[en] The phase equilibrium diagram of the system TeO₂-MoO₃ has been studied using differential thermal analysis. It is shown that a new congruently melting phase, Te₂MoO₇, is formed (melting point 551 ⁰C). The eutectics were found at 526 ⁰C near 55.5 mol% TeO₂ and at 543 ⁰C near 67.5 mol% TeO₂. The compound Te₂MoO₇ shows glass-forming tendency. (author)

[en] The rather complex mixed oxide system TeO₂-Ta₂O₅ has been studied by means of x-ray powder diffraction, at room temperature, using samples prepared in the interval of 500 to 900 ⁰C. Four whitish coloured stable mixed oxide phases have been found, corresponding to the formulas 3TeO₂ . Ta₂O₅, 7TeO₂ . 3Ta₂O₅ and 2TeO₂ . Ta₂O₅ ( in a low and high temperature form). The latter compound is not isostructural with 2TeO₂ . V₂O₅. Approximate stability ranges are: up to 850 ⁰C, 3TeO₂ . Ta₂O₅; 700 - 900 ⁰C, 7TeO₂ . 3Ta₂O₅; 850 ⁰C and higher, 2TeO₂ . Ta₂O₅ (H); 700 - 800 ⁰C, 2TeO₂ . Ta₂O₅ (L). (author)

[en] The system Ce-Mo-O has been examined for ternary compound formation arising from the interaction of Ce(NO₃)₃.6H₂O and (NH₄)₆Mo₇O₂₄.4H₂O between 500 and 850 ⁰C in air. By variation of the Ce/Mo ratio and the oxidation state of cerium, the following compounds were obtained: β-Ce₂Mo₃O₁₃, α- and β-Ce₂Mo₄O₁₅ and Ce₈Mo₁₂O₄₉ (Ce₂Mo₃Osub(12.25)). (Auth.)

[en] The solid-state reaction between TeO₂ and NbO₅ was studied by means of X-ray powder diffraction, at room temperature, using samples prepared in the interval of 500 ⁰C to 850 ⁰C. Several whitish coloured stable mixed oxide phases have been found, corresponding to the formulas TeO₂ . 3 Nb₂O₅, 3 TeO₂ . Nb₂O₅ and 4 TeO₂ . Nb₂O₅. The phase distribution differs from that in TeO₂-V₂O₅ and TeO₂-Ta₂O₅ systems and no isomorphism relationships with phases in these oxide systems have been noticed. (author)

[en] The solid-state reaction between SeO₂ and V₂O₅ in inert atmosphere was studied by X-ray diffraction techniques, and compound formation was observed. The dark red reaction product Se₂V₂O₉ is not isostructural with the corresponding tellurium compound. Above about 400⁰C the substance decomposes into its component oxides. (author)

[en] Ammoxidation of propylene to acrylonitrile (ACN) was investigated over various silica-supported (Te,Ce)O catalysts at 360 and 440⁰C. The binary oxide system used consists of a single nonstoichiometric fluorite-type phase α-(Ce,Te)O₂ up to about 80 mole% TeO₂ and a tellurium-saturated solid solution β-(Ce,Te)O₂ at higher tellurium concentrations. The ACN yield varies almost linearly with the tellurium content of (Ce,Te)O₂. The β-(Ce,Te)O₂ phase is the most active component of the system (propylene conversion and ACN selectivity at 440 C of 76.7 and 74%, respectively) and is slightly more selective to ACN than α-Te0₂. Tellurium reduces the overoxidation properties of cerium and selective oxidation occurs through Te(IV)-bonded oxygen

No abstract available

[en] The solid state reaction between TeO₂ and SeO₂ in inert atmosphere was studied by X-ray diffraction techniques and compound formation was observed. The pale-white reaction product α-TeSeO₄, obtained at 300 ⁰C, is not isostructural with the component oxides. The substance is stable at room temperature under exclusion of moisture but decomposes above about 320 ⁰C in dry atmosphere. Evidence is given for the formation of 3 TeO₂.SeO₂.nH₂O and other hydrated mixed oxides in the system TeO₂-SeO₂-H₂O; d-spacings are reported. (author)

[en] Phase equilibria in the (Ce, Te)O system, originating from interaction between Ce(NO₃)₃.6H₂O and H₆TeO₆ followed by calcination up to 700 ⁰C, have been studied by methods of physico-chemical analysis (DTA, TGA, X-ray diffraction, XPS). Evidence is given for the formation of non-stoichiometric fluorite-type mixed-crystals (Ce, Te)O₂ in the 450 - 500 ⁰C range, up to a tellurium solubility limit corresponding to a lattice parameter of 5.666(3) A. At higher temperatures (500 - 600 ⁰C) Ce₂(TeO₄)₃ is stable and Ce(TeO₃)₂ is formed above about 550 ⁰C. Ce(TeO₃)₂ is also obtained by solid-state interaction between CeO₂ nad TeO₂ and is identical with the previously reported CeTe₃O₈ phase. Preparative conditions of the various compounds are described and X-ray diffraction data are reported. The TeO₂-CeO₂ phase diagram was established in the temperature interval from about 650 to 1100 ⁰C. Eutectic temperatures are 689 ⁰C and 794 ⁰C at the TeO₂ and CeO₂-rich sides. (author)

[en] The thermal degradation products of Ce₂(MoO₄)₃ . 4.5 H₂O were studied by means of thermogravimetric analysis, X-ray diffraction and spectroscopical methods under rigorously controlled conditions. From the crystalline hydrate various amorphous and crystalline products with a Ce/Mo ratio 2/3 may be obtained by variation of the thermal and atmospheric conditions. In nitrogen, the decomposition pattern leads directly to Ce₂(MoO₄)₃ with a pseudo-scheelite structure, in air or oxygen atmosphere oxidation takes place below 450⁰C, resulting in amorphous or crystalline ceric molybdate, γ-Ce₂Mo₃O₁₃. About above 500⁰C both in inert and oxidizing conditions oxygen desorption leads to Ce₂(MoO₄)₃. Reoxidation of this compound to Ce₂Mo₃Osub(12.25) is possible at higher temperatures, giving also CeO₂ by oxidative degradation. The thermal stability of γ-CeMo₃O₁₃ differs from other such substances with the same stoichiometric composition. (author)