Exclusive Production of Chloroaniline from Chloronitrobenzene over Au/TiO₂ and Au/Al₂O₃

The gas-phase continuous hydrogenation of p-chloronitrobenzene (p-CNB) over 1 mol % Au/TiO₂ and Au/Al₂O₃ was compared for the first time. Both catalysts exhibit 100% selectivity in terms of -NO₂ group reduction, resulting in the sole formation of p-chloroaniline (p-CAN). Au/TiO₂ exhibited a narrower particle size (1-10 nm) distribution than Au/Al₂O₃ (1-20 nm) and a smaller surface-area-weighted mean Au size (6 nm versus 9 nm). Au/TiO₂ delivered a higher specific hydrogenation rate (by a factor of up to four), a response that is discussed in terms of Au particle size and a possible contribution of the support to p-CNB activation. A CNB isomer reactivity sequence was established, that is, o> p> m, which is attributed to resonance stabilisation effects. The results presented establish a basis for the development of a sustainable alternative route for the production of haloamines.