A kinetic study of the epoxidation of propene with molecular oxygen and water in the gas phase has been carried out. This reaction avoids the use of hydrogen as co-reactant, reducing operation costs and simplifying the overall process. Two Au-Ti catalysts were evaluated: Au/TS-1 and Au/Ti-SiO2. It was observed that Au/TS-1 promoted by Cs is active for the reaction, producing propene oxide (PO) and acrolein almost in a one to one ratio. On the other hand, Au/Ti-SiO2 produced acrolein with almost 100% selectivity. This difference in activity can be due to the presence of alkali ions and the higher dispersion of Ti atoms in the case of TS-1. Water in the gas stream is essential for the synthesis of OOH* species that are the active species in the epoxidation. A kinetic model was developed to understand the reaction mechanism. It was determined that an excess of oxygen and water is favorable for the PO/acrolein ratio, while propene has a slight detrimental effect. (C) 2015 Elsevier Inc. All rights reserved.