Liquid Phase Hydrogenation Of O-Chloronitrobenzene Over Supported Amorphous Alloy Catalysts

Halogenated anilines are important organic intermediates and raw chemical materials.They are widely used in many chemical fields such as dyes,drugs,herbicides and pesticides.In the synthesis of halogenated anilines,increasing attention has been paid to hydrogenation of halogenated nitrobenzene due to its atomic economy and environment-friendly.However,it is well known that dehalogenation is a key problem in the hydrogenation reactions.The amorphous alloy is a kind of new material with short-range ordering and long-range disordering.The unique structure provides many excellent catalytic properties,such as highly catalytic activity and selectivity,highly resistance to sulfur-poisoning,etc.Moreover,the less environmental pollution during the catalyst preparation is in good accordance with the current trend of green chemical engineering. Therefore,the amorphous alloys have attracted increasing concerns for their special structure and catalytic properties.However,amorphous alloys prepared via conventional methods tend to be agglomerated and dispersed in size.Moreover,the low surface area and poor thermal stability of these amorphous alloys limit their industrial application greatly.There exists a promising ways to overcome those drawbacks, which is to deposit the amorphous alloys on a support with high surface area.In the present thesis,we expect to solve the key problem of dehalogenation in catalytic hydrogenation and improve the hydrogenation selectivity in the synthesis of halogenated anilines.So we have studied the liquid phase hydrogenation of o-chloronitrobenzene by using different activated carbon-supported amorphous alloys as catalysts.Main points of this dissertation are listed as follows:Firstly,the Ni-Co-P/C supported amorphous alloys were prepared with NaH₂PO₄ reduction.The catalytic activity of the supported amorphous alloy catalysts were studied in the hydrogenation of o-chloronitrobenzene.The results showed that when reduction reaction ran at 80℃for 1.5h with pH=11,the product had best catalytic activity. In the liquid phase hydrogenation of o-dichloronitrobenzene,the conversion reached 98.55%and the dehalogenation was only 1.6%and the selectivity was 98.4%.Secondly,The Ni-Co-B/C supported amorphous alloys were prepared with KBH₄ reduction.The catalytic activity of the supported amorphous alloy catalysts were also studied in the hydrogenation of o-chloronitrobenzene.Comparing with Raney-Ni,the Ni-Co-B/C supported amorphous alloy catalysts showed better catalytic activity and selectivity.More importantly,the Ni-Co-B/C supported amorphous alloy catalysts decreased the dehalogenation of catalytic hydrogenation obviously.Thirdly,All these amorphous alloy catalysts were verified by XRD and TEM.Based on the results,it is clarified that the short-range ordering while long-range disordering structure of amorphous alloy,the interaction between different metals and the electronic interaction between B,P and metal are the main reasons for the high hydrogenation selectivity and low dehalogenation.In conclusion,our researches show that the supported amorphous alloy catalysts display better catalytic conversion and selectivity,lower dehalogenation in the hydrogenation of o-chloronitrobenzene to corresponding o-chloroaniline.In comparison with traditional Ni catalysts, the supported amorphous alloy catalysts may be used as a kind of promising catalysts and also provide new opportunities in the hydrogenation reduction reactions.