Insights into the Solvent Effect on the Synthesis of Pd@PC-COFs for Phenol Hydrogenation

Selective phenol hydrogenation is a valuable route to produce cyclohexanone, but it poses a great challenge. Herein, a series of Pd@PC-COFs catalysts were prepared by the wet impregnation with different solvents. The impregnation solvent has a great influence on the microstructures and surface characteristics of the Pd@PC-COFs catalysts and their catalytic properties in the selective phenol hydrogenation to cyclohexanone. The as-prepared Pd@PC-COF-NBA catalyst shows the highest catalytic activity, with a phenol conversion of 98.3% at the cyclohexanone selectivity of 98.9%, which is 5.3 times that of Pd@PC-COF-MeOH and 2.4 times that of Pd@PC-COF-DI. Larger specific surface area, well-developed pore structures, rich mesoporous ratio, higher Pd content and Pd(0) ratio, and improved Pd dispersion are the important reasons for the superior catalytic performance of Pd@PC-COF-NBA. Pd@PC-COF-EA and Pd@PC-COF-Dio exhibit good catalytic stability during five reaction cycles. These findings can aid the development of high-performance Pd@COFs for the selective phenol hydrogenation.