Solid acid

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Solid acids are acids that do not dissolve in the reaction medium. They are often used in heterogeneous catalysts.


Examples include oxides, which function as Lewis acids including silico-aluminates (zeolites, alumina, silico-alumino-phosphate), and sulfated zirconia. Many transition metal oxides are acidic, including titania, zirconia, and niobia.[1] Such acids are used in cracking. Many solid Brønsted acids are also employed industrially, including sulfonated polystyrene, solid phosphoric acid, niobic acid, and heteropolyoxometallates.[2]


Solid acids are used in catalysis in many industrial chemical processes, from large-scale catalytic cracking in petroleum refining to the synthesis of various fine chemicals.[3]

One large scale application is alkylation, e.g., the combination of benzene and ethylene to give ethylbenzene. Another application is the rearrangement of cyclohexanone oxime to caprolactam.[4] Many alkylamines are prepared by amination of alcohols, catalyzed by solid acids.

Zeolite, ZSM-5 is widely used as a solid acid catalyst.

Solid acids can be used as electrolytes in fuel cells.[1]


  1. ^ a b Boysen, Dane A.; Uda, Tetsuya; Chisholm, Calum R. I.; Haile, Sossina M. (2004-01-02). "High-Performance Solid Acid Fuel Cells Through Humidity Stabilization". Science. 303 (5654): 68–70. doi:10.1126/science.1090920. ISSN 0036-8075. PMID 14631049. 
  2. ^ Busca, Guido "Acid Catalysts in Industrial Hydrocarbon Chemistry" Chemical Reviews 2007, volume 107, 5366-5410. doi:10.1021/cr068042e
  3. ^ "Solid Acid Catalysis: From Fundamentals to Applications". CRC Press. Retrieved 2016-09-15. 
  4. ^ Michael Röper, Eugen Gehrer, Thomas Narbeshuber, Wolfgang Siegel "Acylation and Alkylation" in Ullmann's Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2000. doi:10.1002/14356007.a01_185