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Ind. Eng. Chem. Res. 2008, 47, 7496–7500
Dehydrogenation of Alcohol Mixtures to Esters and Ketones F. H. A. Bolder* Fischer-Tropsch Refinery Catalysis, Sasol Technology, Research & DeVelopment, P.O. Box 1, Sasolburg 1947, South Africa
Fischer-Tropsch synthesis produces, among other things, complex mixtures of oxygenated compounds, such as primary and secondary alcohols, which are difficult to separate. The dehydrogenation of alcohol fractions in the C3 and C4 alcohol boiling ranges was investigated to determine whether the process would be suitable to produce different types of oxygenated compounds (esters and ketones), which could find application as solvents. The reaction was conducted in the presence of a Cu/Zn/Al2O3 catalyst in a pilot-plant-scale reactor in the temperature ranges of 219-278 °C with the propanol-rich feed and 219-300 °C with the butanol-rich feed (and at atmospheric pressure). The reaction products consisted of esters, ketones, and aldehydes (in decreasing order). The ester yield passed through a maximum with increasing temperature, as a result of secondary reactions, whereas the yield of ketones increased continually with temperature. The activity of the catalyst decreased by ∼15% over a period of 92 days. The selectivity of propyl propanoate, which is the main ester produced from the propanol feed mixture, decreased with time, while the yield of the ketones increased slightly. 1. Introduction The Fischer-Tropsch process produces mainly hydrocarbons and water from synthesis gas (H2 + CO); however, a substantial fraction of oxygenated compounds also is produced.1 The shortchain polar oxygenated compounds are water-soluble and condense together with the water. At the Sasol high-temperature Fischer-Tropsch refinery, the alcohols, aldehydes, and ketones in the water fraction are distilled off and hydrogenated. The resultant alcohol mixture is complex, and separation into pure compounds is not economical for many of the alcohols. Applications of these mixed alcohols are limited; therefore, the conversion to other oxygen-containing compounds is a potentially attractive reaction to produce solvents or intermediates. The catalytic dehydrogenation of primary and secondary alcohols to corresponding aldehydes and ketones is applied industrially to produce mainly intermediates. Examples are the dehydrogenation of methanol to formaldehyde, ethanol to acetaldehyde, and cyclohexanol to cyclohexanone, which is used in the production of nylon 6.2 Competitive processes exist, but the dehydrogenation process has the advantage of producing very pure hydrogen, which can be used in other processes. The dehydrogenation reaction can also be applied to produce esters that form useful solvents. An example is the reaction of ethanol to ethyl acetate in a single step over bifunctional catalysts, which has been known for a long time.3,4 Interest in the reaction increased, as a result of a drive toward cleaner and more costeffective processes.5,6 A process based on a Cu/Cr catalyst was commercialized in 2000 by Davy Process Technology at Sasol to produce high-purity ethyl acetate.7,8 The process operates under pressure and uses high-purity ethanol derived from the Fischer-Tropsch synthesis process as feed stock. The dehydrogenation reaction of higher alcohols has been investigated,9-11 but esters of higher alcohols are not produced commercially via this route. The formation of esters is thought to proceed via the aldehyde intermediate, which reacts with an alcohol to produce a * To whom correspondence should be addressed.Tel.: +27 16 9604209. Fax: +27 11 5223290. E-mail address: frans.bolder@ sasol.com.
hemiacetal, which, in turn, is dehydrogenated to form the ester.9 Other products also are formed, and the reactions are presented schematically in Figure 1. The overall reaction to form the ester proceeds slowly, not least because of the many steps involved, and a long residence time in the catalyst bed is required to maximize the ester selectivity.10 The dehydrogenation of the alcohol is favored at low operating pressures, whereas the dimerization reaction is favored at high pressures. Therefore, the ester selectivity will increase with reactor pressure, while the conversion will decrease.12 Copper-based catalysts are used industrially for the dehydrogenation of alcohols to aldehydes.13 CuO supported on Al2O3 catalyzes the formation of ether as well as ester.14 The formation of the ether can be ascribed to the acidic properties of the alumina, which catalyzes the dehydration of alcohols. ZnO also is active for the dehydrogenation of alcohols, and the combination of ZnO with Cu/Al2O3 reduces the formation of ethers, because of the basic nature of the ZnO. Other oxides, such as CrO3 and ZrO2, in combination with CuO, on alumina are also effective in the production of ketones and esters from alcohols.4,6,9 Copper oxide can be reduced to the metallic state with H2, CO, or selected organic compounds (e.g. alcohols and aldehydes). Reduction of copper oxides in the presence of alcohols can be performed at a temperature as low as 130 °C but the preferred temperature is ∼200 °C.15,16 Two plant alcohol fractions, containing both primary and secondary alcohols, were reacted to esters and ketones at atmospheric pressure, using a commercial Cu/ZnO/Al2O3 catalyst. Here, we report on the yields of ester and ketone products under various conditions, as well as the stability of the catalyst.
Figure 1. Reaction scheme of dehydrogenation of a primary alcohol to an ester and other products.
10.1021/ie800667p CCC: $40.75 2008 American Chemical Society Published on Web 08/29/2008
Ind. Eng. Chem. Res., Vol. 47, No. 19, 2008 7497 a
Table 1. Composition of Propanol and Butanol Feed
Composition (mass %) feed
EtOH
1-PrOH
1-BuOH
i-BuOH
2-BuOH
2-PeOH
3M2Bu
AcH
2MP2MP
other
propanol feed butanol feed
0.4
87.6 0.2
64.2
2.3 18.9
9.4 0.4
10.9
4.8
0.2
0.3
0.3 0.3
a
Legend of compounds: EtOH, ethanol; 1-PrOH, 1-propanol; 1-BuOH, 1-butanol; 2-PeOH, 2-pentanol; 3M2Bu, 3-methyl-2-butanol; AcH, acetaldehyde; 2MP2MP, 2-methyl-propyl-2-methyl propanoate; and other, not identified.
2. Experimental Section The catalytic test was performed in a demonstration unit using a 1.4-m-long tubular fixed-bed reactor (with an inner diameter of 28 mm) operating in the down-flow mode. A commercial CuO/ZnO/Al2O3 catalyst (290 mL) containing 27% CuO, 42% ZnO, and 11% Al2O3, on a mass basis, was loaded and voids were filled with Carborundum powder (0.5-1.0 mm). On top of the catalyst bed, a layer of glass beads served as a feed preheater. Catalyst bed temperatures were measured by five equally spaced thermocouples inside a centrally placed thermowell. A sixth thermocouple was placed in the preheater zone. The catalyst was not reduced in the conventional way, using H2 diluted in N2, but instead was heated at a rate of 6 °C/h to a temperature of 225 °C in a flowing C3 alcohol mixture at a liquid hourly space velocity (LHSV) of 0.4 L/(L cat/h) and at atmospheric pressure. The alcohol mixture used in the reduction step was the same as the first feed used in the dehydrogenation experiment. At 225 °C, the liquid feed rate was reduced to LHSV ) 0.21 h-1 and maintained at that level throughout the remainder of the experiment. Complete reduction was not the objective, because the unreduced form is also active in the dehydrogenation reaction. The reactor was operated for a period of 92 days at LHSV ) 0.21 h-1, atmospheric pressure, and using different alcohol feeds. Conditions were kept constant for a few days before product samples were analyzed. Over a first 40 days of the experiment, the temperature was increased from 219 °C to 278 °C, using the propanol-rich feed mixture. The conditions of highest ester yield were repeated, followed by a repeat of the start-of-run conditions (i.e., 219 °C). The complete sequence with the mixed propanol feed lasted 55 days, after which the feed was changed to the butanol-rich mixture. Again, the temperature was gradually increased from 219 °C to 300 °C. Finally, the feed was changed back to the propanol-rich mixture and the reactor operated again under start-of-run conditions. Liquid products were collected over 24-h periods, and product samples were analyzed via gas chromatography (GC), using a PONA column (50 m × 0.2 mm × 1 µm) with a flame ionization detector (FID). Gas samples were taken daily and analyzed via GC, using a packed Molsieve column with a thermal conductivity detector (TCD). Product selectivity was expressed in terms of mass percentage of converted alcohols, while product yield was calculated as the fraction of total effluent (including gaseous fractions). Feed material consisted of mixtures of alcohols obtained from the commercial plant. The main component was either 1-propanol or 1-butanol, but several other alcohols were present in the mixtures, together with a small amount of impurities (for example, aldehydes, esters, and unidentified compounds). Compositions of the feed stocks are shown in Table 1. 3. Results and Discussion 3.1. Propanol-Rich Feed. The conversion of the alcohols in the mixed propanol feed over the CuO/ZnO/Al2O3 catalyst, as a function of the temperature, is shown in Figure 2. As the
Figure 2. Conversion of alcohols in propanol feed: ([) 1-propanol, (9) 2-butanol, and (2) iso-butanol.
temperature increased, the conversion of propanol increased steadily but the conversion of 2-butanol and iso-butanol in the feed showed little change. The secondary alcohol exhibited a higher conversion at 220 °C than did the primary alcohols in the feed mixture, which may be explained by a reaction mechanism involving two steps. The first step involves the formation of a surface alkoxide on the reduced copper, as well as on zinc oxide, whereby one hydrogen is removed.17,18 The alkoxide may dehydrogenate further by R-C-H bond breakage to form an aldehyde or ketone. The R-C-H bond strength is lower in secondary alcohols than in primary alcohols,18 which may control the overall rate of reaction of alcohol to carbonyl. The conversion of iso-butanol was not observed to change significantly with temperature, which can be explained as follows. Iso-butanol is less reactive than the other alcohols in the feed and the conversion may be limited at high temperature, because of competing reactions. At high temperature, the conversion of propanol to propyl propanoate ester and ketones is most likely faster than the reaction between propanol and 2-me-propanal. Assuming that 2-me-propanal is in equilibrium (or close to) with iso-butanol, and given the fact that the hydrogen partial pressure increases with temperature, the concentration of iso-butanol could remain more or less constant as a result. The yield as function of temperature of the main products (esters, ketones, and aldehydes) are shown in Figures 3 and 4. At 219 °C, the principal products were propyl propanoate, followed by propanal and 2-butanone in approximately equal amounts. Other ketones also were produced, but in smaller quantities. At temperatures of >260 °C, the propyl propanonate yield decreased, but the yield of 2-methyl-propyl propanoate increased slightly. The yield of ketones increased strongly with temperature. The propanal yield decreased significantly at temperatures of >240 °C. The products of the dehydrogenation of pure 1-propanol over a similar Cu/Zn/Al catalyst were consistent with those identified by Elliott and Pennella:9 propyl propanoate, 3-pentanone, 2-methyl3-pentanone, and propanal. Other compounds identified in our product can be explained by the following reactions: 2-butanol is
7498 Ind. Eng. Chem. Res., Vol. 47, No. 19, 2008
Figure 3. Yield of main product produced from propanol feed: ([) propyl propanoate and (9) propanal.
Figure 5. Change in propyl propanoate ester yield at 219 °C, as a function of time.
Figure 4. Yield of ketones produced from propanol feed: ([) 2-butanone, (9) 3-pentanone, (2) 2-methyl-3-pentanone, and (×) 3-heptanone.
Figure 6. Conversion of alcohols in butanol feed: ([) 1-BuOH, (9) isoBuOH, (2) 2-PeOH, and (×) 3-me-2-BuOH.
Table 2. Products from Propanol-Feed Blend
typically found with Cu/Zn/Al2O3 catalysts used in the methanol synthesis from CO/CO2 + H2 and the deactivation is caused by sintering of copper crystallites.19 Similarly, sintering was reported for a Cu/SiO2 catalyst used in the dehydrogenation of ethanol.20 The loss of activity in our case is likely to be due to thermal sintering and independent of the alcohol feed. The product selectivities, on the other hand, showed a continuous shift from esters to aldehyde and ketones (2-butanone and 2-methyl-3-pentanone) which is probably caused by poisoning of the catalyst. The decrease in catalyst activity combined with a shift in selectivities resulted in a reduction of the yield of propyl propionate with time, shown in Figure 5. 3.2. Butanol-Rich Feed. In the second part of the experiment, the feed was changed to an alcohol blend that contained mostly 1-butanol. The conversion of the various alcohols is shown in Figure 6. As observed with the propanol-rich feed, the secondary alcohols in the butanol-rich feed showed a much higher conversion than that observed for the primary alcohols at low temperature. Apart from the molecular size effect, the catalyst deactivation, which was described previously, will have some effect on the dehydrogenation results for the heavier alcohol feed mixture as well. The maximum yield of butyl butanoate, the main ester (Figure 7), was reached at 275 °C, whereas with propyl propanoate, the maximum was observed at ∼260 °C. The yield of the aldehydes remained higher than in the case of the propanol feed. It has been reported that heavier alcohols undergo reactions similar to those for ethanol, but under similar conditions, the conversion to esters on a molar basis decreases with carbon chain length.9 This is probably a result of the increased stability of longer-chain aldehydes. Increasing the temperature to >280 °C did not result in a further decrease of the aldehydes, which indicated that the aldehyde condensation reactions were becoming rate-limiting. As can be seen by comparing Figures 7 and
Yield (mass %) feed
product
ethanol
ethanal
1-propanol 1-propanol 1-propanol 1-propanol 1-propanol 1-propanol
propanal propyl propanoate 3-pentanone 2-methyl-3-pentanone 2-methyl-3-pentanol 3-pentanol
2-butanol 2-butanol 2-butanol
butanone 1-methyl-propyl propanoate C7 ketone
isobutanol 2-methyl-propanal isobutanol 2-methyl-propyl propanoate common common common common common
water CO2 H2 hydrocarbons other
at 231 °C at 258 °C at 278 °C 0.2
0.2
0.2
6.9 29.7 1.7 2.8 0.2 0.2
4.1 42.4 6.5 5.6 0.3 0.5
2.9 31.7 13.6 8.9 0.5 0.7
6.5 0 0.2
7.5 0.2 0.7
6.7 0.3 1.6
not detected 0.5
not detected 1.1
not detected 1.7
0.5 0.7 2.3 1.3 0.7
0.4 3.1 3.5 2.9 1.3
0.3 7.0 4.0 5.9 2.7
dehydrogenated to 2-butanone. The reaction products of iso-butanol were mentioned earlier. The composition of the reactor effluent at a few temperatures, including the one producing the highest ester yield (258 °C), are shown in Table 2. The products are grouped according to the alcohol from which they derived. The catalyst stability was measured by repeating the startof-run conditions (219 °C) with a propanol feed at day 55 and day 92. Between day 7 and day 55, the propanol conversion decreased from 46% to 38%, whereas on day 92, the propanol conversion was 39%, similar to the conversion on day 55. A pattern of fairly rapid deactivation during the first 50 days is
Ind. Eng. Chem. Res., Vol. 47, No. 19, 2008 7499 Table 3. Product Yields from Butanol Feed Blend Yield (mass %) feed
Figure 7. Ester yield from butanol feed: ([) butyl butanoate, (2) 1-mepropyl-butanoate, (9) 2-me-butyl-propanoate, and (×) 2-me-propyl-2-mepropanoate.
product
1-butanol 1-butanol 1-butanol 1-butanol 1-butanol 1-butanol
butanal butyl butanoate 3-me-4-heptanone 2-me-3-hexanone 1-me-propyl butanoate methyl butanoate
isobutanol isobutanol isobutanol 2-pentanol 2-pentanol
9.4 21.0 1.6 2.3 3.6 0
5.7 27.0 2.8 8.2 8.8 0.4
5.2 19.4 2.8 13.3 10.8 0.2
2-methyl-propanal 2-methyl-propyl butanoate 2-me-propyl 2-me-propanoate
3.2 1.2 0
3.0 3.3 0.8
3.2 4.6 1.7
2-pentanone 4-nonanone
2.3 0
8.2 1.0
5.4 0.9
4.6 36.3
4.5 14.1
4.0 9.6
0.1 0.9 1.6 1.2 2.4
0.2 2.6 2.3 2.5 4.6
0.2 4.5 2.6 4.2 5.0
3-me-2-butanol 3-me-2-butanone unconverted alcohols common common common common common
250 °C 280 °C 300 °C
water CO + CO2 H2 hydrocarbons other
(c) Water-gas shift (WGS) reaction: H2O + CO h H2+CO2
Figure 8. Ketone yield from butanol feed: (-) 2-pentanone; (2) 3-methyl2-pentanone; (9) 3-pentanone; (/) 3-me-4-heptanone; (4) 2-me-3-hexanone; ([) butanone.
8, with increasing temperature, the products formed from 1-butanol shifted from esters toward C8 and C7 ketones; the other alcohols did not show this shift. The decrease in the butyl butanoate yield can be explained by the increasing number of reactions that butanal can undergo at high temperature. With increasing conversion of 1-butanol, more butanal will condense to heavier aldehydes, reducing the yield of butyl butanoate. Second, the rate of formation of ketones increases with temperature, which results in a further reduction of the yield of butyl butanoate. 3.3. Ketone Formation and Side Reactions. With increasing temperature, the formation of the 2n - 1 ketone is favored over the 2n ketone. The overall reactions are as follows: (a) Formation of the 2n ketone:
(b) Formation of the 2n - 1 ketone:
(4)
As shown above in reaction scheme b, the reaction of alcohols to a 2n - 1 ketone results in the formation of CO. The only carbon oxide detected in the gaseous fraction at the lower end of the temperature range was CO2. Cu/Zn/Al2O3 is an active catalyst for the WGS reaction (reaction 4) and is commercially applied at temperatures of 200-300 °C. Below ∼250 °C the equilibrium of the WGS reaction lies to the far right, which may explain why no CO was detected.21 Water, which is required for the WGS reaction, is produced in the reaction with 2n ketones (reaction 2) and from the dehydration of alcohols to olefins and ethers. The presence of hydrocarbons in the product supports the notion of alcohol dehydration (see Tables 2 and 3). An alternative mechanism has been proposed by Elliot and Pennella,9 who concluded that the formation of ketones and CO2 proceeds along a different route. According to them, the metal surface is oxidized by oxygen released in the conversion of an n alcohol to a 2n ketone. Oxygen in the metal oxide lattice, in turn, recombines with CO, which is released in the formation of a 2n - 1 ketone, to CO2. This mechanism resembles the “Surface Redox” mechanism, which has been proposed for the WGS reaction at low pressure.22,23 The production of CO2 increased significantly with temperature, which is consistent with the increase in the fraction of ketones in the reaction product. Above a temperature of 280 °C, the condensation reactions shifted toward the 2n - 1 ketones, while the equilibrium of the WGS reaction moves to the left. Under these conditions, CO should be produced, which was observed, although the volume was small, compared to the volume of CO2. A few side reactions occurred, which resulted in a loss of ester and ketone yield. For example, small amounts of C5 and C6 alcohols were detected in the product which were absent in the propanol-rich feed. The amounts increased with temperature, reaching a level of 2.2 mass % at 278 °C. The Cu/Zn catalyst has hydrogenating properties, and the alcohols were most likely formed via the reaction of the product ketones with the hydrogen generated by the alcohol dehydrogenation reaction. Thus, the presence of 3-pentanol in the product can be explained by the hydrogenation of 3-pentanone.
7500 Ind. Eng. Chem. Res., Vol. 47, No. 19, 2008
A small percentage of C2 and heavier hydrocarbons was formed, and this amount increased with temperature. A likely explanation for the presence of hydrocarbons is the dehydration of alcohols, which is known to be catalyzed by alumina, which is a component of the catalyst. Incomplete coverage of the alumina will result in Lewis acid sites being available to catalyze the dehydration reaction. The rate of propanol dehydration was very small at 231 °C; however, at 278 °C, activity was significant, as shown in Table 2. Furthermore, aldehydes can react with water over supported copper catalysts to form acids. Copper on alumina is not very active but Cu on ZnO strongly catalyzes the reaction.23 The acidity of the product fraction was the highest at low temperature and remained fairly constant at higher temperatures. The reaction is likely to be limited by the low concentration of water, which remained fairly constant during the experiment. An increase in unidentified products occurred with temperature, which may be linked to condensation products catalyzed by acids that formed during dehydrogenation. 4. Conclusions Over Cu/Zn/Al2O3, the dehydrogenation of primary and secondary alcohol mixtures resulted in a complex mixtures of esters, ketones, and aldehydes. The primary alcohols with n carbon atoms formed esters, aldehydes, and ketones with 2n and 2n - 1 carbon atoms, whereas secondary alcohols produced only ketones and esters. The ester yield experiences a maximum at a temperature of 260 °C, using a 1-propanol-rich feed, and at a temperature of 280 °C, using 1-butanol-rich feed. As the temperature increased, the ketone yields with 2n - 1 carbon atoms increased, while the aldehyde yields decreased. The yield of esters progressively decreased with increasing carbon chain length of the alcohol. The ratios of esters to ketones can be varied by changing the reactor temperature. The undesirable formation of hydrocarbons and, presumably, condensation products increased similarly with temperature. Acknowledgment Permission by Sasol to publish these results is appreciated, as well as the contributions made by J. Swart and G. G. Swiegers (183/89). Literature Cited (1) Steynberg, A. P., Dry, M. E., Eds. Fischer-Tropsch Technology; Studies in Surface Science and Catalysis, Vol. 152; Elsevier: Amsterdam, 2004. (2) Kraus, M. In Handbook of Heterogeneous Catalysis, Vol. 4; Ertl, G., Knoezinger, H., Weitkamp, J., Eds.; Wiley-VCH: Weinheim, Germany, 1997. (3) Dolgov, B. N.; Koton, M. M.; Lelchuk, S. L. The synthesis of esters by the dehydrogenation of alcohols at ordinary pressure. J. Chem. Ind. (Moscow) 1935, 12, 1066.
(4) Ivannikov, P. Ya.; Gavrilova, E. Y. The catalytic transformation of alcohol. J. Appl. Chem. (USSR) 1936, 9, 490. (5) Sanchez, A. B.; Homs, N.; Fierro, J. L.G.; Ramirez de la Piscina, P. New supported Pd catalysts for the direct transformation of ethanol to ethyl acetate under medium pressure conditions. Catal. Today 2005, 107, 431. (6) Inui, K.; Kurabayashi, T.; Sato, S.; Ichikawa, N. Effective formation of ethyl acetate from ethanol over Cu-Zn-Zr-Al-O catalyst. J. Mol. Catal. 2004, 216, 147. (7) Fawcett, C. R.; Tuck, M. W. M.; Rathmell, C.; Colley, S. W. Davy Process Technology. Patent WO 0020375, 2000. (8) Colley, S. W.; Tuck, M. W. M. In Catalysis in Application; Jackson, S. D., Hargreaves, J. S. J., Lennon, D., Eds.; Royal Society of Chemistry: London, 2003; p 101. (9) Elliott, D. J.; Pennella, F. The Formation of Ketones in the Presence of Carbon Monoxide over CuO/ZnO/Al2O3. J. Catal. 1989, 119, 359. (10) Dalla Lana, I. G.; Vasudeva, K.; Robinson, D. B. Catalyzed reactions of n-propanol. J. Catal. 1966, 6, 100. (11) Keuler, J. N.; Lorenzen, L.; Miachon, S. The dehydrogenation of 2-butanol over copper-based catalysts: optimising catalyst composition and determining kinetic parameters. Appl. Catal., A 2001, 218, 171. (12) Inui, K.; Kurabayashi, T.; Sato, S. Direct synthesis of ethyl acetate from ethanol carried out under pressure. J. Catal. 2002, 212, 207. (13) Bartholomew, C. H.; Farrato, R. J. Fundamentals of Industrial Catalytic Processes, 2nd Edition; Wiley-Interscience: Hoboken, NJ, 2006; Chapter 7. (14) Sato, S.; Takahashi, R.; Sodesawa, T.; Nozaki, F. Vapor-phase dehydrocoupling of methanol to methyl formate over CuAl2O4. J. Catal. 1997, 169, 447. (15) Satta, A.; Shamiryan, D.; Baklanov, M. R.; Whelan, C. M.; Le, Q. T.; Beyer, G. P.; Vantomme, A.; Maex, K. The removal of copper oxides by ethyl alcohol monitored in situ by spectroscopic ellipsometry. J. Electrochem. Soc. 2003, 150, G300. (16) Sophie, A. J. L.; Sprey, H.; Soininen, P. J.; Elers, K.-E. ASM International NV. In situ reduction of copper oxide prior to silicon deposition, U.S. Patent 6,878,628, April 2005. (17) Pudney, P. D. A.; Francis, S. A.; Joyner, R. W.; Bowker, M. A molecular beam study of the oxidative dehydrogenation of alcohols on Cu(110). J. Catal. A 1991, 131 (1), 104. (18) Bowker, M.; Petts, R. W.; Waugh, K. C. Temperature-programmed desorption studies of alcohol decomposition on ZnO: 1-propanol, 1-butanol and 2-butanol. J. Catal. 1986, 99 (1), 53. (19) Tu, Y.-J.; Chen, Y.-W. Effects of alkali metal oxide additives on Cu/SiO2 catalysts in the dehydrogenation of ethanol. Ind. Eng. Chem. Res. 2001, 40, 5889. (20) Ertl, G.; Knoezinger, H.; Weitkamp, J. Handbook of Heterogeneous Catalysis, 2nd Edition, Vol. 6; Wiley-VCH: Weinheim, Germany, 2008. (21) Leprince, P., Ed. ConVersion Processes; Petroleum Refining, Vol. 3; Editions Technip: Paris, 2001, Chapter 14, p 467. (22) Koryabkina, N. A.; Phatak, A. A.; Ruettinger, W. F.; Farrauto, R. J.; Ribeiro, F. H. Determination of kinetic parameters for the water-gas shift reaction on copper catalysts under realistic conditions for fuel cell applications. J. Catal. 2003, 217, 233. (23) Iwasa, N.; Takezawa, N. Reforming of ethanol;Dehydrogenation to ethyl acetate and steam reforming to acetic acid over copper-based catalysts. Bull. Chem. Soc. Jpn. 1991, 64, 2619.
ReceiVed for reView April 24, 2008 ReVised manuscript receiVed June 24, 2008 Accepted July 11, 2008 IE800667P
