Pd nanoparticles loaded on two-dimensional covalent organic frameworks with enhanced catalytic performance for phenol hydrogenation

Covalent organic frameworks (COFs) have emerged as an excellent support for heterogeneous catalysis due to their regular pore structure and high specific surface area. Herein, a series of porous TpPa-1 with different morphologies and structures were achieved by adjusting the ratio of water to acetic acid in the solvent-thermal process, and Pd@TpPa-1 catalysts were obtained with Pd solution impregnation. Notably, Pd@TpPa-1-100 prepared with 100 wt % water as the catalyst has superior catalytic properties in the phenol hydrogenation to cyclohexanone, and its turnover frequency (TOF) of 33.1 h^-1 is about 7 times higher than that of Pd@TpPa-1-0 synthesized with 100 wt % acetic acid as the catalyst. The two-dimensional (2D) nanosheet structures, highly dispersed Pd nanoparticles (NPs) with small particle size, and superhydrophilicity should be responsible for the superior catalytic performance of Pd@TpPa-1-100. Furthermore, Pd@TpPa-1-100 also has better catalytic performance in the hydrogenation of catechol, resorcinol, and hydroquinone than Pd@TpPa-1-0 and exhibits superior catalytic stability. This study provides a new approach for the structural regulation of metal-based COF catalysts.