DOI: 10.1002/cssc.201500261
Communications
Solvent-Free Synthesis of Zeolite Crystals Encapsulating
Gold–Palladium Nanoparticles for the Selective Oxidation
of Bioethanol
Jian Zhang, Liang Wang,* Longfeng Zhu, Qinming Wu, Chunyu Chen, Xiong Wang,
[
a]
Yanyan Ji, Xiangju Meng, and Feng-Shou Xiao*
The conversion of bioethanol into valuable products is an im-
portant area in the conversion of biomass. We demonstrate
the successful synthesis of bimetallic gold–palladium (Au–Pd)
nanoparticles encapsulated within S-1 zeolite crystals
Palladium-, copper-, and gold-based catalysts are active in
[
3–15]
the oxidation of bioethanol.
In this oxidation reaction, cata-
lyst stability is the biggest challenge, since the metal nanopar-
[
4,5]
ticles easily aggregate into bigger nanoparticles.
To over-
(
AuPd@S-1) by a solvent-free strategy. This strategy allows
come this problem, metal catalysts encapsulated in zeolites
[
18–23]
highly efficient use of the noble metals, with more than 96%
of the gold and palladium being loaded into the final samples.
Electron microscopy characterization and investigations with
probe molecules confirm that the Au–Pd nanoparticles are en-
capsulated inside the S-1 crystals. The AuPd@S-1 catalyst is
very active for the aerobic oxidation of bioethanol, giving
(M@zeolite) have been designed and prepared.
Particular-
ly, S-1 zeolite encapsulating gold nanoparticles was found to
be active, stable, and selective for the production of acetalde-
[
5]
hyde. Normally, zeolites encapsulating metal nanoparticles
are synthesized under hydrothermal conditions; a process in
which utilization of the metal is relatively low (about 34%) and
in which polluted water is produced. Recently, a solvent-free
1
00% conversion and 99% selectivity to acetic acid. Even in
[
24–27]
the presence of 90% water, the catalyst still gives a conversion
higher than 80% and a selectivity of 95%. More importantly,
the AuPd@S-1 catalyst exhibits excellent stability in the oxida-
tion of bioethanol. These features are important for future
practical applications of the AuPd@S-1 catalyst.
strategy for synthesizing various zeolites was reported.
Because the solvent (water) is absent in this strategy the pro-
duction of polluted water is avoided, and hence this strategy is
[
28]
regarded as a green process.
Herein, we demonstrate the solvent-free synthesis of an S-
zeolite encapsulating gold–palladium bimetallic nanoparti-
1
cles (AuPd@S-1), combining the advantages of both M@zeolite
catalysts (stability) and a greener synthesis strategy (solvent-
free). More than 96% of the gold and palladium in the starting
gel are transferred into the AuPd@S-1 product; the catalyst
also exhibits superior catalytic activity, unique selectivity, and
high stability towards the aerobic oxidation of bioethanol in
mixtures with water.
Because biomass is regarded as a renewable source of energy
to reduce the need for fossil sources of oil, the conversion of
biomass-derived feedstocks into valuable products is of great
[
1,2]
importance.
One typical example is bioethanol, which has
already been used as a fuel additive and has great potential
[3–17]
for producing valuable products such as acetic acid.
Con-
ventionally, acetic acid is synthesized by carbonylation of
methanol. This process is not considered green because it in-
volves the use of CO and iodocompounds as catalytic media-
The AuPd@S-1 samples were synthesized by grinding the
solid raw materials [bimetallic gold–palladium nanoparticles
encapsulated with amorphous SiO (AuPd@SiO ) and tetrapro-
2
2
[
8]
tors. Enzymatic oxidation of bioethanol could produce acetic
acid, but enzymatic catalysts are not popular in chemical in-
dustry. Considering the very high output of bioethanol (more
than 100 billion liters every year), there is a strong case for the
development of efficient catalysts for the direct oxidation of
pylammonium hydroxide (TPAOH)], followed by thermal treat-
ment at 1808C for 2–4 days (Scheme 1). The gold and palladi-
um contents could be adjusted, and herein we designate our
samples as Au Pd @S-1, where x and y stand for the molar
x
y
ratio of gold and palladium, respectively.
[1,3–17]
the bioethanol to acetic acid.
Figure 1 shows X-ray diffraction (XRD) patterns of the
AuPd@S-1 samples. All of the samples exhibit XRD peaks typi-
[
29,30]
cal for the MFI zeolite structure.
It is difficult to observe
[
a] J. Zhang, Dr. L. Wang, Dr. L. Zhu, Q. Wu, C. Chen, X. Wang, Y. Ji,
Dr. X. Meng, Prof. F.-S. Xiao
Key Laboratory of Applied Chemistry of Zhejiang Province
Zhejiang University
the peaks related to the Au–Pd nanoparticles, indicating that
these Au–Pd nanoparticles are well-dispersed within the S-
1
crystals. Table 1 lists the textural parameters and metal load-
Hangzhou 310028 (PR China)
E-mail: liangwang@zju.edu.cn
ings of the AuPd@S-1 samples. These samples have high sur-
2
À1
face areas (349–413 m g ) and pore volumes (0.16–
3
À1
0
.18 cm g ) (entries 1–6). The total metal loadings in the sam-
ples are about 1.5%, and their gold and palladium contents
could be effectively adjusted. Through our use of the solvent-
free strategy, the utilization of gold and palladium in the sam-
ples is above 96%. These results confirm that most of the gold
This publication is part of a Special Issue on the “Future Energy” confer-
ChemSusChem 2015, 8, 2867 – 2871
2867
ꢀ 2015 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim