Insights into the Stability of Pd/CN Catalyst in Liquid Phase Hydrogenation of Phenol to Cyclohexanone: Role of Solvent

Abstract

The production of cyclohexanone by liquid phase phenol hydrogenation is sustainable and green. In this work, the effect of solvent, i.e., water and organic solvents (cyclohexane, methanol and acetone) on the stability of Pd/CN catalyst in the production of cyclohexanone by selective phenol hydrogenation was investigated, and the mechanism is explored by comprehensive characterizations. The results suggest that the solvent has significant effect on the reusability of Pd/CN catalyst in phenol hydrogenation, and the catalytic performance of Pd/CN increases gradually in water but decreases in organic solvents with the reaction cycle. The results of XRD, TEM and XPS confirm that the Pd/CN catalyst maintains wonderful dispersion of Pd NPs and forms more ratio of Pd (0) in water with the reaction cycle, while the opposite results are found in cyclohexane (organic solvents). The results of XPS, TG and BET suggest that the Pd/CN catalyst adsorbs continually phenol in water with the reaction cycle, which inhibits the agglomeration of Pd NPs and promotes the formation of Pd (0), thus better catalytic stability. This work would aid the efficient industrial production of cyclohexanone over Pd/CN. The solvent affected significantly the stability of Pd@CN catalyst in liquid phase phenol hydrogenation to cyclohexanone, and the catalytic activity of Pd@CN increased in water but decreased in cyclohexane with the reaction cycle.