The role of palladium on the Fe-K catalyst empirically was studied by use of a periodical pulse technique from a mechanistic point of view. Styrene was formed via either dehydrogenation or oxidative dehydrogenation. The latter reaction was faster than the former, and it proceeded by consuming the surface lattice oxygen in the catalyst. The lattice oxygen was subsequently supplied from steam that is commonly believed to act as the diluent to reduce the partial pressure of styrene, known as a favorable effect to shift the equilibrium of volume-expanding reactions in a thermodynamic sense. Palladium added to the Fe-K oxide catalysts enhanced the rate of regeneration (supplying) of the lattice oxygen, although it hardly changed the rate of dehydrogenation of ethylbenzene or consumption of surface lattice O2 anions. Water molecule (steam) worked as a diluent and as a reactant to form hydrogen and lattice oxygen. This is an abstract of a paper presented at the 17th Annual Saudi-Japanese Symposium on Catalysts in Petroleum Refining and Petrochemicals 2007 (Dhahran, Saudi Arabia 11/11-12/2007).