194
by the partial change of Ru(IV) to Ru(III) in the one-dimensional
structure of the hydrous RuO2.
the Promotion of Science (JSPS). T. Komanoya appreciates the JSPS
Research Fellowship for Young Scientists.
From these results, it is concluded that Ru/CMK-3 has highly
dispersed RuO2·2H2O on CMK-3 as represented in Fig. 7a.
Appendix A. Supplementary data
3.3. Role of Ru in cellulose hydrolysis
As discussed in Section 3.1, the hydrolysis of cellulose and
oligomers are promoted under the hot compressed water by H3O+
from the dissociation of water or by the direct attack of H2O [30],
CMK-3, and the Ru species on CMK-3. In the model experiments
using cellobiose, the Ru species showed promotional effect for the
hydrolysis of -1,4-glycosidic bonds. Hence, we focus on the role
analyses, the Ru species is identified to RuO2·2H2O (Fig. 7a). As
to the acidic property, Ru/CMK-3-dispersed water is neutral (pH
6.3 at 298 K), thus indicating that the Ru species is not a homoge-
neous acid catalyst. It is known that [Ru(H2O)6]3+ produces H+ and
[Ru(H2O)5OH]2+ (pKa = 2.9 at 298 K) [40], implying that RuO2·2H2O
may give a Brønsted acid by the similar mechanism, because the cel-
lulose hydrolysis is performed in water media. On the other hand, it
was proposed that a Ru(III) phosphotungstate catalyzes the hydrol-
ysis of cellulose as a Lewis acid [33]. In our case, the dissociation of
a water molecule coordinated on Ru could give a vacant site with
Lewis acidity.
To investigate the acid sites on Ru, we tried to measure FT-
IR spectra of pyridine adsorbed on Ru/CMK-3, but no peaks of
the peaks at 500 K are attributed to pyridine desorbed from weak
acid sites like COOH on CMK-3 [41]. On 2 wt% Ru/CMK-3, the peaks
of CO (or N2) and CO2 were observed by the decomposition of pyri-
dine on Ru [42,43], but no specific peaks due to acid sites were
observed by comparing the results of CMK-3. Presumably, the acid
site is formed under the reaction conditions in the hot compressed
water. The origin of acidity is now under study.
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The authors thank Prof. K. Asakura for helpful discussions about
XAFS analyses. This work was supported by a Grant-in-Aid for Sci-
entific Research (KAKENHI, 20226016) from the Japan Society for