Showing papers by "Abd El-Aziz A. Said published in 1992"

Influence of Al2O3 support on the thermal decomposition of ammonium metavanadate

Abstract: The thermal decomposition of ammonium metavanadate (AMV) supported on aluminium oxide was investigated using differential thermal analysis, thermogravimetry, infrared and X-ray diffraction techniques. The results obtained revealed that the decomposition of AMV supported on alumina proceeded in three decomposition stages. Alumina was found to enhance only the decomposition of the intermediate ammonium hexavanadate to produce V2O5. In addition, the values of activation energies of the various decomposition stages were accompanied by a significant decrease on decreasing the concentration of AMV. The infrared spectra indicated that the band corresponds to the surface site V=O strongly affected by the presence of Al2O3. Finally, an interaction between Al2O3 and V2O5 occurred at 660 °C giving well-crystallized AlVO4.

Alginate Polyelectrolyte Ionotropic Gels-XVI. Kinetics and Chemical Equilibria Studies for Heterogeneous Ion Exchange of Polyvalent Metal Ions in Alginate Gel Complexes

Abstract: The kinetics or chemical equilibria of exchange of Ca(II), Sr(II), Ba(I), Zn(II), Cd(II), Al(III), Fe(III), Se(IV), Ce(IV) and Th(IV) counter ions in alginate gel complexes by H+ ions have been investigated titrimetrically and conductimetrically at a constant ionic strength of 0.1 mol/dm3. The thermodynamic parameters have been evaluated and are discussed in terms of ionic radii and polarizability of the metal ions, coordination geometry, and stability of the gel complexes.

Role of the Structure and Electronic Properties of Fe2O3-MoO3 Catalyst on the Dehydration of Isopropyl Alcohol

Abstract: Molybdenum oxide catalysts doped or mixed with (1–50) mol% Fe3+ ions were prepared. The structure of the original samples and calcined at 400 °C were characterized using DTA, X-ray diffraction, and IR spectra. The measurements of the electrical conductivity of calcined samples with and without isopropyl alcohol revealed that the conductance increases on increasing the content of Fe3+ ions up to 50 mol%. The activation energies of charge carriers were determined in presence and absence of alcohol. The catalytic dehydration of isopropyl alcohol was carried out at 250 °C using flow system. The results obtained showed that the doped or mixed catalysts are active and selective towards propene formation. However, the catalyst containing 40 mol% Fe3+ ions exhibited the highest activity and selectivity. Correlations were attempted between the catalyst composition and their electronic and catalytic properties. Probable mechanism for the dehydration process is proposed in terms of surface active sites.

Thermal decomposition of sodium azide catalysed by NiO-Co3O4 solids

Abstract: The thermal decomposition of NaN3 to its component elements has long been used as a method for the production of very pure nitrogen. The decomposition characteristics are variable and depend on parameters such as the particle size and shape, heating rate, defect concentration and purity. The catalysed thermal decomposition of NaN 3 has been found to be remarkably sensitive to metal oxide additives. Recently the effect of Mn 2+ doping on the thermal decomposition of sodium azide has been studied [1]. It was found that Mn 2÷ is acting as an electron donor in composition with some intermediate reaction occuring. A literature survey indicated that insufficient attention has been paid to studying the thermal decomposition of NaN3 in the presence of mixed oxide catalysts. Thus, the work reported here was devoted to the study o f the effect of the NiO-C0304 system on the thermal decomposition of sodium azide. The catatysed decomposition of H202 was employed to support our results. The starting materials were Analar-grade chemicals. A series of the NiO-C0304 system in different ratios, 0 .1-50 mol %, were prepared by the impregnation method. The calculated amount of Co(OH)2 (prepared according to the method in [2]) was admixed with nickel basic carbonate (NBC) and some doubly distilled water was added to form a pas te . The paste was dried over a water bath with occasional mixing and was further dried in air at 100 °C to constant weight. The catalysts produced were ground with NaN3 ( 1 0 w t % ) in an agate mortar for thermal decomposition experiments. Differential thermal analysis (DTA) studies were carried out using a Shimadzu DT-40 computerized thermal analysis system. The rate of heating of the samples was kept at 5 °C rain -~ and a 5 mg sample of each solid specimen was analysed, in each case using static air atmosphere, o~-Alumina powder for D T A standard material was applied as a reference. The kinetics of catalytic decomposition of H202 in solution were followed by measuring the volume of oxygen liberated at atmosphere pressure using the gasometric technique [3]. The experiments were carried out at 25 °C using 100 mg catalyst and 0.25 M H202. The surface excess oxygen was estimated by the hydrazine method using the gasometric technique [3]. The D T A curves of the catalytic decomposition of NaN 3 by the system NiO-Co304 in different ratios are shown in Fig. i and the maximum decomposition g