| In this research, a series of supported catalysts containing noble metal Ru, Ir and Pd, prepared and were used in the selective hydrogenation of haloaromatic nitro-compounds. The effects of modifiers on the hydrogenation of haloaromatic nitro-compounds were also studied.The result showed that the catalyst I1 Ru-Ir/γ-Al2O3 (ruthenium: iridium=4:1 molar ratio), prepared by impregnatingγ-Al2O3 in the isopropylalcohol solution of RuCl3 and H2IrCl6, and reducing with hydrogen in ethanol under the conditions of 150℃, H2 pressure 4.0MPa for 18h, exhibited excellent catalytic properties on the selective hydrogenation of p-CNB. The conversion of p-CNB catalyzed by catalyst I1 was 100％and the selectivity to p-chloroaniline (p-CAN) was up to 95.0％under the conditions of 70℃of reaction temperature,150 min of reaction time, 1.0MPa of H2 pressure, and 1000:1 molar ratio of substrate to metal. The additions of ethylenediamine and L-lysine caused remarkably improvement in both the activity and the selectivity under the same conditions. The conversion increased from 37.2％to 95.6％and the selective to p-CAN rose from 97.0％to 100％in the presence of ethylenediamine. The addition of L-lysine enhanced the activity of catalyst from 37.2％to 97.6％and the selectivity forp-CAN was up to 100％.When PVP-Pd/γ-Al2O3 was used as a catalyst for the hydrogenation of p-CNB to form p-CAN, it caused a serious dehalogenation reaction. However, its catalytic property was remarkably affected by some metal cationic additives. Especially, when Sn4+ was introduced into the reaction system, the activity of the catalyst was not only promoted, but the dehalogenation reaction was also greatly suppressed. The average rate of hydrogenation increased from 1.28 molH2/molPd·s on PVP-Pd/γ-Al2O3 catalyst to 1.96 molH2/molPd·s on the PVP-Pd-Sn4+/γ-Al2O3 catalyst (molar ratio of Pd to Sn=1:1), and the selectivity forp-CAN was increased from 66.8％to 96.6％. The dehalogenation reaction was completely restrained as the molar ratio of Sn4+ to Pd was up to 5 and the selectivity of p-CAN was 99.2％. Based on experimental results, the modification mechanism of Sn4+ could be the interaction between Sn4+ and -NO2 group of the substrate increased the polarity of N=O bond and accelerated the hydrogenation of nitro group. Because of the same reason, the polarity of C-Cl bond was decreased and the strength of C-Cl bond was increased, so that the dehalogenation reaction was greatly inhibited.
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