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Abstract  

Nb2O5 supported on SiO2-Al2O3 were prepared with a wide loading range (2, 5, 10, 15, 20 and 25 mass%) and analyzed by simultaneous thermogravimetric (TG) and differential thermal analysis (DTA). The materials presented a phase transition close to 1364°C. This phase transition was studied by XRD, FTIR and Raman spectroscopy. Amixture of orthorhombic (T) andmonoclinic (H andM) crystalline phases was evidenced in the supported samples, which is coverage dependent, in contrast to the formation of only the monoclinic phase (H and M) when pure Nb2O5 is heated under the same conditions. These results indicate the stabilization of Nb2O5 on silica-alumina surface.

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Abstract  

The coke removal of HZSM-12 zeolite deactivated in the reaction of n-heptane cracking was studied by thermogravimetry using two multiple heating rate integral kinetics models proposed by Ozawa-Flynn-Wall and Vyazovkin to obtain the activation energy of process of thermoxidation of coke. The results obtained by both models presented excellent accordance with the related literature.

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prepared by successive deposition of copper, at first, and gallium or tin salt precursors (Cu(C 2 H 3 O 2 ) 2 ·H 2 O, Ga(NO 3 ) 3 ·H 2 O, and SnCl 4 ·5H 2 O, respectively) on a home-made silica alumina (SA) support by an adsorption-equilibrium method [ 52

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Abstract  

Gas phase formation of methyl and ethyl iodides occurs when methanol and ethanol vapors are carried by an inert gas over silica-alumina catalyst supports impregnated with potassium, sodium, cesium, or cadmium iodides at 130–180°. The efficiency of conversion of inorganic to organic iodides by different catalysts was studied using125I-labelled potassium and cadmium iodides. A mechanism of organic iodide formation in the heterogeneous reaction is postulated.

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Abstract  

The thermooxidative degradation of three models of oily soils was studied under non-isothermal conditions, at heating rates of 5, 10, 15 and 20�C min−1. Di-octyl-sebacate, as model for synthetic oil, was adsorbed on silica, alumina and silico-alumina, considered models for the inorganic micelle of a soil. For a kinetic analysis, the TG data were processed by three methods: Flynn-Wall-Ozawa, Friedman and NPK (Nomen-Sempere). The results indicate the NPK as the less speculative method that allows a separation of the elementary steps and at the same time a separation of the temperature, respective conversion dependent part of the reaction rate.

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Investigation of surface phenomena on solid catalysts by simultaneous TG and DTA

Part IV. Adsorption of ammonia on the surface of zeolites and silica-alumina gels treated with sodium hydroxide

Journal of Thermal Analysis and Calorimetry
Authors: M. Malinowski, S. Malinowski, and S. Krzyżanowski

Simultaneous TG and DTA were used to investigate the phenomena of adsorption, desorption and surface reactions of ammonia on NaX and X type exchanged zeolites and silica-alumina gels (Ketjen) treated with sodium hydroxide. On the basis of the quantitative results it is possible to give an interpretation of these surface phenomena and to establish the existence of various active centres on the surface of the catalysts. In the case of the adsorption of ammonia on silica-alumina gels, the quantity of adsorbed ammonia is much smaller than on silica-alumina gel treated with sodium hydroxide.

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Abstract  

The acid-base character of vanadium pentoxide, V2O5/SiO2 and V2O5/γ-Al2O3 catalysts has been investigated by adsorption of ammonia and sulphur dioxide using microcalorimetry. By depositing vanadium oxide on silica; new surface sites are formed which present more acid strength than bulk vanadium pentoxide and pure silica. Alumina-supported vanadium catalysts can be regarded as acidic monolayers VOx. Sulphur dioxide was found to be selective for uncovered alumina.

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Abstract  

The mesoporous molecular sieves (Al-MCM-41) are synthesized with montmorillonite as silica–alumina source by hydrothermal method. The application of Al-MCM-41 for the adsorption of Th(IV) from aqueous solution is studied by batch technique. The effects of contact time, solid content, pH, ionic strength, foreign ions, and temperature are determined, and the results indicate that the adsorption of Th(IV) to Al-MCM-41 is strongly dependent on pH values but independent of ionic strength. The adsorption isotherms are simulated by D–R and Freundlich models well. The thermodynamic parameters (ΔH 0, ΔS 0, ΔG 0) are calculated from the temperature dependent adsorption isotherms at 293, 313 and 333 K, respectively, and the results suggest that the adsorption of Th(IV) on Al-MCM-41 is a spontaneous and endothermic process. Al-MCM-41 is a suitable material for the preconcentration of Th(IV) from large volumes of aqueous solutions.

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Six oxygenated and oxynitrided glasses in the Ca-Si-Al-O-N system were prepared from pure lime, silica, alumina and aluminium nitride. Their enthalpies were measured by drop enthalpimetry with a Calvet calorimeter in a 100–1000° temperature range including glass transitionsT g. Their heat capacityC p in glassy and liquid states were deduced by derivation. TheC p variations atT g were calculated. The glass transition temperature were checked by differential calorimetric analysis.

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