The formation of an alkyl-sulphate complex on Pt(l 1 1) surfaces has been studied by means of periodic DFT calculations. This molecule was proposed to play an important role in the oxidation process of propene on sulphated Pt surfaces. A structure is proposed for this species and it is demonstrated that the propene fragment is highly activated. The simulated infrared spectrum shows two features (1047 and 1078 cm(-1)) that, combined with the splitting of some bands of the sulphate unit, can be used as a fingerprint to identify the presence of the complex on the surface. The existence of an oxymetallacycle intermediate in the further oxidation process is also proposed. (C) 2004 Elsevier B.V. All rights reserved.