Gas-phase oxydehydrogenation of ethylbenzene with nitrobenzene by hydrogen transfer catalyzed reaction to produce styrene and aniline

Gas-phase catalytic hydrogen transfer reaction between ethylbenzene and nitrobenzene, to produce styrene and aniline, has been carried out at 360-460 degrees C on amorphous AlPO4, SiO2, Al2O3, and on a natural sepiolite, as well as on the corresponding 20 wt% supported nickel catalysts. The influence of Cu as a second metal was also studied. Reactions were also carried out without nitrobenzene, under nonoxidative conditions. Catalytic activity under oxidative conditions was always comparatively higher than in nonoxidative conditions. In both cases, styrene yield and selectivity values obtained with support materials directly used as catalysts were better than those obtained with the corresponding Ni or Ni-Cu supported metal catalysts, with the only exception of SiO2. The best results were obtained when amorphous AlPO4 was used as the catalyst. The catalytic activity obtained in both oxidative and nonoxidative conditions, was closely associated to acid-base properties of the catalysts studied. Furthermore, a very similar linear correlation between ln A and E-a known as "compensation effect" was obtained and a common dehydrogenation mechanism was considered for oxidative and nonoxidative conditions. However, without considering the catalyst, nitrobenzene plays an important role as hydrogen acceptor, not only shifting the ethylbenzene dehydrogenation equilibrium but also avoiding secondary reactions by lowering the level of available hydrogen, especially when supported metals are being used as catalysts.