Solid acid

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Solid acids are acids that are insoluble in the reaction medium. They are often used as heterogeneous catalysts. Many solid acids are zeolites. [1] A variety of techniques are used to quantify the strength of solid acids. [2]

Contents

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. Pile of benzoic acid crystals.jpg
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. [3] Such acids are used in cracking. [1] Many solid Brønsted acids are also employed industrially, including polystyrene sulfonate, solid phosphoric acid, niobic acid, and heteropolyoxometallates. [4]

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. [5]

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

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

Acylations are also catalyzed by solid acids. [9] [10]

Solid acids can be used as electrolytes in fuel cells. [3]

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.
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