Amorphous silica-alumina
Amorphous silica-alumina is a synthetic substance that is used as a catalyst or catalyst support.[1] It can be prepared in a number of ways for example:[1]
- Precipitation of hydrous amorphous silica hydrogel
- Reacting a silica sol with an alumina sol
- Coprecipitation from sodium silicate / aluminium salt solution
Water-soluble contaminants, e.g. sodium salts, are removed by washing.[1]
Some of the alumina is present in tetrahedral coordination as shown by NMR studies 29Si
NMR[2]
Amorphous silica-alumina contains sites which are termed
Lewis acid sites it forms complexes and on the Brønsted sites it adsorbs as the pyridinium ion.[3]
As of 2000 examples of processes that use silica-alumina catalysts are the production of pyridine from crotonaldehyde, formaldehyde, steam, air and ammonia[4] and the cracking of hydrocarbons,[1]
References
- ^ ISBN 0-8247-9760-4
- ISBN 0-306-44189-6
- ISBN 0-632-05453-0