(237h) Reaction Coupling of Nitrobenzene Hydrogenation with Ethylbenzene Dehydrogenation: Reaction Pathways and Kinetics

The production of aniline from nitrobenzene hydrogenation and styrene from ethylbenzene dehydrogenation are two important reactions in the petrochemical industry. Nitrobenzene hydrogenation is highly exothermic, which does not require significant energy. However, its main cost comes from the required external hydrogen, primarily produced from steam reforming of methane. On the other hand, ethylbenzene dehydrogenation is highly endothermic and thermodynamically unfavorable with limited equilibrium conversion. Coupling these two reactions has the potential benefits of removing the need for hydrogen in nitrobenzene hydrogenation and increasing the yields and/or reducing the reaction temperature of ethylbenzene dehydrogenation. In this work, the coupling of nitrobenzene hydrogenation with ethylbenzene dehydrogenation has been performed over MoO₃ catalysts, which has shown high deoxygenation and hydrogen adsorption activities in the literature. A hypothesized reaction mechanism is tested by our experimental findings. Our results show that the active sites on the MoO₃ catalyst capture oxygen atoms from nitrobenzene first to produce a phenylhydroxylamine intermediate. The surface adsorbed hydrogen atoms, produced from hydrogen abstraction of ethylbenzene, then react with phenylhydroxylamine to form aniline. Due to this hydrogen transfer process, the equilibrium of ethylbenzene dehydrogenation is shifted such that the conversion is increased. In addition, the hydrogenolysis reaction leading to side products (benzene and toluene) is reduced, improving the selectivity of styrene.