Controllable Synthesis of 1D Pd@N-CNFs with High Catalytic Performance for Phenol Hydrogenation

Abstract: Achieving both high conversion and selectivity under mild conditions still remains a big challenge in the selective hydrogenation of phenol to cyclohexanone. Herein, one-dimensional (1D) N-doped carbon nanofibers (N-CNFs) were successfully fabricated by electrospinning with one-step carbonization, and used to load Pd nanoparticles for synthesizing Pd@N-CNFs catalysts. The dicyandiamide (DICY) and citric acid in the spinning solution exhibited a significant synergistic effect in controlling the morphology and surface property of N-CNFs and the corresponding catalytic activity of Pd@N-CNFs in the selective hydrogenation of phenol to cyclohexanone. The as-prepared Pd@N-CNFs-1.5 catalyst possessed good fibrous morphology, larger surface area, and more amounts of surface N and OH group, and exhibited a phenol conversion of 99.7% with a cyclohexanone selectivity of 97.3% under mild reaction conditions. In addition, the catalytic activity of Pd@N-CNFs-1.5 increased by 2.75 times as compared to Pd@N-CNFs-0 and 1.22 times in comparison with Pd@N-CNFs-100. Furthermore, the 1D Pd@N-CNFs-1.5 was easy to be recovered from the reaction mixture, and showed good reusability. Graphic Abstract: [Figure not available: see fulltext.]The proper molar ratio of dicyandiamide (DICY) and citric acid could significantly adjust the fibrous characteristic and surface properties of the Pd@CNFs catalyst, which contributed to the higher N and OH group contents, thereby improving the loading and distribution of Pd nanoparticles and the dispersibility of Pd@CNFs in water. These properties jointly led to the superior phenol hydrogenation efficiency of the Pd@CNFs catalyst.