Rational design of cobalt catalysts embedded in N-Doped carbon for the alcohol dehydrogenation to carboxylic acids

Abstract

In this work, a series of Co catalysts (namely Co@NC) was designed and developed from the thermal treatment of ZIF-67. Through extensive screening of various parameters, Co@NC700-H2/Ar exhibited the best catalytic performance in the acceptorless alcohol dehydrogenation to carboxylic acids. It was worth noting that Co@NC700-H2/Ar enabled the efficient synthesis of various aromatic and aliphatic carboxylic acids in moderate to high yields. Besides, it was recyclable for 9 consecutive cycles without activity decay. Moreover, the effects of pyrolysis conditions on the catalytic performance of the resulting materials were thoroughly examined, and the rationale for the superiority of Co@NC700-H2/Ar over the other prepared materials was also provided. Specifically, the pyrolysis atmosphere applying 95% of Ar gas and 5% of H2 gas (H2/Ar) resulted in the generation of ideal porosity and carbon nanotubes (CNTs), while utilizing 700 °C as the optimized pyrolysis temperature was ascribed to the comprehensive evaluation of materials crystallinity and defective structures. Furthermore, additional insights were gained by systematically exploring the oxidation states of Co in different catalysts. It was proposed that the Co–N species played a crucial role in this catalysis, while the contribution of other Co species, including Co0 and Co–O, could not be neglected. Finally, a plausible reaction mechanism was proposed based on the above observations and related literature reports.