Liquid Phase Hydrogenation Of Halogenated Nitrobenzene Over Amorphous Alloy Catalysts

Halogenated anilines are important intermediates for synthesis of organic fine chemicals, such as dyes, drugs, herbicides, and pesticides. In the synthesis of halogenated anilines, increasing attention has been paid to hydrogenation of halogenated nitrobenzenes due to its atomic economy and low impact on the environment. However, it is well known that dehalogenation in the hydrogenation reaction is a key problem all along.The amorphous alloy is a kind of new material with short-range ordering while long-range disordering structure which may provide excellent catalytic properties, such as high catalytic activity and selectivity, high resistance to the sulfur poisoning, especially the less environmental pollution during the catalyst preparation, which is in accord with the trend of green chemical engineering. Therefore, the amorphous alloys have attracted increasing concern. On base of catalytic hydrogenation system, the amorphous alloy are selected as catalyst for the study of liquid phase hydrogenation of halogenated nitrobenzenes to produce halogenated anilines in the present thesis, expecting to solve the key problem of dehalogenation in catalytic hydrogenation reaction and improve the hydrogenation selectivity. Meanwhile, the promoting effects of the amorphous alloy catalysts on the hydrogenation selectivity have been discussed. Main points of this dissertation are listed as follows.1. The Ni-B,Co-B,Ni-Co-B,Ni-P,Ni-Ce-P,Ni-Fe-P,Ni-Co-P and Ni-Cu-P amorphous alloys have been prepared by chemical reduction with KBH₄ and NaH₂PO₂ respectively. The catalytic performance of these amorphous alloy catalysts was measured by means of liquid phase hydrogenation of halogenated nitrobenzenes, to improve the hydrogenation selectivity. In comparison with Raney-Ni, these amorphous alloy catalysts exhibited excellent activity and selectivity. For examples, in the liquid phase hydrogenation of 3,4-dichloronitrobenzene, the conversion both reached 99.9% and the dehalogenation was only 0.4 % and 0.5.% when the Ni-Co-B and Ni-Ce-P amorphous alloys were used as catalysts respectively. However, the conversion reached 96.3 % and the dehalogenation reached 9.6 % when the Raney-Ni was used as catalyst.2. The relationship between the catalyst performance and the structure of catalyst, the thermal stability, the surface electronic state, the composition of the as-prepared amorphous alloy has been systematically studied based on a series of characterization of catalysts (XRD, SAED, TEM, SEM, DTA, XPS, EDS). 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, the obtained facts show that the amorphous alloy catalysts display excellent catalytic conversion and selectivity with low dehalogenation in the liquid phase hydrogenation of halogenated nitrobenzenes to corresponding halogenated anilines. They should be promising catalysts for industrial application, and privide new opportunities and alternatives of great interest for this kind of hydrogenation reduction reaction.