Facile synthesis of ultrafine cobalt oxides embedded into N-doped carbon with superior activity in hydrogenation of 4-nitrophenol

Design and synthesis of low-cost catalysts with high activity and stability for hydrogenation reactions is an important research area of applied catalysis. In this work, we present a kind of ultrafine cobalt oxides encapsulated by N-doped carbon (donated as CoOx/CN) as efficient catalysts for hydrogenation of 4-nitrophenol (4-NP) process. The CoOx/CN was fabricated through a pyrolysis strategy using an N containing metal-organic framework (Co-MOF) as precursor followed by a fine thermal-treatment. With an optimized pyrolysis temperature of 500 degrees C, the CoOx species present as ultrafine particles highly dispersed in the obtained catalyst (CoOx/CN-500). CoOx/CN-500 exhibits excellent activity and stability in hydrogenation of 4-NP at ambient conditions. The activity is much higher than that of not only bulk cobalt oxides, but also carbon supported CoOx catalysts. It could be used for more than 8 times without obvious fading in activity. In addition, the concrete role of Co-MOF precursor and pyrolysis condition in the catalyst design was investigated in detail. The interaction between organic ligands and Co ions and the confinement of the crystalline structure of Co-MOF could restrain the aggregation of Co ions during pyrolysis and lead to high dispersion of ultrafine CoOx species. Meanwhile, the N-containing ligands could be transformed into doped N species (pyridinic and pyrrolic N), endowing the CoOx species with high electron density and promoting the formation of active sites for the hydrogenation reaction. (C) 2017 Elsevier Inc. All rights reserved.