Silicotungstic acid or tungstosilicic acid is a heteropoly acid with the chemical formula . It forms hydrates . In freshly prepared samples, n is approximately 29, but after prolonged desiccation, n = 6. It is a white solid although impure samples appear yellow. It is used as a catalyst in the chemical industry.[1]
Silicotungstic acid is used to manufacture ethyl acetate by the alkylation of acetic acid by ethylene:
It has also been commercialized for the oxidation of ethylene to acetic acid:[1]
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.[2]
The free acid is produced by combining sodium silicate and tungsten trioxide followed treatment of the mixture with hydrochloric acid.[3] [4] The polyoxo cluster adopts a Keggin structure, with Td point group symmetry.
Silicotungstic acid is an irritating and odorless substance.