Abstract
The rehydration-dehydration behavior of transition aluminas containing controlled amounts of pentahedral Al has been investigated. Microcalorimetric measurements at the early stage of surface rehydration suggest that the differential heat of water chemisorption rises with increasing crystallinity. The heat released during the dissociative chemisorption varies between 250 and 85 kJ/mol and is larger than the figure corresponding to bulk rehydroxylation (65 kJ/mol). On the average, 5.4 OH per nm{sup 2} are generated during this process. Bulk defects are cured when aluminas are contacted with saturated vapor pressure and thereafter calcined at high temperatures (600 or 750{degree}C). While surface area decreases, the crystallinity increases and 5-fold coordinated Al is transformed into a more stable coordination. 14 refs., 11 figs., 3 tabs.
Published Version
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