The selective hydrogenation of halogenated nitrobenzene over noblemetal catalysts (Pd

Pt

and Ir) has attracted much attention owing to its high efficiency and environmental friendliness. However

the effect of size on the catalytic performance varies among different metal catalysts. In this study

sub-nano (3 nm) Ir and Pd particles were prepared

and their catalytic properties for hydrogenation of halogenated nitrobenzene were evaluated. Results show that high selectivity (99%) was achieved over small Ir nanoparticles

in which the selectivity over the Pd with same size was much lower than that on Ir nanoparticles. Meanwhile

Ir and Pd have different hydrogen consumption rates and reaction rates. Density functional theory calculations showed that

p

-chloronitrobenzene (CNB) has different adsorption properties on Ir and Pd. The distance between oxygen (cholorine) and Ir is much shorter (longer) than that between oxygen and Pd. The reaction barriers of dechlorination of

p

-CNB and

p

-chloroaniline over different Irmodels aremuch larger than those on Pd. Especially

lower coordination of Ir leads to larger barriers of dechlorination reaction. These theoretical results expl

ain the difference between Ir and Pd on hydrogenation of halogenated nitrobenzene.