Catalytic functionalities of Pd catalysts supported on spinel MgAl2O4 for coupling of ethylbenzene dehydrogenation with nitrobenzene hydrogenation

Direct coupling of oxidative dehydrogenation of ethylbenzene with nitrobenzene hydrogenation in a fixed-bed catalytic reactor at atmospheric pressure in the temperature range of 673-823 K over MgAl2O4-supported palladium catalysts has been investigated. Simple dehydrogenation of ethylbenzene (DHEB) is reversible, endothermic and thermodynamically limited. The continuous removal of co-produced hydrogen in DHEB for in situ hydrogenation of nitrobenzene over Pd/MgAl2O4 catalyst improves the performance of the DHEB process. A series of Pd (0.25-4.0 wt%) catalysts supported on MgAl2O4 was prepared. The catalyst samples were characterized by X-ray diffraction (XRD), H-2-Temperature-programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS), Transmission electron microscopy (TEM), CO chemisorption, CO2-Temperature-programmed desorption and BET surface area. Dispersion and particle size of Pd were obtained by CO chemisorption. The reaction profile shows that palladium (0.5 wt%) is an optimum loading to get maximum conversion of ethylbenzene (51.8 %) and nitrobenzene (47.3 %) to give 91.4 and 100 % selectivity of styrene and aniline, respectively.