246
presence of as-prepared poly(CTR-β-cyclodextrin). It was confirmed that carboxylate moieties in the backbone of the polymer could render the surface of the globules
negatively charged and consequently stabilize them due to electrostatic repulsion.
Moreover, these functionalities played an important role in the interaction with
Ru
3+
, affecting the nucleation of metal clusters in the initial stages of reduction.
Finally, the catalytic utility of the hybrid system as an efficient catalyst for aqueous
phase hydrogenation of biomass-derived 2-furaldehyde and 3-(2-furyl)acrolein at
1 MPa pressure and 303 K was confirmed. Notably, the catalyst was reusable for
five reaction runs, and the transmission electron microscopy analyses demonstrated
that the reuse of the catalyst did not induce any significant change in the morphology of the catalyst. It was suggested that the high catalytic activity and stability
came from the ability of poly(CTR-β-cyclodextrin) to provide a good balance of
stabilizing properties with the metal surface, both in terms of steric and electrostatic
interactions without hindering the catalytic activity. Additionally, each globule
could be considered as a confined space, microreactor, for promoting the hydrogenation process.
Another cyclodextrin-based polymer was used to stabilize ruthenium nanoparticles in aqueous medium. This polymer was synthesized by reacting β-cyclodextrin
with epichlorohydrin and glycidyltrimethylammonium chloride in alkaline medium
(Noël et al. 2017). The resulting Ru nanoparticles were tested in the hydrogenation
of different petro and biosourced substrates and showed a catalytic activity close to
the Ru/poly(CTR-β-cyclodextrin) nanoparticles. Interestingly, these nanoparticles
could be used in acidic medium (pH 3) for the hydrogenation of unsaturated carboxylic acids, especially linoleic and oleic acid. The catalytic system showed a strong
robustness because no loss of activity and stability had been observed by transmission electron microscopy experiments after ten consecutive runs in the tetradecene
hydrogenation.
In an interesting study, Au/Ag bimetallic core-shell nanoparticles with different
core diameters were synthesized by Haldar et al. (2014) through a β-cyclodextrinassisted synthetic procedure. The authors investigated the effect of core size
(10–100 nm) on the catalytic properties of the nanoparticles for the reduction of
4-nitrophenol in the presence of sodium borohydride. It was found that the catalytic
activity was influenced by the size of the core and differed from 41.8% to 96.5%.
Noteworthy, the core-shell system with core size of 100 nm was 12 times more
efficient than Au nanoparticles of the same size, indicating the effect of the coreshell structure on the catalytic activity.
Vasconcelos et al. (2016) reported the synthesis of polyurethane nanosponges
through reaction of hexamethylenediisocyanate and β-cyclodextrin and used the
prepared nanosponges as a template for the synthesis of Au n quantum clusters, by
the core etching of glutathione-capped Au nanoparticles. The authors investigated
the effect of the Au: nanosponge ratio on the nanocluster formation step. It was
established that the longer reaction time, the smaller clusters were formed. Initially,
the clusters formed in the cavities of cyclodextrin (Au 7 and Au 15 ), while for longer
reaction time, the cluster concentration in cavities increased. Further increase in the
reaction time led to the formation of larger clusters that could not be hosted in the
S. Noël et al.
presence of as-prepared poly(CTR-β-cyclodextrin). It was confirmed that carboxylate moieties in the backbone of the polymer could render the surface of the globules
negatively charged and consequently stabilize them due to electrostatic repulsion.
Moreover, these functionalities played an important role in the interaction with
Ru
3+
, affecting the nucleation of metal clusters in the initial stages of reduction.
Finally, the catalytic utility of the hybrid system as an efficient catalyst for aqueous
phase hydrogenation of biomass-derived 2-furaldehyde and 3-(2-furyl)acrolein at
1 MPa pressure and 303 K was confirmed. Notably, the catalyst was reusable for
five reaction runs, and the transmission electron microscopy analyses demonstrated
that the reuse of the catalyst did not induce any significant change in the morphology of the catalyst. It was suggested that the high catalytic activity and stability
came from the ability of poly(CTR-β-cyclodextrin) to provide a good balance of
stabilizing properties with the metal surface, both in terms of steric and electrostatic
interactions without hindering the catalytic activity. Additionally, each globule
could be considered as a confined space, microreactor, for promoting the hydrogenation process.
Another cyclodextrin-based polymer was used to stabilize ruthenium nanoparticles in aqueous medium. This polymer was synthesized by reacting β-cyclodextrin
with epichlorohydrin and glycidyltrimethylammonium chloride in alkaline medium
(Noël et al. 2017). The resulting Ru nanoparticles were tested in the hydrogenation
of different petro and biosourced substrates and showed a catalytic activity close to
the Ru/poly(CTR-β-cyclodextrin) nanoparticles. Interestingly, these nanoparticles
could be used in acidic medium (pH 3) for the hydrogenation of unsaturated carboxylic acids, especially linoleic and oleic acid. The catalytic system showed a strong
robustness because no loss of activity and stability had been observed by transmission electron microscopy experiments after ten consecutive runs in the tetradecene
hydrogenation.
In an interesting study, Au/Ag bimetallic core-shell nanoparticles with different
core diameters were synthesized by Haldar et al. (2014) through a β-cyclodextrinassisted synthetic procedure. The authors investigated the effect of core size
(10–100 nm) on the catalytic properties of the nanoparticles for the reduction of
4-nitrophenol in the presence of sodium borohydride. It was found that the catalytic
activity was influenced by the size of the core and differed from 41.8% to 96.5%.
Noteworthy, the core-shell system with core size of 100 nm was 12 times more
efficient than Au nanoparticles of the same size, indicating the effect of the coreshell structure on the catalytic activity.
Vasconcelos et al. (2016) reported the synthesis of polyurethane nanosponges
through reaction of hexamethylenediisocyanate and β-cyclodextrin and used the
prepared nanosponges as a template for the synthesis of Au n quantum clusters, by
the core etching of glutathione-capped Au nanoparticles. The authors investigated
the effect of the Au: nanosponge ratio on the nanocluster formation step. It was
established that the longer reaction time, the smaller clusters were formed. Initially,
the clusters formed in the cavities of cyclodextrin (Au 7 and Au 15 ), while for longer
reaction time, the cluster concentration in cavities increased. Further increase in the
reaction time led to the formation of larger clusters that could not be hosted in the
S. Noël et al.