Behavior of Hydrogen Transfer in the Hydrogenation of Anthracene

The behavior of hydrogen transfer over activated carbon was examined through the hydrogenation of anthracene in the temperature range of 300−400 °C...
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Energy & Fuels 2001, 15, 708-713

Behavior of Hydrogen Transfer in the Hydrogenation of Anthracene over Activated Carbon Zhan-Guo Zhang* and Tadashi Yoshida Hokkaido National Industrial Research Institute, 2-17 Tsukisamu-Higashi, Toyohira-ku, Sapporo 062-8517, Japan Received October 31, 2000. Revised Manuscript Received January 24, 2001

The behavior of hydrogen transfer over activated carbon was examined through the hydrogenation of anthracene in the temperature range of 300-400 °C with three kinds of hydrogen sources: hydrogen gas, hydrogen-donor tetralin, and the combination of both. With hydrogen gas, the hydrogen transfer rate determined from the distribution of hydrogenated anthracene products increased with both hydrogen partial pressure and temperature, while in tetralin it depended on the concentration of hydrogen atoms formed on the surface of activated carbon by the dehydrogenation of tetralin and reached levels at temperatures of 350-400 °C comparable to those obtained in the same temperatures under 6.0 MPa of H2. When both hydrogen gas and tetralin were used together, the hydrogen transfer rate was higher than each one obtained separately with hydrogen gas alone or tetralin alone, but much lower than the simple sum of both rates in the range of 350-400 °C. Simultaneously, the hydrogen formation rate based on the conversion of tetralin in this case was greatly suppressed due to the presence of hydrogen gas and measured to be quite close to the corresponding hydrogen transfer rate. This indicates that the hydrogen transfer in the hydrogenation of anthracene over activated carbon mainly took place from tetralin to anthracene when both hydrogen gas and tetralin donor were used as hydrogen source together.

Introduction Apart from their use as absorbents and catalyst supports, carbon materials such as activated carbons and carbon blacks can be used as catalysts. It is generally known that some of them catalyze reactions1-3 such as chlorinations, oxidations of SO2, NO, and H2S, and oxidative dehydrogenations of hydrocarbons as well as alcohols. Additionally, some recent studies have shown that some carbon materials are active for the cleavage of C-C bonds,4-7 degradation of polyethylene,8,9 dehydrogenation of hydrocarbons,10,11 and dehydration as well as dehydrogenation of ethanol, 2-propanol, and 2-butanol.12-14 Under reduction conditions * Author to whom correspondence should be addressed. Fax: (011) 857-8986. E-mail: [email protected]. (1) Juntgen, H.; Kuhl, H. Chemistry and Physics of Carbon; Marcel Dekker: New York, 1989; Vol. 22, pp 145-195. (2) Radovic, L. R.; Rodriguez-Reinoso, F. Chemistry and Physics of Carbon; Marcel Dekker: New York, 1997; Vol. 25, pp 326-334. (3) Rodriguez-Reinoso, F. Carbon 1998, 36 (3), 159-175. (4) Farcasiu, M.; Smith, C. Energy Fuels 1991, 5 (1), 83-87. (5) Farcasiu, M.; Smith, C.; Hunter, E. A. Proc. Int. Conf. Coal Sci. 1991, 166-169. (6) Farcasiu, M.; Petrosius, S. C.; Eldredge, P. A.; Anderson, R. R.; Ladner E. P. Energy Fuels 1994, 8 (4), 920-924. (7) Farcasiu, M.; Kaufman, P. B.; Ladner, E. P.; Derbyshire, F.; Jagtoyen, M. Proc. Int. Conf. Coal Sci. 1995, 1303-1306. (8) Uemichi, Y.; Kashiwaya, Y.; Ayame, A.; Konoh, H. Chem. Lett. 1984, 41-44. (9) Uemichi, Y.; Makino, Y.; Kanazuka, T. J. Anal. Appl. Pyrolysis 1989, 14, 331-344. (10) Fujimato, K.; Hamada, H.; Kunugi, T. J. Jpn. Pet. Inst. 1972, 12, 1022-1026. (11) Fujimoto, K. J. Jpn. Pet. Inst. 1984, 12, 463-471. (12) Szymanski, G. S.; Rychlicki, G. Carbon 1991, 29 (4), 489-498. (13) Szymanski, G. S.; Rychlicki, G. Carbon 1993, 31 (2), 247-257.

in the presence of hydrogen donor solvents, they are also found to catalyze the hydrogenolysis of benzyl-methylnaphthalenes15 and the dehydroxylation and dehalogenation of substituted polycyclic aromatics with the hydrogenation of ring.16 All these suggest that carbon materials used as supports may not be innocent, but may function as catalysts in some reactions. Therefore, a double catalytic effect could be expected when a carbon-supported catalyst is applied to such specific circumstances. Upgrading of coal-derived liquids or heavy oils includes a number of reactions such as hydrocracking, hydrogenation, hydrogen transfer, and so on. It may be a good application for such carbon and carbon-supported catalysts.17,18 To explore such a possible application of carbonsupported catalysts and to develop a catalyst with a double catalytic effect for upgrading of coal-derived liquids, we have examined the hydrogenation activity of carbon-supported metal catalysts using anthracene as a model compound.19-21 Considering that hydrogen transfer from gas phase and/or hydrogen donor solvents (14) Szymanski, G. S.; Rychlicki, G.; Terzyk, A. P. Carbon 1994, 32 (2), 265-271. (15) Futamura, S. Proc. Int. Conf. Coal Sci. 1997, 1481-1484. (16) Farcasiu, M.; Petrosius, S. C.; Eldredge, P. A.; Ladner, E. P. J. Catal. 1994, 146, 313-316. (17) Aimoto, K.; Nakamura, I.; Fujimoto, K. Energy Fuels 1991, 5 (5), 739-744. (18) Sakanishi, K.; Hasuo, H.; Kishino, M.; Mochida, I. Energy Fuels 1996, 10 (1), 216-219. (19) Zhang, Z.-G.; Yamamoto, M.; Yoshida, T. Proc. 7th Australian Coal Sci. Conf. 1996, 135-141. (20) Zhang, Z.-G.; Okada, K.; Yamamoto, M. Yoshida, T. Proc. Int. Conf. Coal Sci. 1997, 1457-1460.

10.1021/ef000253d CCC: $20.00 © 2001 American Chemical Society Published on Web 03/15/2001

H Transfer in the Hydrogenation of Anthracene

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to feed components in upgrading reactions is the key for achieving efficient process conversion, in these previous studies we mainly focused on the hydrogen transfer capability of the catalysts and have shown that not only supported metals but also carbon support itself is active for the hydrogen transfer from either gas phase or donor solvent to anthracene. In this study, the hydrogen transfer behavior of activated carbon itself in the hydrogenation of anthracene was examined in detail in the temperature range of 300-400 °C with three kinds of different hydrogen sources: hydrogen gas (1.0 and 6.0 MPa), hydrogen donor tetralin, and the combination of both. The aim is quantitatively to evaluate the hydrogen transfer capability of activated carbon and then to provide an indication of catalytic use of carbon materials in systems such as upgrading of coal-derived liquids. Also it is an aim to clarify the roles of gaseous hydrogen as well as solvent hydrogen in such a carboncatalyzed reaction system and to show how hydrogen could be efficiently supplied to the system. Anthracene here was used only as a model hydrogen acceptor and its hydrogenation itself was out of the scope of this paper. Experimental Section Materials Used. Tetralin, anthracene, and benzene all in high purity (Kanto Chemicals Co.) were used without further purification. An activated carbon prepared from coal by steam activation (Kurare Chemical Co.) was ground and sieved to the particle size of 246-495 µm and then used as catalyst. Its surface area and ash content were measured to be 1030 m2/g and 3 wt %, respectively. Additionally, a part of the activated carbon was also washed with a mixture of HF and HNO3, and then heated in a flow of pure N2 at 600 °C for 30 min to prepare a demineralized sample. In some experiments, this demineralized sample with ash content less than 0.1 wt % was used to examine where the catalytic activity of the activated carbon in the hydrogenation of anthracene originated from, carbon itself or its mineral component. Apparatus and Procedure. All experiments were carried out in a downflow fixed bed reactor system, and the flow diagram is shown in Figure 1. The system mainly consists of a micro liquid pump, a high-pressure mass flow meter, a stainless steel tube reactor (10 mm i.d.), and a pressurecontrolling regulator. The reactor was charged with 1.5 g of the activated carbon catalyst, and then pressurized to 10 MPa by flowing a mixture of anthracene (1.782 g) and benzene (200 mL, as solvent) or a mixture of anthracene (1.782 g), tetralin (15 mL, as hydrogen donor), and benzene (185 mL), depending on the objectives of the experiment. After hydrogen gas (when used) was fed through the high-pressure mass flow meter, the reactor was then heated to 300-400 °C. At these reaction temperatures, the hydrogen partial pressure and the feed rate of the mixture were adjusted again to 1.0 or 6.0 MPa and 0.2 mL/min, respectively, and then kept constant until the steady state of the reaction was reached. The reaction product was sampled at the outlet of the pressure regulator every 20 min and simultaneously was analyzed by GC-FID (Shimazu GC16A) equipped with a silicone capillary column (OV-1; 0.25 mm × 25 m) to confirm the approaching of the steady state. A longest period of time needed for the steady state was observed to be about 4 h in this study. All the data shown in this paper were collected at the same reaction time, the fourth hours. In addition, the identification of the products was conducted using a GC-MS (Shimazu GC-17A, QP-5000). (21) Zhang, Z.-G.; Okada, K.; Yamamoto, M.; Yoshida, T. Catal. Today 1998, 45, 361-366.

Figure 1. Schematic diagram of the experiment apparatus.

Results and Discussion Hydrogenation with Hydrogen Gas. The hydrogenation of anthracene with hydrogen gas was first carried out over glass beads (GB, as a reference) and the activated carbon (AC) in the temperature range of 300-400 °C. Figures 2a and 2b show the product distributions at each point of temperatures under the hydrogen partial pressures of 1.0 and 6.0 MPa, respectively. Over glass beads, the conversion of anthracene increases with temperature at both pressures and reaches the highest level of 78 mol % at a condition of 400 °C and 6.0 MPa of H2. Although the hydrogenation of anthracene here takes place mainly to its initial stage, forming 9,10-dihydroanthracene (DiHA), the present results are still very surprising in view of the fact that neither a catalyst nor a radical initiator (H-donor solvent or H2S) was used to activate molecular hydrogen to its atomic form for the reaction. Chiba et al.22 mentioned in their study using an autoclave that 47% of anthracene was hydrogenated to DiHA (44%) and TeHA (3%) in 1-methylnaphthalene under a hydrogen atmosphere at 430 °C. Similarly in some batch experiments using a tube bomb reactor, Fixari and Le Perchec23 obtained a 84% conversion of anthracene also with a good selectivity toward DiHA under 5 MPa of initial hydrogen pressure (room temperature) at 400 °C. McCollom et al.24 reached even higher hydrogenation conversions of anthracene in their hydrothermal experi(22) Chiba, K.; Tagaya, H.; Suzuki, T.; Sato, S. Bull. Chem. Soc. Jpn. 1991, 64 (3), 1034-1036. (23) Fixari, B.; Le Perchec, P. Fuel 1989, 68, 218-221.

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Figure 2. Hydrogenation of anthracene over glass beads and activated carbon with hydrogen gas. (a) H2:1.0 MPa, and (b) H2:6.0 MPa.

ments with formic acid as a source of H2. However, what made molecular hydrogen activated in those cases was not discussed. In the present cases, the wall of reactor, on which condensed carbonaceous materials might form in the reaction, was attributed to being responsible for the activation of molecular hydrogen necessary for the hydrogenation of anthracene, since almost the same results were obtained also with no packed reactor. The activated carbon, compared with glass beads, provided higher conversions at the same hydrogen partial pressure of 1.0 MPa and simultaneously deepened the hydrogenation to a higher stage, yielding not only DiHA but also 1,2,3,4-tetrahydroanthracene (TeHA). This clearly shows that the activated carbon is catalytically active for the dissociation of molecular hydrogen and the subsequent hydrogen transfer to anthracene over it. When hydrogen partial pressure was increased to 6.0 MPa (Figure 2b), the difference in anthracene conversion and hydrogenated product distribution between the activated carbon and glass beads, particularly at higher temperatures, becomes greater, further confirming the catalytic activity of the activated carbon in the hydrogenation of anthracene. In addition, a small amount of a 6-butyltetralin (BuTet) as well as phenanthrene (Phen) was also observed over the activated carbon under 6.0 MPa of H2 at 400 °C, might suggesting a slightly catalytic activity of the activated carbon in the cleavage of C-C bonds4-7 and ring isomerization. Here, a question to be asked is what the catalytically active component of the activated carbon was: carbon itself or inorganic materials contained in it. To answer this question, a series of anthracene hydrogenations was conducted at the same temperatures and the hydrogen partial pressure of 1.0 MPa but with the demineralized activated carbon sample which ash content is less than 0.1 wt % as catalyst. The resulting anthracene conversions and product distributions were found to be almost the same as those with the activated carbon itself shown in Figure 1a, indicating that the catalytic activity of the activated carbon in the hydrogenation of anthracene originated from carbon itself, not its inorganic component. It seems that this conclusion is not questionable, since not only the hydrogen transfer ability of carbon materials has been demonstrated by the spillover of hydrogen from a metal to carbon support itself,25,26 but also their capability to split molecular hydrogen to atomic one has been shown by hydrogen chemisorption (24) McCollom, T. M.; Simoneit, B. R. T.; Shock, E. L. Energy Fuels 1999, 13 (2), 401-410. (25) Robell, A. J.; Ballou, E. V.; Boudart. M. J. Phys. Chem. 1964, 68 (10), 2748-2753. (26) Boudart, M.; Aldag, A. W.; Vannice, M. A. J. Catal. 1970, 18, 46-51.

Figure 3. Hydrogen transfer in the hydrogenation of anthracene over glass beads and activated carbon with hydrogen gas.

on pure carbon in an early study.27 Furthermore, the increased activity observed here with temperature is also supported by the fact reported in this early study that more hydrogen was activated and chemisorbed on pure carbon at higher temperatures. To make a quantitative comparison with cases, as shown in the following sections, using tetralin donor alone or both tetralin and hydrogen gas together as the hydrogen source, the hydrogen transfer rate from gas phase to anthracene was estimated on the hydrogenated product yields obtained. As shown in Figure 3, much higher hydrogen transfer rates were reached over the activated carbon at 6.0 MPa of H2 and higher temperatures, since the hydrogenation proceeded more deeply and a large quantity of 1,2,3,4,5,6,7,8- and 1,2,3,4,4a,9,10,10a-octahydroanthracene (OcHA) was formed at these conditions (Figure 2b). Hydrogenation with Tetralin. To understand the behavior of hydrogen transfer between donor tetralin and anthracene over the activated carbon, the hydrogenation of anthracene was also conducted with tetralin as hydrogen source alone. Figure 4 shows the conversions of dehydrogenation of tetralin and the hydrogenated product distributions of anthracene obtained at all the temperatures, while Figure 5 gives the corresponding hydrogen formation and transfer rates, respectively. Here, the hydrogen formation rate was calculated on the basis of the dehydrogenation conversion of tetralin to naphthalene, while the transfer rate, same as above, from the yields of hydrogenated anthracene. As shown in Figure 4, with tetralin as hydrogen source, the hydrogenation of anthracene, similar to the case above with hydrogen gas, occurs over the activated carbon at all the temperatures, and particularly in the range of 350-400 °C, the conversion reaches levels comparable to those observed in the same temperature range under 6.0 MPa of H2. This indicates that the activated carbon also has a highly catalytic ability to transfer hydrogen from donor tetralin to anthracene. By using the demineralized activated carbon, this catalytic activity of the activated carbon was again attributed to its carbonaceous component. Simultaneously, thermal reaction in the present cases was also examined with glass beads, and its contribution (27) Keren, E.; Soffer, A. J. Catal. 1977, 50, 43-55.

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Figure 6. Hydrogenation of anthracene over activated carbon with different tetralin/anthracene ratios.

Figure 4. Hydrogenation of anthracene over activated carbon with tetralin as hydrogen source.

Figure 5. Hydrogen formation and transfer in the hydrogenation of anthracene over activated carbon with tetralin as hydrogen source.

confirmed to be negligible since the dehydrogenation of tetralin, which provides active hydrogen atoms for the hydrogenation of anthracene, hardly took place over glass beads in the temperature range investigated. The dehydrogenation of hydrocarbons over carbon catalysts has been widely studied. It is generally believed that the dehydrogenation of hydrocarbons takes place with the abstraction of hydrogen atoms into the carbon surface as a first step, and then followed by the releasing of these adsorbed surface hydrogen atoms into gas phase and/or the surface transferring to acceptors when they are present.11,28,29 When metal-free carbon is used, the releasing of the hydrogen atoms occurs thermally. In the present cases, this thermal releasing would be relatively slow, since the temperatures employed were in a low range. Consequently, more hydrogen atoms would remain on the surface as the dehydrogenation of tetralin proceeds with temperature increase. That is, much more hydrogen atoms are left on the carbon surface available for the hydrogenation of anthracene. Therefore, the higher conversions of anthracene were observed at the higher temperatures (Figure 4). On the other hand, it is also known that the (28) Nakamura, I.; Fujimoto, K. Sekiyu Gakkaishi 1995, 38 (5), 291299. (29) Iwasawa, Y.; Mori, H.; Ogasawara, S. J. Catal. 1980, 61, 366373.

hydrogenation of anthracene takes place via successive steps, each of which is reversible.30,31 That is, the hydrogenation reactions of anthracene are limited by their equilibrium constants. The hydrogen transfer rate shows only a slight increase with temperature in the range of 350-400 °C, might indicating that the hydrogenation reached equilibrium at these temperatures. When metal catalysts are used, the equilibrium composition of the hydrogenation generally vary with the hydrogen partial pressure of gas phase because of easy dissociation of molecular hydrogen on the metal surface. Over carbon catalyst, however, it may be more sensitive to the concentration of hydrogen atoms formed on the carbon surface. Actually, the possible hydrogen partial pressures formed presently due to the dehydrogenation of tetralin were extremely low in the whole temperature range. For example, the hydrogen partial pressure was calculated not to be over 0.34 MPa at 400 °C, much lower than that of 6.0 MPa supplied by hydrogen gas in the case using hydrogen gas alone. Although so, the quite high anthracene conversions and hydrogen transfer rates were still reached (Figures 4 and 5). It clearly shows that a high hydrogen pressure is not absolutely required for the hydrogenation of anthracene when carbon was used as catalyst and donor solvent as hydrogen source. This conclusion is also supported by the results of Farcasic et al.16 that dehydroxylation and dehalogenation of aromatic compounds catalyzed by carbon black occurred with the hydrogenation of ring as the first step in the presence of a hydrogen donor under atmospheric pressure. Thus, the amount of solvent used would come to be an important factor in improving the hydrogen transfer performance of the catalyst. Therefore, the effect of molar ratio of tetralin to anthracene in feed was also investigated at 350 and 400 °C. Here, the molar ratio was adjusted by varying the relative amount of tetralin in feed solution. As shown in Figures 6 and 7, both anthracene conversion and hydrogen transfer rate increase with the molar ratio in a range up to about 22, and then remain constant. In other words, 22 mol of tetralin donor are needed for one mole of anthracene to have the best hydrogen transfer performance over the activated carbon catalyst. Since only 4 moles of hydrogen that could be supplied by 2 moles of tetralin is theoretically required for the hydrogenation of one mole of anthracene to OcHA, the value of 22 is significantly great and means that most of the hydrogen from tetralin in these cases was released to the gas phase. (30) Stanislaus, A.; Cooper, B. H. Catal. Rev.sSci. Eng. 1994, 3 (1), 75-123. (31) Korre, S. C.; Klein, M. T.; Quann, R. T. Ind. Eng. Chem. Res. 1995, 34, 101-117.

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Figure 9. Hydrogen formation and transfer in the hydrogenation of anthracene over activated carbon with both hydrogen gas and tetralin together. (a) H2:1.0 MPa, and (b) H2:6.0 MPa.

Figure 7. Hydrogen transfer in the hydrogenation of anthracene over activated carbon with different tetralin/anthracene ratios.

Figure 8. Hydrogenation of anthracene over activated carbon with both hydrogen gas and tetralin together. (a) H2:1.0 MPa, and (b) H2:6.0 MPa.

Hydrogenation with Tetralin and Hydrogen Gas Together. Finally, the hydrogenation of anthracene with both tetralin and hydrogen gas together was performed over the activated carbon. The conversions and product distributions observed at all the temperatures under the hydrogen partial pressure of 1.0 and 6.0 MPa are shown in Figures 8a and 8b, respectively, while the corresponding hydrogen transfer rates are given in Figures 9a and 9b, respectively. Compared with the cases using tetralin alone (Figures 4 and 5), both anthracene conversion and the hydrogen transfer rate were promoted due to the coexistence of 1.0 MPa of H2. When hydrogen partial pressure was increased to 6.0 MPa, this kind of promotion effect becomes more apparent throughout the whole temperature range. Although it is so, the hydrogen transfer rates reached were still much smaller than the simple sum of the corresponding two rates that were obtained separately with hydrogen gas alone (Figure 3) or tetralin alone (Figure 5). When the contributions by the reaction with hydrogen gas over glass beads were excluded in these cases, the resulting “net” hydrogen transfer rates at both 1.0 and 6.0 MPa of H2, as shown in Figure 10, not only become quite close to each other at all the temperatures, but also are comparable to those obtained with tetralin alone, particularly at the higher temperatures. This clearly shows that the hydrogen transfer in the coexistence of tetralin donor and hydrogen gas occurred mainly from donor tetralin to anthracene and not from gaseous hydrogen To make this point more clear, the hydrogen formation rates in the hydrogenation at both 1.0 and 6.0 MPa of H2 were also estimated and compared in Figure 9a and 9b, respectively. At 1.0 MPa of H2, the hydrogen formation rate is slightly lower than the transfer rate in the range of 300-380 °C. It suggests that most of

Figure 10. Comparison of net hydrogen transfer rates reached with both hydrogen gas and tetralin together to that with tetralin alone.

the hydrogen transferred to anthracene was from tetralin and further supports the above conclusion. At 6.0 MPa of H2, however, the formation rate is much lower than the corresponding transfer one at all the temperatures. It appears that the contribution of hydrogen from tetralin to the hydrogenation in this case becomes smaller than that at the low hydrogen temperature of 1.0 MPa. But in fact, the dehydrogenation of tetralin responsible for the hydrogen transfer rate occurred only over the activated carbon, while the hydrogenation of anthracene on which products the transfer rate was calculated always took place not only on the activated carbon but also on glass beads. As shown in Figure 3, the contribution by reaction over glass beads is quite great at 6.0 MPa of H2. If this part is excluded from the present hydrogen transfer rate, that is, only the hydrogen transferred over the activated carbon is accounted, the resulting “net” transfer rate will become smaller and may be comparable to the formation rate. Actually, it was calculated, for example, at 400 °C, to be 2.3 × 10-5 mol/min, very close to the corresponding formation rate of 2.2 × 10-5 mol/min. This means that the above conclusion reached at 1.0 MPa of H2 is still valid at the high hydrogen pressure of 6.0 MPa. That is, in the coexistence of tetralin and gaseous hydrogen, the hydrogen transferring over the activated carbon occurred mainly from tetralin solvent and not from hydrogen gas to anthracene. On the other hand, the main function of hydrogen gas in the coexistence of hydrogen and tetralin may be understood through a comparison of these hydrogen formation rates to those obtained with tetralin alone (Figure 5). The hydrogen formation rate, for example at 400 °C, reached 7.2 × 10-5 mol/min when tetralin was used alone. However, it was observed to be only

H Transfer in the Hydrogenation of Anthracene

Figure 11. Hydrogen transfer in the hydrogenation of anthracene over activated carbon with different tetralin/anthracene ratios and hydrogen partial pressures.

3.2 and 2.8 × 10-5 mol/min, respectively, at the same temperature when hydrogen gas of 1.0 or 6.0 MPa was used together. In terms of tetralin conversion, these numbers are equal to 32.1, 14.2, and 12.8%, respectively. Clearly, the presence of hydrogen gas greatly suppressed the dehydrogenation of tetralin. This is in good agreement with our previous results that the dehydrogenation of pure tetralin over activated carbon was strongly suppressed by gaseous hydrogen.21 According to the mechanism of dehydrogenation discussed before, this kind of suppressive effect must result from the depression of the releasing of hydrogen atoms from the carbon surface into gas phase but not of the surface transferring of hydrogen to anthracene. In other wards, the presence of hydrogen gas would be beneficial for reducing the use of donor solvent without inhibiting the hydrogen transfer between donor and acceptor. As

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shown in Figure 11, when hydrogen gas of 1.0 MPa was supplied together with tetralin, a minimum molar ratio of tetralin to anthracene required for reaching the same hydrogen transfer rate in the hydrogenation is reduced from that of 22 observed in tetralin (Figure 7) to 4 or less at 350 °C. Even at 400 °C, such reductive effect of hydrogen gas is still clear. For example, for the same hydrogen transfer rate of 2.2 × 10-5 (mol/min), the molar ratio of 22 was required in the case using tetralin alone, while that of 4 was enough when both tetralin and hydrogen gas of 1.0 MPa were used together. In this connection, the corresponding two hydrogen formation rates are 7.2 and 2.6 × 10-5 (mol/min), respectively. Conclusions It has been demonstrated that the activated carbon is catalytically active at transferring hydrogen from both hydrogen gas and tetralin into anthracene in the temperature range of 300-400 °C. In the range of 350400 °C, the hydrogen transfer rates reached over the activated carbon with tetralin donor were found to be comparable to those obtained at the hydrogen partial pressure of 6.0 MPa. When both tetralin and hydrogen gas were used together, the hydrogen transfer over the activated carbon mainly occurred from tetralin to anthracene, while the function of hydrogen gas in this case was mainly to suppress the releasing of hydrogen atoms from the carbon surface into gas phase. Therefore, the amount of tetralin solvent being used could be greatly reduced in the coexistence of low-pressure hydrogen gas. EF000253D