(Fig. 33) [121, 122]. A size-dependent oxygen activation pathway was proposed on
the basis of the extended surface areas and irregular electron distributions, involving
the formation of a hydroperoxide species on the surface. Similar characteristics were
observed not only for oxygen reduction but also for aerobic oxidation of toluene, for
which Pt 19 was reported to be the best catalyst.
7 Bimetallic and Multimetallic Catalysts Within
Dendrimers
Bimetallic NPs and clusters have attracted the interest of scientists because of the
synergic effects that emerge from the compositional ratio between two distinct
metals. These novel alloy materials provide catalytic selectivity, activity, and stability that are different from those for monometallic NPs. Three different approaches
(co-complexation, sequential loading, and partial displacement methods) to prepare
dendrimer-stabilized NPs are shown in Fig. 34. (1) The co-complexation method
involves coordination of two metals in the dendrimer, followed by simultaneously
chemical reduction to form alloy NPs. The composite ratios can be controlled by the
amounts of the two metal ions added. This method is suitable for synthesizing
multinuclear NPs composed of more than three metals. (2) The sequential loading
method is effective for the preparation of core@shell NPs. Core@shell NPs are also
interesting because their electronic and catalytic properties can be tuned by manipulating their structure. (3) The particle sizes in the partial displacement method are
increased after the second reduction step. The partial displacement methods are
dependent on the properties of transition metals. Cu NPs undergo galvanic exchange
with less than a stoichiometric amount of Ag
+
, Au
3+ , Pt
2+ , and Pd
2+ to give
bimetallic NPs composed of Cu and these noble metals.
Fig. 33 Catalytic
performance of
subnanosized Pt n particles
(n ¼ 12, 28, and 60) in
aerobic toluene oxidation.
TOFs estimated from the
sum of the TOFs for each
product. Adapted with
permission from
[121]. Copyright 2019
Wiley-VCH Verlag GmbH
& Co. KGaA, Weinheim
Precise Synthesis of Nanoparticles and Their Catalytic Behavior
157
the basis of the extended surface areas and irregular electron distributions, involving
the formation of a hydroperoxide species on the surface. Similar characteristics were
observed not only for oxygen reduction but also for aerobic oxidation of toluene, for
which Pt 19 was reported to be the best catalyst.
7 Bimetallic and Multimetallic Catalysts Within
Dendrimers
Bimetallic NPs and clusters have attracted the interest of scientists because of the
synergic effects that emerge from the compositional ratio between two distinct
metals. These novel alloy materials provide catalytic selectivity, activity, and stability that are different from those for monometallic NPs. Three different approaches
(co-complexation, sequential loading, and partial displacement methods) to prepare
dendrimer-stabilized NPs are shown in Fig. 34. (1) The co-complexation method
involves coordination of two metals in the dendrimer, followed by simultaneously
chemical reduction to form alloy NPs. The composite ratios can be controlled by the
amounts of the two metal ions added. This method is suitable for synthesizing
multinuclear NPs composed of more than three metals. (2) The sequential loading
method is effective for the preparation of core@shell NPs. Core@shell NPs are also
interesting because their electronic and catalytic properties can be tuned by manipulating their structure. (3) The particle sizes in the partial displacement method are
increased after the second reduction step. The partial displacement methods are
dependent on the properties of transition metals. Cu NPs undergo galvanic exchange
with less than a stoichiometric amount of Ag
+
, Au
3+ , Pt
2+ , and Pd
2+ to give
bimetallic NPs composed of Cu and these noble metals.
Fig. 33 Catalytic
performance of
subnanosized Pt n particles
(n ¼ 12, 28, and 60) in
aerobic toluene oxidation.
TOFs estimated from the
sum of the TOFs for each
product. Adapted with
permission from
[121]. Copyright 2019
Wiley-VCH Verlag GmbH
& Co. KGaA, Weinheim
Precise Synthesis of Nanoparticles and Their Catalytic Behavior
157