The role of lattice oxygen on the activity and selectivity of the OMS-2 catalyst synthesized by the hydrothermal method was investigated for the catalytic oxidation of toluene. The OMS-2 catalyst exhibited excellent activity for the catalytic oxidation of toluene, but the by-product benzaldehyde was detected at low temperatures. A DRIFT study showed that the lattice oxygen was both the adsorption site and active catalytic site. The nature of the replenished surface lattice oxygen was found to influence the selectivity, and toluene that was adsorbed on the lattice oxygen replenished by gaseous oxygen could be oxidized easily into benzaldehyde. A possible reaction mechanism has been proposed that could elucidate the toluene oxidation activity over OMS-2 involving two reaction routes, either with or without gaseous oxygen. (C) 2015 Elsevier B.V. All rights reserved.