably on sites of C₂ and C_i symmetry. This increases the activity and selectivity of the catalyst in methanol oxidation to formaldehyde.

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, , MoO₃ CdMoO₄, C₂ C_i. .

     

Interaction of super-finely dispersed Al powders with water

Interaction of super-finely dispersed Al powders (SFDP) with water is characterized by the presence of a considerable section on the kinetic curves, where the conversion rate is maximum and its degree is as high as =0.5–0.7. It is suggested that the essential factor accounting for the conversion kinetics and the phase composition of its products is the self-heating of Al particles.

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() , , () 0,5–0,7. , .

     

Supported catalysts prepared using Ti(C7H11)4 for ethylene polymerization

Supported catalysts for ethylene polymerization were prepared by anchoring tetrakis(1-bicycloheptyl) titanium [Ti(C₇H₁₁)₄] on alumina. The influence of the dehydration temperature of the support and the conditions of catalyst activation on the catalytic properties was studied. At low content of Ti these catalysts were found to be highly active for ethylene polymerization with the formation of superhigh molecular weight polymers.

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(1-) [Ti(C₇H₁₁)₄] . , . , .

     

Röntgenkleinwinkeluntersuchungen an Lösungen eines Polystyrolpräparates mit enger Molekulargewichtsverteilung

Zusammenfassung Es wurde das Streuverhalten von Polystyrol im thermodynamisch schlechten Lösungsmittel Cyclohexan zwischen Entmischungstemperatur und-Temperatur untersucht. Beim -Punkt und nahe dabei liegt das Verhalten eines statistisch verknäuelten Fadenmoleküls vor. Unterhalb der-Temperatur beginnt eine Aggregation. Knapp oberhalb der Entmischungstemperatur entspricht das Molekulargewicht etwa einer Verhängung zweier Fadenmoleküle. Ein Auftreten von kompakten Polymerknäueln ist bei dieser Temperatur nicht festzustellen. Der Einfluß des Fadenquerschnitts auf die Streukurve ist beträchtlich, da der Querschnitt nicht viel kleiner als die Persistenzlänge ist. Trotzdem läßt sich die Persistenzlänge (a=12,2 Å) aus dem Übergangspunkt zwischen den etwa 1/(2)² und 1/(2) proportionalen Bereichen bestimmen, da der Knick im Übergangsbereich infolge der großen Anzahl von Persistenzlängen pro Molekül sehr ausgeprägt ist.

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X-Ray small-angle investigations on solutions of a polystyrene sample with a narrow molecular weight distribution

Investigations were made of the scattering behaviour of polystyrene in the thermodynamically bad solvent cyclohexane between precipitation-temperature and-temperature. At the-point and close to it the behaviour of a statistically coiled chain molecule is found. Below-temperature an aggregation is beginning. Just above precipitation-temperature the molecular weight corresponds to an entanglement of two chain molecules. Appearance of compact polymer coils could not be noted at this temperature. The influence of the chain crosssection upon the scattering curve is considerable as the crosssection is not much smaller than the persistence length. Nevertheless, the persistence length (a=12.2 Å) may be determined from the transition point between the ranges roughly proportional to 1/(2)² and 1/(2) as the break within the transition range is very distinct on account of the great number of persistence lengths per molecule.

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Mit 3 Abbildungen

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Herrn Prof. Dr.E. Broda zum 60. Geburtstag gewidmet.     

Total chromatographic optimization (TOCO) II. Precision and efficiency of analysis

Summary A chromatographic system set at an operating condition takes its own precision and efficiency which are numerically described by the information called FUMI and the information flow , respectively. Optimization for a variable such as mobile phase composition draws a line in the - space. This paper demonstrates that optimization of different variables displays different patterns of lines in the - space. The variables examined here are mobile phase composition, column length, flow rate (velocity) and detection wavelength (or the amount of internal standard). Clear difference in the analytical roles of the variables can be known from the - plots.     

Kinetic, conductivity and ESR studies of superconducting Y?Ba?Cu?O ceramics with controlled oxygen content

The activation energy E_a of oxygen evolution from the YBa₂Cu₃O_7–/gs ceramics has been measured for ranging from 0 to 0.2. In the range from 0.15 to 0.18 oxygen is fairly homogeneous and its evolution is characterized by E_a=(36±3) kcal/mol. Temperature dependence of a low-field ESR signal of the ceramics have been studied at a frequency of 9.3 KHz nearby T_C.

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E_a YBa₂Cu₃O_7- 0 0,2. , 0,006 0,15–0,18 E_a=(36±3) /. 9,3 T_c.

     

Oxydative Deammonisierung von NH4-Zeolithen

Zusammenfassung Es wurde eine vergleichende thermogravimetrische Untersuchung der Deammonisierung von NH₄-Mordenit, NH₄-Chabasit und NH₄-Stilbit ausgeführt. Aus dem Verlauf der TG-Kurven kann geschlossen werden, da\ in O₂-AtmosphÄre eine intrakristalline Oxydation thermisch angeregter Ammonium-Gitterkationen erfolgt. Diese Reaktion verlÄuft bei wesentlich niedrigeren Temperaturen als die thermische Deammonisierung in inerter AtmosphÄre und führt damit zu einer besseren Trennung von Deammonisierung und Dehydroxylierung. Unter den durch die Bildung von Wasser wÄhrend der oxydativen Deammonisierung gegebenen hydrothermalen Bedingungen gehen — im Falle von Chabasit und Stilbit — gewisse strukturelle VerÄnderungen der H-Form vor sich, die sich in einem unterschiedlichen Dehydroxylierungsverhalten zu erkennen geben.

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A comparative thermogravimetric study of the deammoniation of NH₄-mordenite, NH₄-chabazite, and NH₄-stilbite in oxidizing and inert atmosphere has been carried out. The results suggest that in oxygen atmosphere an intracrystalline oxidation of thermally-excited ammonium lattice cations occurs. This reaction proceeds at much lower temperatures than the thermal deammoniation in an inert atmosphere and consequently results in a much better separation of the dehydroxylation process from the deammoniation. Because of the hydrothermal conditions resulting from the formation of water during the oxidizing deammoniation, certain structural changes of the hydrogen form of chabazite and stilbite occur as revealed by changes of the dehydroxylation behaviour.

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Résumé On a effectué une étude thermogravimétrique comparée de la désammoniation de NH₄-mordénite, NH₄-chabazite et NH₄-stilbite, dans des atmosphères oxydantes et inertes. Les résultats permettent de supposer qu'en atmosphère d'oxygène il se produit une oxydation intracristalline des cations du réseau d'ammonium thermiquement excités. Cette réaction s'effectue à des températures bien plus faibles que dans une atmosphère inerte et, par conséquent, conduit à une séparation bien plus distincte du processus de déshydroxylation et de désammoniation. En raison des conditions hydrothermiques qui résultent de la formation d'eau pendant la désammoniation, certains changements de structure de la forme hydrogénée de la chabazite et de la stilbite ont lieu et sont révélés par les changements du comportement de déshydroxylation.

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, . , . , , . - , , , .

     

Influence of external electric field on the rate of hydrogen isotope exchange between hydroxyl-containing molecules in CCl4

Rates of the fast proton-deuteron exchange between CH₃OD and C₆H₅OH (1), and CH₃OD and CH₃COOH (2) in dilute CCl₄ solutions have been measured by a kinetic IR spectroscopy technique. Under an imposed external electric field (10 V/m), the exchange rate in system (2) increases, which is not observed in (1). The effect is interpreted assuming that, in the second case, a cyclic ion pair with a high dipole moment is formed as a reaction intermediate.

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- CH₃OD C₆H₅OH (1), CH₃OD CH₃COOH (2) CCl₄. (IO⁷ B/) (2) , (1). (2) , .

     

Water-gas shift reaction over chromia-promoted magnetite. Use of temperature-programmed desorption and chemical trapping in the study of the reaction mechanism

The mechanism of WGSR has been studied on an Fe–Cr catalyst. Although after reaction (from 250 to 400°C) formate species have been characterized on the Fe–Cr catalyst, by chemical trapping, TPD studies after reaction and after HCOOH adsorption have shown that formates are not the main intermediates. The disproportionation of CO or the regenerative mechanism seems to be more probable.

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CO+H₂OCO₂+H₂ Fe–Cr. ( 250 400°C) Fe–Cr , , , . CO .

     

Physical properties of the catalyst used for partial oxidation of anthracene to anthraquinone. II. Electron paramagnetic resonance study

Electron paramagnetic resonance studies on intermediates and final active catalyst material used for partial oxidation of anthracene to anthraquinone are reported.

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, .

     

Mechanism of catalysis and factors responsible for oxide catalyst activity in deep oxidation reactions

A general scheme for the deep oxidation mechanism on oxide catalysts including stepwise and concerted mechanisms as well as their mutual transformations is suggested. The principal factor responsible for the activity in the concerted mechanism region is the rate of oxygen binding. For the stepwise mechanism the main factor is the rate of catalyst interaction with oxidizable reactant.

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, . , . .

     

Catalytic reduction of nitric oxide with hydrogen over a cobalt-alumina catalyst. The effect of potassium additives

Catalytic reduction of NO with hydrogen has been studied using a differential reactor operated at atmospheric pressure. The process was carried out over a Co/Al catalyst containing potassium oxide as an additive. The presence of potassium generally produces a decrease in activity of the Co/Al catalyst except for very low concentrations of potassium atoms.

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NO , . Co/Al, . Co/Al, , .

     

X-ray diffraction studies of platinum-alumina catalysts in a high-temperature chamber

X-ray diffraction studies of platinum-alumina catalysts in a high-temperature chamber have revealed that for the catalysts obtained by the reduction of preactivated samples, no complete reduction of platinum takes place.

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, , , .

     

A study of the thermal stability of hexaaziridinylcyclotriphosphazene,N3P3(NC2H4)6

Thermal behaviour of N₃P₃Az₆ up to 300 °C was studied by means of TG, DTG and DTA methods. It was found that, when heated in small amounts, N₃P₃Az₆ does not undergo decomposition even up to 300 °C. It rather melts at about 150 °C and then polymerizes at higher temperatures with the formation of an insoluble glassy substance. The proposed polymerization mechanism assumes the opening of aziridine rings and combination of the N₃P₃Az₆ units into a three-dimensional structure. The heating of larger amounts of N₃P₃Az₆ leads to its decomposition, due to the considerable amount of heat evolved during the polymerization.

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Zusammenfassung Mittels TG, DTG and DTA wurde das thermische Verhalten von N₃P₃Az₆ bis 300 °C untersucht. In geringen Mengen erhitzt erleidet N₃P₃Az₆ bis 300 °C keine Zersetzung. Es schmilzt bei etwa 150 °C und polymerisiert bei höheren Temperaturen zu einer unlöslichen glasigen Substanz. Dem angenommenen Mechanismus nach werden die Aziridinringe geöffnet, die N₃P₃Az₆-Einheiten schließen sich unter Bildung einer dreidimensionalen Struktur zusammen. Beim Erhitzen von größeren Mengen an N₃P₃Az₆ wird die Verbindung wegen der bei der Polymerisation entstehenden beträchtlichen Wärme zersetzt.

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, (N₃P₃Az₆) 300°. 300°. 150° , . (N₃P₃Az₆) . (N₃P₃Az₆) , , .

     

Reduction of NO by carbon monoxide on tin dioxide

The reduction of NO by carbon monoxide on SnO₂ has been studied in the temperature range from 90 to 450°C. The complicated temperature dependence of the reaction rate is due to the interaction of CO an CO₂ with the catalyst.

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NO SnO₂ 90–450°C. , CO CO₂ .

     

Ba(OH)2 as catalyst in organic reactions, III. The structure of adsorbed ylids

The nature of adsorbed sulfonium and phosphonate ylids on a new barium hydroxide catalyst (C-200) is analyzed by IR. The catalytic activity of C-200 in solid-liquid phase transfer conditions is explained by these IR studies.

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(C-200) . C-200 - .

     

Synthesis and thermal decomposition of double dimethylammonium sulphate hexahydrates of aluminium and chromium

Double sulphates of trivalent aluminium and chromium with dimethylammonium, with general formula (CH₃NH₂M(SO_{4 2}·6H₂O, were synthesized and studied by means of thermogravimetry and differential thermal analysis over the range 20–600 °C under dynamic conditions in a flow of dry nitrogen or air, and with the methods of chemical analysis. An X-ray powder diffraction study of the above compound was also undertaken. It is assumed that dimethylammonium aluminium sulphate hexahydrate and dimethylammonium chromium sulphate hexahydrate are isostructural. The mechanism of thermal decomposition of these double salts is also suggested.

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Zusammenfassung Verbindungen der Formel (CH₃)₂NH₂M(SO₄)₂·6H₂O mit M=Al(III) oder Cr(III) wurden synthetisiert und mittels TG und DTA im Intervall 20–600 °C unter dynamischen Bedingungen in bewegtem trockenen Stickstoff-oder Luftstrom sowie mittels chemischer Analyse untersucht. Auf Grund einer ebenfalls durchgeführten röntgenografischen Pulvermethode wurde festgestellt, daß Dimethylammonium-aluminiumsulfat-hexahydrat sowie Dimethylammoniumchromsulfat-hexahydrat isostrukturell sind. Ein Mechanismus für die thermische Zersetzung dieser Doppelsalze wird ebenfalls vorgeschlagen.

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(CH₃)₂NH₂M(SO₄)₂· 6H₂O, 20–600° . , . .