On the possibility of formation of Ti?Mo heteropolyacids on Ti?Mo catalysts

According to IR spectroscopic studies, a Ti–Mo heteropolyacid is formed on the surface of Ti–Mo catalysts prepared from ammonium paramolybdate and TiO₂.

---

- , Ti–Mo TiO₂ Ti–Mo .

     

Evaluation of quantum yields in the presence of an absorbing additive

A method is proposed for the evaluation of quantum yields of photochemical reactions studied in the presence of absorbing additives using cylindrical sample tubes.

---

.

     

Determination of activation energy in enzymatic reactions by a single non-isothermal kinetic experiment

A non-isothermal kinetic method with linear heating was applied to enzymatic catalysis and rapidly provided the activation energy. The results obtained showed the excellent precision of the method.

---

. , . .

     

Activation of magnesia by hydrogen spillover

Magnesia aerogel activated by hydrogen spillover at 430 °C or at 200 °C becomes a catalyst for the hydrogenation of ethylene. This catalytic activity, observed already at 50 °C, is further enhanced by a treatment in oxygen at 430 °C.

---

, 430 200°C, . 50°C 430°C.

     

A gradientless flow microreactor

A simple flow microreactor can perform as a gradientless microreactor under suitable conditions so that, thanks to molecular diffusion, the reactant concentration is leveled out considerably. This was demonstrated on the basis of a mathematical analysis of the reactant concentration distribution in a flow reactor and the observation was confirmed experimentally. A simple flow microreactor was designed and its gradientless property was verified using carbon dioxide hydrogenation as a test reaction.

---

. . , . , .

     

Variation of the surface potential of zinc oxide under illumination

Spectral and kinetic dependences of the decrease in the surface potential (SP) of ZnO under illumination and processes of SP relaxation in the dark have been studied. A significant contribution to the decrease of SP in the less-than-bandgap light absorption region is shown to be due to the photodissociation of specific surface bonds with the formation of localized Zn _s ⁺ and O _s ^– .

---

() ZnO . , Zn _s ⁺ O _s ^– .

     

Hysteresis of thermogravimetric curves of nickel catalysts for methane conversion in CH4+CO2 mixture

Characteristic peculiarities of the supercarbonization peak, i. e. the effect of carbon accumulation on the catalyst surface and its subsequent removal under heating in the CH₄+CO₂ mixture have been studied. Hysteresis of thermogravimetric curves in the heating/cooling cycle has been established.

---

— . -.

     

Hexadiene formation during decomposition of 2-propanol over Ca?P?O catalysts

Hexadiene formation from 2-propanol was investigated in view of acid-base properties of Ca–P–O catalysts with the Ca/P atomic ratio varying from 1.5 to 5.0. The catalytic activity in hexadiene formation increased up to a maximum at Ca/P=2.0, having almost the same amount of weak acidic sites as weak basic sites, and decreased with futher increase in Ca/P ratio.

---

2- - Ca–P–O Ca/P, 1,5 5,0. , Ca/P=2, , Ca/P.

     

Kinetics and mechanism of OsO4 catalyzed oxidation of maleic, fumaric, cinnamic and acrylic acids by acid bromate

The title reactions are zero order in bromate, first order in both substrate and catalyst. The order of reactivity is cinnamic acid>acrylic acid>fumaric acid>maleic acid. A plausible mechanism is discussed.

---

, . : > > > . .

     

A new preparation technique of catalysts characterized by small metal crystallites

The present study reports a new and original technique for obtaining nickel catalysts characterized by small metal crystallites. The catalysts were prepared on -Al₂O₃. The total surface of the carrier was 37.5 m²/g. The preservation of the appropriate procedure and conditions of preparation allow a large expansion of active nickel surface (mean crystallite size 2.0–3.0 nm) in spite of the quite hard conditions of reduction (773 K and 3 h).

---

, . -Al₂O₃. 37,5 ²/. ( 2,0–3,0 ) (3 773 ).

     

The thermal dehydration of Sr(HCOO)2·2(H,D)2O. Influence of the isotopic substitution on the kinetics

The kinetics of thermal dehydration of Sr(HCOO)₂·2(H, D)₂O were investigated using a dynamic thermogravimetric technique. Differences were found when the hydrogen was partially substituted by deuterium. These differences were explained by means of a microscopic approach based on the static and dynamic microscopic properties.

---

Zusammenfassung Die Kinetik der thermischen Dehydratisierung von Sr(HCOO)₂·2(H, D)₂O wurde mittels dynamischer Thermogravimetrie untersucht. Bei partieller Substitution von Wasserstoff durch Deuterium wurden Unterschiede gefunden, die durch eine auf den statischen und dynamischen mikroskopischen Eigenschaften beruhende Betrachtungsweise erklärt werden.

---

Sr(HCOO)₂ · 2(H, D)₂O. , .

---

---

The authors whish to thank Dr. J. M. Pastor for valuable discussions, and Prof. O. Garcia of the Instituto de Quimica Inorgánica Elhuyar (C.S.I.C.) for the use of the experimental devices.     

Kinetic measurements on polymers — Applications and limits

A modern kinetic evaluation method for nonisothermal reactions measured with TG or DSC is presented. The obtained kinetic data are the basis for computation of a reaction process under any condition, e.g. isothermal or adiabatic. The measurements were performed on a Mettler TA3OOO system with built-in evaluation software. Mainly the following reactions are discussed: polyaddition of an epoxy premix and pyrolysis of polystyrene. To judge the reliability of the results, 4 check procedures are recommended.

---

Zusammenfassung Es wird eine moderne kinetische Auswertungsmethode für durch TG oder DSC verfolgte nichtisotherme Reaktionen vorgestellt. Die erhaltenen kinetischen Daten stellen die Basis der Berechnung der Reaktionsprozesse unter jeder, z.B. isothermer oder isobarer Bedienung dar. Die Messungen wurden mit dem Mettler-System TA3000 mit Auswertungs-software ausgeführt. In erster Linie werden die folgenden Reaktionen diskutiert: Polyaddition eines Epoxy-Vorgemisches, Pyrolyse von Polystyrol. Zur Beurteilung der Zuverlässigkeit der Ergebnisse werden 4 Testverfahren empfohlen.

---

, . - , , . TA 3000 . - . .

     

A method for preliminary estimation of solid oxidation kinetics and mechanism

The possibility of preliminary estimation of the oxidation kinetics and mechanism using the quantity t_o from the exponential kinetic rate equation is discussed.

---

, t_o .

     

Activity of γ-Al2O3 modified by NaOH in disproportionation of methanethiol

Na⁺/Al₂O₃ catalysts in disproportionation of methanethiol are highly selective towards dimethyl sulfide but less active compared to -Al₂O₃. Their activity falls with increasing Na⁺ in the sample. This decrease is due to the neutralization of Brönsted acid centers on the catalyst.

---

Na⁺/Al₂O₃ , , -Al₂O₃. Na⁺ . .

     

Kinetics of thermal decomposition of MCO3 to MO (M=Ca,Sr and Ba)

The kinetics of the thermal decompositions of CaCO₃, SrCO₃ and BaCO₃ into their oxides were studied by thermogravimetry at constant and linearly increasing temperatures. The kinetics of the isothermal decompositions of calcium and strontium carbonates were described by the lawR _n =1–(1–)^1/n , wheren=1.8 and 1.2, respectively. The kinetics of the non-isothermal decompositions of the two carbonates, analysed by the Ozawa and Coats-Redfern methods, were in keeping with the isothermal kinetics. True kinetic compensation laws were established for each decomposition of the two carbonates, including the data under both isothermal and non-isothermal conditions.As concerns the decompositions of BaCO₃, however, there was some difference between the kinetic features relating the isothermal and non-isothermal conditions. A true kinetic compensation law was not established in this case.

---

Zusammenfassung Die Kinetik der thermischen Zersetzung von CaCO₃, SrCO₃ und BaCO₃ zu den Oxiden wurden durch Thermogravimetrie bei konstanter und linear ansteigender Temperatur untersucht. Die Kinetik der isothermen Zersetzung von Calcium- und Strontium-carbonat folgt dem GesetzR _n =1–(1 –)^1/n, won=1,8 bzw. 1,2. Die Kinetik der nichtisothermen nach den Methoden von Ozawa und Coats-Redfern analysierten Zersetzung der zwei Carbonate ist in Übereinstimmung mit der isothermen Zersetzung. Wahre kinetische Kompensationsgesetze wurden für die Zersetzung der beiden Carbonate erhalten, einschließlich der sich sowohl auf isotherme als auch auf nichtisotherme Bedingungen beziehenden Daten. Was die Zersetzung von Bariumcarbonat betrifft, so wurden einige Unterschiede im kinetischen Verhalten bei der Zersetzung unter isothermen und nichtisothermen Bedingungen festgestellt. Ein wahres kinetisches Kompensationsgesetz konnte in diesem Falle nicht ermittelt werden.

---

, . R _n =1–(1–)^1/n , , , 1,8 1,2. , -, . « » , . , , . - «» .

     

Some peculiarities of cyclohexane conversion on zeolite catalysts

Cyclohexane conversion on zeolite and zeolite-containing catalysts has been examined. The formation of cracking, isomerization and dehydrogenation products is suggested to follow two parallel independent mechanisms through different intermediate carbocations.

---

. , .

     

Calorimetric study of the interaction of oxygen with Pd-black and Pd/Al2O3

The kinetics of molecular hydrogen oxidation by palladium(II) has been studied under homogeneous conditions, excluding Pd-black formation. The rate constants for PdCl_i(H₂O)_4–i complexes for i=0, 1, 2, 3 and 4 are 0.12±0.003; 3.4±0.4; 5.2±0.3; 2.34±0.07 and 0 M^–1s^–1, respectively.

---

, Pd-, H₂ (II). PdCl_i(H₂O)_4–i 0,12±0,003; 3,4±0,4; 5,2±0,3; 2,34±0,07 0 ^{–1 –1}, .

     

Molybdenum hexacarbonyl catalyzed photooxygenation of cyclohexane by air dioxygen in acetonitrile solution

ESR and XPS investigations on Cu/–Al₂O₃ catalysts with various amounts of Cu loading are reported. Experimental data are related to the surface structure and dispersed state of catalysts. The results show that ESR can be used as a means of charaterizing monolayer dispersed state for paramagnetic supported catalysts.

---

Cu/–Al₂O₃ . . .

     

Two mechanisms of the interaction between atoms and solids

The chemical action of atoms on solids can be due to both direct reactions with the structural units of solids and heterogeneous recombination energy transfer to the crystal lattice.

---

, .

     

Basicity and catalytic properties of multicomponent catalysts for oxidative ammonolysis of propane

Studies of the effect of phosphorus and tungsten on the basicity and catalytic properties of catalysts for oxidative ammonolysis of propane indicate that, besides the common decrease in the number of active centers on the catalyst surface, the sharply decrease the concentration of strong basis centers.

---

. , , , .