A photoemission study of the SO 2 adsorption on TiO 2 110) surfaces D.I. Sayago a,b , P. Serrano a,c ,O.B ohme a , A. Goldoni a,d , G. Paolucci a,d , E. Rom an a , J.A. Mart õn-Gago a, * a Instituto Ciencia de Materiales de Madrid-CSIC. Cantoblanco, 28049 Madrid, Spain b Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin-Dahlem, Germany c SpLine, Spanish CRG Beamline at ESRF, B.P. 220, F-38043 Grenoble Cedex 09, France d Sincrotrone Trieste, SS 14, km 163.5, in Area Science Park, 34014-Basovizza-Trieste, Italy Abstract We have investigated the adsorption of the SO 2 molecule on a TiO 2 110) single crystal at a substrate temperature of 120 K by means of core level synchrotron radiation photoemission. By studying the S 2p and O 2s core level peaks, we show that from the ®rst adsorption stages up to the saturation coverage, SO 2 adsorbs molecularly on the TiO 2 110)- 1 1 surface forming a sulphite±sulphate-like mixed and disordered adsorbed layer. The bridge oxygen atoms of the clean surface are involved in the oxidation of the molecule. Ó 2001 Elsevier Science B.V. All rights reserved. Keywords: Synchrotron radiation photoelectron spectroscopy; Chemisorption; Titanium oxide; Sulphur dioxide 1. Introduction The interaction of molecules with single crystal transition metals oxide surfaces is of a great im- portance to understand the basic mechanisms of catalytic reactions [1]. Particularly, the TiO 2 rutile single crystal presents a high interest in catalysis because it is one of the most used catalytic support and,especially,the110)facehasbeenusedtotest the fundamental mechanisms of reactivity [2]. Moreover, the interaction of SO 2 with TiO 2 sur- faces is of technological relevance because sulphur is one of the most common catalyst poisons. Furthermore, the rutile TiO 2 110) face exhibit several types of surface atoms and defects [3]. It is known that both, the reactivity of the surface to- wards dierent molecules and the reaction mech- anisms, are strongly aected by the presence of surface defects [4,5]. Thus, SO 2 /TiO 2 110) is a model system for understanding important tech- nological and fundamental processes related to gas adsorption on insulating surfaces. However, despite the important technological applications and fundamental processes that could take place at the surface, little experimental work has been carried out on the adsorption of SO 2 on single crystal TiO 2 substrates. Moreover these works lead to contradicting conclusions. Thus, at room temperature either little reaction [6] or for- mation of surface sulphite SO 2 3 ) [7] was reported. Two recent works deal with low temperature ad- sorption around 105 K) [8,9]. The ®rst one was Surface Science 482±485 2001) 9±14 www.elsevier.nl/locate/susc * Corresponding author. Fax: +34-91-3720623. E-mail address: gago@icmm.csic.es J.A. Mart õn-Gago). 0039-6028/01/$ - see front matter Ó 2001 Elsevier Science B.V. All rights reserved. PII:S0039-602800)00998-5