Solid acid

[1] A variety of techniques are used to quantify the strength of solid acids.

[2] Examples of inorganic solid acids include silico-aluminates (zeolites, alumina, silico-aluminophosphate), and sulfated zirconia.

Many transition metal oxides are acidic, including titania, zirconia, and niobia.

[5] One large scale application is alkylation, e.g., the combination of benzene and ethylene to give ethylbenzene.

[6][7][8] Many alkylamines are prepared by amination of alcohols, catalyzed by solid acids.

Crystalline benzoic acid shown here is a solid and an acid, but, in the context of this article, it is not a "solid acid", which are polymeric materials and typically stronger acids.
Zeolite, ZSM-5 is widely used as a solid acid catalyst.