3
Table 1 Catalytic performances of the Ru/Cs PW12O40 catalyst for
a
the conversion of ball-milled cellulose in water in H
2
Yield (%)
Entry No. Temperature/K Cellobiose Glucose Sorbitol Mannitol
1
2
3
4
5
6
393
403
413
423
433
433
0
0.1
0.2
0.2
0.2
0.3
1.0
1.1
5.5
12
25
43
40
0
0.1
0.2
0.2
1.0
0.1
0.2
0.6
1.2
2.1
3.1
b
a
3
Reaction conditions: catalyst, 0.10 g; cellulose, 0.10 g; water, 15 cm ;
b
, 2 MPa; time, 24 h. The catalyst was pretreated in H
H
2
2
at 573 K
for 5 h.
Fig. 4 Pyridine-adsorbed FT-IR spectra of Ru/Cs
with different pressures at 303 or 323 K. (a) At 303 K after pretreatment
in H at 573 K followed by evacuation, (b) 12.8 kPa H and 303 K,
c) 19.2 kPa H and 323 K, (d) 25.6 kPa H and 323 K, (e) 33.3 kPa H
and 323 K, (f) 44.8 kPa H and 323 K.
3 2
PW12O40 in H
In conclusion, we have found that the Keggin-type
polyoxometalate-supported Ru nanoparticles exhibit unique
catalytic behaviours for the conversions of cellobiose and
ball-milled cellulose into sorbitol in neutral water in the
2
2
(
2
2
2
2
presence of H
that the Ru/Cs
intrinsic acidity, shows superior sorbitol yield and good
stability. It has been demonstrated that the H -originated
2
under relative mild conditions. It is unexpected
Moreover, the yield of glucose was also enhanced by loading a
small amount of Ru onto the Cs
The generation of Brønsted acid sites from molecular H
3
PW12O
40, which does not possess strong
3
40
PW12O .
2
2
1
2
was proposed by Hattori et al. and this kind of reversible
acidity has found applications in the hydroisomerisation and
cracking of alkanes over a few metal oxide-supported transition
Brønsted acid sites play a key role in the conversions of
cellobiose and cellulose into sorbitol over the present catalyst.
This work was supported by the NSF of China (20873110,
2
À
4a
metal catalysts such as Pt/SO4 -ZrO . Fukuoka and Dhepe
2
2
0923004 and 21033006) and the National Basic Research
assumed that such reversible Brønsted acidity might contribute
to the conversion of cellulose over a Pt/Al catalyst. To gain
Program of China (2010CB732303).
2 3
O
evidence for the generation of such Brønsted acidity, we have
performed FT-IR studies of the adsorbed pyridine (Fig. 4).
Notes and references
1
S. van de Vyver, J. Geboers, P. A. Jacobs and B. F. Sels,
ChemCatChem, 2011, 3, 82–94.
3 2
The Ru/Cs PW12O40 catalyst was pretreated in H at 573 K,
followed by evacuation at the same temperature, and then,
was exposed to pyridine at 423 K for 0.5 h. After evacuation
2 B. Kusserow, S. Schimpf and P. Claus, Adv. Synth. Catal., 2003,
45, 289–299.
(a) R. D. Cortright, R. R. Davda and J. A. Dumesic, Nature, 2002,
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Angew. Chem., Int. Ed., 2004, 43, 1549–1551.
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161–5163; (b) N. Yan, C. Zhao, C. Luo, P. J. Dyson, H. Liu and
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and Y. Wang, J. Catal., 2010, 271, 22–32.
3
3
and cooling down to 303 K, FT-IR spectra were recorded.
À1
4
After the introduction of H , an IR band at 1540 cm , which
2
was attributable to pyridine adsorbed on the Brønsted acid
sites, grew significantly, confirming the generation of the
5
Brønsted acid sites in the presence of H
2
. We performed the
same pyridine-adsorbed FT-IR studies over the Ru/Al
2
3
O ,
which was selected as an example of other supported Ru
catalysts. However, we did not observe the generation of
5
6
(a) L. Ding, A. Wang, M. Zheng and T. Zhang, ChemSusChem,
2010, 3, 818–821; (b) S. Van de Vyver, J. Geboers, M. Dusselier,
H. Schepers, T. Vosch, L. Zhang, G. Van Tendeloo, P. A. Jacobs
and B. F. Sels, ChemSusChem, 2010, 3, 698–701.
N. Ji, T. Zhang, M. Zheng, A. Wang, H. Wang, X. Wang and
J. G. Chen, Angew. Chem., Int. Ed., 2008, 47, 8510–8513.
2
Brønsted acid sites over the catalyst in H , and this may have
caused its low activity in sorbitol formation (Fig. S5, ESIw).
Our results described in this work clearly demonstrate the
unique role of such H -originated Brønsted acidity in the
2
conversion of cellobiose into sorbitol over the Ru/Cs PW O
3
7 (a) R. Palkovits, K. Tajvidi, J. Procelewska, R. Rinaldi and
A. Ruppert, Green Chem., 2010, 12, 972–978; (b) J. Geboers,
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and B. F. Sels, Chem. Commun., 2010, 46, 3577–3579;
(c) R. Palkovits, K. Tajvidi, A. M. Ruppert and J. Procelewska,
Chem. Commun., 2011, 47, 576–578.
12 40
catalyst, which does not possess notable intrinsic acidity.
The Ru/Cs PW O catalyst was also exploited for the
3
12 40
2
conversion of ball-milled cellulose in water medium in H .
Table 1 shows that sorbitol is the main product, and the yield
of sorbitol increases with temperature and can reach 43% at
8
9
T. Okuhara, Chem. Rev., 2002, 102, 3641–3666.
K. Shimizu, H. Furukawa, N. Kobayashi, Y. Itaya and
A. Satsuma, Green Chem., 2009, 11, 1627–1632.
4
33 K. The pretreatment of the Ru/Cs
73 K for 5 h did not significantly change the sorbitol yield.
atmosphere at the same
3 2
PW12O40 by H at
5
10 W. Deng, M. Liu, Q. Zhang, X. Tan and Y. Wang, Chem.
Commun., 2010, 46, 2668–2670.
The hydrolysis of cellulose in an N
2
1
1 T. Nakato, M. Kimura, S. Nakata and T. Okuhara, Langmuir,
998, 14, 319–325.
temperature only provided very low yields of glucose irrespective
of catalyst pretreatment (Table S2, ESIw), further suggesting
the key role of the presence of gaseous H2.
1
1
2 (a) H. Hattori and T. Shishido, Catal. Surv. Jpn., 1997, 1, 205–213;
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This journal is c The Royal Society of Chemistry 2011
Chem. Commun., 2011, 47, 9717–9719 9719