C O M M U N I C A T I O N S
∼16 nm (Figure 1 inset). Supportive of these TEM results, the BET
surface area (60.02 m2 g-1) of the Rh NPs modified with CTAB was
considerably higher than that for their counterparts not modified with
CTAB (17.08 m2 g-1) (Figure S5),10 indicating the size-tuning role
of CTAB. The selected-area electron diffraction (SAED) patterns
(Figures 1 and 3 insets) suggest that the synthesized Rh(0) NPs are
crystalline in both cases. Powder X-ray diffraction (XRD, Figure S6)
and energy-dispersive X-ray spectroscopy (EDS) (Figure S7) confirmed
that rhodium is the exclusive component of the Rh(0) NPs.10 Hence,
the observed enhanced activity of the Rh(0) NPs prepared in the
presence of CTAB might be due to their smaller particle size and
therefore larger catalytic surface.
In summary, we have found that Rh(0) NPs are highly active
for catalytic decomposition of hydrous hydrazine to generate H2
and N2 under aqueous and ambient reaction conditions. The fact
that the catalytic activity and selectivity strongly depend on the
catalyst used inspires us to search for more efficient and selective
catalysts for this promising system. The results presented here offer
a new prospect for an on-board hydrogen storage system. Explora-
tion of improving the catalytic activity and selectivity is underway.
Figure 2. Mass spectral profile for the decomposition of hydrazine in
aqueous solution in the presence of Rh(0) NPs (Rh/N2H4 ) 1:10) under an
argon atmosphere at 298 K.
as the M/N2H4 ratio (M ) Co, Ru, Ir) decreased from 1:10 to 1:20
(Figure S3).10 In comparison with the Rh(0) NPs, the Co, Ru, and
Ir NPs prefer the activation of the N-N bond to that of the N-H
bond, giving rise to the formation of more ammonia. Also, the pH
values for the Co, Ru, and Ir NP-catalyzed reaction media were in
the range 9.9-9.7, whereas the pH value for the Rh-catalyzed
reaction medium was 9.5, in agreement with the observation that
more ammonia is produced in the former than the latter. Moreover,
the metals Cu, Ni, Fe, Pt, and Pd are inactive for hydrazine
decomposition in aqueous solution, whereas they were reported to
be active for the gas-phase catalytic decomposition of hydrazine.4b
It is obvious that the presence of water significantly influences the
activity and selectivity of the catalysts for the hydrazine decomposition.
It has been reported that surfactants might play key roles in the
preparation of metal NPs.12 The reduction of aqueous rhodium(III)
nitrate with NaBH4 in the presence of hexadecyltrimethyl ammonium
bromide (CTAB) results in the formation of remarkably more active
Rh(0) NPs, with which the decomposition of hydrazine was completed
in only 55 and 125 min at Rh/N2H4 molar ratios of 1:10 and 1:20,
respectively, with the release of 1.5 equiv of gases (Figure 3). The
observed enhancement in catalytic activity of the Rh(0) NPs could be
attributed to the fact that the modification of metal particles during
the synthetic process could presumably control the efficacy of the
catalyst.12,13 In addition, under the described experimental conditions,
the activities of Rh(0) NPs synthesized from the rhodium(III) chloride
and nitrate precursors were analogous. Similar to the case of Rh(0)
NPs, the use of CTAB in the preparation of Co, Ru, and Ir NPs did
not change the total volumes of the released gases but did decrease
the completion time for the reactions (Figure S4).10
Acknowledgment. The authors thank the reviewers for valuable
suggestions and AIST and JSPS for financial support. S.K.S. thanks
JSPS for a postdoctoral fellowship.
Supporting Information Available: Details concerning the prepara-
tion of Rh(0) NPs; their characterization by powder XRD, STEM, TEM,
and EDS; and the catalytic hydrazine decomposition experiment. This
References
(1) (a) Graetz, J. Chem. Soc. ReV. 2009, 38, 73–82. (b) Hamilton, C. W.; Baker,
R. T.; Staubitz, A.; Manners, I. Chem. Soc. ReV. 2009, 38, 279–293. (c)
Chandra, M.; Xu, Q. J. Power Sources 2006, 156, 190–194. (d) Xu, Q.;
Chandra, M. J. Power Sources 2006, 163, 364–370. (e) Gutowska, A.; Li,
L.; Shin, Y.; Wang, C. M.; Li, X. S.; Linehan, J. C.; Smith, R. S.; Kay,
B. D.; Schmid, B.; Shaw, W.; Gutowski, M.; Autrey, T. Angew. Chem.,
Int. Ed. 2005, 44, 3578–3582. (f) Rosi, N. L.; Eckert, J.; Eddaoudi, M.;
Vodak, D. T.; Kim, J.; O’Keeffe, M.; Yaghi, O. M. Science 2003, 300,
1127–1129. (g) Chen, P.; Xiong, Z.; Luo, J.; Lin, J.; Tan, K. L. Nature
2002, 420, 302–304.
(2) (a) U.S. Department of Energy. Hydrogen, Fuel Cells & Infrastructure
Technologies Program Multi-Year Research, Development, and Demonstra-
tionPlan:HydrogenStorageTechnicalPlan,2007.http://www1.eere.energy.gov/
hydrogenandfuelcells/mypp/ (accessed July 2, 2009). (b) Deluga, G. A.;
Salge, J. R.; Schmidt, L. D.; Verykios, X. E. Science 2004, 303, 993–997.
(3) Schmidt, E. W. Hydrazine and its DeriVatiVes: Preparation, Properties,
Applications, 2nd ed.; John Wiley & Sons: New York, 1984.
(4) (a) Cho, S. J.; Lee, J.; Lee, Y. S.; Kim, D. P. Catal. Lett. 2006, 109, 181–
187. (b) Zheng, M.; Cheng, R.; Chen, X.; Li, N.; Li, L.; Wang, X.; Zhang,
T. Int. J. Hydrogen Energy 2005, 30, 1081–1089.
(5) Armstrong, W. E.; Ryland, L. B.; Voge, H. H. U.S. Patent 4,124,538, 1978.
(6) (a) Zheng, M.; Chen, X.; Cheng, R.; Li, N.; Sun, J.; Wang, X.; Zhang, T.
Catal. Commun. 2006, 7, 187–191. (b) Chen, X.; Zhang, T.; Zheng, M.;
Wu, Z.; Wu, W.; Li, C. J. Catal. 2004, 224, 473–478. (c) Nakajima, Y.;
Inagaki, A.; Suzuki, H. Organometallics 2004, 23, 4040–4046.
(7) (a) Santos, J. B. O.; Valenc¸a, G. P.; Rodrigues, J. A. J. J. Catal. 2002,
210, 1–6, and references therein. (b) Schrock, R. R.; Glassman, T. E.; Vale,
M. G.; Kol, M. J. Am. Chem. Soc. 1993, 115, 1760–1772.
(8) Gu, H.; Ran, R.; Zhou, W.; Shao, Z.; Jin, W.; Xu, N.; Ahn, J. J. Power
Sources 2008, 177, 323–329.
(9) Prasad, J.; Gland, J. L. Langmuir 1991, 7, 722–726.
(10) See the Supporting Information.
(11) (a) Field, L. D.; Li, H. L.; Magill, A. M. Inorg. Chem. 2009, 48, 5–7. (b)
Field, L. D.; Li, H. L.; Dalgarno, S. J.; Turner, P. Chem. Commun. 2008,
1680–1682. (c) Crossland, J. L.; Zakharov, L. N.; Tyler, D. R. Inorg. Chem.
2007, 46, 10476–10478.
(12) Grzelczak, M.; Pe´rez-Juste, J.; Rodr´ıguez-Gonza´lez, B.; Spasova, M.;
Barsukov, I.; Farle, M.; Liz-Marza´n, L. M. Chem. Mater. 2008, 20, 5399–
5405.
(13) (a) Dash, P.; Scott, R. W. J. Chem. Commun. 2009, 812–814. (b) Zhang,
X.-B.; Yan, J.-M.; Han, S.; Shioyama, H.; Xu, Q. J. Am. Chem. Soc. 2009,
131, 2778–2779. (c) Yan, J.-M.; Zhang, X.-B.; Han, S.; Shioyama, H.;
Xu, Q. Angew. Chem., Int. Ed. 2008, 47, 2287–2289. (d) Clark, T. J.;
Whittell, G. R.; Manners, I. Inorg. Chem. 2007, 46, 7522–7527.
Figure 3. Time-course plots for the decomposition of hydrazine in aqueous
solutions in the presence of Rh(0) NPs [Rh/N2H4 ) (a) 1:10 and (b) 1:20]
prepared in the presence of CTAB at 298 K. The inset shows a TEM image
of Rh(0) NPs prepared in the presence of CTAB and the corresponding
SAED pattern. Scale bar, 20 nm.
A typical transmission electron microscopy (TEM) image (Figure
3 inset) illustrates that nearly monodispersed Rh(0) NPs with an
average particle size of ∼5 nm were obtained in the presence of CTAB.
In contrast, without CTAB the Rh NPs had an average particle size of
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