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and selectivity (Table 3). The TOF for the oxidation of benzylamine was
93.9 h ,
À1 21 which is higher than other gold catalysts of Au(OAc)3/CeO2
(3.2 hÀ1),6d Au/Al2O3 (0.3 hÀ1) and Au powder (0.001 hÀ1).6e
In summary, we have demonstrated that gold nanoparticles
supported on the ceria{110} crystal planes were more reactive
than on the {111} and {100} crystal planes in the oxidative
dehydrogenation of alcohols and amines.
This work was supported by the National Natural Science
Foundation of China (21303183, 21273231, 21233008) and
Hundred Person Project of the Chinese Academy of Sciences.
Fig. 2 Hammett plot for the oxidation of substituted benzyl alcohols
catalyzed by Au/CeO2–R. The inset is the proposed way for the cleavage
of the C–H bond by cationic gold.
Notes and references
1 (a) J. L. He, T. Xu, Z. H. Wang, Q. H. Zhang, W. P. Deng and Y. Wang,
Angew. Chem., Int. Ed., 2012, 51, 2438; (b) N. Ta, J. Y. Liu and
W. J. Shen, Chin. J. Catal., 2013, 34, 838; (c) X. S. Huang, H. Sun,
L. C. Wang, Y. M. Liu, K. N. Fan and Y. Cao, Appl. Catal., B, 2009,
90, 224; (d) R. Si and M. Flytzani-Stephanopoulos, Angew. Chem., Int.
Ed., 2008, 47, 2884; (e) N. Ta, J. Y. Liu, S. Chenna, P. A. Crozier, Y. Li,
A. L. Chen and W. J. Shen, J. Am. Chem. Soc., 2012, 134, 20585.
2 X. W. Xie, Y. Li, Z. Q. Liu, M. Haruta and W. J. Shen, Nature, 2009,
458, 746.
3 (a) M. Tamura, A. Satsuma and K.-i. Shimizu, Catal. Sci. Technol., 2013,
3, 1386; (b) Y. Zhang, F. Hou and Y. W. Tan, Chem. Commun., 2012,
48, 2391; (c) L. Vivier and D. Duprez, ChemSusChem, 2010, 3, 654.
4 Y. H. Wang, F. Wang, Q. Song, Q. Xin, S. T. Xu and J. Xu, J. Am. Chem.
Soc., 2013, 135, 1506.
step in the oxidation of alcohols over noble metal catalysts.17 The
apparent activation energy, Ea, associated with the C–H bond
cleavage is determined from the Arrhenius plot (Fig. S8b and S9,
ESI†). The least-square fit analysis yields an Ea value of 24.5 kJ molÀ1
for Au/CeO2–R, which is lower than 35.1 kJ molÀ1 for Au/CeO2–P and
42.3 kJ molÀ1 for Au/CeO2–O. And, it is also lower than the reported
values of 28.1 kJ molÀ1 17a
,
32.3 kJ molÀ1 18 45.7 kJ molÀ1 (ref. 19)
,
and 45.8 kJ molÀ1 20
.
This result indicates that the ceria{110}-
supported positively charged gold can greatly lower the C–H bond
activation energy, and thus increase catalytic activity. The reaction
rate increased with increasing cationic gold content (Fig. S10, ESI†).
A linear relationship between log(kX/kH) and Brown–Okamoto
constant s+ (Fig. 2) was established for the oxidation of substituted
benzyl alcohols (X = p-Cl, p-H, p-Me and p-OMe). The resulting
Hammett parameter r was À0.264, suggesting that the reaction is
substituent-sensitive and carbocation intermediates are involved.
Electron-donating groups can stabilize the carbocation intermedi-
ates and thus are more favored to be oxidized.17b Based on our
previous study, we postulate that the positively charged gold may
favor the hydride abstraction via b-H elimination to form gold
hydride, generating a carbocation-type intermediate.
5 K. Deori, D. Gupta, B. Saha, S. K. Awasthi and S. Deka, J. Mater.
Chem. A, 2013, 1, 7091.
6 (a) M. T. Schumperli, C. Hammond and I. Hermans, ACS Catal., 2012,
2, 1108; (b) B. N. Wigington, M. L. Drummond, T. R. Cundari,
D. L. Thorn, S. K. Hanson and S. L. Scott, Chem.–Eur. J., 2012,
18, 14981; (c) Q. H. Zhang, W. P. Deng and Y. Wang, Chem. Commun.,
2011, 47, 9275; (d) L. Aschwanden, T. Mallat, F. Krumeich and A. Baiker,
J. Mol. Catal. A, 2009, 309, 57; (e) B. L. Zhu, M. Lazar, B. G. Trewyn and
R. J. Angelici, J. Catal., 2008, 260, 1; ( f ) J. P. Ma, Z. T. Du, J. Xu, Q. H. Chu
and Y. Pang, ChemSusChem, 2011, 4, 51; (g) T. Ishida, R. Takamura,
T. Takei, T. Akita and M. Haruta, Appl. Catal., A, 2012, 413, 261.
7 A. Abad, P. Concepcion, A. Corma and H. Garcia, Angew. Chem., Int.
Ed., 2005, 44, 4066.
8 A. Tanaka, K. Hashimoto and H. Kominami, J. Am. Chem. Soc., 2012,
134, 14526.
Besides alcohol oxidation, amines oxidation could also smoothly
take place over Au/CeO2–R. This extends its application to the
conversion of benzylamine in the presence of electron-donating
or electron-withdrawing substituents and heterocycle amines to
N-benzylidene-methanamine derivatives with moderate to high activity
9 (a) M. Alhumaimess, Z. J. Lin, W. H. Weng, N. Dimitratos,
N. F. Dummer, S. H. Taylor, J. K. Bartley, C. J. Kiely and
G. J. Hutchings, ChemSusChem, 2012, 5, 125; (b) S. Mandal,
K. K. Bando, C. Santra, S. Maity, O. O. James, D. Mehta and
B. Chowdhury, Appl. Catal., A, 2013, 452, 94; (c) M. J. Beier,
T. W. Hansen and J. D. Grunwaldt, J. Catal., 2009, 266, 320.
10 L. Aschwanden, B. Panella, P. Rossbach, B. Keller and A. Baiker,
ChemCatChem, 2009, 1, 111.
Table 3 Oxidation of amines over the Au/CeO2–R catalysta
11 L. Aschwanden, T. Mallat, M. Maciejewski, F. Krumeich and
A. Baiker, ChemCatChem, 2010, 2, 666.
12 H. X. Mai, L. D. Sun, Y. W. Zhang, R. Si, W. Feng, H. P. Zhang,
H. C. Liu and C. H. Yan, J. Phys. Chem. B, 2005, 109, 24380.
13 Z. L. Wu, M. J. Li, J. Howe, H. M. Meyer and S. H. Overbury,
Langmuir, 2010, 26, 16595.
14 M. Guo, J. Q. Lu, Y. N. Wu, Y. J. Wang and M. F. Luo, Langmuir, 2011,
27, 3872.
15 T. X. T. Sayle, S. C. Parker and D. C. Sayle, Phys. Chem. Chem. Phys.,
2005, 7, 2936.
16 M. Nolan, S. Grigoleit, D. C. Sayle, S. C. Parker and G. W. Watson,
Surf. Sci., 2005, 576, 217.
17 (a) F. Wang, W. Ueda and J. Xu, Angew. Chem., Int. Ed., 2012, 51, 3883;
(b) A. Abad, A. Corma and H. Garcia, Chem.–Eur. J., 2008, 14, 212.
18 M. K. Dalal, M. J. Upadhyay and R. N. Ram, J. Mol. Catal. A, 1999, 142, 325.
19 F. Wang and W. Ueda, Appl. Catal., A, 2008, 346, 155.
20 D. I. Enache, J. K. Edwards, P. Landon, B. Solsona-Espriu,
A. F. Carley, A. A. Herzing, M. Watanabe, C. J. Kiely, D. W. Knight
and G. J. Hutchings, Science, 2006, 311, 362.
a
Reaction conditions: 0.2 mmol substrate, catalyst (0.25 mol% Au), 2 mL
1,4-dioxane, 3 atm oxygen, 100 1C, 6 h. The results were presented as
21 The TOF value is calculated based on the cationic gold.
conversion/selectivity. The main byproducts were aldehydes and nitriles.
294 | Chem. Commun., 2014, 50, 292--294
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