A.M. Youssef

Moisture sorption by modified-activated carbons

Abstract Modified activated carbons were prepared by the partial oxidation of activated maghara coal with concentrated nitric acid and potassium permanganate. This treatment fixes more oxygen on the carbon surface leading thus to the formation of carbon-oxygen complexes which act as primary centers for water adsorption. Not only the number of oxygen complexes that can determine the water adsorption properties but the pore size may be considered as another factor. The oxygen complexes outgassed as carbon dioxide can be qualitatively determined by neutralization with sodium hydroxide. These oxygen complexes are responsible for the irreversibly adsorbed water.

Adsorption properties of carbons in relation to the various methods of activation

Abstract The absorption of nitrogen at -196 °C, of carbon dioxide at 25 °C and of water vapour at 35 °C has been measured on non-activated, zinc chloride-activated and oxidizing gas-activated carbons. The following conclusions are drawn. The adsorption of nitrogen by ultrafine microporous carbons is controlled by activated diffusion. The surface area of microporous carbon has no significance because micropore filling rather than surface coverage is expected to take place. For mesoporous carbons, nitrogen areas are comparable with carbon dioxide areas, indicating that nitrogen can be satisfactorily used to measure the surface area of these carbons. Water adsorption is not a measure of the carbon surface area but is related to the chemistry of the carbon surface.

Studies on the mixed oxide catalyst Al2O3-Cr2O3 I. Surface properties

Abstract The surface properties of pure alumina and its calcination products and of alumina-chromia mixed gels calcined in the temperature range 300–750 °C were studied by the adsorption of nitrogen at -195 °C. The surface areas, micropore volumes and the pore volume distributions were evaluated for the calcination products. With the rise of calcination temperature above 500 °C, the surface areas decreased considerably while the mean pore radius increased. Sintering at temperatures higher than 500 °C resulted in pore widening. Chromia inhibited the sintering of alumina when present in amounts of 5 or 15 mol.%.

Determination of small surface areas by krypton adsorption

The adsorption of krypton at 77 K was measured on ten kernels (i.e. uranium dioxide samples coated with silicon carbide). The adsorption data were interpreted by the application of both the Brunauer-Emmett-Teller and Dubinin-Radushkevich (DR) models. Application of the DR isotherm generally gave higher surface areas. Two more important quantities which are related to the nature of the solid surface—the pore dimension and the average binding energy—were obtained by applying the DR equation.

Molecular sieve carbons from agricultural wastes

Abstract Activated charcoals were obtained from agricultural wastes (date stones and bagasse) by impregnation with zinc chloride and by steam gasification. Non-activated charcoals exhibit molecular sieve properties but their capacities are very low. Zinc chloride activation and steam activation to low burnouts improve the adsorption capacity and keep the molecular sieve action operating. However, steam gasification to high burnouts is accompanied by a loss of the molecular sieve property, leaving the pore structure accesible to adsorbates of various sizes.

The activity and selectivity of chromia-alumina catalysts: The influence of reaction temperature on isopropanol conversion

Abstract The activity and selectivity of chromia, alumina and mixed chromia-alumina catalysts in the conversion of isopropanol in the temperature range 200–360 °C were studied as functions of the reaction temperature. The activity and selectivity of pure alumina show no dependence on the calcination temperature whereas the activity and selectivity of pure chromia are sensitive to it. In general, the activity and selectivity of the catalysts investigated depend markedly on the reaction temperature and on the nature of the condensation products formed on the catalyst surface.

Studies of dehydrogenating catalysts I: Structural and textural properties of some dehydrogenating catalysts

Abstract The structure of metal-metal oxide dehydrogenating catalysts depends on the metal content. Reduction with hydrogen is incomplete for catalysts with a high metal content and severe conditions may be required. Molybdenum metal and the lower valence state oxide Mo9O26 were detected in Mo-Al2O3 catalysts. A thin skin of aluminate is formed on Ni-Al2O3 and Co-Al2O3 catalysts; this retards their reduction with hydrogen. The deposition of the reduced metal or the formation of metal oxide or spinel on the alumina are associated with significant variations in the textural properties (surface area and pore volume distribution).

Selective adsorption of NaX zeolite and its scandium-substituted zeolites

Abstract The adsorption of argon and nitrogen at -195% °C, of CO2 at -78 °C and of benzene, cyclohexane, methanol and water vapour at 30 °C was measured on NaX zeolite and on its scandium-substituted zeolites. In all cases, cyclohexane measures the lowest adsorption capacity and water vapour measures the highest. The adsorption capacity depends on the extent of cation replacement and on the nature and mode of interaction between the adsorbed molecules and the surface of the zeolites. The lattice contraction due to the substitution of sodium ions by smaller scandium ions unexpectedly resulted in an increase in the adsorption capacity of all the adsorbates investigated.

Changes in the sorption properties of coal and cokes due to storage in ambient air

Abstract The sorption of water vapour, methanol, benzene and nitrogen on Egyptian Maghara coal and its carbonization products, stored either in ambient air or in sealed evacuated tubes, was studied. The results were compared with the results of tests performed on the same samples in 1965 when they were originally prepared for a previous investigation. The changes in the sorption properties were correlated with the extent of oxidation as determined by the variation in the base neutralization capacity. The fixation of oxygen on the surface of coals and cokes stored in ambient air caused significant variations in their sorption properties. The variations follow the order nitrogen > water > methanol > benzene. An explanation for these variations is presented.

Reforming activity in relation to the textural properties of the catalyst

Abstract Ni-Al2O3 catalysts containing various weight percentages of nickel were prepared together with other metal-alumina catalysts. Nickel catalysts were also prepared using a mixture of kaolin and dolomite as the carrier. The activities of these catalysts in reforming natural gas with steam were determined and were correlated with their textural properties evaluated from nitrogen adsorption results. The activity of the metal-alumina catalysts follows the order Ni-Al2O3 > Co-Al2O3 > V-Al2O3 > W-Al2O3. The surface area and total pore volume are not important factors in determining the reforming activity. More important are the pore volume distribution and the dispersion of the active metal on the surface of the support.