Amorphous silica alumina is a synthetic substance that is used as a catalyst or catalyst support. It can be prepared in a number of ways for example:

• Precipitation of hydrous alumina onto amorphous silica hydrogel
• Reacting a silica sol
  Sol
  Soľ is a village and municipality in Vranov nad Topľou District in the Prešov Region of eastern Slovakia.-Geography:The municipality lies at an altitude of 140 metres and covers an area of 10.286 km². It has a population of about 2,293 people....
  
   with an alumina sol
• Coprecipitation from sodium silicate
  Sodium silicate
  Sodium silicate is the common name for a compound sodium metasilicate, Na2SiO3, also known as water glass or liquid glass. It is available in aqueous solution and in solid form and is used in cements, passive fire protection, refractories, textile and lumber processing, and automobiles...
  
   / aluminium salt solution

Water soluble contaminants e.g. sodium salts are removed by washing.

Some of the alumina is present in tetrahedral coordination as shown by NMR studies ²⁹Si MAS

Magic angle spinning

In nuclear magnetic resonance, magic angle spinning is a technique often used to perform experiments in solid-state NMR spectroscopy.By spinning the sample at the magic angle θm In nuclear magnetic resonance, magic angle spinning (MAS) is a technique often used to perform experiments in...

NMR and ²⁷Al NMR 

Amorphous silica-alumina contains sites which are termed Brønsted acid (or protic) sites,with an ionizable hydrogen atom, and Lewis acid

Lewis acid

]The term Lewis acid refers to a definition of acid published by Gilbert N. Lewis in 1923, specifically: An acid substance is one which can employ a lone pair from another molecule in completing the stable group of one of its own atoms. Thus, H+ is a Lewis acid, since it can accept a lone pair,...

 (aprotic), electron accepting sites and these different types of acidic site can be distinguished by the ways in which, say, pyridine attaches. On Lewis acid

Lewis acid

]The term Lewis acid refers to a definition of acid published by Gilbert N. Lewis in 1923, specifically: An acid substance is one which can employ a lone pair from another molecule in completing the stable group of one of its own atoms. Thus, H+ is a Lewis acid, since it can accept a lone pair,...

 sites it forms complexes and on the Brønsted sites it adsorbs as the pyridinium

Pyridinium

Pyridinium refers to the cationic form of pyridine. This can either be due to protonation of the ring nitrogen or because of addition of a substituent to the ring nitrogen, typically via alkylation. The lone pair of electrons on the nitrogen atom of pyridine is not delocalized, and thus pyridine...

 ion.
Examples of processes that use silica-alumina catalysts are the production of pyridine

Pyridine

Pyridine is a basic heterocyclic organic compound with the chemical formula C5H5N. It is structurally related to benzene, with one C-H group replaced by a nitrogen atom...

 from crotonaldehyde

Crotonaldehyde

Crotonaldehyde is a chemical compound with the formula CH3CH=CHCHO. The compound is usually sold as a mixture of the E- and Z-isomers, which differ with respect to the relative position of the methyl and formyl groups. The E-isomer is more common...

, formaldehyde

Formaldehyde

Formaldehyde is an organic compound with the formula CH2O. It is the simplest aldehyde, hence its systematic name methanal.Formaldehyde is a colorless gas with a characteristic pungent odor. It is an important precursor to many other chemical compounds, especially for polymers...

, steam, air and ammonia

Ammonia

Ammonia is a compound of nitrogen and hydrogen with the formula . It is a colourless gas with a characteristic pungent odour. Ammonia contributes significantly to the nutritional needs of terrestrial organisms by serving as a precursor to food and fertilizers. Ammonia, either directly or...

and the cracking of hydrocarbons,