be noted that the average numbers represent a statistical distribution of the metal ions
coordinated to the dendrimers. Chemical reduction of the metal ions to zero-valent
metals by reducing agents (e.g., NaBH 4 ) provokes the agglomeration of metal atoms
to form monodisperse NPs inside the dendrimer. Esumi reported a reagent-free
photochemical reduction to form Au NPs in the same year [9], which had an
advantage with the respect to the purification processes.
A great variety of dendritic nanocatalysts has been developed over the 20 years
since the first discovery of metal NPs stabilized within dendrimers. The advantages
of dendritic nanocatalysts include the following:
1. The most important role of the dendrimer is to act as a synthesis template for
precisely controlled synthesis of NPs, whereby the number of atoms in the
particles and the blending ratio of the different atoms are controlled. These factors
significantly affect the catalytic activity and selectivity for catalysis.
2. The encapsulation effect provides catalytic stability to prevent the metastable NPs
from aggregation, leaching, and passivation of metals during reactions. The
dendrimer is functionalized as a size-selective molecular nanofilter of the
reactants.
3. Dendrimer-encapsulated NPs can immobilize to organic polymer solids or inorganic solids on supports for heterogeneous applications. These heterogenized
homogeneous catalysts are expected to surpass the catalytic performance of
homogeneous catalysts and classical solid-state catalysts.
The catalytic properties of the dendritic NPs influent strongly on relationship
between the particles and the dendrimers. Figure 3 summarizes the frequently
=
Encapsulation effect
(Shell effect)
dendron
core
M n+
generation
NaBH4
Metal nanoparticle
Dendrimer complex
Fig. 2 Procedure for the synthesis of metal NPs encapsulated by a dendrimer
(a)
(c)
(b)
Fig. 3 Various metallodendritic structures of metal NPs for catalytic reactions with (a) interior, (b)
exterior, and (c) core types
134
M. Tanabe and K. Yamamoto
coordinated to the dendrimers. Chemical reduction of the metal ions to zero-valent
metals by reducing agents (e.g., NaBH 4 ) provokes the agglomeration of metal atoms
to form monodisperse NPs inside the dendrimer. Esumi reported a reagent-free
photochemical reduction to form Au NPs in the same year [9], which had an
advantage with the respect to the purification processes.
A great variety of dendritic nanocatalysts has been developed over the 20 years
since the first discovery of metal NPs stabilized within dendrimers. The advantages
of dendritic nanocatalysts include the following:
1. The most important role of the dendrimer is to act as a synthesis template for
precisely controlled synthesis of NPs, whereby the number of atoms in the
particles and the blending ratio of the different atoms are controlled. These factors
significantly affect the catalytic activity and selectivity for catalysis.
2. The encapsulation effect provides catalytic stability to prevent the metastable NPs
from aggregation, leaching, and passivation of metals during reactions. The
dendrimer is functionalized as a size-selective molecular nanofilter of the
reactants.
3. Dendrimer-encapsulated NPs can immobilize to organic polymer solids or inorganic solids on supports for heterogeneous applications. These heterogenized
homogeneous catalysts are expected to surpass the catalytic performance of
homogeneous catalysts and classical solid-state catalysts.
The catalytic properties of the dendritic NPs influent strongly on relationship
between the particles and the dendrimers. Figure 3 summarizes the frequently
=
Encapsulation effect
(Shell effect)
dendron
core
M n+
generation
NaBH4
Metal nanoparticle
Dendrimer complex
Fig. 2 Procedure for the synthesis of metal NPs encapsulated by a dendrimer
(a)
(c)
(b)
Fig. 3 Various metallodendritic structures of metal NPs for catalytic reactions with (a) interior, (b)
exterior, and (c) core types
134
M. Tanabe and K. Yamamoto