Solid acid

Solid acids are acids that are insoluble in the reaction medium. They are often used as heterogeneous catalysts. Many solid acids are zeolites. A variety of techniques are used to quantify the strength of solid acids.

Examples

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. Such acids are used in cracking. Many solid Brønsted acids are also employed industrially, including polystyrene sulfonate, solid phosphoric acid, niobic acid, and heteropolyoxometallates.

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.

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. Many alkylamines are prepared by amination of alcohols, catalyzed by solid acids.

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

Acylations are also catalyzed by solid acids.

Solid acids can be used as electrolytes in fuel cells.

References

  1. 1 2 Kresge, Charles T.; Dhingra, Sandeep S. (2004). "Molecular Sieves". Kirk-Othmer Encyclopedia of Chemical Technology. doi:10.1002/0471238961.1315120511210812.a01.pub2. ISBN 978-0-471-48494-3.
  2. ↑ Zheng, Anmin; Liu, Shang-Bin; Deng, Feng (2017). "31P NMR Chemical Shifts of Phosphorus Probes as Reliable and Practical Acidity Scales for Solid and Liquid Catalysts". Chemical Reviews. 117 (19): 12475–12531. doi:10.1021/acs.chemrev.7b00289. PMID 28952317.
  3. 1 2 Boysen, Dane A.; Uda, Tetsuya; Chisholm, Calum R. I.; Haile, Sossina M. (2004-01-02). "High-Performance Solid Acid Fuel Cells Through Humidity Stabilization" (PDF). Science. 303 (5654): 68–70. Bibcode:2004Sci...303...68B. doi:10.1126/science.1090920. ISSN 0036-8075. PMID 14631049. S2CID 10829089.
  4. ↑ Busca, Guido (2007-11-01). "Acid Catalysts in Industrial Hydrocarbon Chemistry". Chemical Reviews. 107 (11): 5366–5410. doi:10.1021/cr068042e. ISSN 0009-2665. PMID 17973436.
  5. ↑ "Solid Acid Catalysis: From Fundamentals to Applications". CRC Press. Retrieved 2016-09-15.
  6. ↑ Röper, Michael; Gehrer, Eugen; Narbeshuber, Thomas; Siegel, Wolfgang (15 June 2000), "Acylation and Alkylation", Ullmann's Encyclopedia of Industrial Chemistry, John Wiley & Sons, Ltd, doi:10.1002/14356007.a01_185, ISBN 978-3-527-30673-2, retrieved 2022-01-18
  7. ↑ Corma, A. (1995). "Inorganic Solid Acids and Their Use in Acid-Catalyzed Hydrocarbon Reactions". Chemical Reviews. 95 (3): 559–614. doi:10.1021/cr00035a006.
  8. ↑ Busca, Guido (2007). "Acid Catalysts in Industrial Hydrocarbon Chemistry". Chemical Reviews. 107 (11): 5366–5410. doi:10.1021/cr068042e. PMID 17973436.
  9. ↑ Sartori, Giovanni; Maggi, Raimondo (2006). "Use of Solid Catalysts in Friedel−Crafts Acylation Reactions". Chemical Reviews. 106 (3): 1077–1104. doi:10.1021/cr040695c. PMID 16522017.
  10. ↑ Sartori, Giovanni; Maggi, Raimondo (2011). "Update 1 of: Use of Solid Catalysts in Friedel−Crafts Acylation Reactions". Chemical Reviews. 111 (5): PR181–PR214. doi:10.1021/cr100375z. PMID 21488695.