H. Mao et al. / Catalysis Communications 12 (2011) 1177–1182
1181
Pd-BT-CF
Pd-C
Table 2
Effect of molar ratio of HCOOH to MBA on the CTH of MBA .
⁎
300
250
200
150
100
50
Entry
Molar ratio of
HCOOH/MBA
Conversion
(%)
Average TOF
Selectivity
(%)
(mol mol−1 h−1
)
EB
AP
1
2
3
4
5
1.0
1.5
2.0
3.0
4.0
91.2
96.7
99.2
99.7
100
291.2
308.6
316.6
318.2
319.1
87.5
95.8
99.0
99.2
99.5
12.5
4.2
1.0
0.8
0.5
⁎
Reaction conditions: 1.5 mmol MBA, 50.0 mg Pd–BT–CF catalyst, 10.0 mL ethanol,
2.0 mL H2O, 60 °C and 30 min.
3.2.5. Reusability of the Pd–BT–CF catalyst
0
As shown in Fig. 6, the catalytic activity of the Pd–BT–CF catalyst
was almost unchanged after six times repeated application (the TOF
value was a little changed from 318.2 to 310.9 mol mol−1 h−1),
exhibiting satisfied reusability of the Pd–BT–CF catalyst. On the
contrary, the reusability of commercial Pd/C catalyst should be
improved, of which the TOF in sixth time was only about 59.5% of
the fresh catalyst (from 60.0 to 35.7 mol mol−1 h−1). We believed
that the anchoring effect of plant tannins to the Pd nanoparticles
should be the main reason for the high stability of this novel catalyst.
1
2
3
4
5
6
Catalysts Cycles
Fig. 6. Recycling of the Pd–BT–CF catalyst in the CTH of MBA.
3.2.3. Effect of molar ratio of HCOOH to MBA
As mentioned above, the HCOOH provides both HCOO−and H+ in
CTH of MBA, thus the molar ratio of HCOOH to MBA should influence
the conversion of MBA as well as the selectivity to EB. We therefore
investigated the effect of molar ratio of HCOOH to MBA in CTH of MBA.
The corresponding results are summarized in Table 2. As expected, the
conversion of MBA and the selectivity to EB are both considerably
increased with the increase of molar ratio of HCOOH to MBA, which
roughly reaches the maximum when the molar ratio is 2.0. When the
molar ratio is 4.0, the conversion, TOF and selectivity of EB were 100%,
319.1 and 99.5%, respectively.
4. Conclusions
Highly active and selective heterogeneous Pd catalyst was
prepared by using collagen fiber grafted plant tannin as the
supporting matrix. Due to the presence of plant tannin on collagen
fiber, the supported Pd nanoparticles were stably anchored and well
dispersed. Moreover, the fibrous morphology of collagen fiber
ensured a high catalytic activity due to its nature of low mass transfer
resistance. The as-preapred can be used for the catalytic transfer
hydrogenolysis of α-methylbenzyl alcohol, which exhibited the
distinct advantages of high activity, selectivity and reusability.
3.2.4. Effect of reaction temperature
The effect of reaction temperature on the catalytic activity of the
Pd–BT–CF catalyst was also investigated, and the corresponding
results are shown in Fig. 5. It can be seen that the increase of reaction
temperature accelerates the reaction rate in CTH of MBA. When the
temperature is increased from 20 °C to 60 °C, the conversion of MBA is
significantly increased from 21.1% to 99.2%. As for the selectivity to EB,
it is also steadily increased along with the increase of temperature in
the temperature range of 20–60 °C. Therefore, the reaction temper-
ature should not be lower than 60 °C in order to obtain high
conversion and selectivity.
Acknowledgements
We acknowledge the financial supports provided by the National
Natural Science Foundation of China (20776090) and theFoundation
for the Author of National Excellent Doctor Dissertation of PR China
(FANEDD200762). We also give thanks to the Test Central for the TEM
analyses.
Appendix A. Supplementary data
Supplementary data to this article can be found online at
doi:10.1016/j.catcom.2011.04.009.
Table 1
⁎
Effect of hydrogen donors on the CTH of MBA .
References
Entry
Hydrogen
donor
Conversion
(%)
Average TOF
Selectivity (%)
(mol mol−1 h−1
)
EB
AP
1
[1] M. Nagy, K. David, G.J.P. Britovsek, A.J. Ragauskas, Holzforschung 63 (2009) 513.
[2] J. Feng, J.B. Wang, Y.F. Zhou, H.Y. Fu, H. Chen, X.J. Li, Chem. Lett. 36 (2007) 1274.
[3] J. Feng, M.L. Yuan, H. Chen, X.J. Li, Prog. Chem. 19 (2007) 651.
[4] R. Radinov, S.D. Hutchings, Tetrahedron Lett. 40 (1999) 8955.
[5] N. Thakar, N.F. Polder, K. Djanashvili, H. van Bekkum, F. Kapteijn, J.A. Moulijn, J.
Catal. 246 (2007) 344.
1a
2b
3c
4d
5a
6a
5a
6a
HCOOH
HCOOH
HCOOH
HCOOH
HCOOLi
HCOONa
HCOOK
HCOONH4
99.2
18.8
3.4
16.4
9.8
8.1
17.3
21.5
316.6
60.0
10.9
52.3
31.3
25.9
55.2
68.6
99.0
98.7
65.4
76.7
39.9
57.6
81.2
32.3
1.3
34.6
23.3
60.1
42.4
18.8
67.7
[6] J. Muzart, Tetrahedron 61 (2005) 9423.
[7] V.S. Ranade, R. Prins, Chem. Eur. J. 6 (2000) 313.
[8] M. Yasuda, Y. Onishi, M. Ueba, T. Miyai, A. Baba, J. Org. Chem. 66 (2001) 7741.
[9] A.P.G. Kieboom, J.F. de Kreuk, H. van Bekkum, J. Catal. 20 (1971) 58.
[10] F.J. Urbano, J.M. Marinas, J. Mol. Catal. A Chem. 173 (2001) 329.
[11] D. Albanese, M. Leone, M. Penso, M. Seminati, M. Zenoni, Tetrahedron Lett. 39
(1998) 2405.
[12] D.C. Gowda, B. Rajesh, S. Gowda, Indian J. Chem. B 39 (2000) 504.
[13] N.C.P. Araujo, A.F. Brigas, M.L.S. Cristiano, E.M.O. Guimaraes, R.M.S. Loureiro, J.
Mol. Catal. A Chem. 215 (2004) 113.
⁎
Reaction conditions: 1.5 mmol MBA, 3.0 mmol hydrogen donor, 10.0 mL ethanol,
2.0 mL H2O, 60 °C and 30 min.
a
50.0 mg Pd–BT–CF (10 μmol) was used as the catalyst.
50.0 mg Pd/C (10 μmol) was used as the catalyst.
50.0 mg Pd/SiO2 (10 μmol) was used as the catalyst.
50.0 mg Pd/Al2O3 (10 μmol) was used as the catalyst.
b
c
d
[14] B.S. Kwak, T.J. Kim, S.I. Lee, Appl. Catal. A Gen 238 (2003) 141.