Gas-phase hydrogenation of adiponitrile with high selectivity to primary amine over supported Ni-B amorphous catalysts

Gas-phase hydrogenation of adiponitrile (ADN) was performed at 1 atm pressu re over the Ni-B/SiO2 amorphous catalyst, which exhibited high selectivity to 1,6-hexanediamine (HDA) at 100% ADN conversion. The selectivity to HDA c ould be further enhanced by MgO dopant. The product analysis revealed that the selectivity to HDA was mainly dependent on the contents of 6-aminohexan enitrile and azacycloheptane formed during the ADN hydrogenation. The 6-ami nohexanenitrile was an intermediate in the reaction; it resulted from the h alf-hydrogenation of ADN; and its content was strongly affected by the acti vity of the catalyst. The azacycloheptane was a side-product (secondary ami ne) formed via the nucleophilic addition of the primary amine on one side o f ADN chain to the aldimino carbon atom on the other side which was adsorbe d by the Ni active sites. The electronic density of the Ni active sites pla yed a key role in determining the content of azacycloheptane. The presence of the alloying B resulted in the electron-enriched Ni active sites which e ffectively inhibited the formation of azacycloheptane and in turn, resulted in the high selectivity to HDA. (C) 2001 Elsevier Science B.V. All rights reserved.