The desorption of products from a series of alkaline-earth exchanged Y zeolites after room-temperature propane selective oxidation was investigated by in situ infrared and mass spectroscopy. The intermediate product, isopropylhydroperoxide (IHP), did not desorb during temperature-programmed-desorption experiments but converted into acetone and water. Decomposition rate of IHP, produced from propane and oxygen at room temperature, into acetone increased in the order BaY < SrY < CaY ( 250 degreesC) under dry conditions. Addition of water, however, results in gas phase acetone already at room temperature. From the results it can be concluded that water clearly facilitates acetone desorption, most likely via shielding of the electrostatic field and creation of additional sites.