Hydrogenation Of Chloronitrobenzene Catalyzed By Pd Nanoparticles Supported On Ordered Mesoporous Carbon Materials

In recent years,catalytic hydrogenation of chloronitrobenzene is considered to be the most economical and green method for preparing high-value-added chloroaniline.However,the side reactions of hydrogenolysis and dechlorination readily occur during the catalytic hydrogenation reaction,resulting in low selectivity to the target product.Pd-based catalysts are widely used in this reaction due to their mild reaction conditions and good catalytic performances.However,the activities of Pd-based catalysts are rather high,which easily leads to deep hydrogenation of products,and the selectivity of chloroaniline is poor.Therefore,the research and development of new hydrogenation catalysts are the key to realize the efficient conversion of chloronitrobenzene to chloroaniline.Thus,two kinds of ordered mesoporous carbons were used as supports to prepare supported Pd-based catalysts in an impregnation method,and their catalytic performances for the hydrogenation of chloronitrobenzene were preliminarily evaluated.The pore structures and surface chemistry of the supports and catalysts were analyzed by means of XRD,TEM,N₂ sorption measurment,XPS,etc.The research contents are described as follows:（1）First,body-centered cubic ordered mesoporous carbons were prepared by the soft-templating method,and following supported Pd-based catalysts were prepared via an impregnation method.The effect of calcination temperature on the pore structure and surface chemistry of the catalyst was preliminarily investigated.The study found that the increase of calcination temperature caused the pore structure of the support to shrink gradually,and the specific surface area showed a trend of first increasing and then decreasing.At the same time,the number of oxygen-containing functional groups on the surface of the support gradually decreased.After the metal Pd being loaded,the pore structure of the catalyst support did not significantly change.However,with the increase of the specific surface area of the support,the dispersion of Pd particles in the catalyst increases,and thus the utilization of Pd active components is higher.Based on the evaluation results,it is found that different calcination temperatures have a great influence on the hydrogenation performance of the catalyst.Among them,the chloroaniline selectivity of Pd/C-700 was 78%at 60℃and 5 bar hydrogen pressure during 1 h,which was much higher than that of Pd/C-T（T=500,600 and800 ^oC）catalysts.In addition,4 cycles experiments were carried out,and the results showed that the catalyst had good stability.（2）Secondly,the x-Pd/C-T catalyst was prepared by an impregnation method with two-dimensional hexagonal ordered mesoporous carbon as the support,and the physicochemical properties of the support and catalyst were characterized.It was found that the pore structure and surface chemistry of the 2D hexagonal ordered mesoporous carbon showed the same trend as that of the body-centered cubic ordered mesoporous carbon with the calcination temperature.The evaluation results show that when the Pd loading is 5%,the5-Pd/C-800 catalyst exhibits the best hydrogenation performance under this experimental conditions,and the selectivity is as high as 95.8%.By comparing the hydrogenation performance of 2D hexagonal ordered mesoporous carbon support,body-centered cubic ordered mesoporous carbon support supported Pd catalyst and Pd/AC at different calcination temperatures,it was found that the order of the support pore structure was important for the hydrogenation selection of the catalyst and its influence is distinct.The hydrogenation selectivity of the ordered mesoporous carbon-supported Pd catalysts is higher than that of the Pd/AC catalysts with the disordered slit pore structure,and the two-dimensional hexagonal ordered mesoporous structure is more efficient than the body-centered cubic ordered mesoporous structure,which is more favorable for mass transfer.In addition,4 cycles experiments over 5-Pd/C-800 show that the catalyst has good hydrogenation activity,selectivity and stability.