Role of acid sites and surface hydroxyl groups in isophthalonitrile hydrogenation catalyzed by supported Ni–Co catalysts

Abstract

meta-Xylylenediamine (m-XDA) is industrially produced by the hydrogenation of isophthalonitrile (IPN) using Raney® Ni/Co and basic additives. Compared with Raney® Ni/Co, the supported Ni/Co catalysts are safer and have better mechanical strength. This work aimed at studying the catalytic performance of the supported Ni–Co catalysts in hydrogenation of IPN to m-XDA. The active sites for the condensation side reactions were studied using Ni–Co catalysts supported on different oxides and with different loadings. It was found that the acid sites catalyzed the condensation reactions between intermediate imines and amines. Two types of acid sites existed on the supported Ni–Co catalysts, namely, the original acid sites of the support and new acid sites formed by Ni/Co aluminates. In addition to acid sites, the surface hydroxyl groups on the oxide supports also catalyzed the condensation reactions, but were not active for the hydrogenation reaction. By increasing the Ni–Co loading, the selectivity to m-XDA was significantly enhanced, which was attributed to the suppression of both acid sites and hydroxyl groups. Compared to the low-loading catalysts (5Ni–1.25Co/Al₂O₃ and 5Ni–1.25Co/SiO₂), the high-loading catalysts (20Ni–5Co/Al₂O₃ and 20Ni–5Co/SiO₂) increased the m-XDA selectivity from ∼45.5 to 99.9%.