Selective Hydrogenation Of Chloronitrobenzene To Chloroaniline Over Activated Carbon Supported PtM

Chloroanilines are an important class of organic intermediates for a variety of specific and fine chemicals, including pharmaceuticals, pesticides, dyes etc. Chloroanilines are mainly synthesized by the reduction of chloronitrobenzene. The main reduction methods include iron powder reduction method, alcali sulphide reduction method, electrochemical reduction method and catalytic hydrogenation reduction method etc. The catalytic hydrogenation reduction method is more suitable for the requirements of green chemistry and atom economy in modern chemical industry because of its advanced technology, low energy consumption, high yield and little waste emission. The chloronitrobenzene hydrogenation to chloroaniline is a complicated reaction process. In addition to the chloroaniline, chloronitrobenzene hydrogenation can generate a range of intermediates and by-products such as chloronitrosobenzene, chlorophenylhydroxylamine, dichloroazoxybenzene, dichloroazobenzene, aniline etc. The co-occurrence of hydrodehalogenation reaction of the substrates must be suppressed, which significantly limits selectivity to the desired chloroanilines. Furthermore, hydrogen chloride(HCl) produced from the dechlorination contributes to the corrosion of the reactor. To improve selectivity, dechlorination inhibitors are used in the reaction system or the catalysts are modified. But the former will make product separation difficult and the latter still cannot completely avoid the dechlorination.Activated carbon supported Pt M(M=Fe、Co、Ni、Cu) catalyst was prepared by impregnation reduction method, and their catalytic performance for selective hydrogenation of p-chloronitrobenzene to p-chloroaniline was investigated. The as-prepared catalysts were characterized using X- ray diffraction(XRD), transmission electron microscopy(TEM), and X-ray photoelectron spectroscopy(XPS). The results showed that the addition of Fe significantly improve the activity and selectivity of Pt/AC for p-chloronitrobenzene hydrogenation to p-chloroaniline and completely suppress hydrodehalogenation reaction of the p-chloronitrobenzene. The higher activity and excellent selectivity of the Pt-Fe/AC are primarily derived from the electron-deficient state of the Pt due to the electronic effect of Pt nanoparticles with Fe, which weakened the extent of electron feedback from the Pt particles to the aromatic ring in p-chloronitrobenzene and suppressed the hydrodechlorination of p-chloronitrobenzene.Using Pt-Fe/AC as catalyst, the effect of the activated carbon produced by different manufacturers, processing method, Fe loading, calcination temperature, reaction temperature, hydrogen pressure, solvent etc. on p-chloronitrobenzene hydrogenation to p-chloroaniline were investigated in detail. The results showed that the activated carbon produced by Chongqing Chuandong Chemical Co., Ltd. has little impurities and show excellent performance via oxidation treatment at 250℃ in flowing air. The loading of Fe in the Pt-Fe/AC have a significant influence on the catalytic performance of Pt-Fe/AC for p-chloronitrobenzene hydrogenation to p-chloroaniline. It was found that p-chloronitrobenzene conversion and p-chloroaniline selectivity reach the maximum when the Fe loading was 4%. The Pt0.003Fe0.04/AC catalyst calcined at 300℃ in nitrogen show excellent performance for p-chloronitrobenzene hydrogenation to p-chloroaniline. Reaction temperature, hydrogen pressure and solvent have great influence on p-chloronitrobenzene hydrogenation. For the Pt0.003Fe0.04/AC catalyst, polar solvent, high temperature and hydrogen pressure are the optimum reaction conditions for p-chloroaniline synthesis from p-chloronitrobenzene.Pt0.003Fe0.04/AC catalyst also exhibited high activity and excellent selectivity to hydrogenation of o-chloronitrobenzene and m-chloronitrobenzene to corresponding chloroaniline.