The Catalytic Performance Of Au-Pd/γ-Al₂O₃ For Synthesis Of Imine

Imines are excellent organic ligands and intermediates which play vital roles in the fields of catalysis, analysis chemistry, bio-medical science and functional materials. In this paper, a series of Au, Pd and Au-Pd/γ-Al2O3 catalysts were prepared by the impregnation reduction method using NaBH4 as reducing agent and L-lysine as protection agent. The performance of these catalysts for synthesis imine with different method was studied. UV-Vis, XRD, TEM, XPS, BET and AAS were employed to investigate the dependence of dispersion, composition, chemistry morphology of the active composition and actual loading on the catalytic performance.Firstly, a series of Au, Pd, Au-Pd catalysts were prepared using ZrO2 as support and their performance for benzylalcohol and benzylamine coupling synthesis imine was investigated. 3wt% Au-Pd/ZrO2 bimetallic catalyst showed high activity for the base-free synthesis of imine(N-Benzylidenebenzylamine). At ambient condition, no added oxidation agents and bases, the yield of product imine is 30% at 70 ℃. At the same time, we found 3wt% Au-Pd/γ-Al2O3 catalyst has good catalytic performance for the benzylamine self-coupling reaction.Then, the performance of Au, Pd, Au-Pd catalysts supported on γ-Al2O3 was investigated for benzylamine self-coupling reaction to synthesis imine. 3wt% Au-Pd/γ-Al2O3 catalyst displayed high activity for the base-free synthesis of imine(N-Benzylidenebenzylamine) from benzylamine self-coupling. The yield of imine is 93% at the reaction temperature of 70 ℃. The 3wt% Au-Pd/γ-Al2O3 catalyst could be recycled whereas the yield of imine decreased to 44%after reused 5 runs.Oxidation dehydrogenation of dibenzylamine is an important reaction of synthesis imine. 3wt% Au-Pd/γ-Al2O3 catalyst exhibits excellent catalytic properties on synthesis imine from oxidation dehydrogenation of dibenzylamine. Over 3wt% Au-Pd/γ-Al2O3 catalyst, 95% yield of imine was achieved at the temperature of 60 ℃. After recycled 4 times, the yield of imine reduced to 80%.The characterization showed that catalysts prepared by the impregnation reduction method possess small particle diameter and highly dispersion. In addition, the existing electron transformation between Au and Pd in 3wt% Au-Pd/γ-Al2O3 catalyst might promote the catalytic activity. The leaching of the active component could lead to the losing of activity. The leaching rate of Au and Pd is different in defferent reactions.Based on the above results, it could be seen, the optimized Au-Pd bimetallic catalyst displayed excellent performance of benzylamine self-coupling reaction and oxidation dehydrogenation of dibenzylamine for base-free synthesis imine. The high efficient utilization of atom, no addition of oxidation agents and bases, comparable low reaction temperate conformed to green synthesis of imine.