Quantum Chemical Investigation of Photocatalytical Sulfoxidation of Hydrocarbons on TiO2

The production of sulfonic acids which are required as precursors for detergents, dyes, and drugs can be performed by the sulfoxidation of hydrocarbons. In this industrial process, SO2 is electronically excited by UV light, and a CH-bond activation is initiated. This leads to a radical reaction mechanism that eventually results in the formation of sulfonic acid as a product. Recent research has demonstrated that the sulfoxidation of hydrocarbons on titanium dioxide as a photocatalyst can be carried out by using visible light (400–420 nm). This offers new efficient industrial possibilities. However, first studies have shown that the reaction mechanism on the titanium dioxide surface may contrast with the known gas phase mechanism. In this work, the sulfoxidation of hydrocarbons on titanium dioxide (anatase and rutile modification) is investigated in more detail with regard to the adsorption of SO2, the CH-bond activation, and other reaction steps using quantum chemical simulations from first principles. Discrepancies with regard to the up-to-now established reaction mechanism will be elucidated, and important aspects, such as the poisoning of the catalyst, will be identified.