265
short reaction time of 30 min in the absence of organic solvents. FTIR experiment
was done, and it clearly showed that β-cyclodextrin was attached to reduced graphene oxide. By thermogravimetric analysis, the amount of β-cyclodextrin was
determined and was about 28 wt%. This grafting of β-cyclodextrin could prevent the
aggregation of the bimetallic clusters. The hybrid system was used as an electrocatalyst for promoting methanol and ethanol oxidation. The comparison of the catalytic activity of this hybrid system with conventional Pd/C and Pd@β-CD-rGO,
Pt@β-CDrGO, and Pd-Pt@rGO confirmed its superior catalytic activity, poison
tolerance, and durability which could emerge from very tiny size, high monodispersity, and uniformity of bimetallic catalyst, using a hybrid support with high surface
area and synergistic effects due to the coexistence of Pd and Pt atoms on the surface.
Putta et al. (2015) disclosed a novel hybrid system, Pd@cyclodextrin-graphene
nanosheets, containing Pd nanoparticles, β-cyclodextrin, and graphene nanosheets
with the utility as a catalyst for promoting phosphine-free Suzuki-Miyaura, HeckMizoroki, and C-C coupling reactions in aqueous media. To prepare cyclodextringraphene nanosheets, the suspension of graphene oxide in deionized water was well
dispersed by using ultrasonic irradiation and mixed with the solution of
β-cyclodextrin and ammonia. Then, hydrazine solution was added, and the resulting
mixture reacted under stirring to afford cyclodextrin-graphene nanosheets. To incorporate Pd nanoparticles, cyclodextrin-graphene nanosheets in ethanol were dispersed and reacted with PdCl 2 . Ethanol played the role of green solvent and in situ
reducing agent. The Pd loading in the final catalyst was calculated to be 6.2 wt%.
The authors believed that the presence of cyclodextrin on graphene nanosheets
could stabilize the Pd nanoparticles, improve their dispersion, and avoid agglomeration. Moreover, the cyclodextrin cavity could serve as an inclusion site for the
reagents. These factors as well as “Breslow effect” and formation of ternary cyclodextrin/substrate/additive complexes on the Pd-graphene nanosheet surface led to
high catalytic activity of the hybrid system. Notably, the catalyst was reusable and
could promote four successive reaction runs with loss of the catalytic activity to
some extent (about 20% for the fourth reaction run compared to the first run). The
hot filtration test as well as ICP-AES analysis proved 0.31 wt% Pd leaching in the
reused catalyst after three reaction runs compared to fresh catalyst. Low amount of
the catalyst, high yields, green and simple procedure, and wide substrate scope were
the merits of this strategy.
To improve the water disposability of fullerene, C 60 , it was modified with
hydroxypropyl-β-cyclodextrin. The hybrid system was then applied for supporting
Pd nanoclusters with mean particle size of 2.5 nm (Zhang et al. 2015). Hydroxypropylβ- cyclodextrin acted as a coordination agent and surfactant and improved the disparity and compositional uniformity of nanoparticles. The hybrid system with an
electrochemical surface area of 41.6 m
2
g
−1
exhibited outstanding electrocatalytic
activity for the oxidation of formic acid. Moreover, the much more negative onset
potentials and better stability compared to electrodes modified by other electrocatalysts were observed, implying the promising utility of this system for use in a direct
formic acid fuel cell.
5 Metal Nanoparticles and Cyclodextrins for Catalytic Applications
short reaction time of 30 min in the absence of organic solvents. FTIR experiment
was done, and it clearly showed that β-cyclodextrin was attached to reduced graphene oxide. By thermogravimetric analysis, the amount of β-cyclodextrin was
determined and was about 28 wt%. This grafting of β-cyclodextrin could prevent the
aggregation of the bimetallic clusters. The hybrid system was used as an electrocatalyst for promoting methanol and ethanol oxidation. The comparison of the catalytic activity of this hybrid system with conventional Pd/C and Pd@β-CD-rGO,
Pt@β-CDrGO, and Pd-Pt@rGO confirmed its superior catalytic activity, poison
tolerance, and durability which could emerge from very tiny size, high monodispersity, and uniformity of bimetallic catalyst, using a hybrid support with high surface
area and synergistic effects due to the coexistence of Pd and Pt atoms on the surface.
Putta et al. (2015) disclosed a novel hybrid system, Pd@cyclodextrin-graphene
nanosheets, containing Pd nanoparticles, β-cyclodextrin, and graphene nanosheets
with the utility as a catalyst for promoting phosphine-free Suzuki-Miyaura, HeckMizoroki, and C-C coupling reactions in aqueous media. To prepare cyclodextringraphene nanosheets, the suspension of graphene oxide in deionized water was well
dispersed by using ultrasonic irradiation and mixed with the solution of
β-cyclodextrin and ammonia. Then, hydrazine solution was added, and the resulting
mixture reacted under stirring to afford cyclodextrin-graphene nanosheets. To incorporate Pd nanoparticles, cyclodextrin-graphene nanosheets in ethanol were dispersed and reacted with PdCl 2 . Ethanol played the role of green solvent and in situ
reducing agent. The Pd loading in the final catalyst was calculated to be 6.2 wt%.
The authors believed that the presence of cyclodextrin on graphene nanosheets
could stabilize the Pd nanoparticles, improve their dispersion, and avoid agglomeration. Moreover, the cyclodextrin cavity could serve as an inclusion site for the
reagents. These factors as well as “Breslow effect” and formation of ternary cyclodextrin/substrate/additive complexes on the Pd-graphene nanosheet surface led to
high catalytic activity of the hybrid system. Notably, the catalyst was reusable and
could promote four successive reaction runs with loss of the catalytic activity to
some extent (about 20% for the fourth reaction run compared to the first run). The
hot filtration test as well as ICP-AES analysis proved 0.31 wt% Pd leaching in the
reused catalyst after three reaction runs compared to fresh catalyst. Low amount of
the catalyst, high yields, green and simple procedure, and wide substrate scope were
the merits of this strategy.
To improve the water disposability of fullerene, C 60 , it was modified with
hydroxypropyl-β-cyclodextrin. The hybrid system was then applied for supporting
Pd nanoclusters with mean particle size of 2.5 nm (Zhang et al. 2015). Hydroxypropylβ- cyclodextrin acted as a coordination agent and surfactant and improved the disparity and compositional uniformity of nanoparticles. The hybrid system with an
electrochemical surface area of 41.6 m
2
g
−1
exhibited outstanding electrocatalytic
activity for the oxidation of formic acid. Moreover, the much more negative onset
potentials and better stability compared to electrodes modified by other electrocatalysts were observed, implying the promising utility of this system for use in a direct
formic acid fuel cell.
5 Metal Nanoparticles and Cyclodextrins for Catalytic Applications