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Single-atom dispersed Co–N–C catalyst: structure identification and performance for hydrogenative coupling of nitroarenes

Single-atom dispersed Co–N–C catalyst: structure identification and performance for hydrogenative... M–N–C (M refers to transition metals, typically Fe and Co), a type of metal and nitrogen bi-modified carbon material which is usually evolved from the pyrolysis of metal complexes with macrocyclic N4 ligands, has been widely investigated in electrocatalysis as a potential substitute for platinum.1–7 Owing to their capability of activating both hydrogen and oxygen, this class of noble-metal-free catalysts has recently been explored for a variety of hydrogenation and oxidation reactions in organic synthesis,8–13 such as reduction of nitroarenes to anilines,9,10 esterification of alcohols,11,12 and oxidation of ethylbenzene.13 One key issue associated with the catalysis of Co(Fe)–N–C materials is the identification of active sites.3,14–19 As most of the catalysts prepared by pyrolysis at high temperatures (600–900 °C) are composed of nanoparticles ranging from a few to tens of nanometers, both exposed and encapsulated, as well as of dispersed single atoms that are invisible with normal electron microscopy techniques, the unambiguous identification of active sites is still a pending challenge. In literature reports, big CoOx nanoparticles,3 encapsulated Fe or FeOx nanoparticles,15,20 as well as invisible FeNx were all respectively assumed as the active sites,4,16 without compelling evidence. Very recently, we prepared a Co–N–C catalyst on mesoporous carbon and investigated its catalytic capability for aerobic oxidative cross-coupling of primary and secondary alcohols.8 By conducting control experiments of acid leaching and extensive characterization of the catalysts before and after acid treatment, we proposed that the single Co atoms bonded with N within graphitic layers were catalytically active sites, whereas those particles of Co or CoOx were merely spectators. Nevertheless, this claim is still to be proved unequivocally given that multiple species of cobalt co-exist in the catalyst. On the other hand, the heterogeneity of such catalysts, not only complicates the understanding of the catalytic mechanism, but also greatly decreases the atomic efficiency, and even results in undesirable side-reactions. To tackle these problems, it is highly desirable to synthesize a single-atom M–N–C catalyst wherein M is exclusively dispersed as single atoms by bonding with N atoms. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Chemical Science Royal Society of Chemistry

Single-atom dispersed Co–N–C catalyst: structure identification and performance for hydrogenative coupling of nitroarenes

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References (50)

Publisher
Royal Society of Chemistry
Copyright
This journal is © The Royal Society of Chemistry
ISSN
2041-6520
eISSN
2041-6539
DOI
10.1039/c6sc02105k
Publisher site
See Article on Publisher Site

Abstract

M–N–C (M refers to transition metals, typically Fe and Co), a type of metal and nitrogen bi-modified carbon material which is usually evolved from the pyrolysis of metal complexes with macrocyclic N4 ligands, has been widely investigated in electrocatalysis as a potential substitute for platinum.1–7 Owing to their capability of activating both hydrogen and oxygen, this class of noble-metal-free catalysts has recently been explored for a variety of hydrogenation and oxidation reactions in organic synthesis,8–13 such as reduction of nitroarenes to anilines,9,10 esterification of alcohols,11,12 and oxidation of ethylbenzene.13 One key issue associated with the catalysis of Co(Fe)–N–C materials is the identification of active sites.3,14–19 As most of the catalysts prepared by pyrolysis at high temperatures (600–900 °C) are composed of nanoparticles ranging from a few to tens of nanometers, both exposed and encapsulated, as well as of dispersed single atoms that are invisible with normal electron microscopy techniques, the unambiguous identification of active sites is still a pending challenge. In literature reports, big CoOx nanoparticles,3 encapsulated Fe or FeOx nanoparticles,15,20 as well as invisible FeNx were all respectively assumed as the active sites,4,16 without compelling evidence. Very recently, we prepared a Co–N–C catalyst on mesoporous carbon and investigated its catalytic capability for aerobic oxidative cross-coupling of primary and secondary alcohols.8 By conducting control experiments of acid leaching and extensive characterization of the catalysts before and after acid treatment, we proposed that the single Co atoms bonded with N within graphitic layers were catalytically active sites, whereas those particles of Co or CoOx were merely spectators. Nevertheless, this claim is still to be proved unequivocally given that multiple species of cobalt co-exist in the catalyst. On the other hand, the heterogeneity of such catalysts, not only complicates the understanding of the catalytic mechanism, but also greatly decreases the atomic efficiency, and even results in undesirable side-reactions. To tackle these problems, it is highly desirable to synthesize a single-atom M–N–C catalyst wherein M is exclusively dispersed as single atoms by bonding with N atoms.

Journal

Chemical Science – Royal Society of Chemistry

Published: Aug 16, 2016

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