Amorphous silica-alumina is a synthetic substance that is used as a catalyst or catalyst support.

Julius Scherzer Julius Scherzer (born 17 February 1928) is a retired chemist. He has published two scientific-technical books, and two editions of an autobiography, along with dozens of scientific papers. Early life Julius Scherzer was born on 17 February 192 ...

, Adrian J. Gruia, (1996), ''Hydrocracking Science and Technology'', CRC Press, It can be prepared in a number of ways for example: * Precipitation of hydrous alumina onto

amorphous silica Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...

hydrogel A hydrogel is a crosslinked hydrophilic polymer that does not dissolve in water. They are highly absorbent yet maintain well defined structures. These properties underpin several applications, especially in the biomedical area. Many hydrogels ar ...

* Reacting a silica sol with an alumina sol * Coprecipitation from

sodium silicate Sodium silicate is a generic name for chemical compounds with the formula or ·, such as sodium metasilicate , sodium orthosilicate , and sodium pyrosilicate . The anions are often polymeric. These compounds are generally colorless transparent ...

/ 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

NMR Nuclear magnetic resonance (NMR) is a physical phenomenon in which nuclei in a strong constant magnetic field are perturbed by a weak oscillating magnetic field (in the near field) and respond by producing an electromagnetic signal with ...

and ²⁷Al

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

Lewis acid A Lewis acid (named for the American physical chemist Gilbert N. Lewis) is a chemical species that contains an empty orbital which is capable of accepting an electron pair from a Lewis base to form a Lewis adduct. A Lewis base, then, is any sp ...

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

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

pyridinium Pyridinium refers to the cation . It is the conjugate acid of pyridine. Many related cations are known involving substituted pyridines, e.g. picolines, lutidines, collidines. They are prepared by treating pyridine with acids. As pyridine is oft ...

ion. As of 2000 examples of processes that use silica-alumina catalysts are the production of

pyridine Pyridine is a basic heterocyclic organic compound with the chemical formula . It is structurally related to benzene, with one methine group replaced by a nitrogen atom. It is a highly flammable, weakly alkaline, water-miscible liquid with a d ...

from

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 ...

formaldehyde Formaldehyde ( , ) (systematic name methanal) is a naturally occurring organic compound with the formula and structure . The pure compound is a pungent, colourless gas that polymerises spontaneously into paraformaldehyde (refer to section F ...

, steam, air and

ammonia Ammonia is an inorganic compound of nitrogen and hydrogen with the formula . A stable binary hydride, and the simplest pnictogen hydride, ammonia is a colourless gas with a distinct pungent smell. Biologically, it is a common nitrogenous was ...

John Arthur Joule, Keith Mills, 2000, Heterocyclic Chemistry, 4th edition, Blackwell Publishing, and the cracking of hydrocarbons,

References

{{reflist Catalysis Inorganic silicon compounds Acid catalysts