Effect of the support on the coking of nickel catalysts in hydrocarbon steam reforming

Experiments on the coking rates of variously prepared nickel catalysts on TiO₂, Al₂O₃ and MgO in n-butane steam reforming show that changes in the relative coking rate at a rising steam excess in the gas phase depend mainly on the kind of support. The results obtained are accounted for by changes in the electron density at the site of nickel crystallite contact with the surface of various supports.

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, TiO₂, Al₂O₃ MgO, - , , , , , . .

     

NO adsorption on tin(IV) oxide

The adsorption of NO on SnO₂ has been studied in the temperature range from 0 to 86°C, at pressures from 0.4 to 3.5 Torr. The adsorption isotherms are described by the Freundlich equation. The rate of adsorption obeys the Roginskii-Zeldovitch equation and decreases with increasing temperature. The reduction of SnO₂ with carbon monoxide results in a drop in the adsorption rate and in the amount of adsorbed NO.

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NO SnO₂ 0°–86°C 0,4–3,5 . . - . SnO₂ NO.

     

Stability and catalytic activity of various cobalt (II)-cyanide complexes in water-monoethanolamine solutions

Stability constants of mono-, di-, tri-, tetra- and pentacyanocobaltate in water-monoethanolamine solution have been calculated. Concentration distributions of these complexes depending on the cyanide to cobalt ratio and rate constants for their isotope exchange in mixed water-monoethanolamine solutions have been determined.

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

     

Effect of reduction temperature and support on the surface electronic state of supported Pd catalysts

The effect of metal precursor, support and reduction temperature on the surface reduction of Pd on -Al₂O₃ and SiO₂ has been studied. For catalysts prepared from PdCl₂, temperatures as high as 450 °C are necessary to obtain surface Pd⁰.

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, Pd -Al₂O₃ SiO₂. , , PdCl₂, Pd^o - 450°C.

     

Effect of the nature of carrier on dinitrogen fixation by supported titanium complexes

Cyclopentadienyltitanium (IV) complexes supported on Al₂O₃, SiO₂ and MgO reduced with BuLi were tested in dinitrogen fixation at room temperature under normal pressure. Only the system supported on Al₂O₃ is active in this reaction.

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- (IV), Al₂O₃, SiO₂ MgO, BuLi, . Al₂O₃.

     

Synthesis of high-silicon zeolites in bialkaline systems

Rubidium and cesium zeolites (SiO₂Al₂O₃=4–9.2) of the faujasite, chabazite, erionite, offretite, phillipsite and pollucite type, L-zeolites as well as ZKF-2, ZKF-8 and ZKF-18 of unknown structure have been obtained. Their pore size is 4–10 Å and their thermostability is 1073–1223 K, which permits to use these zeolites as catalyst components.

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, , , , , , L, -2 -8 (SiO₂Al₂O₃=4–9,2). 4–10 Å 1073–1223 K, .

     

Intraframework thermal reactions of solids

Temperature-activated reactions of decomposition, the synthesis of new compounds, and reduction and oxidation, termed here intraframework reactions, take place within the structural framework of solids. They are distinguished in that they occur within the bulk volume of the substance, in the area of the influence of crystal fields. The atoms and ions participating in these reactions are displaced by diffusion, which is usually directional diffusion. The regularities governing some of these reactions are presented in the paper.

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Zusammenfassung Im Strukturgefüge von Feststoffen treten sogenannte Intratexturreaktionen auf: durch Wärme hervorgerufene Zersetzungsreaktionen, Sýnthese neuer Verbindungen, Reduktion und Oxidation. Diese sind dadurch gekennzeichnet, daß sie im gesamten Volumen der Substanz, in einem vom Kraftfeld des Kristalles beeinflußten Raum ablaufen. Der Austausch der an den Reaktionen teilnehmenden Atome und Ionen wird durch eine stets gerichtete Diffusion verursacht. Es werden Gesätzmäßigkeiten beschrieben, denen einige dieser Reaktionen unterliegen.

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

     

31P-NMR studies on the interaction between Rh(AA)(CO)(PPh3) complexes and free PPh3

Uncoordinated phosphine exchanges with that in Rh(AA)(CO)(PPh₃) (AA—anthranilate and phenylanthranilate ions, respectively) via an S_N2 mechanism.

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Rh (AA) (CO) (PPh₃) (AA — ) S_N2.

     

Catalytic activity of CaO?CaF2 binary systems in the Claus reaction

Activity of CaO–CaF₂ catalysts in the Claus reaction has been studied as a function of catalyst composition and of the time of catalyst operation in the reaction. Opposite effects of low and high fluoride content on the Claus activity have been found. A new type of reducing centers is suggested to be responsible for the increase in the activity observed in the case of fluorine-rich catalysts.

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CaO–CaF₂ . , . , , .

     

ESR identification of formation stages for TiCl3 particles in catalysts for isoprene polymerization

The analysis of ESR spectra from the system TiCl₄+ TIBA in solution under defreezing from 77 to 200 K permitted to identify formation stages of TiCl₃ particles. At first well-ordered Ti ₂ ⁷⁺ structures, and upon subsequent reduction [Ti ₂ ⁶⁺ ]_n are formed. It is the crystallization of the latter that produces TiCl₃ particles.

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TiCl₄+ 77 200 K TiCl₃: Ti ₂ ⁷⁺ , -[Ti ₂ ⁶⁺ ]_n, TiCl₃.

     

CO hydration over catalysts prepared via supporting Fe3(CO)12 and (NEt4)2[Fe2Mn(CO)12] on oxide supports

A comparison of the properties of iron-containing catalysts prepared through carbonyl clusters Fe₃(CO)₁₂ and (NEt₄)₂[Fe₂Mn(CO)₁₂] and iron and manganese nitrates in CO hydration indicates that the addition of Mn incorporated in (NEt₄)₂[Fe₂Mn(CO)₁₂] decreases the methane yield and increases the portion of higher hydrocarbons.

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, Fe(CO)₁₂ (NEt₄)₂[Fe₂Mn(CO)₁₂] , CO. Mn (NEt₄)₂[Fe₂Mn(CO)₁₂] .

     

Catalysts for metathesis of olefins, prepared by anchoring of MoO2(acac)2 to Al2O3

New highly active catalysts for metathesis of olefins were obtained through the interaction of bis(acetylacetonato)dioxymolybdenum(VI) with surface OH groups of -Al₂O₃ and subsequent reduction in H₂ or CO.

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()(VI) OH -Al₂O₃ H₂ CO .

     

Kinetics and mechanism of the decomposition of pyrite under conventional and quasi-isothermal — quasi-isobaric thermoanalytical conditions

The kinetics and mechanism of the thermal decomposition of pyrite were examined by the method of quasi-isothermal and quasi-isobaric thermogravimetry (Q-TG). It emerged that by means of this technique the overlapping partial processes of the complicated oxidation and decomposition reactions of pyrite can be separated and studied independently from one another. It was found that the partial reactions FeS₂=FeS +S and Fe₂O_3–x(SO₄)_x=Fe₂O₃+SO₃ are endothermic processes taking place quasiisothermally and leading to equilibrium, while the oxidation FeS+O₂=Fe₂O_3–x(SO₄)_x is an exothermic process which takes place in an oscillating manner in a rather broad temperature interval.

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Zusammenfassung Autoren untersuchten die Kinetik und den Mechanismus der thermischen Zersetzung von Pyrit durch quasi-isotherme und quasi-isobare Thermogravimetrie (Q-TG). Es stellte sich heraus, daß sich überlagernde Teilprozesse der komplizierten Oxydations- und Zersetzungsprozesse von Pyrit mit Hilfe dieser Technik absondern und unabhängig voneinander untersuchen lassen. Es wurde festgestellt, daß die Teilreaktionen FeS₂=FeS+S und Fe₂O_3–x(SO₄)_x=Fe₂O₃+SO₃ endotherme Prozesse sind, die quasi-isotherm verlaufen und zu einem Gleichgewicht führen, während die Oxydation FeS+O₂=Fe₂O_3–x(SO₄)_x ein exothermer Prozeß ist, der oszillierend in einem ziemlich breiten Temperaturintervall verläuft.

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(Q-) . . , FeS₂=FeS+S Fe₂O_3–x(S₂O₄)_x=Fe₂O₃+SO₃ , . FeS+O₂ =Fe₂O_3–x(SO₄)_x , .

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The authors thank Prof. E. Pungor for valuable discussions, and Mrs. M. Kiss and Miss I. Fabian for their technical assistance.     

Selective hydrogenation of cyclopentadiene in the liquid phase on palladium catalysts

The catalytic hydrogenation of cyclopentadiene to cyclopentene was investigated under atmospheric pressure and 20°C in liquid phase with palladium carrier catalysts. The reaction was carried out in methanol and toluene in the presence of n-octylcatechol as a polymerization inhibitor. Using 0.56% Pd/Al₂ O₃, a 100% selectivity of the hydrogenation of cyclopentadiene to cyclopentene was achieved in toluene. In methanol, the selectivity of hydrogenation was lower and a partial polymerization of cyclopentadiene took place.

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20° C Pd- . -. 0,56% Pd/Al₂ O₃ 100%. , .

     

Influence of the chlorine content of Al2O3 on its catalytic activity and coke formation

The catalytic activities of aluminas with different chlorine contents for cumene cracking, o-xylene isomerization, n-hexane isomerization and cracking and methylcyclopentane cracking were studied. The catalytic activity and the acidity increase continuously when the chlorine content increases. Coke formation is only noticiable with methylcyclopentane, increasing with the chlorine content of the alumina.

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, -, - . . - , - .

     

Discrimination of the kinetic model of overlapping solid-state reactions from non-isothermal data

A method has been developed that allows the deconvolution of up to 15 overlapping solidstate reactions without previous assumptions. Both the kinetic parameters and the reaction mechanisms fitted by the unit reactions can be determined from a series of non-isothermal experiments carried out at different heating rates.

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Zusammenfassung Es wurde eine methode zur Dekonvolution von bis zu 15 einander überlappenden Festphasenreaktionen entwickelt, die keinerlei vorherige Annahmen notwendig macht. Mittels einer Reihe nichtisothermer Experimente mit unterschiedlichen Aufheizgeschwindigkeiten können sowohl die kinetischen Parameter als auch der Reaktionsmechanismus der Teilreaktionen bestimmt werden.

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, 15. .

     

Ag(I) solid solutions in zirconium dihydrogen phosphate. Thermal behaviour and phase changes

The thermal and redox behaviours of some Ag-low-converted zirconium phosphates have been investigated by thermoanalytical and X-ray methods: the conditions for obtaining Ag solid solutions in phases are reported.

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Zusammenfassung Das thermische und Redoxverhalten einiger Zirkoniumphosphate niedriger Ag-Konversion wurde durch thermoanalytische und Röntgenmethoden studiert; über die Bedingungen zum Erhalten von Ag-Festphasenlösungen in HH-Phasen wird berichtet

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Résumé On a étudié le comportement thermique et oxydo-réducteur de quelques phosphates de zirconium faiblement converti par Ag, en se servant des méthodes d'analyse thermique et des rayons X: on communique les conditions permettant d'obtenir des solutions solides d'Ag dans les phases .

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- Ag- . HH.

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Paper in part presented at the 6th ICTA, in Bayreuth (Germany), July 1980.

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We thank Dr. M. A. Massucci, of our Institute, for helpful discussions and suggestions.     

Compensation effect in solid-state reactions. Thermolysis of one substance under differing experimental conditions

The compensation effect (lgZ=aE+wb) appearing at the thermolysis of one substance under different experimental conditions is discussed. The compensation effect of one and the same substance has no other physical meaning except the simple confirmation of the analytical relationship between lgZ andE that follows from the Arrhenius equation, and of the impossibility to determineZ from any independent experiment. Values of the coefficienta can not be the measure of the ruptured bond strength.

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(lgZ=+b), . , lgZ E ( ) Z . a .