This study shows that minor amount of water plays a very important role in solvent-free hydrogenation of halogenated nitrobenzenes.For dried sponge Pd,the reaction cannot occur in the absence of water.For Pd/C catalyst,minor amount of water reduces the induction time,increases the reaction rate and reaction TOFs.Water might enhance the diffusion,adsorption and dissociation of H_2 on Pd catalysts.
Jing-Hui LyuXiao-Bo HeChun-Shan LuLei MaQun-Feng ZhangFeng FengXiao-Nian LiJian-Guo Wang
Halogenated anilines have a wide range of applications in the production of pharmaceuticals and agrochemical substances, and thus it is of great importance to develop highly active and selective catalysts for the hydrogenation of halogenated nitrobenzenes. We approach this challenge by probing noble metal/non-noble metal oxide nanoparticles(NPs) catalysts. Carbon-supported Pd/SnO2catalysts were synthesized by the chemical reduction method, and their catalytic activity was evaluated by the hydrogenation reaction of 2,4-difluoronitrobenzene(DFNB) to the corresponding 2,4-difluoroaniline(DFAN), showing a remarkable synergistic effect of the Pd and SnO2 NPs. The as-prepared Pd/SnO2/C catalysts were characterized using TEM, XRD, H2 TPD and XPS techniques. Modifications to the electronic structure of the Pd atoms through the use of SnO2 led to the suppression of the hydrogenolysis of the C–F bond and the acceleration of nitrosobenzene(DFNSB) conversion and consequently, resulted in the inhibition of the formation of reactive by-products and may be responsible for the enhancements observed in selectivity.
