Inorganic Salts Modulating The Hydrogenation Of Nitro Aromatic Compounds Over Raney Ni Catalyst

Aromatic amines(ANs) are commercially important for the large scale production of many fine chemicals. Liquid-phase hydrogenation of nitro aromatic compounds(NBs) over metal catalyst is recognized as an efficient and environmentally friendly procedure to produce ANs because no other harmful effluents are produced except water. In catalytic reaction, the catalyst plays a very important part. Catalysts base on noble and non-noble metals have been widely studied. Raney Ni is applied more widely than noble metal catalysts in industry production of ANs because of its abundant resources and low price. However, the catalytic activity of Raney Ni is lower than noble metal catalysts, and the accumulation of phenylhydroxylamines produced in hydrogenation of NBs is harmful, both of which need to be improved.To solve the problem mentioned above, we investigated the hydrogenation of NBs over Raney Ni under the influence of some metal salt additives, and the possible reason for the effect of these metal salts was discussed. The main results are listed as following.Raney Ni catalyst with addition of a moderate amount of metal salts, especially metal fluorides(Na F, KF, Mg F2 and Ca F2) exhibited much higher catalytic performance for the hydrogenation of 4-chloronitrobenzene(4-CNB). The metal flourides also showed the promoting effect on the hydrogenation of some other NBs, such as nitrobenzene, p-nitrophenylnitrile and m-dinitrobenzene. The possible reason of the promoting effect of these metal fluorides might be interpreted by a speculation of electronic effect. The added metal fluoride could absorb on Raney Ni surface, and there might exist some electronic interaction between the deposited fluoride and Raney Ni. The electronic interaction might change the electronic property of Raney Ni. And as a result, the changed Raney Ni could accelerate the conversion of the substrate to the target product.Raney Ni catalyst with addition of some transition metal salts, especially Fe Cl2, exhibited a remarkable inhibiting effect on the accumulation of phenylhydroxylamines produced in hydrogenation of NBs. The accumulation of phenylhydroxylamines could be reduced to zero by controlling the Fe Cl2 amount within 0.5~1.0%. The inhibiting effect of Fe Cl2 was also found in the hydrogenation of some other NBs only if there was phenylhydroxylamine produced.The possible reason of the inhibiting effect of these metal fluorides might be interpreted by the formation of a new kind of Ni-Fe active site. The deposited Fe Cl2 could possibly cover part of the original Ni active site and a new kind of Ni-Fe active site might form, which benifited the conversion of phenylhydroxylamine leading to its disappearance.In conclusion, Raney Ni catalyst with a moderate amount of metal fluorides exhibited much higher catalytic performance for the NBs hydrogenation, which could enhance productivity. And Fe Cl2 exhibited a remarkable inhibiting effect on the accumulation of phenylhydroxylamines produced in NBs hydrogenation over Raney Ni.