Decomposition of ammonia on rhenium II. Nitrogen adsorption on rhenium

Field emission microscopy and thermal desorption studies of nitrogen adsorption on a monocrystal tip and a polycrystalline rhenium wire indicate the formation of molecular () and dissociative () forms of adsorption. Adsorption-desorption characteristics have been measured.

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. - - , - .

     

Catalytic properties of nitrides in ammonia synthesis

Ammonia synthesis on nitrides CeN, UN_1.70 and iron catalyst CA-1 has been examined at pressures of up to 100 bar. Reaction kinetics is described by the Temkin-Pyzhev equation. Activation energy for all samples is similar and equals about 200 kJ/mol. Specific catalytic activity of nitrides is lower than that of the iron catalyst by a factor of 3–4 for uranium and 10 for cerium.

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100 CeN, UN_{1, 70} CA-1. -. 200 /. : 3–4 10 .

     

The influence of CSH phase nuclei on Ca3SiO4Cl2 hydration

The influence of CSH phase nuclei on calcium chlorosilicate hydration has been studied by means of calorimetry, QXRD, DTA and TG methods.

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Zusammenfassung Mittels kalorimetrischen, QXRD-, DTA- und TG-Verfahren wurde der Einfluß von CSH Phasenkörpern auf die Hydratierung von Kalziumchlorosilikat untersucht.

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, , .

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C=CaO, S=SiO₂, H=H₂O     

Energy dissipation and selectivity in the catalytic oxidation of ammonia

A qualitative interpretation of selectivity changes in ammonia oxidation, based on considerations of energy dissipation processes is presented.

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, .

     

Modelling of self-oscillations in the combustion of n-heptane-isooctane mixtures

A mathematical model has been constructed to describe the self-oscillation regime of the cool-flame combustion of an n-heptane-isooctane mixture. The character of the dependence of the amplitude and oscillation period on the temperature and mixture composition is in a qualitative agreement with the similar experimental data.

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, --. .

     

Studies of supported catalysts for ethylene polymerization, prepared using organovanadium compounds

Catalysts containing trimethylsilyl complexes of V(IV) and (III) supported on SiO₂ and Al₂O₃, have been synthesized and examined for ethylene polymerization. The state of vanadium in solution and on the support and catalysts interaction with C₂H₄, CO, H₂ and pyridine have been studied using ESR and IR spectroscopy.

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, (IV) (III), SiO₂ Al₂O₃. , C₂H₄, CO, H₂ .

     

Influence of neodymium content on the catalytic properties of zeolite NDHNaY

The influence of neodymium content on the catalytic properties of a HNaY zeolite was investigated using the cracking of n-heptane as model reaction. Neodymium zeolites were found to be more active for cracking and hydrogen transfer reactions than zeolites containing lanthanum, cerium or praseodymium.

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HnaY . , , , .

     

Quantum chemical calculations on the catalytic dehydration of 2-propanol

The charge on atoms and the bond strengths in CH₃CHOHCH₃, CH₃ CH₃, CH₃CHOHCH ₂ ^– , CH₃ CH ₂ ^– and CH₃ CH₃...O(H)CH(CH₃)₂ have been calculated by the CNDO/2 method. The results are in agreement with published experimental observations on catalytic dehydration. A modified mechanism of anti-elimination on solid catalysts is proposed.

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CH₃CHOHCH₃, CH₃ CH₃, CH₃CHOHCH ₂ ^– , CH₃ CH ₂ ^– CH₃ CH₃...O(H)CH(CH₃)₂, CNDO/2. . .

     

Calculation of the mass transfer coefficient with a chemical reaction in a gas-liquid system

A solution of the problem of mass transfer in a turbulent boundary layer has been obtained with a first-order chemical reaction occurring in the liquid phase. The dependence of the enhancement factor for absorption and of the mass transfer coefficient on the model parameters can be used for building up a hierarchic model of the gas-liquid reactor.

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. .

     

M?ssbauer spectroscopic studies of passivated layers of iron-containing catalysts for ammonia synthesis

Combined conversion electron (CEMS) and transmission -ray (MS) Mössbauer spectroscopy was used to study the structure of passivated layers of promoted and unpromoted iron-containing catalysts. In both catalysts the oxide-coated films were found to consist of small paramagnetic (at 300 K) clusters of ferric oxide.

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. , ( 300 ) .

     

Decomposition of ammonia on rhenium I. Hydrogen adsorption on rhenium

Field emission microscopy and thermal desorption studies of hydrogen adosrption on a monocrystal tip and a polycrystalline rhenium wire indicate dissociative adsorption which proceeds with an initial sticking coefficient of S_o0.2 and an isosteric adsorption heat of about 138 kJ/mol.

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. , , S_o0.2 138 /.

     

Acid strength distributions in the Mo?Al?Si and the Ni?Mo?Al oxide systems determined by ammonia adsorption

Acid strength distributions of Mo–Al–Si and Ni–Mo–Al oxide systems have been found by means of a relationship that gives pK_a values from amounts of ammonia adsorption. Molybdenum is suggested to cause a homogenization in the acid strength distribution of alumina but a heterogenization in silicaalumina, whereas nickel is found to neutralize strong acid sites inherent to molybdenum.

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Mo–Al–Si Ni–Mo–Al , . , , .

     

Nonsteady-state oxidation of propylene on supported silver catalysts

Nonsteady-state epoxidation of propylene on silver has been studied to establish the reason for the low catalyst activity and selectivity that appear to be due to side reactions of the formation of hydrogen-deficient deposits.

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, .

     

Influence of sodium on the catalytic properties of bismuth-molybdenum oxide catalysts

In the ammoxidation of propylene, the presence of a normal NaBi(MoO₄)₂ phase in bismuth molybdenum oxide catalysts decreases the acrylonitrile yield due to its oxidation

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NaBi(MoO₄)₂ -- .

     

Influence of different variables on the catalytic activity of Pt/AlPO4 systems used in the reduction of nitrobenzene

This work deals with the hydrogenation of nitrobenzene to aniline with gaseous hydrogen over different supported Pt catalysts. We studied the reaction kinetics for the different catalysts and the influence of the solvent used. The metal salts used as catalyst precursors were reduced chemically with -phellandrene and the dispersions obtained were better than in the conventional reduction with gaseous H₂.

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Pt. , . , , - , H₂.

     

Influence of ammonia on propylene oxidation on tin-antimony and bismuth-antimony catalysts

The influence of ammonia on the direction of the oxidative transformations of propylene has been studied. Ammonia has been shown to block the surface oxygen of antimony catalysts. As a result, an increase in the selectivity with respect to the products of partial oxidation is observed.

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. , , .

     

Dehydroxylation and catalytic activity of dealuminated Y zeolites

Dehydroxylation and catalytic conversion of m-xylene over dealuminated zeolites were studied.

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- .

     

Effects of additional metals on catalyst life of vanadium-containing high silica zeolites in methanol to hydrocarbon conversion

Catalyst life of vanadium-containing high silica zeolites having the ZSM-5 structure was greatly affected by an additional metal incorporated into the crystal. Chromium ion was effective to increase the catalyst life, while zirconium ion decreased it significantly. Temperature-programmed desorption spectra of NH₃ revealed a correlation between the catalyst life and the number of strong acid sites, suggesting that the additional metal affects the catalyst life by changing the number of strong acid sites.

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, ZSM-5, , . , . NH₃ , , , .

     

Free radical additions to the C=O bond of formaldehyde

The reactions between formaldehyde and n-propyl radicals were studied at 333 and 363 K. Addition to the C=O bond was found to be several times faster than abstraction of the formyl hydrogen atom. With a TST estimate of log(A/dm³ mol^–1 s^–1)=7.9±0.5, 28.0±2.1 kJ mol^–1 was obtained for the activation energy of the addition reaction.

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- 333 363 . C=O . 28.0±2.1 ^–1 , lg(A/ ^{–1 –1})=7.9±0.5 .