Adsorption of sulfur on TiO 2 ( 110 ) studied with STM , LEED and XPS : temperature - dependent change of adsorption site combined with O – S exchange

We have studied the adsorption of elemental sulfur on TiO 2 (110) for exposure at room temperature and at 300°C. Depending on the substrate temperature we found different adsorption sites with scanning tunneling microscopy (STM). At room temperature sulfur adsorbs on the titanium rows with a high mobility along the [001] direction. At 300°C sulfur adsorbs at the position of the bridging oxygen rows and forms short chains along the [11 :0] direction at low coverages. High coverages result in the formation of a (3×1) superstructure. X-ray photoelectron spectroscopy (XPS) shows a 2 eV shift of the sulfur 2p peak to lower binding energy concurrently with the change of adsorption site from the titanium to the oxygen rows. For the (3×1) structure a distinct Ti3+ shoulder appears at the Ti 2p 3/2 peak. Based on these measurements we present a model where sulfur replaces every third bridging oxygen atom of the substrate and the other bridging oxygens are completely removed. 1. Introduction like CO to the surface and inhibits their hydrogena-tion, which is essential to many catalytic processes. Because sulfur is a common poison for catalytic Industrial catalysts are very complex systems in reactions, the adsorption of sulfur compounds has which impurities containing sulfur cannot be been studied extensively. An overview of the avoided completely. Therefore a profound knowl-adsorption of S containing molecules on metal and edge of the interaction of sulfur with model cata-oxide surfaces is given in Refs. [1,2] and references lysts like TiO 2 (110) might help in developing cited therein. The poisoning properties of sulfur catalysts which are less affected by the poisoning are multifaceted [3–7]. In many cases the presence properties of sulfur. The TiO 2 (110) surface has of sulfur weakens the bonding of small molecules been studied with scanning tunneling microscopy (STM) and other methods in much detail [8–14], and the structure of the (1×1) surface is very well