F. Di Renzo

Heterogenized boron(III)-molybdenum(VI) mixed oxo derivatives as new bimetallic catalysts for cyclo-hexene liquid-phase epoxidation

Abstract The catalytic epoxidation of cyclohexene has been studied in the liquid phase using as catalysts molybdenum-boron mixed oxo derivatives supported on new polymeric resins. The binary system catalysts, in which the formation of B-O-Mo chemical bonds is suggested on the basis of spectral data, retain constant activity when recycled. Relative to conventional homogeneous molybdenum catalysts, no chemical degradation is observed.

Bimetallic boron(III)-molybdenum(VI) catalysts as new model compounds in the epoxidation of cyclohexene

Abstract The epoxidation of cyclohexene has been kinetically investigated in the presence of bimetallic boron(III)-molybdenum(VI) model compounds in order to determine with respect to conventional catalysts the influence of boron in terms of oxygen transfer and catalyst deactivation.

Formation and properties of the solid solution of NiO in NiMoO4

Abstract The insertion of excess nickel into the lattice of NiMoO 4 stabilizes the β-NiMoO 4 high-temperature phase at room temperature. The formation of the solid solution corresponds with an increase in the lattice parameters and results in improved reducibility of the system. Kinetically controlled separation of the solid solution takes place above 800° C.

How thermal treatment influences the phase transition of NiMoO4

Abstract Thermal treatment raises the temperature of the α→βNiMoO 4 transition and lowers the temperature of the β→α return transition. This effect is attributed to a temperature-induced relaxation of strain.

Heterogenized B(III)-Mo(VI) Mixed OXO Derivatives as New Bimetallic Catalysts for Liquid-Phase Oxygen-Transfer Reactions to Olefins

Abstract New molybdenum containing dihydroxyboryl-substituted resins have been prepared and some of their properties studied. SEM was used to assess the effect of the grafting procedure on the textural morphology of the resins. Additional informations were obtained by using an image analyzer coupled with an optical microscope. The catalytic properties of these materials have been evaluated by using cyclohexene epoxidation as a test with respect to conventional molybdenum peroxo complexes stabilized by picolinato and pyridine-2,6-dicarboxylato ligands.

Molybdenum Catalyzed Oxygen-Transfer Reactions. Heterogenization of Homogeneous Catalysts by Using New Dihydroxyboryl-Substituted Resins

Conventional molybdenum catalysts have been heterogenized by using new dihydroxyboryl-substituted resins. The specific activity of the grafted catalyst increases with increasing protonation of the grafted complex. The optimum molar ratio of molybdenum to boronic groups of the support is equal to one. No degradation of the catalyst is observed.

Thermal stability of polymer-supported boronic acids functionalized with molybdenum derivatives

Abstract Two novel molybdenum-containing dihydroxyboryl-substituted resins (used as catalysts for oxygen-transfer reactions) have been prepared and thermally analyzed. Simultaneous TG-DTA experiments were run to assess the effect of the grafting procedure on their thermal behaviour. Additional information concerning the structural modifications observed was obtained by infrared spectroscopy.

Thermal stability of substituted poly-xylylenes

The insertion of meta units in the chain of poly-p-xylylene decreases both the onset temperature of oxidative degradation and the rate of decomposition.Functionalization of the polymer with chlorine and sulphonic groups makes the chain more resistant to high temperature treatments, notwithstanding the low stability of the substituent groups.ZusammenfassungDie Einführung von Metaeinheiten in die Kette von Poly-p-xylen setzt sowohl die Einsetztemperatur des oxydativen Abbaues als auch die Zersetzungsgeschwindigkeit herab. Die Einführung von Chlor und Sulfogruppen erhöht trotz der geringen Stabilität der Substituenten die Temperaturbeständigkeit der Kette.РезюмеВведение мета-замест ителей в поли-п-ксилен приводит к уменьшени ю температуры окислительного расп ада и скорости разлож ения. Наличие в полимере су льфогруппы и хлора делает цепь более сто йкой к высокотемпера турной обработке, несмотря н а низкую устойчивост ь таких заместителей.

Spurious thermoluminescence in archaeological ceramics: A study of affecting factors

Abstract The presence of spurious emission heavily affects thermoluminescence measurements, and attempts were made to identify its causes and to circumvent or eliminate it. Samples showing spurious TL, as well as samples with an excellent thermoluminescent behaviour have been analyzed by means of DTA-TG (Differential Thermal Analysis-Thermogravimetric Analysis) and X-ray diffraction. It has been found that more than one kind of spurious thermoluminescence exists, and that calcium carbonate, magnesium carbonate, organic matter and moisture cannot be considered as a general source of spurious TL. Where spurious emission is present, the magnetic fraction of the sample is heavily affected, while in the low magnetic susceptibility fraction a reduction of such emission is obtained.

investigation of the thermal stability of CaCO3-SrCO3 solid solutions

Abstract The decomposition of solid solutions of CaCO 3 -SrCO 3 , covering the whole range of composition, has been studied by simultaneous TG-DTA. In all cases a two-stage decomposition occurs and the presence of strontium stabilizes CaCO 3 . The effect of the different amounts of calcium and strontium ions present in the samples has been separately evaluated by comparison with the results obtained by decomposing mechanical mixtures of CaCO 3 and SrCO 3 of the same composition.