Green Chemistry
Paper
numbers (TONs) based on the initial surface and bulk Ni
atoms were 218 and 14, respectively, thus showing that Ni
clearly worked as a catalyst. Ni(70)/KB catalyst was fairly
durable, but the yields decreased to 49% (8th run) and 42%
(9th run). The particle diameter of Ni on the catalyst was
26 nm after the 9th run. Since the diameter of Ni was already
21 nm after the treatment for 2 h as mentioned in the previous
paragraph, the sintering of Ni was limited in the repeated reac-
tions. Ni of 35 ppm, corresponding to 0.45% of the catalyst,
leached out into the reaction solution in each run, and thus
96% of Ni remained on the catalyst after the 9th run. The
major cause of deactivation would be the oxidation of Ni as
indicated in the model reactions using glucose. On the other
hand, Ni(50)/KB deactivated in the 3rd run; the yields of hexi-
tols were 59% (1st), 53% (2nd) and 35% (3rd) [Fig. 7(b)].
Higher Ni loading is the key to the better durability in the con-
version of cellulose. From that viewpoint, it is noteworthy that
Ni(3)/CNF is durable for 3 times regardless of the low loading
amount.4 We speculate that the special features of this catalyst,
namely, the large crystal size of Ni (ca. 100 nm) and fixation of
Ni on the rigid carbon frame may avoid sintering and coverage
by oxides.
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Conclusion
We have demonstrated that a simple carbon-supported Ni cata-
lyst, Ni(70)/KB, is active for the production of hexitols from cel-
lulose, and that the catalyst is fairly durable. In addition, the
catalyst can be separated by a magnet thanks to the high
content of Ni. The use of carbon supports has two benefits: no
basicity and high water-tolerance. CeO2, ZrO2, γ-Al2O3 and
TiO2 have basicity causing side-reactions, and SiO2, γ-Al2O3
and CeO2 are less stable in hot water. Another important
factor is the high loading amount of Ni as the increase of Ni
content from 10 wt% to 70 wt% significantly improves the
yield of hexitols and durability. Larger crystalline Ni particles
are more resistant to sintering and the surface coverage by Ni
oxide species. These findings can help the understanding of
the performance of various Ni catalysts in hydrolytic hydrogen-
ation and also be useful to design more active and durable Ni
catalysts for the conversion of cellulose.
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Acknowledgements
This work was supported by a Grant-in-Aid Scientific Research
(KAKENHI, 20226016) from Japan Society for the Promotion of
Science (JSPS).
7 J. Pang, A. Wang, M. Zheng, Y. Zhang, Y. Huang, X. Chen
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