6 Catalysis with MNPs on N-Doped Carbon
205
6.2 Supported Cobalt-Based Nanoparticles Surrounded
by Nitrogen Doped Graphene/Graphitic Shells
In addition to iron nanocatalysts [1] Beller and coworkers have also developed
nitrogen doped graphene encapsulated cobalt-oxide nanoparticles supported on
carbon (Co 3 O 4 -NGr@C) [12, 13]. These cobalt nanocatalysts were prepared again
by the immobilization and pyrolysis of cobalt-nitrogen complexes on heterogeneous support (Fig. 6.3). In order to prepare active cobalt nanoparticles-based catalysts, different nitrogen ligands such as phenanthroline, terpyridine and 2,6-bis(2benzimidazolyl)pyridine and pyridine have been used (Fig. 6.3) [12]. Among these,
the material prepared using phenanthroline produced the most active catalyst for the
hydrogenation of nitroarenes. Materials prepared using terpyridine and 2,6-bis(2benzimidazolyl)pyridine gave less active catalysts, while the ones prepared using
1,1
-bipyridine and pyridine are completely inactive [12].
Detailed characterization using TEM and EDX of this cobalt-oxide (Co 3 O 4 -
NGr@C) catalyst revealed the formation of Co 3 O 4 particles of wide size distribution
with a fraction of particles of 2–10 nm, and particles and agglomerates in the range
20–80 nm [12, 13]. XPS analysis showed that nitrogen is present in states such as
pyridinic, pyrrolic and quaternary amine (R 4 N
+ ). Like in the case of Fe 2 O 3 nanoparticles [1], these cobalt-oxide particles are surrounded by nitrogen doped graphene
layers. Carbon supported cobalt-oxide nanoparticles exhibit excellent hydrogenation
and oxidation, as well as reductive amination activity [13]. Applying these catalysts, functionalized nitroarenes were highly selectively hydrogenated to produce
the corresponding anilines in good to excellent yields (Scheme 6.8) [12].
Further, one-pot reductive amination of nitro compounds and carbonyl compounds
for the synthesis of amines has been demonstrated for the preparation of various
amines by using a Co 3 O 4 -NGr@C catalyst (Scheme 6.9) [13]. Here, different
nitro compounds as well as aldehydes underwent reaction to form imine first, and
then hydrogenation of the corresponding imine to produce the desired secondary
amines. This methodology constitutes a green and economic one-step process for
the preparation of higher value amines [13].
In addition to hydrogenations, the Co 3 O 4 /NGr@C catalyst exhibited excellent
activity and selectivity for direct oxidative esterification of alcohols to synthesize
various esters [14], which represent an abundant class of chemicals used as important
building blocks for the fine and bulk chemical industry [15]. This cobalt catalyst
enabled both cross and self-rectification of alcohols under mild reaction conditions
to obtain different kinds of esters in good to excellent yields by using atmospheric
oxygen (Scheme 6.10) [14].
Further by applying Co 3 O 4 /NGr@C catalyst, green synthesis of nitriles from
alcohols and ammonia via aerobic oxidation process has been performed [5].
Organic nitriles constitute major building blocks for organic synthesis and represent a versatile motif found in numerous medicinally and biologically important
compounds [16]. In general, functionalized nitriles are synthesized by cyanation
205
6.2 Supported Cobalt-Based Nanoparticles Surrounded
by Nitrogen Doped Graphene/Graphitic Shells
In addition to iron nanocatalysts [1] Beller and coworkers have also developed
nitrogen doped graphene encapsulated cobalt-oxide nanoparticles supported on
carbon (Co 3 O 4 -NGr@C) [12, 13]. These cobalt nanocatalysts were prepared again
by the immobilization and pyrolysis of cobalt-nitrogen complexes on heterogeneous support (Fig. 6.3). In order to prepare active cobalt nanoparticles-based catalysts, different nitrogen ligands such as phenanthroline, terpyridine and 2,6-bis(2benzimidazolyl)pyridine and pyridine have been used (Fig. 6.3) [12]. Among these,
the material prepared using phenanthroline produced the most active catalyst for the
hydrogenation of nitroarenes. Materials prepared using terpyridine and 2,6-bis(2benzimidazolyl)pyridine gave less active catalysts, while the ones prepared using
1,1
-bipyridine and pyridine are completely inactive [12].
Detailed characterization using TEM and EDX of this cobalt-oxide (Co 3 O 4 -
NGr@C) catalyst revealed the formation of Co 3 O 4 particles of wide size distribution
with a fraction of particles of 2–10 nm, and particles and agglomerates in the range
20–80 nm [12, 13]. XPS analysis showed that nitrogen is present in states such as
pyridinic, pyrrolic and quaternary amine (R 4 N
+ ). Like in the case of Fe 2 O 3 nanoparticles [1], these cobalt-oxide particles are surrounded by nitrogen doped graphene
layers. Carbon supported cobalt-oxide nanoparticles exhibit excellent hydrogenation
and oxidation, as well as reductive amination activity [13]. Applying these catalysts, functionalized nitroarenes were highly selectively hydrogenated to produce
the corresponding anilines in good to excellent yields (Scheme 6.8) [12].
Further, one-pot reductive amination of nitro compounds and carbonyl compounds
for the synthesis of amines has been demonstrated for the preparation of various
amines by using a Co 3 O 4 -NGr@C catalyst (Scheme 6.9) [13]. Here, different
nitro compounds as well as aldehydes underwent reaction to form imine first, and
then hydrogenation of the corresponding imine to produce the desired secondary
amines. This methodology constitutes a green and economic one-step process for
the preparation of higher value amines [13].
In addition to hydrogenations, the Co 3 O 4 /NGr@C catalyst exhibited excellent
activity and selectivity for direct oxidative esterification of alcohols to synthesize
various esters [14], which represent an abundant class of chemicals used as important
building blocks for the fine and bulk chemical industry [15]. This cobalt catalyst
enabled both cross and self-rectification of alcohols under mild reaction conditions
to obtain different kinds of esters in good to excellent yields by using atmospheric
oxygen (Scheme 6.10) [14].
Further by applying Co 3 O 4 /NGr@C catalyst, green synthesis of nitriles from
alcohols and ammonia via aerobic oxidation process has been performed [5].
Organic nitriles constitute major building blocks for organic synthesis and represent a versatile motif found in numerous medicinally and biologically important
compounds [16]. In general, functionalized nitriles are synthesized by cyanation