Comparative study of the catalytic properties of V2O5, Nb2O5 and Ta2O5 in the oxidation of methanol to formaldehyde

The selectivity of the oxides under consideration to the oxidation of methanol to formaldehyde is shown to increase in the sequence V₂O₅–Nb₂O₅–Ta₂O₅. The same sequence corresponds to the decrease in specific activity. The activation energy of the reaction is 12 kcal/mol for V₂O₅, 14 kcal/mol for Nb₂O₅ and 22 kcal/mol for Ta₂O₅.

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, V₂O₅–Nb₂O₅–Ta₂O₅. . : V₂O₅ 12 /, Nb₂O₅ 14 / Ta₂O₅ 22 /.

     

Investigation on the TeO2–MoO3–V2O5 System. II. Properties of the obtained glasses

Some of the properties of glasses obtained in the systems TeO₂–MoO₃ and TeO₂–MoO₃–V₂O₅ had been studied. A good correlation between the properties and the phase diagram of the TeO₂–MoO₃ system was established. The glass resistance-composition function varied between 6.85 · 10⁹ ohm · cm and 2.93 · 10¹⁰ ohm · cm. The isolines of the properties (softening temperature, density, resistance at room and higher temperatures and activation energy) of the glasses obtained from the TeO₂–MoO₃–V₂O₅ system were ploted. The electrical resistance is influenced by the concentration of V₂O₅ and MoO₃ and by temperature. The glass absorption characteristics of thin layers were determined in the visible range.     

Selective oxidation of methanol on V2O5 and V2O5?MoO3 supported on montrmorillonite

Methanol oxidation on V₂O₅ and V₂O₅–MoO₃ catalysts supported on montmorillonite has been studied in the temperature range of 250–500°C. The V₂O₅–MoO₃ containing sample shows higher selectivity towards formaldehyde formation than the V₂O₅ catalyst.     

Exchange of molecular oxygen with the oxygen of an Al2(MoO4)3 catalyst

The kinetics of exchange of¹⁸O-containing molecular oxygen with the oxygen of an Al₂(MoO₄)₃ catalyst has been studied in the temperature range 579–680 °C at Torr. The activation energy of exchange is 57 kcal/mol, and the specific rate of exchange varies between 0.79×10¹¹ and 21.2×10¹¹ molec. cm^–2 sec^–1. Assumptions are made concerning the activity and selectivity of Al₂(MoO₄)₃ with respect to oxidation reactions.

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, O¹⁸, Al₂(MoO₄)₃ 579–680 °C . , 57 /, 0,79·10¹¹ 21,2·10¹¹ O₂/².. Al₂(MoO₄)₃ .

     

Investigation on the TeO2-MoO3-V2O5 System I. Phase Equilibrium

The phase equilibrium in the TeO₂-MoO₃-V₂O₅ system has been determined in air at atmospheric pressure. Differential thermal analysis (DTA), X-ray diffraction and optical microscopy were used for establishing the phase transitions. Two congruently melting ternary compounds (Te₃Mo₂V₂O₁₇ and TeMoV₂O₁₀) were identified by the above methods. Their fields of primary crystallization are entirely within the glass-formation range. The character and behaviour of the phases, the invariant points as well as the temperature maxima have been discussed. The glass-formation range correlates with the phase distribution in the system and includes all ternary invariant points.     

A study of the preparation of solid solutions in the system α-Fe2O3Al2O3

In order to elucidate the formation of precipitated iron catalysts for ammonia synthesis, the formation of solid solutions between α-Fe₂O₃ and Al₂O₃ was studied in the temperature range 500–950°C. The Al₂O₃ content in the solid solutions was found to be below 15 mole%. At temperatures of 800–950°C, solid solutions are formed at an appropriate rate. Specimens with relatively large specific surface areas are obtained at 800°C.     

Methanol oxidation to formaldehyde on bismuth phosphate-based catalysts

A bismuth (III) phosphate catalyst has been prepared by precipitation and characterized by X-ray diffraction, thermogravimetric analysis, and X-ray photoelectron and infrared spectroscopy. Its activity and selectivity toward selective methanol oxidation to formaldehyde has been studied by a flow method. A high selectivity has been found, similar to that reported for typical catalysts used for this reaction. The possible importance of the strength and covalency of the P–O bonds is discussed.     

Thermal decomposition of basic copper sulphate monohydrate

The thermal decomposition of copper sulphate hydroxide hydrate, (CuO·CuSO₄). 2Cu(OH)₂·H₂O, to copper oxysulphate and CuO was investigated by X-ray phase analysis, IR spectroscopy, complex thermal analysis and electron microscopy. The effect of water vapour and time of treatment on the formation of decomposition products with a large surface area is studied. The strong decrease in specific surface area of the precipitate (from 80 m²/g to 20 m²/g) thermally treated at a temperature above 250°C is associated with the elimination of water having a coordination bond with the Cu²⁺ ion. During this process, the interplanar distances of the crystal lattice of copper sulphate hydroxide hydrate decrease. The time of decomposition of this compound essentially affects the decrease of the specific surface area. When the decomposition proceeds in an atmosphere containing water vapour sintering processes are predominating and the phase obtained has a considerably smaller specific surface area than in cases of decomposition under dry air.     

Isotopenaustausch von molekularem Sauerstoff mit dem Sauerstoff von Ni-Molybdat

Ohne Zusammenfassung     

The Catalytic Oxidation of Hydrogen on Nickel Oxides

The catalytic oxidation of hydrogen on highly-dispersed and sintered nickel oxides has been studied by a static method and the existence of two different kinetic rcgions established. Between 0 and 100°C the initial catalytic activity was not ionary and a strong poisoning effect of the reaction product was observed at all temperatnres up to 250°C. The activation energy of the reaction based on the initial reaction rates on freshly- outgassed oxide surfaces had a low value of 1–2 kcal. mole^?1 with both preparations. Between 250 and 350°C stationary catalytic activity was observed and the activation energy of the reaction was significantly higher, 12–14 kcal . mole^?1. The change of the activation energy is discussed in terms of the participation in the reaction of oxygen species in the catalyst surface layer which have different reactivities in the two temperature regions. A close analogy is noted between the carbon monoxide and hydrogen oxidation reactions on nickel oxide and a compensation effect is illustrated for a series of oxidation reactions on the oxide.