Selective Catalytic Hydrogenation Of Nitroarenes Containing Other Reducible Groups

Aromatic amine compounds containing other reducible groups, such as-CHO,-CN,-HC=CH- et al, are important raw materials for industrial production. The difficulties in selective hydrogenation of aromatic nitro compounds to prepare the corresponding aromatic amine are both the preparation of efficient catalysts and the choice of appropriate green solvent. Protecting the other reducing molecules, such as-CHO,-CN and-HC=CHet al, reducing the accumulation of intermediates and restraining dechlorination reaction.0.5wt%Pd/ATO with Sb-doped SnO₂（ATO） as the carrier were prepared. Using the preparation of 3-aminobenzontrile by the selective hydrogenation of 3-nitrobenzenitrile as probe reaction to investigate the effect of Sn/Sb ratio, catalyst reduction temperature, the type of solvent, and other factors on the catalyst performance. The results shown that the best Sn/Sb atom ratio was 80 and the catalyst activity was significantly decreased with the increase of Sb content in the carrier. Reduction temperature influenced catalyst activity significantly and the best reduction temperature was between 50 and 100℃. Catalyst activity decreased significantly when the reduction temperature was larger than 100℃. The accumulation of harmful intermediates in a polar solvent such as ethanol, H₂ O and CO₂ expansion of ethanol, non-polar solvent n-heptane, toluene, CO₂-expansion n-heptane and CO₂-expansion toluene, may inhibited harmful intermediates cumulative substantially. Catalysts were characterized by XRD, XPS, H₂-TPR, H₂-TPR, CO-FTIR and high-pressure ATR-FTIR was employed to investigate the interaction of CO₂ between reactant molecules in CO₂ expanded system. The results shown that Sn/Sb ratio of the support influence the catalyst composition on catalyst surface and the electronic state of Pd. Reduction temperature influenced the reduction strength of Pd and the interaction between Pd and support. The interaction of CO₂ between-NO₂ of reactant molecules in a non-polar solvent decreased the hydrogenation activity of-NO₂, thus reducing the accumulation of intermediates favorable. Pd/ATO also adapted to Selective catalytic hydrogenation of 2-chloro-nitrobenzene, 2-chloro-5-nitrobenzonitrile and 4-nitrobenzaldehyde to prepare their corresponding aniline compounds. The yields of 2-chloro-aniline, 2-chloro-5-aminobenzonitrile and 4-amino-benzaldehyde was larger than 98%, 89% and 87%, respectively.0.5wt%Pd-Zn（1:x）/ATO（9:1） with the ATO as the support that 9:1 atom ratio of tin antimony and different atom ratio of palladium zinc, were prepared by impregnation method. We used these catalysts in the hydrogenation of nitro aromatic compound. The results shown that, catalyst Pd-Zn/ATO（9:1） gave the best catalytic performance with the 1:2 atom ratio of palladium and zinc. Catalyst 0.5wt%Pd-Zn（1:2）/ATO（80:1） that with the ATO as the support that 80:1 atom ratio of tin and antimony and 1:2 atom ratio of palladium and zinc, were prepared by incipient-wetness impregnation method. We used them in the hydrogenation of 4-Nirtrobenzaldehyde at different reaction medium. The result shown that catalyst 0.5wt%Pd-Zn（1:2）/ATO（80:1） gave the best catalytic performance and the selectivity of the objective product was highest when used CO₂-expanded n-heptane as reaction medium.