Catalytic Dechlorination of Carbon Tetrachloride in Liquid Phase with Methanol as H-Donor Over Ag/C Catalyst
Lu et al.
Table II. Particle size of catalyst calculated from Scherrer equation.
3.4. Reaction Mechanism
Here, we propose a plausible reaction mechanism for
the dechlorination of CCl4 over sole Ag catalysts with
methanol as hydrogen donor, involving the dehydrogena-
tion of methanol to formaldehyde with the formation of
Ag–H active species and the abstraction of Cl− from
adsorbed CCl4 by Ag to form CCl3 and CCl2 radicals,
combined with Ag–H to generate reaction products, CHCl3
and CH2Cl2. The regeneration of Ag from AgCl would be
related to the HCHO intermediate (Fig. 5).
Sample
D (nm)
Fresh Ag/C catalyst
Used Ag/C catalyst
Fresh Ag/C catalyst after reaction with 5 ꢁl of CCl4 for 0.5 h
Fresh Ag/C catalyst after reaction with 10 ꢁl of CCl4 for 0.5 h
21
54
41
47
Ag
CHCl3; CH2Cl2
CH3OH
HCHO
4. CONCLUSION
In summary, we reported here an efficient catalytic process
for the dechlorination of CCl4 to CH2Cl2 and CHCl3 in liq-
uid phase over sole silver catalysts, where methanol is taken
as H-donor, and its dehydrogenated product, formaldehyde,
facilitates the regeneration of formed AgCl to Ag.
Ag–H
AgCl
–CCl3; = CCl2
Acknowledgment: The authors greatly acknowledge
the funding from NSFC (Grant Nos.: 20976076 and
21307009) and the Priority Academic Program Develop-
ment of Jiangsu Higher Education Institutions (PAPD).
Ag
CCl4
CO; HCl
Figure 5. Reaction scheme for dechlorination of CCl4 by supported
silver catalyst in the presence of methanol.
References and Notes
well as the incorporation of chloride ion (Cl−) into the Ag
domains. The rapid transformation of Ag to AgCl during
1. F. Alonso, I. P. Beletskaya, and M. Yus, Chem. Rev. 102, 4009
(2002).
Delivered by Publishing Technology to: Rice University
the reaction was also illustrated by adding trace amounts
of CCl4 (5 and 10 ꢁl, respectively) into the reactor and
reacting for 0.5 h, also shown in Figure 1. The AgCl parti-
cle size increases with CCl4 amount monotonously (41 nm
for 5 ꢁl of CCl4 added and 47 nm for 10 ꢁl, Table II), indi-
cating the incorporation of Cl− into the Ag particles. The
certain degree of aggregation of Ag particles was found
in the used catalyst (Fig. 4(c)), implying the weak interac-
tion of Ag domains with activated carbon support. But no
very large Ag particles were observed, indicating the sin-
tering of Ag did not occur during the reaction, evidenced
from the identical performance of recycled catalysts.
The chemical states of surface silver species of used Ag/C
catalyst were determined by XPS,14ꢀ15 calibrated with C1s
(284.6 eV). The XPS of used catalyst (Fig. 4) clearly
shows that the coexistence of Ag and Ag1+ at the outer
sphere of the reacted Ag particles, indicating the reduc-
tion of AgCl by formaldehyde (HCHO) with formation of
carbon monoxide (CO) and hydrogen chloride (HCl), at
elevated temperatures.
2. V. I. Kovalchuk and J. L. d’Itri, J. Catal. 271, 13 (2004).
IP: 186.139.0.78 On: Thu, 25 Feb 2016 13:38:53
3. X. Wu, Y. A. Letuchy, and D. P. Eyman, J. Catal. 161, 164 (1996).
Copyright: American Scientific Publishers
4. N. Bovet, D. I. Sayago, F. Allegretti, E. A. Kröger, M. J. Knight,
J. Barrett, D. P. Woodruff, and R. G. Jones, Surf. Sci. 600, 241
(2006).
5. H. Zhang, Q. Fu, Y. X. Yao, Z. Zhang, T. Ma, D. L. Tan, and X. H.
Bao, Langmuir 24, 10874 (2008).
6. J. Hohmeyer, E. V. Kondratenko, M. Bron, J. Kröhnert, F. C. Jentoft,
R. Schlögl, and P. Claus, J. Catal. 269, 5 (2010).
7. K. Shimizu, Y. Miyamoto, and A. Satsuma, J. Catal. 270, 86 (2010).
8. A. Montoya and B. S. Haynes, J. Phys. Chem. C 111, 9867 (2007).
9. S. C. Fung and J. H. Sinfelt, J. Catal. 103, 220 (1987).
10. M. H. Lu, J. Z. Sun, D. B. Zhang, M. S. Li, J. J. Zhu, and Y. H.
Shan, React. Kinet. Mech. Catal. 100, 99 (2010).
11. B. Heinrichs, J. P. Schoebrechts, and J. P. Pirard, J. Catal. 200, 309
(2001).
12. W. S. Sim, P. Gardner, and D. A. King, J. Phys. Chem. 99, 16002
(1995).
13. T. E. Felter, W. H. Weinberg, G. Y. Lastushkina, P. A. Zhdan, G. K.
Boreskov, and J. Hrbek, Appl. Surf. Sci. 16, 351 (1983).
14. A. Samokhvalov, S. Nair, E. C. Duin, and B. J. Tatarchuk, Appl.
Surf. Sci. 256, 3647 (2010).
15. H. Kannisto, H. H. Ingelsten, and M. Skoglundh, J. Mol. Catal. A-
Chem. 302, 86 (2009).
Received: 30 November 2012. Accepted: 4 October 2013.
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