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Energy & Fuels 2004, 18, 1500-1504
Activated Carbon-Catalyzed Hydrogenation of Polycyclic Arenes Lin-Bing Sun, Zhi-Min Zong, Jia-Hui Kou, Li-Fang Zhang, Zhong-Hai Ni,† Gui-Yun Yu, Hong Chen, and Xian-Yong Wei* School of Chemical Engineering, China University of Mining and Technology, Xuzhou 221008, Jiangsu, China
Chul Wee Lee Advanced Chemical Technology Division, Korea Research Institute of Chemical Technology, P.O. Box 107, Yuseong, Daejeon 305-600, Republic of Korea Received February 28, 2004. Revised Manuscript Received June 19, 2004
Benzene and four polycyclic arenes (PAs) were used as substrates and their hydrogenation reactions were conducted over activated carbon (AC) at 300 °C to examine the relationship between their molecular structures and reactivities. The results show that the AC catalyzed the hydrogenation of the PAs selectively and that the reactivities of the arenes toward hydrogenation were dependent on the hydrogen-accepting abilities of the arenes and on the adsorption strengths of the arenes on the catalyst surface. The related mechanisms for hydrogen transfer were also discussed.
Introduction It is known that more than 60% of the C atoms in coal exist in aromatic forms,1,2 mainly consisting of 1-4 fused aromatic rings;3 thus, coal reactivity is strongly dependent on the aromatic structure.4 Because the large bonding energy of aromatic rings is lessened by reducing the CdC bonds to C-C bonds, the cracking reactivity of the polycylic aromatic system can be greatly enhanced by hydrogenation of the aromatic rings.5 Wei et al.6 reported that hydrogenated di(1-naphthyl)methanes are much more reactive than di(1-naphthyl)methane (DNM), implying that the hydrogenation of aromatic rings connected by a bridge linkage such as -CH2- favors cleavage of the bridge linkage, which is an important reaction in coal liquefaction. In addition, the hydrogenation of aromatic rings is important in regard to the release of aniline and alkylanilines from coal7 and the upgrading of coal-derived oil and heavy fractions from petroleum.8,9 Under given reaction conditions, the re* Author to whom correspondence should be addressed. E-mail:
[email protected]. † Present address: Department of Chemistry, Tsinghua University, Beijing 100084, China. (1) Solum, M. S.; Pugmire, R. J.; Grant, D. M. Energy Fuels 1989, 3 (2), 187-193. (2) Sakawa, M. J. Fuel Soc. Jpn. 1991, 70 (8), 782-789. (3) Winans, R. E.; Hayatsu, R.; McBeth, R. L.; Scott, R. G.; Botto, R. E. Prepr. Pap.sAm. Chem. Soc., Div. Fuel Chem. 1988, 33 (1), 407. (4) Takagi, H.; Isoda, T.; Kusakabe, K.; Morooka, S. Energy Fuels 2000, 14 (3), 646-653. (5) Isoda, T.; Takagi, H.; Kusakabe, K.; Morooka, S. Energy Fuels 1998, 12 (3), 504-511. (6) Wei, X.-Y.; Ogata, E.; Futamura, S.; Kamiya, Y. Fuel Process. Technol. 1990, 26 (2), 135-148. (7) Wei, X.-Y.; Ni, Z.-H.; Xiong, Y.-C.; Zong, Z.-M.; Wang, X.-H.; Cai, C.-W.; Ji, Y.-F., Xie, K.-C. Energy Fuels 2002, 16 (2), 527-528. (8) Girgis, M. J.; Gates, B. C. Ind. Eng. Chem. Res. 1991, 30 (9), 2021-2058.
activities of aromatic rings toward hydrogenation are dependent on their molecular structures; therefore, understanding the relationship between the reactivities of aromatic rings toward catalytic hydrogenation and their molecular structures is of significance for clarifying the hydroliquefaction mechanism of coal. Deep hydrogenations of polycyclic arenes (PAs) have been extensively investigated. Huang and Kang10 investigated the hydrogenation of naphthalene over some noble metals such as platinum and palladium. They found that such catalysts promoted deep hydrogenation of naphthalene and produced decalins rather than tetralin. Zhang et al.11 mentioned in their study, which used a nickel metal catalyst at 300 °C, that anthracene hydrogenation not only reached complete conversion, but also afforded large amounts of octahydroanthracenes, in addition to 9,10-dihydroanthracene and 1,2,3,4tetrahydroanthracene. Similarly, in base-catalyzed hydrogenation, Yang and Stock’s results12 demonstrated that anthracene and phenanthrene were hydrogenated, using a bis(trimethylsilyl)amide catalyst, to a mixture of corresponding octahydro derivants with 99% and 96% yields, respectively, and that chrysene was converted by the same reagent to 1,2,2a,3,4,5,6,6a,9,10,11,12dodecahydrochrysene (70%) and 1,2,2a,3,4,5,6,6a-octahydrochrysene (25%). The use of the aforementioned expensive catalysts did not lead to selective hydrogenation of the PAs. Considering the importance of obtaining valuable aromatics and hydroaromatics from coal, pe(9) Mochida, I.; Sakanishi, K.; Korai, Y.; Fujitsu, H. Fuel 1986, 65, 1090-1093. (10) Huang, T.-H.; Kang, B.-C. Chem. Eng. J. 1996, 63 (1), 27-36. (11) Zhang, Z.-G.; Okada, K.; Yanamoto, M.; Yoshida, T. Catal. Today 1998, 45, 361-336. (12) Yang, S.; Stock, L. M. Energy Fuels 1996, 10 (6), 1181-1186.
10.1021/ef049946a CCC: $27.50 © 2004 American Chemical Society Published on Web 07/28/2004
Hydrogenation of Polycyclic Arenes
Energy & Fuels, Vol. 18, No. 5, 2004 1501
Figure 1. Mass spectra of the hydrogenated polycyclic arenes (PAs).
troleum, and other raw materials, the selective hydrogenation of PAs should be given more attention. Because of their relatively high surface area, carbon materials such as carbon black and activated carbons (ACs) have been widely used as supports to prepare highly dispersed catalysts. However, several studies have shown that supported metals as well as carbon supports themselves have catalytic activity, e.g., for 4-(1naphthylmethyl)bibenzyl decomposition,13 chlorobenzene dechlorination,14 ethylbenzene dehydrogenation,15 and DNM hydrocracking.16
In this study, we use an AC as a catalyst and five arenes, including four polycyclic arenes (PAs), as substrates to investigate the relationship between the reactivities of the arenes toward catalytic hydrogenation and their molecular structures, as well as the regioselectivity of the catalytic hydrogenation over the AC. Materials. An AC (Darco KB-B,
