Ind. Eng. Chem. Res. 2007, 46, 8471-8479
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Steam Reforming of Ethanol Using a Commercial Nickel-Based Catalyst Pankaj V. Mathure, Shouvik Ganguly,† Anand V. Patwardhan,* and Ranajit K. Saha Department of Chemical Engineering, Indian Institute of Technology-Kharagpur, Kharagpur 721302, India
Kinetic study of ethanol steam reforming over a commercial nickel-magnesia-alumina (Ni/MgO/Al2O3) catalyst was conducted in a fixed-bed reactor 15 mm in diameter. The effects of temperature (673-873 K), molar ratio of steam to ethanol in the feed (in the range of 3:1 to 18:1), feed flow rate (W/FEtOH ) 46.2555.25 g-cat min/mol), catalyst particle size (2.25-0.75 mm), and time-on-stream study was studied. Maximum conversion (>95%) was obtained at 873 K, with a molar ratio of steam to ethanol of 12:1 and a W/FEtOH value of >185 g-cat min/mol at atmospheric pressure. A maximum yield of 3.0 moles of hydrogen per mole of ethanol fed was obtained at a temperature of 873 K, a steam-to-ethanol molar feed ratio of 12:1, and a W/FEtOH value of >110 g-cat min/mol. The acquired data was fitted to a power-law kinetic model and the kinetic parameters were evaluated. The activation energy was determined to be 23 kJ/mol. The average absolute deviation (AAD) for the predicted rates of reaction was determined to be 10.2%. The work also tested the feasibility of using the Eley-Rideal mechanism proposed in the literature and concludes that a more-elaborate scheme of reactions is necessary to describe the complex reactions that occur during the steam reforming process. A considerable amount of coke formation was observed during the process; yet, the catalyst showed a negligible loss of activity, exhibiting the feasibility of using this catalyst for ethanol steam reforming. In an attempt to reduce this coke formation, it is suggested that the process may be performed in the presence of hydrogen gas. 1.0. Introduction
(
CmHn + mH2O f mCO + m +
Hydrogen has been termed as the “energy carrier of the future”.1 It has the highest energy content per unit weight (120.7 kJ/g).2 It burns cleanly, producing no polluting emissions such as SOx, NOx, CO, volatile organic compounds (VOC), etc. However, it is available in nature only in the bound form. This makes it necessary to process the primary fuel to obtain H2 and then use it in energy-producing devices such as fuel cells3 or use it as fertilizer feedstock. A comparison of hydrogen manufacturing processes is available in the literature.1,2,4 Das and Veziroglu1 have reported that 90% of the hydrogen generated today is produced via the steam reforming of natural gas and light oil fractions. The major reason for this observation is the commercial viability of such plants by which hydrogen can be produced (at $2.11/ kg of H2).2,5 This is, by far, the most energy efficient process available. The steam reforming (catalytic) of hydrocarbons,6 alcohols, and light oil fractions involves the reaction of steam with methane, ethane, natural gas, liquefied petroleum gas (LPG), naphtha, gasoline, alcohols (such as methanol, ethanol, and propanol) over catalysts at elevated temperatures (200-900 °C) and pressures (1-30 atm). The technology has matured over the last 55 years; however, the major concerns still are the endothermic nature of the reactions, which makes the process energy-intensive, and coke formation, which results in catalyst deactivation. Work is still in progress to use lower-value or more-ambient operating parameters and minimize coke formation, increasing catalyst life and, hence, reducing reformer downtime. The reactions that occur during the steam reforming process are as given by eqs 1-5: * To whom correspondence should be addressed. Tel: +913222-283950. Fax: +91-3222-255303. E-mail address: avp@ che.iitkgp.ernet.in. † Present address: West Bengal Pollution Control Board (Durgapur Regional Office), Durgapur 713216, India.
n H 2 2
)
(1)
Ethanol steam reforming (main reaction):
C2H5OH + 3H2O f 2CO2 + 6H2 (∆H ) + 347.4 kJ/mol) (2) Side reactions: Carbon formation:
CmHn f xC + Cm-xHn-2x + xH2
(3a)
2CO f C + CO2
(3b)
CO + H2 f C + H2O
(3c)
CO2 f O2 + C
(3d)
Water-gas-shift reaction:
CO + H2O f CO2 + H2
(∆H ) -41.15 kJ/mol) (4)
Oxidation reactions:
1 CO + O2 f CO2 2
(5a)
1 H 2 + O 2 f H 2O 2
(5b)
2.0. Previous Studies A large amount of research has been directed toward the steam reforming of ethanol for the past 10 years, because ethanol can be produced by biological means and, hence, can be considered to be a renewable source of energy. Ethanol reforming would be beneficial to Indian conditions, where most of the ethanol can be produced via the biological degradation of molasses, which is obtained during manufacture of sugar. A
10.1021/ie070321k CCC: $37.00 © 2007 American Chemical Society Published on Web 10/30/2007
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major portion of earlier work has been devoted to the use of catalysts made specifically for this process.7-22 A review on the current status of ethanol reforming2 discusses the use of ethanol as a suitable choice of the feedstock. The authors have concluded, based on their review, that the best results for ethanol reforming can be obtained using Co/ZnO, ZnO, Rh/Al2O3, Rh/ CeO2, and Ni/La2O3-Al2O3 catalysts at atmospheric pressure and a temperature range of 573-1073 K. The use of copper/ zinc oxide-based catalysts10,11,15,16,19 has also been suggested by another recent review,7 based on the fact that low temperatures are required, resulting in low energy requirements for the process. The review7 suggests the use of two layers of different catalysts, namely, a layer of copper-based catalyst using temperatures of 573-673 K and a second layer of nickel-based catalyst at a temperature of 723 K to maximize production of hydrogen and reduce formation of methane, carbon monoxide, and coke. Despite such a huge list of highly selective catalysts synthesized specifically for the reforming of ethanol, there have been only seven proposed mechanisms for the process with no clear consensus as to which reaction mechanism is followed.2,7 Recent reviews2,7,8 on ethanol reforming indicate that coke formation is largely observed because of the presence of -CC- bonds, which aid in the formation of ethylene, which, when polymerized at high temperature, forms coke. Coke can also be formed from the Boudouard reaction or the decomposition of methane. Nickel possesses hydrogenation activity but limited water-gas-shift activity. It is a low-cost but effective catalyst for the cleavage of O-H, -CH2-, -C-C-, -and -CH3 bonds. The presence of the basic (magnesia) and acidic support (alumina) aid in the water-gas-shift reaction, increasing the hydrogen yield as well as restricting the formation of coke. Hence, in this study, ethanol steam reforming was performed using a commercial natural gas reforming catalyst, which is composed of Ni/MgO/Al2O3, making use of the coke resistance of the magnesia, along with the reforming properties of nickel supported on alumina. Thus, the study is unique from the point of use of a catalyst containing a higher amount of basic oxide, such as magnesia along with alumina. To the best of our knowledge, no other literature reports the use of this catalyst or its performance. Because this work uses a nickel-based catalyst, the literature review will mainly focus on work previously done using nickel-based catalysts. Akande et al. have used coprecipitated Ni/Al2O3 catalysts for the steam reforming of crude bio-ethanol.9 They have studied the kinetics in the temperature range of 593-793 K and reported the complete conversion of ethanol and a maximum hydrogen yield of 4.33 moles of hydrogen per mole of crude ethanol. They have collated the results in the form of a power law and also proposed a deterministic model based on the Eley-Rideal mechanism in an attempt to shed light on the reaction pathway followed. The model does not account for the formation of a large number of intermediate species such as acetaldehyde, acetic acid, diethyl ether that is observed in their product stream, and solid carbon that has been deposited on the catalyst surface. Yet, to date, it is the only study that provides values of the adsorption rate constants of their proposed mechanistic model. Yang et al. determined that the Ni/ZnO catalyst gives a complete conversion of ethanol at a temperature of 603 K and reported the hydrogen selectivity (which is defined as the ratio of the number of moles of hydrogen formed per mole of ethanol consumed, as per stoichiometry) to be ∼95% at 923 K and a space velocity of 5 h-1.22 They determined that the hydrogen selectivity of the catalyst to be greater than Ni/La2O3, Ni/MgO, and Ni/Al2O3.
Velu et al. reported the use of mixed Cu-Ni-Zn-Al catalysts for the partial oxidation of bio-ethanol and reported a possible reaction pathway that involved the dehydrogenation of ethanol to acetaldehyde (because of the presence of copper) and the subsequent cleavage of -C-C- bonds (because of the activity of nickel).15 The kinetic study by Sun et al. reported first-order kinetics, with respect to ethanol, for a temperature range of 523-623 K when using nickel-supported catalysts.23 The hydrogen selectivity (the mole percentage of gaseous products), catalytic activity, and stability reduced in the following order:
Ni/La2O3 > Ni/Y2O3 > Ni/Al2O3 The activation energy increased from 1.87 kJ/mol to 7.04 kJ/ mol to 16.88 kJ/mol, respectively. The study also reported an ethanol conversion of >90% at a space velocity of 5.4 g s/cm3, resulting in a hydrogen content of 53% in the product gas stream. Morgenstern and Fornango proposed ethanol steam reforming kinetics, which proceeds via two first-order reactions that involve the dehydrogenation of ethanol to acetaldehyde and the decarbonylation of acetaldehyde.24 They have studied ethanol steam reforming using copper-plated Raney nickel as a catalyst. They have observed that nickel is an effective, stable catalyst at low temperature (523-573 K) and displays methanation but very limited water-gas-shift reaction. Kugai et al. reported the complete conversion of ethanol from low temperature (648-723 K) using a Rh-Ni/CeO2 catalyst for a partial oxidation process.25 The catalyst showed reduced selectivity toward carbon monoxide (CO). Comas et al. used Ni/Al2O3 for the steam reforming of ethanol in the temperature range of 573-773 K.13 They have reported 100% ethanol conversion and >91% hydrogen selectivity at 773 K and at a space time of 0.06 g s/cm3 and an ethanol-to-steam molar ratio of 1:6. They have proposed a reaction scheme in which acetaldehyde and ethylene are formed as intermediates during the reaction and the final products consist of CO, carbon dioxide (CO2), methane (CH4), and hydrogen (H2). Fatsikostas and Verykios used Ni catalysts supported on γ-Al2O3, La2O3, and La2O3/γ-Al2O3.26 They observed that the impregnation of La2O3 in γ-Al2O3 reduced carbon deposition and steam reforming of ethanol could, hence, be performed at higher temperature and a high water-to-ethanol feed ratio. Frusteri et al. evaluated the performance of Ni/MgO and alkali-doped Ni/MgO catalyst when the steam reforming of bioethanol was performed.20 The Ni/MgO showed high hydrogen selectivity (95% is observed for W/FEtOH ) 185 g-cat min/mol at a molar ratio of 12:1 and a temperature of 873 K. The rate of reaction (that is, the rate of disappearance of ethanol) at different operating temperatures was obtained by measuring the slopes (dX/d(W/FEtOH)) of the curves shown in Figure 6. As reported, only four gases (H2, CO, CH4, and CO2) and some traces of water vapor (steam) were detected using a TCD block and a Spherocarb column. No other hydrocarbon was detected. The plots of the product gas concentrations (Figures 7 and 8) clearly show that, for the lower temperature (673 K), a CH4 content of ∼10%-14% (v/v dry gas basis) is generated, whereas the CH4 concentration decreases to ∼5% (v/v dry gas basis) when the temperature is increased to 873 K. This means that, initially, the ethanol cracks to form methane at lower temperature, which is fully reformed at higher temperature, leading to a higher quantity of hydrogen in the outlet stream. This explanation is further corroborated by the fact that, among the side reactions that occur during steam reforming, the watersgassshift reaction
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Figure 10. Effect of molar ratio of steam to ethanol in the feed at 873 K.
Figure 8. Hydrogen concentration (dry gas basis) in the product gas at different temperatures: (2) 673 K, (]) 773 K, and (9) 873 K.
Figure 11. Yield of hydrogen under different operating conditions ((4) 673 K, (() 773 K, and (0) 873 K). Other conditions: feed molar ratio ) 12:1, reactor diameter ) 15 mm, dp ) 1.0 mm.
Figure 9. Carbon monoxide (CO) concentration in the product gas at different temperatures: (2) 673 K, (]) 773 K, and (9) 873 K.
(reaction 4) is exothermic in nature and, hence, is favored by a decrease in temperature. Theoretically, the amount of CO should be effectively higher at high temperature. This is not observed in the results obtained in this study; instead, the exit gas composition shows a low amount of CO at high temperature (873 K), as shown in Figure 9. Thus, the catalyst does not promote the watersgassshift reaction but strongly promotes the CH4 steam reforming reaction. The liquid content was analyzed using a Porapack Q column and a TCD block and was determined to contain largely unreacted ethanol and the excess water. The literature9 reported the presence of very small quantities (110 g-cat min/mol. The hydrogen yield above this W/FEtOH value remains more or less constant. Thus, the catalyst promotes maximum hydrogen yield at high temperature (typically >873
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Figure 12. Parity plot for rates of reaction calculated using different proposed models versus the experimental reaction rates: (]) model 1, AAD% ) 38.5%; (9) model 2, AAD% ) 21.34%; (2) model 3, AAD% ) 69.3%; (*) model 4, AAD% ) 34.32%; (b) power-law model, AAD% ) 10.2%.
K). The smallest hydrogen yield was obtained at a temperature of 673 K, a steam-to-ethanol molar feed ratio of 12:1, and W/FEtOH ) 69.5 g-cat min/mol. This yield is relatively low, in comparison with other tailor-made catalysts that yield 1-5.5 mol H2/mol ethanol. However, note that this is an off-the-shelf, ready-to-use commercial catalyst, unlike the other catalysts, and provides a reasonable yield of hydrogen at the experimental process parameters for use as an ethanol steam reforming catalyst. 5.0. Kinetic Models 5.1. Power Law. The kinetic data obtained by the aforementioned experiments has been correlated in the form of a simplistic power-law kinetic model, as described below. The parity plot for this model, and the models proposed by Akande et al.,9 is shown in Figure 12. The average absolute deviation (AAD%) of the model is ∼10.2%, which is the least among the five models tested and, hence, gives a good representation of the data.
(
rEtOH ) (4.39 × 102) exp -
)
4
2.3 x 10 × RT (pEtOH)0.711(pH2O)2.71 (6)
The kinetic parameters, activation energy, and the exponents for both reacting species were determined using a nonlinear regression program based on the Levenberg-Marquart algorithm. The activation energy was determined to be 23 kJ/ mol, and the exponents for the partial pressure of ethanol and water were determined to be 0.711 and 2.71, respectively. The collision frequency factor was determined to be 4.39 × 102 mol (min g-cat)(atm)3.42. Therdthianwong et al.18 performed a steam reforming of ethanol at a temperature of 673 K, using a nickelalumina catalyst, and reported reaction orders of 2.52 and 7 for the partial pressure of ethanol and water, respectively. Sun et al. used nickel supported on three different metal oxides and reported the rate to be first order, with respect to ethanol, in all three of these cases.23 They reported the activation energy for a nickel-alumina-based catalyst to be 16.88 kJ/mol. The values obtained in our work are very similar to those obtained by Sun et al.23 However, it must be noted that the catalyst used in the current work also contains a fair amount of MgO, which may have resulted in the difference in the reaction order, with respect to ethanol. Akande et al.2 reported the activation energy for a
nickel-alumina-based catalyst to be 4.41 kJ/mol for a temperature range of 593-793 K. Every researcher has proposed different kinetic models, the reason for which could be the difference in process conditions, as well as the support material of the catalyst. The order of the reaction, with respect to water, has been reported by one other researcher,18 who reported an unusally high value of 7. The rationale for using the partial pressure of steam as a component in the rate law is to account for the effect of the steam-to-ethanol ratio in the feed. The high exponent value of the partial pressure of steam reaffirms the non-elementary nature of the steam reforming process. The power-law model so obtained is an empirical correlation that enables the estimation of the rate of ethanol consumption. The power-law model is not mechanistic in nature but acts as a useful indicator of the expected rate of disappearance of ethanol while designing an ethanol-based steam reformer unit. 5.2. Eley-Rideal Mechanism. Recently, Akande et al. proposed a model based on the Eley-Rideal mechanism for the steam reforming of crude ethanol using Ni/Al2O3 catalysts.9 This is the only mechanistic model to date for the steam reforming of ethanol when Ni/Al2O3 catalysts are used, and, hence, an attempt was made to fit our experimental data to the proposed model. Thus, the objective of the current study is to test the Eley-Rideal mechanism proposed by Akande et al.9 and compare which of the aforementioned rate models fits the experimental data the best. The results after using a nonlinear regression program based on the Levenberg-Marquart algorithm have been represented in the form of a parity plot. The steps involved in the model are as follows: Step 1: Adsorption of ethanol on actiVe sites k1,-1
C2H6O + (a) 798 C2H6O(a)
(7)
Step 2: Dissociation of adsorbed ethanol into hydrocarbon and oxygenated hydrocarbon fractions k2,-2
C2H6O(a) + (a) 798 CH4O*(a) + CH2*(a)
(8)
Step 3: Surface reaction of the adsorbed oxygenated hydrocarbon fraction with non-adsorbed steam k3,-3
CH4O*(a) + H2O(g) 798 CO2 + 3H2 + (a)
(9)
Step 4: Surface reaction of the adsorbed hydrocarbon fraction with non-adsorbed steam k4,-4
CH2*(a) + 2H2O(g) 798 CO2 + 3H2 + (a)
(10)
The basic assumption is that mass- and heat-transfer limitations were absent. Table 2 gives the rate expressions derived by assuming one of the aforementioned steps as the rate-determining step. Table 3 gives the values of the model parameters obtained by fitting the experimental data to the derived rate expressions. Although, as per Model 2, the dissociation of adsorbed ethanol to hydrocarbon and an oxygenated hydrocarbon fraction seems to be a logical rate-determining step (the presence of methane in the outlet gas stream is physical proof) and correspondingly gives the smallest AAD% value of 21%, the error is great. Also, the formation of a CH2 species as an intermediate is highly unlikely and will require further investigation. The kinetic study does not report the absence of gasphase mass-transfer resistance and intraparticle diffusion resistance. It also does not account for intermediate species (such as acetaldehyde and acetic acid) that are observed in their
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Table 2. Table of Kinetic Modelsa model number
rate-determining step
models based on partial pressures of species
( )[ ( )]
k0 exp M1
adsorption of ethanol
rEtOH ) 1+
KFpCO2pH23 pH2O
dissociation of adsorbed ethanol
rEtOH )
[
M4
a
surface reaction of adsorbed hydrocarbon fraction with non-adsorbed steam
KEpCO22pH26 pH2O3
E RT
+
pH2O
pH2O2
pCO2pH23
2
) ( )]
3
pEtOHpH2O
]
KGpCO2pH23
-
pCO2pH23 K1
2
KGpCO2pH23 KQpEtOHpH2O 1 + KApEtOH + pCO2pH23 pH2O2
( )[(
k0 exp rEtOH )
+
[
E RT
) ( )] ]
pEtOHpH2O3 pCO2pH23 3
-
pCO2pH23 K1
KFpCO2pH2 KHpEtOHpH2O 1 + KApEtOH + pH2O p p 3 CO2 H2
Data taken from ref 9.
Table 3. Estimates of the Model Parameters parameter
M1
M2
M3
M4
ko E (kJ/mol) K1 KA KE KF KG KH KQ n for EtOH for steam AAD%a
33 10.1 2.33 × 109
2.97 × 102 21 1.49 × 104 5.00
7.31 × 1012 2 3.00 × 109 2.00 × 1016
2.10 × 1010 13.9 3.00 × 109 2.73 × 1012
0 0
0
a
rEtOH )
pH2O2
KFpCO2pH23
( )[(
k0 exp surface reaction between adsorbed oxygenated hydrocarbon fraction with non-adsorbed steam
KGpCO2pH23
pCO22pH26 E pEtOH RT K1pH2O3
1 + KApEtOH
M3
+
( )[ ( )]
k0 exp M2
pCO22pH26 E pEtOH RT K1pH2O3
0 0 0
21.3%
439 23
of 873 K at a steam-to-ethanol molar feed ratio of 12:1 and W/FEtOH >110 g-cat min/mol. Kinetic models in the form of a power law and the EleyRideal mechanism have been fitted to the acquired data. The power-law model is as follows and gives the smallest average absolute deviation (AAD%) of 10.2%. The activation energy was determined to be 23 kJ/mol.
(
1.00 × 105 3.30 × 107
38.5%
power law 1
69.3%
rEtOH ) (4.39 × 102) exp -
0
34.3%
0.711 2.71 10.2%
Average absolute deviation.
product analysis. Therefore, the proposal of a new kinetic model has been included in the scope of future work. 6.0. Conclusions A detailed literature review for the steam reforming of ethanol using nickel-based catalysts has been reported in this work. The catalyst was characterized using X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET) specific surface area (SSA) analysis, and energy-dispersive spectroscopy (EDS)-X-ray techniques. Kinetic study of the ethanol steam reforming over a nickel-magnesia-alumina catalyst was conducted. The effect of temperature (673-873 K), molar ratio of steam to ethanol in the feed (3:1 to 18:1), feed flow rate (residence time in terms of W/FEtOH ) 46.2-555.25 g-cat min/mol), catalyst particle size (2.25-0.75 mm), and time-on-stream study have been reported. Maximum conversion (>95%) was obtained at 873 K, with molar ratio of 12:1 and W/FEtOH > 185 g-cat min/mol at atmospheric pressure. A maximum yield of 3.0 moles of hydrogen per mole of ethanol fed was obtained at a temperature
)
2.3 x 104 (pEtOH)0.711(pH2O)2.71 RT
However, a more elaborate scheme of reactions is necessary to describe the complex reactions that occur during the steam reforming process. A considerable amount of coke formation was observed during the process; yet, the catalyst showed a negligible loss of activity, exhibiting the feasibility of use of this catalyst for ethanol steam reforming for short-duration, on-board, in situ hydrogen production units, which can be used in vehicles due to the ability of catalyst to generate hydrogen at a steady rate. In an attempt to reduce this coke formation, it is suggested that the process may be conducted in the presence of hydrogen gas (H2). 7.0. Proposed Future Work Work is currently underway to improve the mechanistic kinetic model and to use a copper/zinc oxide based catalyst,7 for the steam reforming of ethanol, which may significantly reduce the reaction temperature. In an attempt to reduce the observed coke formation, it is suggested that the process may be conducted in the presence of hydrogen gas (H2). Acknowledgment The authors wish to thank the Department of Fertilizers, Ministry of Chemicals & Fertilizers, (Government of India) for providing the financial assistance for the execution of the project
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titled “Studies on Reforming of Methane to Synthesis Gas Using Micro-reactors for Production of Hydrogen (MPH)” sanctioned vide letter, 15011/1/2004-FP, dated 05/03/2004. Nomenclature E ) activation energy (kJ/mol) FC2H5OH ) molar flow rate of feed (ethanol) (mol/min) ko ) collision frequency factor (mol (min g-cat)(atm)3.42) ki ) forward rate constant corresponding to step i (respective units) k-i ) backward reaction rate constant corresponding to step i (respective units) K1 ) overall equilibrium constant n ) order of the reaction pCO2 ) partial pressure of carbon dioxide (atm) pH2 ) partial pressure of hydrogen (atm) pEtOH ) partial pressure of methanol (atm) pT ) total pressure (atm) pH2O ) partial pressure of steam (atm) rEtOH ) rate of reaction of ethanol (mol/(min g-cat)) R ) universal gas constant; R ) 8.3144 J/(mol K) T ) temperature (K) W ) weight of catalyst (g) W/F ) ratio of weight of catalyst to molar flow rate of ethanol (space time) (g-cat min/mol) XEtOH ) fractional conversion of ethanol yC2H5OH ) mole fraction of ethanol yCO ) mole fraction of carbon monoxide yCO2 ) mole fraction of carbon dioxide yH2 ) mole fraction of hydrogen AbbreViations BET-SSA ) Brunauer-Emmett-Teller specific surface area method EDS X-ray ) energy dispersive spectroscopic X-ray analysis GC-TCD ) thermal conductivity detection, in combination with gas chromatography HPLC ) high-pressure liquid chromatography XRD ) X-ray diffraction Literature Cited (1) Das, D.; Veziroglu, T. N. Hydrogen production by biological processes: a survey of literature. Int. J. Hydrogen Energy 2001, 26, 13. (2) Harayanto, A.; Fernando, S.; Murali, N.; Adhikari, S. Current status of hydrogen production techniques by steam reforming of ethanol: a review. Energy Fuels 2005, 19, 2098. (3) Hoogers, G., Ed. Fuel Cell Technology Handbook; CRC Press: Boca Raton, FL, 2003. (4) Momirlan, M.; Veziroglu, T. N. Current status of hydrogen energy. Renewable Sustainable Energy ReV. 2002, 6, 141. (5) National Research Council and National Academy of Engineering. The Hydrogen Economy: Opportunities, Costs, Barriers, and R&D Needs; National Academic Press: Washington, DC, 2004; p 256. (6) Rostrup-Neilsen, J. R. Catalytic Steam Reforming. In Catalysis, Science & Technology; Anderson, J. R., Boudart, M., Eds.; SpringerVerlag: Berlin, 1984. (7) Vaidya, P. D.; Rodrigues, A. E. Insight into steam reforming of ethanol to produce hydrogen for fuel cells. Chem. Eng. J. 2006, 117, 39. (8) Cheekatamarla, P. K.; Finnerty, C. M. Reforming catalysts for hydrogen generation in fuel cell applications. J. Power Sources 2006, 160, 490. (9) Akande, A.; Aboudheir, A.; Idem, R.; Dalai, A. K. Kinetic modeling of hydrogen production by the catalytic reforming of crude ethanol over a
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ReceiVed for reView March 2, 2007 ReVised manuscript receiVed September 6, 2007 Accepted September 17, 2007 IE070321K
