Silicotungstic_acid

Silicotungstic acid

Silicotungstic acid

Chemical compound

Silicotungstic acid or tungstosilicic acid is a heteropoly acid with the chemical formula H4[SiW12O40]. It forms hydrates H4[SiW12O40]·nH2O. In freshly prepared samples, n is approximately 29, but after prolonged desiccation, n = 6.[1] It is a white solid although impure samples appear yellow. It is used as a catalyst in the chemical industry.[2]

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Applications

Silicotungstic acid is used to manufacture ethyl acetate by the alkylation of acetic acid by ethylene:

C2H4 + CH3CO2H → CH3CO2C2H5

It has also been commercialized for the oxidation of ethylene to acetic acid:[2]

C2H4 + O2 → CH3CO2H

This route is claimed as a "greener" than methanol carbonylation. The heteropoly acid is dispersed on silica gel at 20-30 wt% to maximize catalytic ability.

It has also recently been proposed as a mediator in production of hydrogen through electrolysis of water by a process that would reduce the danger of explosion while allowing efficient hydrogen production at low current densities, conducive to hydrogen production using renewable energy.[3]

Synthesis and structure

The free acid is produced by combining sodium silicate and tungsten trioxide followed treatment of the mixture with hydrochloric acid.[1][4] The polyoxo cluster adopts a Keggin structure, with Td point group symmetry.

Hazards

Silicotungstic acid is an irritating and odorless substance.

References

  1. [1]
    Dias, J. A.; Dias, S. C. L.; Caliman, E. (2014). "Keggin Structure Polyoxometalates". Keggin Structure Polyoxoometalates. Inorganic Syntheses. Vol. 36. p. 210-217. doi:10.1002/9781118744994.ch39. ISBN 9781118744994.
  2. [2]
    Misono, Makoto (2009). "Recent progress in the practical applications of heteropolyacid and perovskite catalysts: Catalytic technology for the sustainable society". Catalysis Today. 144 (3–4): 285–291. doi:10.1016/j.cattod.2008.10.054.
  3. [3]
    Rausch, Benjamin; Symes, Mark D.; Chisholm, Greig; Cronin, Leroy (September 12, 2014). "Decoupled catalytic hydrogen evolution from a molecular metal oxide redox mediator in water splitting". Science. 345 (6202). American Association for the Advancement of Science: 1326–1330. Bibcode:2014Sci...345.1326R. doi:10.1126/science.1257443. PMID 25214625. S2CID 20572410.
  4. [4]
    Handbook of Preparative Inorganic Chemistry, 2nd Ed. Edited by G. Brauer, Academic Press, 1963, NY.


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