Ultra-selective gas phase catalytic hydrogenation of aromatic nitro compounds over Au/Al₂O₃

We report, for the first time, the exclusive (and time invariant) gas phase hydrogenation of p-chloronitrobenzene to p-chloroaniline over Au/Al₂O₃ where 393 K = T = 523 K (?E_a = 49 kJ mol^-1). Under the same conditions, Pd/Al₂O₃ promoted the formation of nitrobenzene and aniline, i.e. composite hydrodechlorination and hydrogenation. Reaction over Au-Pd/Al₂O₃ delivered equivalent activity/selectivity to that obtained with Pd/Al₂O₃. Temperature programmed reduction analysis and hydrogen uptake measurements suggest there is negligible Au-Pd interaction in the bimetallic. Exclusive formation of the corresponding haloaniline is also demonstrated over Au/Al₂O₃ for a series of mono- and di-substituted halonitroarenes; the activity sequence is consistent with electron withdrawing substituent activation. © 2007 Elsevier B.V. All rights reserved.