Zeolitic microcapsule with encapsulated platinum nanoparticles for one-pot tandem reaction of alcohol to hydrazone

Article abstract of DOI:10.1039/c2cc33701k

A zeolitic platinum-encapsulated microcapsule was successfully employed in the one-pot tandem synthesis of hydrazone directly from cyclohexanol with high conversion, selectivity and reusability due to the promising protection of the zeolitic shell around the catalyst.

Full text of DOI:10.1039/c2cc33701k

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Zeolitic microcapsule with encapsulated platinum nanoparticles for
one-pot tandem reaction of alcohol to hydrazonew
Jing Shi, Lifeng Chen, Nan Ren, Yahong Zhang and Yi Tang*
Received 23rd May 2012, Accepted 28th June 2012
DOI: 10.1039/c2cc33701k
A zeolitic platinum-encapsulated microcapsule was successfully
employed in the one-pot tandem synthesis of hydrazone directly
from cyclohexanol with high conversion, selectivity and reusability
due to the promising protection of the zeolitic shell around the
catalyst.
chemicals (Fig. 1).12–16 In addition, it has broad biological and
pharmaceutical activities, including antimicrobial, anticonvulsant,
analgesic, anti-inflammatory, antiplatelet, antitubercular, anti-
tumoral, vasodilator, antiviral and schistosomiasis control
activities etc.17 So far, the most effective approach for hydrazone
preparation is based on the condensation of the N–H group in
phenylhydrazine (N-Boc) and the carbonyl group in ketone.18,19
Nowadays, a ketone is mainly prepared by the selective oxidation
of an alcohol on the catalysts of metal, titanosilicalite or
supramolecules etc.20,21 If these two operations could be
integrated into one reactor, that is, synthesizing hydrazone
directly from alcohol, as shown in Fig. 2, the eco-efficiency and
the value of the manufacture process would be significantly
enhanced by avoiding the cost of separation, transference and
reservation of intermediates.22 However, the problem for
achieving such a goal lies in the fact that the platinum (as the
catalyst for alcohol oxidation) would lose its activity due to the
strong interaction with N atoms in phenylhydrazine.23,24 Herein, a
zeolitic microcapsule with encapsulated Pt species and silicalite-1
shell (denoted as Pt@S1) is demonstrated as an effective catalyst
for the one-pot synthesis of hydrazone from alcohol via a tandem
reaction. By comparing the commercial Pt–SiO2 and the heavily
ground broken capsules (B-Pt@S1) with the open structure, it is
found that the existence of the microcapsule structure is crucial to
realize such a tandem process and further endows the catalyst
with outstanding reusability due to the anti-leaching and poison-
resistance characters of the zeolitic shell.
During the last few decades, the application of tandem reactions
from A to B and then B to C has emerged as a hot topic due to the
sequential integration of different reactions in one-pot, which
endows the process with simplicity, high efficiency and low waste
outcome.1–3 The key factor for achieving such a goal largely relies
on the rational design of the structure of a catalyst able to avoid
interferences among different reactions, as well as various reactants/
intermediates/products, or catalytic species within the reaction
system.4 One of the promising approaches is to insulate the
interfering reactions by separating their catalytic species into
different regions of catalyst.5 Microcapsule reactors with
encapsulated active sites (such as Pt, Pd and Fe) and thin
zeolite shells have been recently prepared via hydrothermally
treating seeded mesoporous spheres with pre-encapsulated
catalytic components.6–9 Their superior catalytic performances,
e.g., shape-selectivity, poison-resistance and anti-leakage effect of
active species, have been successfully proved via reactions both in
liquid and gaseous phases, including alcohol oxidation and
dynamic kinetic resolution of phenylethylamine reactions.8,9
Meanwhile, some groups also developed core–shell structure
catalysts by coating zeolite film onto industrial catalysts. Their
applications have been explored via one-step dimethyl ether
synthesis from syngas and Fischer–Tropsch synthesis with high
middle isoparaffins fabrication.10,11
The Pt@S1 was prepared through a hydrothermal treating
process according to our previous report.8,9,25 Fig. 3 displays
typical SEM and TEM images of Pt@S1. This catalyst possesses
uniform spherical morphology with a size of about 1.6 mm (Fig. 3A)
and the outside shell was roughly packed with silicalite-1 crystals.
The hollow interior can be clearly observed from the TEM
As a versatile intermediate, Boc-hydrazone possessing a proton
from an azomethine group (–NHNQCH–) can act as both
electrophile and nucleophile for production of a lot of useful fine
Department of Chemistry, Shanghai Key Laboratory of Molecular
Catalysis and Innovative Materials and Laboratory of Advanced
Material, Fudan University, Shanghai, 200433, PR China.
E-mail: yitang@fudan.edu.cn; Fax: (+86)-21-65641740;
Tel: (+86)-21-55664125
w Electronic supplementary information (ESI) available: The detailed
synthesis process of Pt@S1 and 1-tert-butoxycarbonyl-1-phenylhydra-
zine (N-Boc) and their corresponding XRD, IR, N2 adsorption–
desorption isotherms and TGA results, as well as the 1H NMR results.
The detailed tandem reaction conditions and the SEM image of the
Pt@S1 after ten runs. See DOI: 10.1039/c2cc33701k
Fig. 1 Various transformations of Boc-hydrazone.
Chem. Commun., 2012, 48, 8583–8585 8583
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Fig. 2 The equation of the tandem reaction from alcohol to
hydrazone.
Fig. 3 (A) SEM and (B) TEM images of Pt@S1. The high magnifica-
tion TEM image is displayed in inset of Fig. 3B.
image (Fig. 3B). The inset image of Fig. 3B reveals the highly
dispersive Pt nanoparticles. The content of Pt is about 3 wt%,
as determined by ICP-AES test. The composition of Pt@S1 is
proved by the co-existence of XRD peaks of platinum and
silicalite-1 (Fig. S1, ESIw). The infrared spectrum (Fig. S2,
ESIw) and N2 sorption isotherms (Fig. S3, ESIw) further prove
the high crystallinity of the silicalite-1 shell.26 Different from
the commercial Pt–SiO2, which possesses low surface area and
volume of micropores, the Pt@S1 has about 341 m2 gÀ1 of
BET surface area and 0.12 cm3 gÀ1 of micropore volume
calculated by the t-plot method, close to that of the ordinary
silicalite-1 nanocrystals (Table S1, ESIw).27 The TGA data
(Fig. S4, ESIw) of the as-synthesized Pt@S1 before calcination
clearly displays two weight loss steps at room temperature–200 1C
and 200–500 1C, which are ascribed to the loss of adsorbed
water and decomposition of the organic template in the
zeolitic micropores, respectively.
Fig. 4 Conversion and selectivity for (A) tandem reaction and (B) oxida-
tion reaction with benzothiazole of Pt@S1, B-Pt@S1 and commercial
Pt–SiO2.
with big molecular sizes can be isolated from the sensitive
active sites and the catalyst could keep its reactivity in the
tandem reaction. The mechanism is illustrated in Fig. 5.
To further prove the effect of the zeolitic shell, the Pt@S1 was
further used for oxidation of cyclohexanol with benzothiazole as
a poison material in the system. The commercial Pt–SiO2 and
the B-Pt@S1 were used as references under the same conditions.
As shown in Fig. 4B, the active Pt species with the protective
silicalite-1 shell are not affected by benzothiazole and
could retain their activities. The reaction could proceed success-
fully with high conversion at 80% and selectivity at 90%.
The tandem reaction was carried out by oxidation of
cyclohexanol to cyclohexanone at first on Pt@S1, followed
by continuously condensing between the newly formed ketone
with N-Boc to form hydrazone in the same pot (Fig. 228). To
confirm the key importance of the zeolitic shell, the B-Pt@S1
and commercial Pt–SiO2 catalysts were measured under the
same conditions. As observed in Fig. 4A, the Pt@S1 catalyst
with intact zeolitic shell presents high conversion (92%) and
selectivity (70%) for the tandem reaction. Nevertheless, the
reactivity dramatically decreases for the catalyst with exposed
Pt species, such as commercial Pt–SiO2 and B-Pt@S1. The
conversion of commercial Pt–SiO2 reduces to 10% and its
selectivity to target product is only 44%. Similarly, the
B-Pt@S1 with an open structure has a selectivity of only
18% and a conversion of nearly zero. On the basis of these
observations, it is speculated that the encapsulated Pt in the
Pt@S1 catalyst is protected by the silicalite-1 shell towards
being in contact with the big N-Boc molecules. Therefore, its
catalytic activity could be well-retained with the presence of
N-Boc in the reaction system. However, if the outside shell is
heavily destroyed, the active sites inside the microcapsule are
exposed and then interact with N-Boc in the system, resulting
in their poor catalytic performances. Thereafter, the existence
of the zeolitic shell is significant for successfully conducting a
controllable tandem reaction. With the intact shell, the toxins
Fig. 5 Schematic illustrations of the whole process of the tandem
reactions on Pt@S1 and B-Pt@S1.
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8584 Chem. Commun., 2012, 48, 8583–8585
This journal is The Royal Society of Chemistry 2012

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Education Commission, Shanghai Education Development
Foundation (09CG02), STCSM (09DZ2271500 and
11JC1400400) and the Major State Basic Research Develop-
ment Program of China (2009CB930400 and 2009CB623506).
Notes and references
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oxidation conversion and selectivity.
The recyclability of this microcapsule catalyst is also tested. As
shown in Fig. 6, the catalytic activity of Pt@S1 remains almost the
same after 10 runs, indicating the very high reusability of the
zeolitic microcapsule. The intact zeolitic shell not only protects the
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to the low density of their hollow structure. Moreover, owing to
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In summary, the Pt encapsulated microcapsule catalyst with
intact zeolitic shell has been successfully applied for the
synthesis of hydrazone directly from cyclohexanol through a
tandem reaction with high conversion and selectivity. The
protective effect of the zeolitic shell was proved by comparing
the performances with commercial Pt–SiO2 and B-Pt@S1 with
exposed Pt species. Additionally, the easy and stable dispersive
capability and recollection ability further enforce the efficiency
of the hollow catalyst. These superior features could endow
the encapsulated catalyst with more competence in one-pot,
tandem synthesis of important fine chemicals.
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This work is supported by NSFC (20890122 and 21073041),
‘‘Chen Guang’’ project supported by Shanghai Municipal
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This journal is The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 8583–8585 8585