Effects of the preparation methods on the performance of the Cu–Cr–Fe/γ-Al2O3 catalysts for the synthesis of 2-methylpiperazine

Co-precipitation, impregnation and ultrasonic sol–gel (USG) methods have been used to prepare Cu–Cr–Fe/γ-Al2O3 catalysts, which were further used to synthesize 2-methylpiperazine. The catalysts were characterized by XRD, XPS, TG/DSC, BET, TPR, AAS and TEM. It is found that preparation method can greatly impact the catalytic performance of the catalysts, the Cu–Cr–Fe/γ-Al2O3 catalyst prepared by the ultrasonic sol–gel method proved to be the most active and stable for this reaction. The dispersion and stabilization of Cu0 in the reduced catalysts are attributed to the existence of CuCr2O4 and Fe2O3. A surprising copper migration was detected by XPS analysis for the Cu–Cr–Fe/γ-Al2O3-USG catalyst after the calcination process, which may be crucial to the high activity and stability of this catalyst.