Alkali-free hydrogenation of adiponitrile to hexamethylenediamine by Co@C skeleton strengthened with carbon nanotubes

Abstract

Catalytic hydrogenation of adiponitrile to hexamethylenediamine (HMDA) via alkali-free processes is essential to produce high-value downstream chemicals. In this work, we synthesized a series of Co@CCNTx catalysts using CNT promotion to strength the carbon skeleton derived by ZIF-67. Compared to the Co@C without CNT promotion, great enhancement of HMDA yield was achieved by Co@CCNTx. Characterizations suggested that CNT in the precursor modified the crystallization of the active Co centers as well as the surface composition in the Co@CCNTx. Strong Co-carbon interaction was formed via Co-N coordination caused by the facilitated re-dispersion of N- containing functionalities. The ethanol contact angle on Co@CCNTx was changed for better mass transfer and diffusion of reaction liquid on the catalyst. As a final result, the oxidation of cobalt sites was greatly suppressed in Co@CCNT0.3 and Co@CCNT0.5, which was proved an essential factor for their fast reaction rates. 88 % yield of HMDA with the rate of 4.5 molHMDA/molCo/h was reached under a much higher utilization rate of Co center.