intercalation. Elemental analysis revealed that the carbon con-
tents (C(%, w/w)) of intercalated saccharides, which were pre-
pared by washing the samples with water as shown in Fig.
over HNbMoO
6
is probably due to the difference of intercala-
tion behavior between glucose and cellobiose. We prolonged
the reaction time to 72 h, resulting in 8.8 mmol of glucose and
0.25 mmol of HMF. Although the yield of glucose was
decreased, turnover number was significantly increased to
0.67. Further improvement will be achieved by increasing
2(c)–(e) were 0.44, 0.56 and 0.10 for glucose, sucrose and
cellobiose, respectively. These values correspond to 1.75, 1.12
and 0.21 mol% of saccharides per mol of catalyst. For the FT-IR
spectrum, several peaks attributed to glucose were clearly ob-
served for the glucose-intercalated sample (See ESI Fig. S2w).
The difference in intercalation ability of sucrose and cellobiose
the surface area of HNbMoO
6
and by dissolving cellulose in
an ionic liquid such as 1-butyl-3-methylimidazolium chloride
7
or 1-allyl-3-methylimidazolium chloride.
In summary, layered HNbMoO was demonstrated to ex-
1
into HNbMoO
6
is considered to be another important factor
6
influencing hydrolysis activity in addition to the difficulty of
cleavage of b-1,4-glycosilic bonds. In these experiments, the
amounts of intercalated saccharides seem to be small. This is
due to weak interaction of such saccharides with the interlayer of
hibit high catalytic performance as a solid acid catalyst for the
hydrolysis of saccharides. The high activity of this material is
attributed to the ease of intercalation into the substrate and
the strong acidity of the interlayer gallery.
HNbMoO . The intercalated saccharides are easily released from
6
This work was supported by the Development in a New
Interdisciplinary Field Based on the Nanotechnology and
Materials Science program of the Ministry of Education,
Culture, Sports, Science and Technology (MEXT) of Japan
and the Global Center of Excellence (COE) Program for
Chemistry Innovation.
the interlayer space by water washing. Similar results have been
14
reported in montmorillonite.
The acidity of the interlayer gallery of HNbMoO
6
, determined
by P magic angle spinning (MAS) nuclear magnetic resonance
3
NMR) spectroscopy using trimethylphosphine oxide and NH -
31
(
11
TPD, is comparable to that of strongly acidic H-type zeolites
1
5
16
(
H-ZSM5 and H-MOR ). The high catalytic performance of
layered HNbMoO is therefore attributable to its strong acidity,
water tolerance, and facile intercalation of saccharides.
Notes and references
6
1
A. E. Farrell, R. J. Plevin, B. T. Turner, A. D. Jones, M. O’Hare
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Layered HNbMoO was also applied for the hydrolysis of
6
2 G. W. Huber, S. Iborra and A. Corma, Chem. Rev., 2006, 106, 4044.
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polysaccharide. Fig. 3 shows results for the hydrolysis of
starch and cellulose over layered HNbMoO and Amberlyst-15.
6
In these reactions, 0.2 g of catalyst and 0.1 g of starch (Kanto,
soluble) or cellulose (Avicel, Merck, microcrystalline) were
added to 5 mL of water. The mixture was then heated at 373 K
for 15 h for starch and 403 K for 12 h for cellulose. Layered
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J. H. Clark, Green Chem., 1999, 1, 1; P. T. Anastas and M. M.
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HNbMoO
starch and cellulose. The glucose yield over layered
HNbMoO was 21%, much higher than that over Amberlyst-15
3.4%). Maltose (disaccharide of glucose connected by
6
successfully catalyzed the hydrolysis of both
6 T. Mizota, S. Tsuneda, K. Saito and T. Sugo, Ind. Eng. Chem. Res.,
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(
7
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6
C. Buttersack and J. C. Martin, J. Mol. Catal. A: Chem., 1994, 94,
`
831; C. Moreau, R. Durand, F. Alies, M. Cotillon, T. Frutz and
0
.25 mmol (45%) of glucose and 0.14 mmol of HMF due to
further acid-catalyzed reaction. The turnover number of
HNbMoO reached 1.44 for starch hydrolysis under optimal
2
M. A. Theoleyre, Ind. Crops Prod., 2000, 11, 237.
`
9 T. Okuhara, Chem. Rev., 2002, 102, 3641.
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1
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The total yield of products (glucose and cellobiose) was
estimated to be 8.5% in the hydrolysis of cellulose, corre-
sponding to 0.07 of TON. Preferential cellobiose production
1
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1
1
1
Fig. 3 Hydrolyis of polysaccharides (A) starch and (B) cellulose over
6
HNbMoO and Amberlyst-15.
This journal is ꢀc The Royal Society of Chemistry 2008
Chem. Commun., 2008, 5363–5365 | 5365