A new reverse flow reactor is developed where endothermic reactants (propane dehydrogenation) and exothermic reactants (fuel combustion) are fed sequentially to a monolithic catalyst, while periodically alternating the inlet and outlet positions. Upon switching from reductive to oxidative conditions hydrocarbons come into contact with air. Due to mixing in the monolith channels and in the inlet sections, combustible gas mixtures can be formed. In this work the effects during reaction phase switching are studied by detailed numerical simulations and some qualitative experiments. Due to the reverse flow concept and the use of a monolithic catalyst switching between oxidative and reductive conditions can be carried out without intermediate flushing with inert gases, if proper precautions are taken.