Zaihong Guan et al. / Chinese Journal of Catalysis 36 (2015) 1535–1542
1541
References
Table 5
Catalytic activity of Pt/CNTs(in) and Pt/CNTs(out) under different H2
pressures in the asymmetric hydrogenation of EtPy.
[1] Zhang Y, Zhang H B, Lin G D, Chen P, Yuan Y Z, Tsai K R. Appl Catal
A, 1999, 187: 213
[2] Zhang A M, Dong J L, Xu Q H, Rhee H K, Li X L. Catal Today, 2004,
93-95: 347
[3] Castillejos E, Debouttiere P J, Roiban L, Solhy A, Martinez V, Kihn Y,
Ersen O, Philippot K, Chaudret B, Serp P. Angew Chem Int Ed, 2009,
48: 2529
[4] Chen W, Fan Z L, Pan X L, Bao X H. J Am Chem Soc, 2008, 130: 9414
[5] Abbaslou R M M, Tavassoli A, Soltan J, Dalai A K. Appl Catal A,
2009, 367: 47
Entry
Catalyst
H2 (MPa)
6.5
TOF (h–1)
9.6 × 104
1.5 × 104
0.6 × 104
1.6 × 104
210
ee (%)
95
88
86
74
1
2
3
4
5
6
Pt/CNTs(in)
Pt/CNTs(in)
Pt/CNTs(in)
Pt/CNTs(out)
Pt/CNTs(out)
Pt/CNTs(out)
1.0
0.1
6.5
1.0
62
0.1
140
60
Reaction conditions: 10 mg of Pt/CNTs, 2.0 mg cinchonidine (6.725
μmol), 0.1 mL of substrate, 2 mL acetic acid (containing 0.96 wt.% wa-
ter), 25 °C. Reaction time: 1 min for Pt/CNTs(in) and 3 min for
Pt/CNTs(out).
[6] Pan X L, Fan Z L, Chen W, Ding Y J, Luo H Y, Bao X H. Nat Mater,
2007, 6: 507
[7] Guo S J, Pan X L, Gao H L, Yang Z Q, Zhao J J, Bao X H. Chem Eur J,
2010, 16: 5379
[8] Zhang J, Muller J O, Zheng W Q, Wang D, Su D S, Schlogl R. Nano
Lett, 2008, 8: 2738
[9] Zhang H B, Pan X L, Liu J Y, Qian W Z, Wei F, Huang Y Y, Bao X H.
ChemSusChem, 2011, 4: 975
[10] Pan X L, Bao X H. Chem Comm, 2008: 6271
[11] Serp P, Castillejos E. ChemCatChem, 2010, 2: 41
[12] Pan X L, Bao X H. Acc Chem Res, 2011, 44: 553
[13] Castillejos E, Serp P. In: Guldi D M, Martin N eds. Carbon Nano-
tubes and Related Structures. Weinheim WILEY-VCH, 2010. 321
[14] Balázsik K, Szori K, Szollosi G Bartok M. Chem Commun, 2011, 47:
1551
drogen pressure and KP is defined as the enrichment factor of
Pt/CNTs(in) under a hydrogen pressure of P. From the results
in Table 5 (entry 4 and 5), the index n in Eq. (1) was estimated
to be 2.3. Therefore, the enrichment factor KP under different
hydrogen pressures can be calculated. For Pt/CNTs(in),
K6.5 MPa = 2.3; K1.0 MPa = 6.3; K0.1 MPa = 5.2. From the kinetic point
of view, hydrogen was enriched in the channels, which led to
the much higher activity of Pt/CNTs(in) than that of
Pt/CNTs(out) at low hydrogen pressure. These results clearly
demonstrated that the enrichment of hydrogen in the channels
also contributed to the high activity.
[15] Szollosi G, Makra Z, Kovacs L, Fulop F, Bartok M. Adv Synth Catal,
2013, 355: 1623
[16] Szollosi G, Kovacs L, Makra Z. Catal Sci Technol, 2015, 5: 697
[17] Xing L, Du F, Liang J J, Chen Y S, Zhou Q L. J Mol Catal A, 2007, 276:
191
[18] Szollosi G, Nemeth Z, Hernadi K, Bartok M. Catal Lett, 2009, 132:
370
[19] Chen Z J, Guan Z H, Li M R, Yang Q H, Li C. Angew Chem Int Ed,
2011, 50: 4913
[20] Guan Z H, Lu S M, Chen Z J, Li C. J Catal, 2013, 305: 19
[21] Szollosi G, Hanaoka T, Niwa S, Mizukami F, Bartok M. J Catal, 2005,
231: 480
[22] Szollosi G, Herman B, Felfoldi K, Fulop F, Bartok M. Adv Synth
Catal, 2008, 350: 2804
[23] Sugimura T, Uchida T, Watanabe J, Kubota T, Okamoto Y, Misaki T,
Okuyama T. J Catal, 2009, 262: 57
[24] Guan Z H, Lu S M, Li C. J Catal, 2014, 311: 1
[25] Wagner C D. In: Muilenberg G E ed. Handbook of X-Ray Photoelec-
tron Spectroscopy. Minnesota Perkin-Elmer Corporation, 1979.
4. Conclusions
Highly oxidized Pt species can be stabilized inside the
channels of CNTs when Na+ is present. The more electrophilic
Pt species in the highly oxidized state promoted the interaction
between the chiral modifier/reactant with the Pt nanoparticles,
which is crucial for high enantioselectivity in the asymmetric
hydrogenation of EtPy. The enrichment of hydrogen in the
channels also contributed to the high activity. These results
provide information for understanding why the catalytic per-
formance of Pt located inside the channels of CNTs is much
higher than that outside the channels. This work also revealed
that the function of the CNTs as a nano-reactor is not only to
enrich the molecules inside the channels but also to stabilize
the chemical state of Pt in the higher oxidative state.
Graphical Abstract
Chin. J. Catal., 2015, 36: 1535–1542 doi: 10.1016/S1872-2067(15)60831-2
Highly oxidized Pt species stabilized inside carbon nanotubes
for asymmetric hydrogenation
Zaihong Guan, Shengmei Lu, Can Li*
Dalian Institute of Chemical Physics, Chinese Academy of Sciences
Pt/CNTs
Pt4+ species stabilized inside carbon nanotubes facilitated the co-
ordination of the chiral modifier and entrapment of the reactant to
give high enantioselectivity in the asymmetric hydrogenation of
α-ketoester.