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. 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.