Silico tungstic acid

Neutralization of a silico-tungstic acid solution in the presence of Ca, Fe, and Mn " " ions in laboratory experiments yields successive precipitation of Fe, Mn, and Ca tungstate. This order parallels a frequently observed mineral paragenesis, where ferberite, huebnerite, and scheelite are deposited successively. 

H4SiWi204o-a H20 Silico tungstic acid H4Si04l2W0s- rHjO 12-Tungstosilicic acid... 

B. Tazi, O. Savadogo, Parameters of PEM fuel cells based on new membranes fabricated from Nafion , silico-tungstic acid and thiophene. Electrochemical Acta 45 (2000) 4329-4339. 

Furthermore, an industrial process using this method of esterification successfully produced ethylacetate from ethylene and acetic acid in a gas-phase process that was catalyzed by silico tungstic acid supported on silica (Fig. 8) (39,40). Currently, ethyl acetate is prepared via the Wacker process, which uses PdCl2/CuCl2 and results in serious economic and environmental drawbacks, including the use and subsequent disposal of the HCl feed. Therefore, the... 

Fig. 8. Ethyl acetate production catalyzed by silico tungstic acid on silica.

H4[SiW12O40]—silico-tungstic acid (STA) H3[P(W3O10)4]—phospho-tungstic add (PTA) H3[P(Mo3O10)4]— phospho-molybdic acid (PMA)... 

C. Miscellaneous Methods a)Reaction with hydriodic acid (p342) b) Reaction with ammonium hexanitrocerate reagent (p343) c) Precipitation with silico-tungstic or phosphomolybdic acid (p344) and d) Determination as the ditrityl ether (p345)... 

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