Silica-alumina
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'''Silica-alumina''' is also known as alumino-silicate(s). It is an oxide-like combination of [[aluminium]], [[silicon]] and [[oxygen]], and it has a major component of [[kaolin]] and [[clay]]s.
When amorphous silica-alumina is treated with strong acids such as hydrochloric and hydrofluoric acids, the material acts as a solid acid and becomes capable to promote reactions that require acid [[catalysis]]. Under other circumstances, when trivalent aluminum is forced by surrounding tetravalent silicon to crystallize in a [[tetrahedron|tetrahedral]] symmetry, a partial electron deficiency occurs at the aluminum site allowing it to act as a [[Lewis acid]], or to react with a water molecule and form a [[Conjugated system|conjugated]] [[Johannes Nicolaus Brønsted|Brønsted]]. Natural and synthetic [[zeolite]]s can be such crystalline alumino-silicates if aluminum precursors are added in the synthesis process.
See also: [[acid site]], [[catalysis]], [[catalyst]], [[active site]].
[[category: Aluminium minerals]]
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