This research work on the catalytic dehydrogenation of ethylbenzene (EB) to styrene (ST) had a primary goal of developing improved catalysts for dehydrogenation processes both in CO2 as well as with O2 that can compete with the conventional dehydrogenation process in steam. In order to achieve this goal, all these processes need to be properly understood. After having worked on catalytic dehydrogenation reactions in steam, in nitrogen, in carbon dioxide and with oxygen, it appeared that these reactions show many parallels. Carbon deposit formation on the catalyst is closely connected to all dehydrogenation reactions of ethylbenzene to styrene. They always go hand-in-hand and cannot be separated. Yes, these coke deposits will also be a cause of deactivation. But foremost the coke is an active ingredient of the ‘catalyst’ in the ethylbenzene (EB) dehydrogenation reactions. In the oxidative dehydrogenation it is without any doubt that the selective dehydrogenation reaction proceeds over the deposited coke on the catalyst or support. The dehydrogenations experiments in CO2 or N2 in this thesis and characterizations of the samples also clearly show the involvement of coke in the dehydrogenation reaction to styrene (ST). Also in the direct dehydrogenation in steam, coke deposits play an important role in the dehydrogenation, based on literature and our experiments presented in this thesis (Ch. 2). By applying catalyst- and technology developments, a competitive process with O2 appears to be within reach. This process applies a P/SiO2 catalyst and staged feeding of O2, whereby the stability of the catalyst as a function of the time on stream still remains a topic of concern.