Comparative studies on catalytic behaviors of various Co- and Ni-based catalysts during liquid phase acetonitrile hydrogenation

Abstract

The Ni-B and Co-B amorphous alloys exhibited much higher activity and selectivity to ethylamine (C 2H 5NH 2) than their corresponding crystallized counterparts and Raney Ni during liquid phase hydrogenation of acetonitrile (CH 3CN). In comparison with the Ni-B amorphous alloy, the Co-B amorphous alloy exhibited longer lifetime and better selectivity, though its activity was slightly lower. The maximum yield of C 2H 5NH 2 could reach 93.5%, showing a good potential in industrial application. The higher activity of the amorphous alloys could be attributed to the large active surface area, the unique amorphous structure together with the suitable structural parameters, and the electron donation of the alloying B to the metallic Ni or Co. The resulted electron-enriched metallic active sites may also account for the better selectivity to C 2H 5NH 2 of the amorphous alloys since, on one hand, it could promote the hydrogenation of CH 3CHNH toward C 2H 5NH 2 by activating the CN bond; and on the other hand, it may retard the condensation between CH 3CHNH and C 2H 5NH 2 leading to (C 2H 5) 2NH by inhibiting the adsorption of C 2H 5NH 2 which was essential for the condensation. The Co-B amorphous alloy was more selective than the Ni-B owing to its stronger adsorption for CH 3CN and the higher electron density on the Co active sites, both of them could inhibit the adsorption for C 2H 5NH 2 and in turn, retard the condensation. This could also account for its longer lifetime. However, such stronger adsorption for CH 3CN was harmful for the competitive adsorption for hydrogen and in turn resulted in a slightly lower hydrogenation activity than the Ni-B since the CH 3CN hydrogenation was first-order with respect to hydrogen while zero-order to CH 3CN.