Characterization of silica-supported dodecatungstic heteropolyacids as a function of their dehydroxylation temperature

Abstract

Dodecatungsto-silicic H₄SiW₁₂O₄₀ and -phosphoric acids H₃PW₁₂O₄₀ were deposited on silica by a classical impregnation technique. The resulting materials were studied by in situ Raman and infrared spectroscopy, XPS and by solid-state ¹H MAS NMR as a function of their dehydroxylation temperature. The data show that in the case of H₃PW₁₂O₄₀ three silanol groups are protonated while in the case of H₄SiW₁₂O₄₀ at least one acidic proton remains. Upon heating this proton reacts leading to a disordered structure and a broadening of the W–O Raman bands.