The objective of the study reported here was to unravel the reaction mechanism of TiO2 catalysts used for CS2 conversion in Claus process gas mixtures. Previously, it was demonstrated that the activity of titania exceeds that of alumina when used in the presence of H2S/SO2 mixtures. In this study, it has been demonstrated that the presence and formation of Ti3+ cation substantially improves CS2 conversion activity for hydrolysis of CS2 and for the Claus reaction process. This improvement is explained by a dual-centre adsorption model for CS2 over titania which consists of chemisorption at adjacent Ti3+-Ti4+O groups. Understanding the role of Ti3+ has allowed development of a more active Claus catalyst by introducing a pseudo "permanent Ti3+" cation, Sc3+, into the framework structure of titania. Commercial implications based on above observation are also suggested for both catalyst designers and plant operation. (C) 2014 Elsevier B.V. All rights reserved.