Hydrogenation of CO on thoria supported group VIII (Pd, Pt, Ir) metal catalysts

Comparative studies of the transformation of CO/H₂ mixtures on Pd supported (MgO, Al₂O₃, ThO₂) catalysts reveal the promoting effect of thoria, particularly towards hydrocarbon products.

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CO/H₂ Pd MgO, Al₂O₃ ThO₂ ThO₂, .

     

Decomposition of N2O over CuxMg1?xAl2O4 catalysts

The results show that there is not difference between the catalytic activities of two series of Cu_xMg_1–xAl₂O₄ catalysts, despite a small but significant difference in cation distribution. The activity is mainly affected by the presence of CuO.

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, , , , - Cu_XMg_1–XAl₂O₄. CuO.

     

51V NMR studies of a system vanadium pentoxide-potassium pyrosulfate

Two states of pentavalent vanadium in the system K₂S₂O₇–V₂O₅ have been found by the⁵¹V NMR method. For state 1 a polynuclear structure with greater distorted local environment compared with V₂O₅ is retained. For state 2 the nearest environment of vanadium differs significantly from V₂O₅, and is probably characterized by the higher ionic nature of the vanadium-oxygen bond.

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⁵¹V K₂S₂O₇–V₂O₅ . V₂O₅. , V₂O₅ , , -.

     

Effect of pressure on the primary photochemical processes of n-butyraldehide at 313 nm

The effect of pressure on the primary processes of n-butyraldehyde photolysis has been studied and a scheme of photochemical and photophysical steps is suggested.

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- .

     

Kinetic equations of isotope redistribution in an elementary reaction

Kinetic equations for the redistribution of isotopic molecules in an elementary reaction have been derived on the basis of atom distribution matrices.

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.

     

Quantum chemical study of the physical characteristics of the hydroxy groups of zeolites, V

The CNDO/2 method is employed in the study of the acid strength of O–H groups of the HY and HX zeolites using their cluster models of the Si₄Al₂O₆(OH) ₁₂ ^2– and Si₃Al₃O₆(OH) ₁₂ ^3– type. It is shown that the O–H groups of the HY zeolites are of more acidic character than those of the HX zeolites. The reasons of the heterogeneity of O–H groups are shortly discussed on the basis of the theoretical results.

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/2 OH HY HX, Si₄Al₂O₆(OH) ₁₂ ^3– Si₃Al₃O₆(OH) ₁₂ ^3– . , OH HY , OH HX . OH.

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Part IV, cf. Ref. /1/     

Hydrodewaxing studies over a pentasil ferrisilicate zeolite

The catalytic dewaxing of an atmospheric gas oil has been carried out over Pt-loaded catalysts containing a ferrisilicate zeolite of the ZSM-5 structure. It is observed that the mode of incorporation of the metallic function has a profound effect on the activity on the catalyst. Further, the use of alumina (instead of bentonite) as binder increases the activity of the catalyst.

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, ZSM-5. , . , ( ) .

     

Influence of external electric field on oxygen and carbon monoxide adsorption

The induction of negative charge in a ZnO film causes oxigen adsorption on an oxidized surface apparently in the form of O ₂ ^– . Electroadsorbed oxygen forms CO adsorption centers. On coadsorption from a 2CO+O₂ mixture, equal quantities of CO and O₂ are adsorbed with the formation of CO ₃ ^– complexes decomposing above 400 °C with CO₂ liberation into the gas phase.

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ZnO , -, O ₂ ^– . CO. 2CO+O₂ CO O₂ CO ₃ ^– , 400 °C CO₂ .

     

Determination de la purete des substances chimiques par analyse calorimetrique differentielle (A. C. D.)

Purity determination by DSC is possible if the impurity concentration lies within the limits 0.01 to 20 mole%. The thermodynamic equation of Schröder-Van Laar was used.This equation takes into account the effect of the departure of solutions from ideality, and the difference between the heat capacities in the solid and molten states.

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Zusammenfassung Eine Reinheitbestimmung mittels DSC ist möglich, wenn die Konzentration der Verunreinigung zwischen 0.01 und 20 Mol-% liegt. Es wurde die thermodynamicshe Gleichung von Schröder-Van Laar angewandt. Diese Gleichung berücksichtigt den durch die Abweichung der Lösungen vom idealen Zustand bedingten Effekt und den Unterschied der Wärmekapazität im festen Zustand und in der Schmelze.

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, 0.01–20 %. --, .

     

Thermoanalytical studies on cation distribution in submicronic titanomagnetites

Non-isothermal and isothermal TG studies on the cation distribution in submicronic titanomagnetites; Fe_3–xTi_xO₄ with 02O₃. The DTA results show that the temperature of oxidation of Fe²⁺ to Fe³⁺ ions is increased, whereas the temperature of phase change is decreased with increasing titanium substitution. The kinetics of oxidation is found to be governed by the law of diffusion for variable working conditions and for different extents of the vacancies created at the solid-gas interface. The diffusion of iron(II) ions located at octahedral sites proceeds with a lower activation energy than that of iron(II) ions located at tetrahedral sites. Diffusion rates were discerned to be composition-dependent and the variations can be identified with the distribution of the iron ions in sublattices.

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Zusammenfassung Es wird über nicht-isotherme und isotherme TG-Untersuchungen der Kationenverteilung in submikronen Titanomagnetiten (Fe_3–x Ti _x O₄ mit 0<x<0.82) berichtet. Titanomagnetite mitx<0.61 konnten unter 500° zu Titan-substituierten Magnetiten oxydiert werden, die eine größere Leerstellenkonzentration als-Fe₂O₃ aufweisen. Die DTA-Ergebnisse zeigen, daß die zur Oxydation von Fe²⁺- zu Fe³⁺-Ionen notwendige Temperatur mit zunehmender Titansubstitution ansteigt, die Phasenübergangstemperatur dagegen absinkt. Die Kinetik der Oxydation ist unter verschiedenen Arbeitsbedingungen und bei unterschiedlichen Konzentrationen der an der Fest-Gas-Grenzfläche gebildeten Fehlstellen diffusionsbestimmt. Die Aktivierungsenergie der Diffusion von an den oktaedrischen Stellen lokalisierten Fe(II)-Ionen ist geringer als die von tetraedrisch koordinierten Fe(II)-Ionen. Diffusionsgeschwindigkeiten werden als von der Konzentration abhängig erkannt und die Variationen können mit der Verteilung der Eisenionen im Subgitter identifiziert werden.

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Fe_3–x Ti _x O₄ c 0<x<0.82. x< 0.61 500° , -Fe₂O₃. , , . , — . , , . , .

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Paper presented at the World Conference on Thermal Analysis, Madeira (Portugal), 1986.     

Thermal properties of binary polyolefin blends

The thermal properties of binary polyolefin blends (LDPE/HDPE, LDPE/PP, HDPE/PP) were examined by differential scanning calorimetry. The additon of a second polymer lowers the melting temperature although the melting temperature depression is not a defined function of the blend composition. DSC curves show two melting and two crystallization temperatures. The difference between crystallization temperatures for blends containing PP is smaller than the difference between melting temperatures. The enthalpies of fusion are nearly monotonic functions of blend composition.

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Zusammenfassung Die thermischen Eigenschaften binärer Polyolefinmischungen (LDPE/HDPE, LDPE/PP, HDPE/PP) wurden mittels DSC untersucht. Durch Zugabe eines zweiten Polymers wird die Schmelztemperatur erniedrigt, obwohl die Erniedrigung der Schmelztemperatur keine Funktion der Mischungszusammensetzung ist. Die DSC-Kurven zeigen zwei Schmelz- und zwei Kristallisationspeaks. Bei PP enthaltenden Mischungen ist der Unterschied zwischen den Kristallisationstemperaturen geringer als zwischen den Schmelztemperaturen. Die Schmelzenthalpie ist eine nahezu monotone Funktion der Mischungszusammensetzung.

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— , — , — . , . . , . .

     

Influence of Cr loading on the catalytic properties of CrO3/SiO2 catalysts in 2-propanol conversion

Catalytic activity of CrO₃/SiO₂ samples for 2-propanol conversion is governed by only a small amount of active centers (estimated to be around 10¹⁷ per gram of catalyst), whereas excess chromium neither develops catalytic activity nor inhibits the reaction on the active sites. Only when the chromium loading is high enough to allow formation of bulk-like agglomerates (5 wt.% Cr) is 2-propanol converted also on this CrO_x surface phase, but with a significant higher activation energy.

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CrO₃/SiO₂ 2- ( 10¹⁷ ), . , - (5 .% Cr), 2- CrO_x , .

     

Pressure effects on oxygen interaction with ruthenium catalysts

Statistical adsorption and TPD studies of P_{O 2}=1.33 and 90,440 Pa and T_ads=163–523 K have revealed that Ru oxidation at high pressures begins already at T_ads=300 K, while at low ones it starts at 353 K. Temperature increase leads to its surface oxidation at low pressures (1.33 Pa) and to the deep oxidation with the formation of stoichiometric oxides at high pressures (90,4440 Pa).

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P_{O 2}=1,33 90440 163–523 . , Ru =300 , - 353 . Ru (1,33 ), (90440 ) .

     

Retrieval of thermodynamic properties of M(OH)2 (M=Mn,Ni and Cd) phases from hydrothermal phase equilibria of MO-H2O systems

The standard thermodynamic properties of M(OH)₂ (M=Mn, Ni and Cd) solid phases have been retrieved using a graphical approach based on the already reportedP vs. T curves obtained from hydrothermal studies of MO-H₂O systems. This approach avoids the use of heat capacity effects. The values retrieved by this modified approach are in good agreement with the calorimetric values.

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Zusammenfassung Basierend auf unlängst beschriebenen, aus hydrothermischen Untersuchungen von MO-H₂O Systemen gewonnenenp-T Kurven wurden mittels einer graphischen Näherung die thermodynamischen Standardeigenschaften von M(OH)₂ Festphasen (M=Mn, Ni und Cd) bestimmt. Dieses Verfahren umgeht den Gebrauch von Wärmekapazitätseffekten. Die durch dieses modifizierte Verfahren erhaltenen Werte stehen in guter Übereinstimmung mit den kalorimetrischen Werten.

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- , O-H₂O, M(OH)₂, M=, . . .

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The authors express their grateful thanks to Prof. V. Venkatachalapathy, Director of the Minerological Institute, for his encouragement during the course of this work.     

On the interpretation of differences in mechanisms, kinetics and dynamics of oxidation reactions on metal and oxide catalysts

Langmuir-Hinshelwood type mechanisms with competitive adsorption are suggested to be more typical for metal catalysts, since, unlike on oxide systems, oxidizable substance and molecular oxygen can be adsorbed on the same (reduced) active sites. Therefore, multiple steady states and critical phenomena are more characteristic for catalysis on metals.

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, - , , () . .

     

Influence of HCl on butene isomerization catalyzed by ethanolic rhodium trichloride II. Calculation and interpretation of the rate constants of the triangle scheme

The values of the rate constants of the triangle scheme, calculated by means of a non-linear least-squares method, depend systematically on the HCl concentration. The alteration of the cis-trans selectivity expressed by the ratio k_1c/k_1t might indicate a change in the mechanism of isomerization with the HCl concentration.

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, , . - , k_1c/k_1t, .

     

Combined thermoanalytical-mass-spectrometric investigation of crupodexR dextranomer

A cross-linked dextranomer, which is used as a wound drying and cleansing powder (Crupodex^R), has been investigated by several thermoanalytical methods. First the TG, DTG and DTA characteristics were studied and compared with those of another product (Debrisan^R), marketed earlier. The TG curves were also used for the examination of water uptake and the drying process. The traces of organic solvents (mainly ethanol) remaining from the manufacturing process were studied with a quadrupole mass-spectrometer coupled to a derivatograph. From the results of these experiments, several conclusions were drawn about the mechanism of water and solvent uptake.

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Zusammenfassung Crupodex^R-Puder, ein vernetztes Dextranomer zum Trocknen und Säubern von Wunden, wurde mittels einiger thermoanalytischer Methoden untersucht. Zuerst wurden die TG, DTG und DTA Charakteristiken betrachtet und mit denen eines schon früher auf den markt gekommenen Produktes (Debrisan^R) verglichen. Die TG-Kurven wurden auch zur Untersuchung der Wasseraufnahme- und Trocknungsprozesse verwendet. Aus dem Produktionsprozeß verbliebene Lösungsmittelreste — hauptsächlich Ethanol — wurden mit einer Instrumentenanordnung Quadrupolmassenspektrometer-Derivatograph bestimmt. Mittels dieser Ergebnisse konnten einige Schlußfolgerungen betreffs des Mechanismus der Wasser- und Lösungsmittelaufnahme getroffen werden.

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(), . , , . . , , , -, . , .

     

Isotope exchange in molecular hydrogen on films of some rare-earth metals

3,3- () . , -- (Br, OCH₃, OC₂H₅) . , () .

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The kinetic parameters for the condensation of benzaldehyde with 3,3-bis-(chloromethyl)oxacyclobutane have been determined. It has been established by competition methods that aliphatic and p-substituted (Br, OCH₃, OC₂H₅) aromatic aldehydes are more reactive than benzaldehyde. The proposed rate-determining step involves nucleophilic attack on a hydroxyalkyl (aryl) carbonium ion.

     

Hydrocarbon from methanol over amorphous silica-alumina: Operational conditions for maximum C5+ fraction yields

The operational conditions (temperature, pressure and mass of catalyst: mass flow rate of methanol ratio) which allow a maximum in the C₅+ fraction during methanol to hydrocarbon transformation over an amorphous silica-alumina have been studied. Reaction pressure is a very important parameter to increase hydrocarbon production. Armoatics are not the only coke precursors during these transformation.

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(, : ), C₅+ -. . - .

     

Influence of mechanical activation on decomposition of a chalcopyrite-pyrite mixture in an oxidizing atmosphere

The influence of the addition of pyrite and mechanical activation on an oxidative decomposition of chalcopyrite was studied. The course of the thermoanalytical curves and X-ray identification of the products showed that addition of pyrite affects mainly the endothermic processes taking place in region of low temperatures but does not significantly influence the temperature of CuSO₄ formation and its content in the products of decomposition. Changes in fine and superfine structure of chalcopyrite brought about by mechanical activation at grinding cause the complex of exothermic oxidative reactions to proceed at temperatures as much as 180 deg lower than for a non activated sample. The endothermic effect of these oxidation reactions become more marked and the proportion of CuSO₄ in the products of the oxidative decomposition increases significantly.

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Zusammenfassung Am oxidativen Zerfall von Chalkopyrit wurde der Einfluss der Zugabe von Pyrit sowie der mechanischen Aktivierung untersucht. Der Verlauf der thermoanalytischen Kurven und Röntgendiffraktionsanalyse der Produkte zeigten, dass die Zugabe von Pyrit hauptsächlich die sich bei niedrigeren Temperaturen abspielenden endothermen Prozesse beeinflusst, nicht aber die Bildungstemperatur von CuSO₄ sowie dessen Gehalt in den Zersetzungsprodukten. Durch mechanisches Aktivieren mittels Feinmahlen hervorgerufene Veränderungen in der Fein- und Superfeinstruktur lassen die Gesamtheit der exothermen oxidativen Reaktionen bei Temperaturen ablaufen, die etwa 180 Grad unterhalb derer für unaktivierte Proben liegen. Die endotherme Färbung dieser Oxidation wird eindeutiger und der Anteil von CuSO₄ in den Produkten des oxidativen Zerfalles nimmt eindeutig zu.

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. , . , , - , 180° , . - .