Selective hydrogenation of phenol to cyclohexanone in water over Pd@N-doped carbons derived from ZIF-67: Role of dicyandiamide

Abstract

Highly efficient Pd@CN catalysts for selective hydrogenation of phenol to cyclohexanone in water were successfully fabricated by loading Pd nanoparticles (NPs) in N-doped carbons (CN) derived from ZIF-67 with dicyandiamide (DICY) as the additional nitrogen source. For comparison, polyvinylpyrrolidone (PVP) was also used as the additional nitrogen source during the ZIF-67 synthesis. The results showed that the PVP and DICY had significantly different impacts on the microstructures of as-obtained CN materials and the catalytic performance of Pd@CN catalysts in the phenol hydrogenation. The addition of DICY had the positive promotion effect on the surface area of the obtained CN materials. Moreover, the introduction of DICY could increase the nitrogen content of CN and then prevent the re-oxidation of Pd NPs during air contact, resulting in higher Pd0 ratio. In comparison with PVP, the DICY was more suitable as the additional nitrogen source for the formation of CN and Pd@CN (Pd@CND, Pd@CNP). The Pd@CND exhibited superior catalytic activity as compared to Pd@CNP (phenol conversion 96.9% vs. 67.4%). More importantly, the as-prepared Pd@CND catalyst could be reused for four times without catalytic performance reduction. The work would aid the development of Pd@CN catalysts with superior catalytic properties.