Theoretical Study On Selective Hydrogenation Of Chloronitrobenzene Over Nobel Metal Catalysts

Chloroaniline is a remarkably versatile organic chemical intermediate which plays a pivotal role in the fine chemical industry. It is usually produced by the reduction of the corresponding chloronitrobenzene. Catalytic hydrogenation process has been gradually gained researchers’ favor because of the growing environmental awareness. During the selective hydrogenation process of chloronitrobenzene to chloroaniline, a proper catalyst should be selected for reducing the side reaction of dechlorination, thus improving the yield of the target product. Precious metal palladium and iridium catalysts in the selective hydrogenation reactions have been experimentally studied. However, the mechanisms of the selective hydrogenation of chloronitrobenzene to chloroaniline and the side reaction of dechlorination have not been reported in the theoretical study so far. Therefore, we carried out the related research to provide reasonable explanation and forecast for the experiment.In this work, we firstly investigated the adsorption behaviors of two organic molecules (chloronitrobenzene and chloroaniline) on the Pd surface and clusters by density functional theory calculations. Their most stable configurations were respectively obtained. By studying the adsorption strength of chloroaniline on the Pd catalyst and D center, we found a good linear relationship between them, verifying the d-band center model proposed by Hammer and N(?)rskov. The partial density of states (PDOS) and frontier orbital theory analysis were also done for explaining different adsorption strengths between surfaces and clusters. We also studied the energy barriers of each elementary reaction in the selective hydrogenation of chloronitrobenzene on two active surfaces of palladium catalysts. The results showed that the hydrogenation reaction is not affected by the catalyst surface. Meanwhile, we studied the energy barriers of each elementary reaction in the dechlorination of chloronitrobenzene and chloroaniline on the palladium catalyst surfaces and clusters. Considering the hydrogenation reaction barrier, we concluded that large particle size is more conducive to improve the selectivity of palladium catalyst and inhibit the dechlorination side reaction.Furthermore, we studied the catalytic performance of iridium by selecting two representative planes (Ir (111) and Ir (211)) and a icosahedral cluster (Ir (13)). Firstly, we studied the adsorption behaviors of chloronitrobenzene and chloroaniline on these catalysts models. It was found that clusters deformed slightly, and that the adsorption strength on clusters was much larger than surfaces. Then the energy barriers of dechlorination elementary reactions on the catalyst surface and clusters were studied. The results showed that the energy barrier was high for the dechlorination of the two molecules, indicating that iridium catalyst may inhibit dechlorination side reactions and improve the selectivity of the hydrogenation reaction, having very broad market prospects.