ChemComm
Communication
ꢀ
be very similar to that of a molecular catalyst. It provides H
radicals as active sites under discharge conditions, and the active
sites selectively activate the C–H bonds of the methyl group
resulting in the abstraction of hydrogen atoms from the group.
ꢀ
The coupling of the CH OH formed gives an EG product. The
2
hydrogen molecules take part in the reaction, but are recovered
without consumption after reaction.
In summary, EG can be selectively synthesized through the one-
step plasma reaction of methanol using a DDBD reactor. It was
found that the moderate discharge intensity benefited the high
selectivity of EG. The discharge intensity can be optimized by the
configuration of the reactor and the discharge conditions. Further-
more, the hydrogen co-feed can significantly improve the methanol
conversion and EG selectivity. In the reaction, hydrogen molecules
ꢀ
play an obvious catalytic role by releasing a H radical which
2 3
Fig. 5 Effect of the H flow rate on the conversion of CH OH with reactor A.
ꢀ
selectively accelerated the formation of the CH
2
OH intermediate
via the abstraction of methyl hydrogen of methanol.
Among them, eqn (2) is a C–H bond dissociation process
which generates a CH OH intermediate, the recombination of
the CH OH intermediate produces EG. The other paths will
lead to CH
2
Notes and references
2
1
(a) L. F. Chen, P. J. Guo, M. H. Qiao, S. R. Yan, H. X. Li, W. Shen,
H. L. Xu and K. N. Fan, J. Catal., 2008, 257, 172; (b) A. Y. Yin,
X. Y. Guo, W. L. Dai and K. N. Fan, Chem. Commun., 2010, 46, 4348;
(c) G. H. Xu, Y. C. Li, Z. H. Li and H. J. Wang, Ind. Eng. Chem. Res.,
1995, 34, 2371; (d) H. R. Yue, Y. J. Zhao, X. B. Ma and J. L. Gong, Chem.
Soc. Rev., 2012, 41, 4218; (e) X. B. Ma, H. W. Chi, H. R. Yue, Y. J. Zhao,
Y. Xu, J. Lv, S. P. Wang and J. L. Gong, AIChE J., 2013, 59, 2530.
4
and CO by-products. The energy barrier for these
À1
reactions is approximately 80–100 kcal mol . Generally, the
electron energy of non-equilibrium plasma ranged from 23.06
À1
to 230.61 kcal mol . This means that any of these reaction
paths of methanol is possible in the present electric barrier
discharge. As mentioned above (Fig. 3 and 4), reactor A that had
moderate discharge intensity showed the best EG selectivity.
This is in line with the results of theoretical calculation, which
shows that eqn (2) has a medium level of energy barrier.
In addition, the significant effect of the hydrogen co-feed on
the DBD discharge of methanol was observed. As indicated by
Fig. 5, in the absence of hydrogen the discharge of methanol
2 (a) Z. He, H. Q. Lin, P. He and Y. Z. Yuan, J. Catal., 2011, 277, 54;
b) A. Y. Yin, C. Wen, X. Y. Guo, W. L. Dai and K. N. Fan, J. Catal., 2011,
(
2
80, 77; (c) A. Y. Yin, X. Y. Guo, W. L. Dai and K. N. Fan, J. Phys. Chem. C,
2
009, 113, 11003; (d) H. Q. Lin, X. L. Zheng, Z. He, J. W. Zheng,
X. P. Duan and Y. Z. Yuan, Appl. Catal., A, 2012, 445–446, 287.
3
4
(a) H. Q. Li, J. J. Zou, Y. P. Zhang and C. J. Liu, Chem. Lett., 2004, 744;
(
2
b) H. Q. Li, J. J. Zou, Y. P. Zhang and C. J. Liu, J. Chem. Ind. Eng.,
004, 55, 1989; (c) X. Z. Liu, C. J. Liu and B. Eliasson, Chin. Chem.
Lett., 2003, 14, 631.
(a) S. Tanabe, H. Matsuguma, K. Okitsu and H. Matsumoto, Chem.
Lett., 2000, 1116; (b) S. Futamura and H. Kabashima, Prepr. Pap. - Am.
Chem. Soc., Div. Fuel Chem., 2003, 48, 816; (c) H. Kabashima, H. Einaga,
S. Futamura, IEEE, 2001, vol. 1, p. 680; (d) H. Kabashima, H. Einaga
and S. Futamura, IEEE Trans. Ind. Appl., 2003, 39, 340; (e) S. Futamura
and H. Kabashima, IEEE Trans. Ind. Appl., 2004, 40, 1459; ( f ) V. J. Rico,
J. L. Hueso, J. Cotrino and A. R. Gonz ´a lez-Elipe, J. Phys. Chem. A, 2010,
114, 4009; (g) V. J. Rico, J. L. Hueso, J. Cotrino, V. Gallardo,
B. Sarmiento, J. J. Brey and A. R. Gonz ´a lez-Elipe, Chem. Commun.,
4
vapor in reactor A mainly produced CO and CH , their selectivities
were 55.2% and 16.6%, respectively. While the selectivity of EG
was only about 8.0%. As the flow rate of hydrogen increased from
À1
0
to 40 mL min , the CO selectivity rapidly decreased from 55.2%
4
to 17.4%; the selectivities of CH and other by-products also
obviously decreased. Consequently, the EG selectivity quickly
increased from 8.0% to 68.5%. A continuous improvement in
the EG selectivity can be seen when the hydrogen flow rate is
2
009, 6192; (h) S. Yao, X. Zhang and B. Lu, AIChE J., 2005, 51, 1558.
5
Z. C. Yan, C. Li and W. H. Lin, Int. J. Hydrogen Energy, 2009, 34, 48.
further increased. It is interesting that the conversion of methanol
6 R. Burlica, K. Y. Shih, B. Hnatiuc and B. R. Locke, Ind. Eng. Chem.
Res., 2011, 50, 9466.
À1
also increased with the hydrogen flow rate up to 80 mL min
.
7
8
(a) Y. F. Wang, Y. S. You, C. H. Tsai and L. C. Wang, Int. J. Hydrogen
Energy, 2010, 35, 9637; (b) D. H. Lee and T. Kim, Int. J. Hydrogen
Energy, 2013, 38, 6039.
(a) J. C. Zhou, H. C. Guo, X. S. Wang, M. X. Guo, J. L. Zhao,
L. X. Chen and W. M. Gong, Chem. Commun., 2005, 1631;
This means that the introduction of hydrogen can selectively
accelerate the C–H bond dissociation of methanol. The in situ
OES diagnoses (shown in Fig. S1–S3, ESI†) indicated that the
introduction of the hydrogen co-feed not only enhanced the
(
b) Y. H. Yi, J. C. Zhou, H. C. Guo, J. L. Zhao, J. Su, L. Wang,
ꢀ
discharge of methanol, but also increased the H radical concen-
X. S. Wang and W. M. Gong, Angew. Chem., Int. Ed., 2013, 52, 8446,
DOI: 10.1002/anie.201304134; (c) L. Wang, Y. Zhao, C. Y. Liu,
W. M. Gong and H. C. Guo, Chem. Commun., 2013, 49, 3787.
(a) A. H. H. Chang and S. H. Lin, Chem. Phys. Lett., 2002, 363, 175;
(b) Y. Han, J. G. Wang, D. G. Cheng and C. J. Liu, Ind. Eng. Chem.
Res., 2006, 45, 3460; (c) C. W. Bauschlicher, Jr. and S. R. Langhoff,
J. Chem. Phys., 1992, 96, 450; (d) W. S. Xia, R. S. Zhu, M. C. Lin and
A. M. Mebel, Faraday Discuss., 2001, 119, 191.
ꢀ
tration in the plasma. The H radical can abstract hydrogen from
ꢀ
the methyl group to generate the CH
2
OH intermediate: CH
3
OH +
9
ꢀ
ꢀ
10
2 2
H - CH OH + H . According to the literature, the methyl
hydrogen atoms are preferentially abstracted rather than alcoholic
ꢀ
hydrogen when the H radical reacts with methanol; the reaction
À1 9b
has an activation energy of 11.78 kcal mol
,
which is very low 10 (a) G. Lendvay, T. B ´e rces and F. M ´a rta, J. Phys. Chem. A, 1997,
01, 1588; (b) Y. Y. Chuang, M. L. Radhakrishnan, P. L. Fast,
C. J. Cramer and D. G. Truhlar, J. Phys. Chem. A, 1999, 103, 4893;
c) A. Monod, A. Chebbi, R. D. Jolibois and P. Carlier, Atmos.
Environ., 2000, 34, 5283.
1
compared with those of the other possible reactions of methanol
plasma mentioned above. It is worth mentioning that the role of
the hydrogen co-feed in the methanol plasma reactions seems to
(
1
0108 Chem. Commun., 2013, 49, 10106--10108
This journal is c The Royal Society of Chemistry 2013