Selective hydrogenation of quinolines into 1,2,3,4-tetrahydroquinolines over a nitrogen-doped carbon-supported Pd catalyst

Abstract

In this study, we have developed a sustainable method for the hydrogenation of quinolines to 1,2,3,4-tetrahydroquinolines under mild conditions over a nitrogen-doped carbon-supported Pd catalyst with abundant porous structures (abbreviated as Pd/CN). The mesoporous structure of the nitrogen-doped carbon support was prepared by the pyrolysis of glucose and melamine using eutectic salts of KCl and ZnCl₂ as the porogen. Due to the high nitrogen content in the support, Pd nanoparticles were homogeneously dispersed on the surface of nitrogen-doped carbon materials with an ultra-small size of 1.9 nm in a narrow size distribution. The as-prepared Pd/CN catalyst showed high catalytic activity towards the hydrogenation of quinolines at 50 °C and 20 bar H₂, affording the corresponding 1,2,3,4-tetrahydroquinolines with yields in the range of 86.6–97.8%. More importantly, the Pd/CN catalyst was highly stable without the loss of its catalytic activity during the recycling experiments. The use of renewable resources to prepare the catalyst makes this method promising for the sustainable 1,2,3,4-tetrahydroquinolines from the hydrogenation of quinolines.