Surface Acidity of Solid Acids and Superacids: A Ft-Ir Study of the Behaviour of Titania Doped with Phosphoric, Sulphuric, Tungstic and Molybdic Acids

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The surface structure and the acid behaviour of titanias doped with sulphuric (TS), tungstic (TW), molybdic (TMo) and phosphoric (TP) acids has been studied using FT-IR spectroscopy. The acidity scale detected using the olefin oligomerization activity in the IR cell as the discriminant is TS « TW < TMo « TP « TiO2 and seems to agree with catalytic activity data. It is deduced that the enhanced acidity of doped samples is of the Bronsted type, the Lewis sites of titania being only weakly perturbed. Moreover, doping strongly poisons basic sites. Surface mono-oxo anionic species are very evident on TS, TW and TMo, while on TP tridentate hydrogenphosphate ions seem to be predominant. © 1989.

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