{{Short description|Acid that is insoluble in the reaction medium}} {{Acids and bases}} '''Solid acids''' are acids that are insoluble in the reaction medium. They are often used as heterogeneous catalysts. Many solid acids are zeolites.<ref name=Kresge/> A variety of techniques are used to quantify the strength of solid acids.<ref>{{cite journal |doi=10.1021/acs.chemrev.7b00289 |title=<sup>31</sup>P NMR Chemical Shifts of Phosphorus Probes as Reliable and Practical Acidity Scales for Solid and Liquid Catalysts |date=2017 |last1=Zheng |first1=Anmin |last2=Liu |first2=Shang-Bin |last3=Deng |first3=Feng |journal=Chemical Reviews |volume=117 |issue=19 |pages=12475–12531 |pmid=28952317 }}</ref>
==Examples== thumb|left|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.
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.<ref name=":1">{{Cite journal|last1=Boysen|first1=Dane A.|last2=Uda|first2=Tetsuya|last3=Chisholm|first3=Calum R. I.|last4=Haile|first4=Sossina M.|date=2004-01-02|title=High-Performance Solid Acid Fuel Cells Through Humidity Stabilization|journal=Science|language=en|volume=303|issue=5654|pages=68–70|doi=10.1126/science.1090920|issn=0036-8075|pmid=14631049|bibcode=2004Sci...303...68B|s2cid=10829089 |url=https://www.science.org/cms/asset/e6d3515e-2142-430a-bf80-4cecb2346943/pap.pdf}}</ref> Such acids are used in cracking.<ref name=Kresge>{{cite book |doi=10.1002/0471238961.1315120511210812.a01.pub2 |chapter=Molecular Sieves |title=Kirk-Othmer Encyclopedia of Chemical Technology |date=2004 |last1=Kresge |first1=Charles T. |last2=Dhingra |first2=Sandeep S. |isbn=978-0-471-48494-3 }}</ref> Many solid Brønsted acids are also employed industrially, including polystyrene sulfonate, solid phosphoric acid, niobic acid, and heteropolyoxometallates.<ref>{{Cite journal|last=Busca|first=Guido|date=2007-11-01|title=Acid Catalysts in Industrial Hydrocarbon Chemistry|url=https://doi.org/10.1021/cr068042e|journal=Chemical Reviews|volume=107|issue=11|pages=5366–5410|doi=10.1021/cr068042e|pmid=17973436 |issn=0009-2665|url-access=subscription}}</ref>
== Applications == 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.<ref name=":0">{{Cite web|title=Solid Acid Catalysis: From Fundamentals to Applications|url=https://www.crcpress.com/Solid-Acid-Catalysis-From-Fundamentals-to-Applications/Hattori-Ono/p/book/9789814463287|access-date=2016-09-15|website=CRC Press}}</ref>
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.<ref>{{Citation|last1=Röper|first1=Michael|title=Acylation and Alkylation|date=15 June 2000|url=https://onlinelibrary.wiley.com/doi/abs/10.1002/14356007.a01_185|encyclopedia=Ullmann's Encyclopedia of Industrial Chemistry|publisher=John Wiley & Sons, Ltd|language=en|doi=10.1002/14356007.a01_185|isbn=978-3-527-30673-2|access-date=2022-01-18|last2=Gehrer|first2=Eugen|last3=Narbeshuber|first3=Thomas|last4=Siegel|first4=Wolfgang|url-access=subscription}}</ref><ref>{{cite journal |doi=10.1021/cr00035a006 |title=Inorganic Solid Acids and Their Use in Acid-Catalyzed Hydrocarbon Reactions |date=1995 |last1=Corma |first1=A. |journal=Chemical Reviews |volume=95 |issue=3 |pages=559–614 }}</ref><ref>{{cite journal |doi=10.1021/cr068042e |title=Acid Catalysts in Industrial Hydrocarbon Chemistry |date=2007 |last1=Busca |first1=Guido |journal=Chemical Reviews |volume=107 |issue=11 |pages=5366–5410 |pmid=17973436 }}</ref> Many alkylamines are prepared by amination of alcohols, catalyzed by solid acids. [[File:Zeolite-ZSM-5-vdW.png|thumb|right|Zeolite, ZSM-5 is widely used as a solid acid catalyst.]]
Acylations are also catalyzed by solid acids.<ref>{{cite journal |doi=10.1021/cr040695c |title=Use of Solid Catalysts in Friedel−Crafts Acylation Reactions |date=2006 |last1=Sartori |first1=Giovanni |last2=Maggi |first2=Raimondo |journal=Chemical Reviews |volume=106 |issue=3 |pages=1077–1104 |pmid=16522017 }}</ref><ref>{{cite journal |doi=10.1021/cr100375z |title=Update 1 of: Use of Solid Catalysts in Friedel−Crafts Acylation Reactions |date=2011 |last1=Sartori |first1=Giovanni |last2=Maggi |first2=Raimondo |journal=Chemical Reviews |volume=111 |issue=5 |pages=PR181–PR214 |pmid=21488695 }}</ref>
Solid acids can be used as electrolytes in fuel cells.<ref name=":1" />
== References == {{Reflist}}
Category:Acids Category:Acid–base chemistry Category:Acid catalysts