Efficient Cu–Ni/W₂₀O₅₈ Catalysts for Hydrogenation of Nitriles to Secondary Amines

Abstract

The hydrogenation of nitriles is an environmentally friendly and atom-economical route to prepare high-value amines; however, it is still a challenge to control selectivity because of the occurrence of hydrogenation, self-coupling, and hydrogenolysis reactions during the hydrogenation process. It is highly desirable to develop efficient non-noble-metal catalysts for the hydrogenation of nitriles to secondary amines, although several noble metal catalysts have been reported. Herein, we successfully prepared a Cu–Ni/W 20 O 58 catalyst and found that the Cu 4.4 –Ni 0.6 /W 20 O 58 catalyst showed a 92.3% yield with initial TOF s of 270.0 h –1 at 373 K and 3 MPa H 2 for the hydrogenation of benzonitrile (BN) to dibenzylamine (DBA), which was much superior to that of the monometallic Cu 4.4 /W 20 O 58 and Ni 0.6 /W 20 O 58 catalysts. Moreover, the Cu 4.4 –Ni 0.6 /W 20 O 58 catalyst could be reused at least 4 times and was effective for the hydrogenation of various nitriles with superior selectivity to secondary amines. Furthermore, the reaction mechanism of BN hydrogenation for the Cu–Ni alloy of Cu 4.4 –Ni 0.6 /W 20 O 58 was proposed on the basis of spectroscopic studies such as XRD, TPR, TEM, XAFS, and XPS, kinetic studies such as the effect of BN concentration and H 2 pressure, the isotopic effect of hydrogen, and the effect of the reaction temperature and DFT calculations. The rate-determining step was the hydrogenation of benzylidenamine (BI) to the half-hydrogenated intermediate by one H atom over the Cu 4.4 –Ni 0.6 /W 20 O 58 catalyst. The Ni–W 20 O 58 interface was responsible for the adsorption and activation of BN, and the electron-rich Cu acted as the site for H 2 dissociation; the synergistic effect of Cu and Ni led to the superior catalytic performance of the Cu 4.4 –Ni 0.6 /W 20 O 58 catalyst.

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