Isophthalonitrile (IPN) hydrogenation over K modified Ni–Co supported catalysts: catalyst characterization and performance evaluation

Abstract

The hydrogenation of isophthalonitrile (IPN) to meta-xylylenediamine (m-XDA) is usually catalyzed by the Raney or supported Ni based catalysts in the presence of basic additive. Although the supported catalysts are safer than the Raney Ni catalysts, they have lower selectivity to m-XDA. This work revealed that the acid sites of NiCo/Al₂O₃ were responsible for the condensation reactions between amines and imines, which were the dominant side reactions. Besides the original acid sites on γ-Al₂O₃, the loading of Ni–Co introduced new acid sites, which had a greater contribution to the condensation reactions. The K modification significantly enhanced the selectivity to m-XDA by reducing the two kinds of acid sites. Due to the formation mechanism of new acid sites and the K modification mechanism on these sites, both the K loading and K impregnation sequence affected the catalytic performance. When 3.0 wt% K was introduced to NiCo/Al₂O₃ by co-impregnation (3KNiCo/Al₂O₃), the catalyst acidity decreased by 82%, and the selectivity to m-XDA increased from 45.5% to 99.9%. The superiority of the optimized catalyst 3KNiCo/Al₂O₃ was also confirmed when no basic additive was used.