Abstract
The effect of drying of rare-earth (RE) exchanged Na-Y-zeolites on the formation of acid sites was studied using well-known analytical techniques as the Karl Fischer titration and the LiAlH 4 reaction. It was found that during drying of RE-Y-zeolite from total water content of 30-14% d.b. hydrated RE ions move from the supercages into the sodalite cages, while the formation of acidic hydroxyl groups takes place during zeolite drying from total water contents of 14-10% d.b. Each RE ion in the zeolite produces one acidic hydroxyl group in the supercages. Prolonged drying of RE-Y-zeolite results in dehydroxylation. For RE-Y-zeolite with a SiO 2 Al 2O 3 molar ratio of 5.0, and 75% of the sodium exchanged by RE, the density of acidic OH groups (Brönsted sites) was found to be 7 × 10 20 sites/g, which is about 70 times higher than for amorphous silica-alumina catalyst.
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