Ind. Eng. Chem. Res. 2002, 41, 1419-1424
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KINETICS, CATALYSIS, AND REACTION ENGINEERING Steam Cracking of Naphtha in Packed Bed Reactors Jafar Towfighi,*,† Heinz Zimmermann,‡ Ramin Karimzadeh,† and Mohammad M. Akbarnejad§ Chemical Engineering Department, Tarbiat Modares University, P.O. Box. 14115-111, Tehran, Iran, LINDE AG, Process Engineering and Contracting Division, Dr.-Carl-von-Linde-Str. 6-14, D-82049 Hoellriegelskreuth, Germany, and Research Institute of Petroleum Industry, National Iranian Oil Company, Tehran, Iran
Thermal steam cracking of naphtha in packed bed reactors has been compared with cracking in an empty tube. A laboratory-scale packed bed reactor has been used to investigate the effects of inert and catalytic active materials on the steam cracking of naphtha. Different sizes of ceramic materials as inert materials have been tested at various reactor temperatures. The results show that lower molecular weight products, such as hydrogen, methane, and ethylene, have been increased by steam cracking in packed bed reactors compared to a conventional approach in an empty tube. Steam cracking of naphtha over six different catalysts consisting of mixtures of alumina and metal oxides, such as CaO, TiO2, SrO, MgO, Cr2O3, and MnO, has been tested, and the results are compared with those for a ceramic packed bed reactor. It could be demonstrated that the catalysts used do not improve the yields of ethylene and propylene as main products. However, the same catalysts have shown significant gasification activity, indicated by the increased yield of H2, CO, and CO2 with a reduction of the yields of ethylene, propylene, and other cracking products. Among those catalysts, it has been found that calcium aluminate (12CaO‚7Al2O3) selectively gasifies aromatics produced during the cracking reactions without any reduction of ethylene and propylene. 1. Introduction Light olefins, ethylene and propylene, are produced commercially via steam cracking of various hydrocarbons, such as ethane, naphtha, and gas oil. These low molecular weight olefins are among the most important base chemicals for the petrochemical industry. Modern steam cracking plants today typically are the center of petrochemical complexes producing 500 0001 000 000 tons per year of ethylene, the main petrochemical building block. Ethylene yield on a weight basis is typically 30% with naphtha feedstock and goes down to 25% for gas oil feedstock. The cracking reactions inside the coils are endothermic, and the temperature is increased from 600 °C at the inlet of the cracking coil to 820-870 °C at the outlet. Under these conditions the feedstock is converted in a free radical mechanism to the products. To improve the yield of light olefins and to decrease the process temperatures, the application of catalysts could be an option. However, the use of packed bed catalysts in commercial coils has pressure drop limitations. Higher pressures are required for processing the feed over a packed catalyst bed, reducing the yield of lower molecules in steam cracking. Several research groups have tried to overcome the disadvantages of the technology by using catalysts in steam cracking, but so far no commercial application has been achieved, though some of the results are promising. †
Tarbiat Modares University. LINDE AG. § National Iranian Oil Company. ‡
Chernykh et al.1 proposed a promoted vanadium catalyst on a low surface alumina carrier. With this catalyst, the yield of ethylene in the pyrolysis of gasoline at 780 °C, at a steam-to-feed ratio of 1:1, and at a residence time of 0.15 s is 40 wt %. This yield is approximately 5-10 wt % higher than the yield of ethylene in conventional steam cracking of naphtha in commercial reactors. The calcium aluminate catalyst T12 was investigated by Kikuchi et al.2 under various conditions of temperatures, pressures, steam ratios, residence times, and feedstocks to produce olefins. In this work the conditions to produce olefins using a catalyst have been optimized, but there is no comparison between the yields of products with and without a catalyst. Benzene, toluene, 1-methylnaphthalene, and n-heptane were studied over the temperature range 550-950 °C, by passing a low concentration of the compounds through 5.5 cm deep packed beds of calcium oxide.3 It was shown that calcium oxide significantly increased the rate of pyrolysis of the aromatics, reducing the temperature for a given percentage conversion by around 150 °C. In contrast, CaO decreased the comparable temperature for n-heptane by 40 °C. Lemonidou et al.4,5 proposed several types of catalysts consisting of different phases of calcium aluminate and other complexes of various metal oxides such as Mg, Mn, Ti, In, and Zr which have been tested in steam cracking of n-hexane. The selectivity ratio, defined as the weight of the target product (ethylene or propylene) to the weight of reacted n-hexane, is 10-18% higher than the
10.1021/ie010636e CCC: $22.00 © 2002 American Chemical Society Published on Web 02/16/2002
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selectivity ratio over R-alumina. The selectivity ratio over R-alumina is already 7% higher than the ratio achieved in an empty tube. The best results of selectivity ratio were obtained with a calcium aluminate catalyst at the CaO-to-Al2O3 molar ratio 12:7. Talaras et al.6 found that the use of MgO for catalytic steam cracking increases the conversion of n-heptane. Taralas also studied the catalytic steam cracking of n-heptane using dolomites (CaMg(CO3)2) and NiMo/ Al2O3. He showed that the conversion of n-heptane is constant over NiMo catalyst and decreases over dolomite.7,8 Mukhopadhyay et al.9 reported that yields of ethylene and propylene in steam cracking of naphtha over 12CaO‚7Al2O3 at 780 °C, at a steam-to-feed ratio of 1:1, and at a residence time of 0.23 s increased by 7 wt % compared to those for an empty tube under identical conditions. Steam cracking of naphtha has been studied over 12CaO‚7Al2O3 catalyst in a fixed bed reactor in the temperature range 700-850 °C. Conversion of naphtha increased in the presence of the catalyst, reducing the temperature required for a given conversion by approximately 50 °C. Compared to thermal pyrolysis, addition of the catalysts significantly increased the production of methane, ethylene, and propylene.10 Golombok et al.11 investigated vanadium oxide, magnesium oxide, potassium containing catalysts, and inert packings such as quartz and alumina materials. In these experiments it was shown that the improvements of yields over the inert materials are in a similar range as those with catalysts. The authors have shown that increased light olefin yields during catalytic steam cracking are mainly due to a surface/volume effect and are not due to a catalytic effect. The only effect that has been observed was the suppression of coking activity by a catalyst containing potassium. In summary, some investigators found that the ethylene yield was affected by the active sites of the catalysts while others found that this was due to the surface of packed bed materials. The work reported in the present paper is aimed at determining the reasons for the increase of light components in the product of steam cracking of naphtha through a packed bed reactor. The effect of inert materials and the catalytic effect on the distribution of products were investigated in a bench scale steam cracking unit. Bench scale unit experiments including empty tube tests, different packings, and different catalysts are described below. 2. Experiments 2.1. Reactor Specifications. Naphtha and water are pumped to two separate vaporizers and mixed at the outlet of the vaporizers as shown in Figure 1. The mixed stream is routed through a preheater and then enters the reactor at approximately 400 °C. Thermal steam cracking of naphtha is performed in a vertical tube of length 120 cm and inside diameter 1.9 cm. A screen is welded inside the tube to hold approximately 150 cm3 of the ceramic or catalytic active materials. The reactor is placed in a vertical furnace heated by three equal zones. The skin temperature profile of the reactor is measured with chromel-alumel thermocouples. The products leaving the reactor are cooled in an ice-cooled water condenser, where steam and heavier hydrocarbons are condensed. The gas product is sampled at point
Figure 1. Schematic of the experiemental setup. Table 1. Operating Conditions for Steam Cracking of Naphtha parameter
value
naphtha flow rate, g/min steam-to-naphtha ratio, g/g residence time, s maximum skin temperature, °C packing material volume, cm3 catalyst size, mm
6.1-7.8 0.7 0.6 770-890 150 4.0 ( 0.5
Table 2. Specification of Naphtha Feed (All Components Are in wt %) carbon no. n-paraffins iso-paraffins naphthenes aromatics olefins 3 4 5 6 7 8 9 10 11 12 total
0.17 3.79 10.05 5.37 3.86 2.14 2.23 0.91 0.09 0.02 28.65
0.82 9.91 12.74 5.87 3.12 4.61 3.5 0.61 0.1 41.28
1.07 4 6.95 7.06 2.08 0.36 0.05
0.6 1.37 2.34 2.57 0.57 0.09
21.59
7.55
0.18 0.35 0.3 0.12
0.94
1, and the liquid product is sampled at points 2 and 3 as shown in Figure 1. The gases are analyzed in gas chromatographs to determine H2, CO, CO2 and C4components. The liquid and gas phases are analyzed separately with a PONA column to determine the C5+ components. The experiments can be classified into three categories according to the use of an empty tube, the inert, or ceramic materials and the catalysts. All the experiments were carried out under the same operating conditions as shown in Table 1. The maximum skin temperature is set between 770 and 890 °C in the experiments. The residence time in all experiments is 0.6 s at a steam/ hydrocarbon ratio of 0.7 (g/g). To maintain a constant residence time in all experiments, the naphtha flow rate is changed from 6.1 g/min for packed bed reactors to 7.8 g/min for an empty tube. 2.2. Naphtha Specification. The same naphtha feedstock was used in all experiments. The specification of the naphtha feed is shown in Table 2. 2.3. Packing Material Specifications. Ceramic material of a cylindrical shape is used as inert material packing. Three different sizes of cylindrical ceramic materials were used to determine the effect of inert inserts and also the effect of the surface of the inert packings on the results of the steam cracking of naphtha. Table 3 lists the dimensions of the inert materials used in the experiments. Six catalysts consisting of mixtures of alumina with different metal oxides have been prepared. A list of
Ind. Eng. Chem. Res., Vol. 41, No. 6, 2002 1421 Table 3. Configuration and Composition of Inert Materials Configuration of Inert Materials no.
shape
Din, mm
Dout, mm
length, mm
bulk density, g/cm3
specific area, cm2/cm3
1 2 3
cylindrical cylindrical cylindrical
0.5 2.41 5.95
2 5.7 10.35
3.95 6.01 9.9
1.08 0.93 0.57
17.9 3.66 1.31
elements wt %
Composition of Chemical Elements of Inert Materials aluminum iron potassium titanium
silicon 34.90
13.25
0.69
2.14
0.66
magnesium
oxygen
0.26
48.10
Table 4. Catalyst Composition and Properties no.
catalyst composition
calcination temp, °C
surface area, m2/g
1 2 3 4 5 6
12CaO‚7Al2O3 MgO‚Al2O3 SrO‚Al2O3 MnO‚Al2O3 TiO2‚Al2O3 Cr2O3‚Al2O3
1200 1200 1200 950 950 950
1.2 2.5 1.8 3.2 4.7 5.2
catalysts, calcination temperatures, and measurements of the surface area is shown in Table 4. The method of catalyst preparation is the same as that described by Lemonidou.4 The required amounts of the metal oxide and alumina were mixed, and then small amounts of distilled water and binding agent were added to facilitate moulding. The mixture was moulded into cylinders and placed in a desiccator for aging. After aging for 24 h, the particles were placed into a furnace and the temperature was gradually increased to achieve complete dehydration of the mouldings and burn off the organic binder. The temperature was then raised at a rate of 250 °C/h until it reached the sintering temperature. The sample was calcined at the sintering temperature for 48 h to complete the solid reaction between the two oxides and to increase the crushing strength of the sintered product. 3. Results and Discussion 3.1. Inert Material Effect. Steam cracking of naphtha was tested in different ranges of skin temperature between 770 and 890 °C in an empty tube and a ceramic packed bed reactor. The product distribution is a function of feedstock, gas temperature, pressure, steam ratio, and residence time. Only the gas temperature was considered variable in the experiments. However, since temperature measurements in this range are not very precise, the severity, defined as propylene/ethylene ratio, was used for correlation. Figures 2 and 3 show the comparison of the results of the products obtained in a packed bed reactor of 5 mm diameter ceramic with an empty tube at different severities. Figure 2 shows that ethylene yields in a packed bed reactor are higher than in an empty tube over a wide range of severities. A different result was achieved with the C5+ products as shown in Figure 3. The lower concentration of C5+ in packed bed reactors leads to the assumption that the packing material in the reactor improves the conversion of feed to lower hydrocarbon molecules in naphtha steam cracking reactions. To determine the effect of the specific surface area of packing material inside the reactor, different sizes of ceramic materials have been tested. The yields of ethylene and propylene are compared in Figures 4 and
Figure 2. Yield of C2H4 in steam cracking of naphtha in an empty tube and in a ceramic packed bed reactor.
Figure 3. Yield of C5+ in steam cracking of naphtha in an empty tube and in a ceramic packed bed reactor.
Figure 4. Yield of C2H4 in the ceramic packed bed reactor at different surfaces of the packings.
5 at different surface-to-volume ratios of packings and different severities. As shown above, the specific surface area of inert materials does not affect the product yields over a wide range. These results do not agree with those presented by Golombok,11 who attributes enhanced ethylene production to the surface-to-volume ratio increase. In an empty tube, the gas is mainly heated by contact with the walls
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Table 5. Yields of Products of Steam Cracking of Naphtha over Ceramic Packing and Different Catalysts under Identical Conditions (Skin Temperature ) 830 °C) product wt % over the following H2 CH4 C2H2 C2H4 C2H6 C3H4 C3H6 C3H8 C4H6 C4H8 C4H10 C5+ COx
ceramic
12CaO‚7Al2O3
MgO‚Al2O3
SrO‚Al2O3
MnO‚Al2O3
TiO2‚Al2O3
Cr2O3‚Al2O3
1.04 15.26 0.53 28.60 2.57 0.88 14.38 0.37 4.57 4.07 0.53 27.18 0.11
1.35 15.28 0.51 28.26 2.66 0.87 14.67 0.38 4.46 4.19 0.61 26.16 3.13
1.36 16.10 0.58 27.71 2.69 0.90 12.80 0.33 4.20 3.22 0.29 29.71 0.41
1.22 15.16 0.56 28.72 2.55 0.91 14.36 0.38 4.73 4.27 0.57 24.87 1.71
1.30 14.73 0.51 26.58 2.54 0.85 13.30 0.34 4.25 3.77 0.44 30.02 1.38
1.08 15.43 0.54 28.80 2.61 0.85 14.13 0.35 4.30 3.86 0.36 27.55 0.13
1.28 14.53 0.49 27.32 2.65 0.87 14.75 0.38 4.66 4.42 0.55 27.83 1.07
Figure 5. Yield of C3H6 in the ceramic packed bed reactor at different surfaces of the packings.
and the heat is transferred from the wall to the gas by a convective mechanism. In a packed bed reactor, packings act as a heat sink to absorb the radiative heat from the reactor wall and then transfer the heat into the cracked gas by a convective mechanism. The absorbed radiative heat of the ceramic particle is transferred to the gas surrounding the particle. 3.2. Catalytic Effects. Steam cracking of naphtha over six different catalysts consisting of mixtures of alumina and metal oxides, such as CaO, TiO2, SrO, MgO, Cr2O3, and MnO, has been tested at different skin temperatures, and the yields of products are shown in Table 5. The experiments carried out show that the yield of ethylene as a main product of steam cracking of naphtha does not change for some of the catalysts and for some catalysts it decreases compared to that for a packed bed reactor with inert material. This result is in contradiction to results published by others.1-10 Figure 6 compares the yield of ethylene over the metal oxide catalysts with the yield of ethylene in a ceramic packed bed reactor at different cracking severities. The catalysts 12CaO‚7Al2O3, SrO‚Al2O3, and Cr2O3‚Al2O3 do not affect the yield of ethylene, but the catalysts MgO‚Al2O3, MnO‚Al2O3, and Ti2O3‚Al2O3 reduce the yield of ethylene. Figures 7 and 8 show that the yields of CO, CO2, and H2 in steam cracking of naphtha over the metal oxide catalysts are increased dramatically compared to the yields of CO, CO2, and H2 in a ceramic packed bed reactor. The metal oxide catalyts improve the gasification of the mixture of steam and hydrocarbons and increase the yields of CO, CO2, and H2. H2, CO, and CO2 are also observed in steam re-forming of hydrocarbons such as naphtha cracking across metal catalyst supported on a metal oxide.12
Figure 6. Yield of C2H4 in a ceramic packed bed reactor and over different metal oxide catalysts.
Figure 7. Yield of H2 in a ceramic packed bed reactor and over different metal oxide catalysts.
It could be concluded that the used catalyst acts as a steam re-forming catalyst. The components CO, CO2, and H2 are produced in the highest amount over a 7CaO‚12Al2O3 catalyst. Thus, among these catalysts, 12CaO‚7Al2O3 has the strongest effect on the rate of the gasification reactions, although ethylene does not participate in the gasification reactions over this catalyst and thus is not decreased. Figure 9 shows that the yields of C5+ hydrocarbons are reduced over the 12CaO‚7Al2O3 and SrO‚Al2O3 catalysts in comparison with the yields of C5+ over the ceramic particles. It can be concluded that the 12CaO‚7Al2O3 and SrO‚Al2O3 catalysts facilitate the gasification of some of the components of the C5+ hydrocarbons and increase the yield of CO, CO2, and H2. Among the C5+ hydrocarbons, it has been found that the aromatics yield is lower, and it is assumed that these components are preferentially gasified over the
Ind. Eng. Chem. Res., Vol. 41, No. 6, 2002 1423 Table 6. Yields of CO and CO2 and Aromatics in Steam Cracking of Naphtha in a Ceramic Packed Bed Reactor (All Components Are in wt %) T, °C
CO
CO2
benzene
toluene
xylene
styrene
ethyl benzene
C9 aromatics
C9/C10 aromatics
770 800 830 860 890
0.022 0.04 0.071 0.122 0.189
0.022 0.034 0.035 0.038 0.036
2.58 4.6 7.39 8.88 10.6
2.82 3.18 3.66 3.64 4.4
1.89 1.37 1.44 1.24 1.33
0.57 0.74 1.24 1.64 2.4
0.56 0.43 0.38 0.22 0.16
2.18 1.57 1.52 1.26 1.23
0.94 0.33 0.62 0.87 1.68
Table 7. Yields of CO and CO2 and Aromatics in Steam Cracking of Naphtha over 12CaO‚7Al2O3 Catalyst (All Components Are in wt %) T, °C
CO
CO2
benzene
toluene
xylene
styrene
ethyl benzene
C9 aromatics
C9/C10 aromatics
770 800 830 860 890
0.042 0.076 0.149 0.307 0.572
0.931 1.58 2.985 4.813 6.869
2.79 4.96 6.45 7.85 9.69
2.83 2.88 3.48 4.09 3.48
1.71 1.24 1.43 1.1 1.03
0.59 0.59 1.1 1.33 1.7
0.48 0.33 0.33 0.16 0.11
1.92 1.19 1.5 1.07 1.06
0.55 0.43 0.59 0.77 1.14
Figure 8. Yield of CO + CO2 in a ceramic packed bed reactor and over different metal oxide catalysts.
Figure 10. Yield of benzene in a ceramic packed bed reactor and over the 12CaO‚7Al2O3 catalyst. Table 8. Weight of Elementary Carbon of Reacted Aromatics and Produced CO and CO2 in Gasification Reactions of Steam Cracking of Naphtha over 12CaO‚7Al2O3 Catalyst
Figure 9. Yield of C5+ in a ceramic packed bed reactor and over different metal oxide catalysts.
12CaO‚7Al2O3 catalyst. Figure 10 compares the yield of benzene over the 12CaO‚7Al2O3 catalyst with the yield of benzene over the inert particles. The yield of benzene is decreased noticeably across the 12CaO‚ 7Al2O3 catalyst at lower severities. The difference between the yield of benzene in catalyst and the ceramic material is more pronouced at low severity. This trend shows that the gasification rate of benzene over the catalyst increases at high temperature or low severity. Tables 6 and 7 show the yields of CO, CO2, and the aromatic components in a ceramic packed bed reactor and over the 12CaO‚7Al2O3 catalyst at different maximum temperatures of the reactor. The composition data in Tables 6 and 7 show the reduction of aromatic weight percent between inert materials and catalyst. For example, the weight percent of benzene at 860 °C
T, °C
weight of carbon in the reacted aromatics (g)
weight of carbon in the produced CO and CO2 (g)
770 800 830 860 890
0.26 0.44 0.84 1.38 2.03
0.60 0.54 1.26 1.26 3.26
reduces from 8.88 for ceramic material to 7.85 for catalyst. A stoichiometric relationship between the reacted amount of aromatics and the produced amount of CO and CO2 in the gasification reactions over the 12CaO‚7Al2O3 catalyst can be shown by calculation of the carbon weight balance. The amounts of the reacted aromatics in the gasification reactions over the 12CaO‚ 7Al2O3 catalyst are equal to the yield of aromatic components in the inert ceramic packed bed reactor minus the yield of the aromatic components over the 12CaO‚7Al2O3 catalyst. As a result, the amounts of the produced CO and CO2 in the gasification reactions over the 12CaO‚7Al2O3 catalyst are equal to the yield of the CO and CO2 produced over the 12CaO‚7Al2O3 catalyst minus the yield of the CO and CO2 in the inert ceramic packed bed reactor. The weights of elementary carbon in the reacted aromatic components are approximately equal to the weights of elementary carbon of the CO and CO2 produced in the gasification reactions at the temperatures 800, 830, and 860 °C as shown in Table 8. From the results discussed above, it can be concluded that aromatics are the preferred species that are gasified by a 12CaO‚7Al2O3 catalyst.
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4. Conclusions Yields of light molecular weight products, such as hydrogen, methane, ethylene, and propylene, are increased over packed inert materials in steam cracking of naphtha. The surface area of packed bed materials has no considerable effect on the product yields in the range of investigated surface areas. The catalytic active metal oxides used do not increase the ethylene yield compared to those for ceramic materials in steam cracking of naphtha. The calcium aluminate catalyst (12CaO‚7Al2O3) selectively gasifies aromatic components without affecting the yield of ethylene in catalytic steam cracking of naphtha. Acknowledgment This work has been performed with the financial support of Linde AG, Germany. The authors would like to thank Dr. Anton Kirzinger and Mr. Josef Freisinger for assistance with the setup of the equipment and analysis of the products and the companies of Suedchemie and KataLeuna for preparation of the catalysts. Literature Cited (1) Chernykh, S. P.; Adelson, S. V.; Rudyk, E. M.; Zhagfarov, F. G.; Motorina, I. A.; Nikonov, V. I.; Mukhina, T. N.; Barabanov, N. L.; Pyatiletov, V. I. Catalytic Pyrolysis of Straight-Run Gasoline on a Promoted Vanadium Catalyst. Catal. Sov. Chem. Ind. 1983, 15 (4), 414.
(2) Kikuchi, K.; Tomita, T.; Sakamoto, T.; Ishida, T. A New Catalytic Cracking Process. Chem. Eng. Prog. 1985, June, 54. (3) Ellig, D. L.; Lal, C. K.; Mead, D. W.; Longwell, J. P.; Peters, W. A. Pyrolysis of Volatile Aromatic Hydrocarbons and n-Heptane over Calcium Oxide and Quartz. Ind. Eng. Chem. Process Des. Dev. 1985, 24, 1080. (4) Lemonidou, A. A.; Vasalos, I. A. Preparation and Evaluation of Catalysts for the Production of Ethylene via Steam Cracking. Appl. Catal. 1989, 54, 119. (5) Lemonidou, A. A.; Vasalos, I. A.; Hirschberg, E. J.; Bertolacini, R. J. Catalyst Evaluation and Kinetic Study for Ethylene Production. Ind. Eng. Chem. Res. 1989, 28, 524. (6) Taralas, G.; Vassilatos, V.; Sjo¨stro¨m, K. Thermal and Catalytic Cracking of n-Heptane in the Presence of CaO, MgO and Calcined Dolomites. Can. J. Chem. Eng. 1991, 69, 1413. (7) Taralas, G. Catalytic Steam Cracking of n-Heptane with Special Reference to the Effect of Calcined Dolomites. Ind. Eng. Chem. Res. 1996, 35, 2121. (8) Taralas, G. Catalytic Steam Pyrolysis of a Selected Saturated Hydrocarbon on Calcined Mineral Particles. Can. J. Chem. Eng. 1998, 76, 1093. (9) Mukhopadhyay, R.; Kunzru, D. Catalytic Pyrolysis of Naphtha on Calcium Aluminate Catalysts. Effect of potassium carbonate Impregnation. Ind. Eng. Chem. Res. 1993, 32, 1914. (10) Basu, B.; Kunzru, D.; Catalytic Pyrolysis of Naphtha. Ind. Eng. Chem. Res. 1992, 31, 146. (11) Golombok, M.; Kornegoor, M.; Brink, P.; Dierickx, J.; Grotenberg, R. Surface-Enhanced Light Olefin Yields during Steam Cracking. Ind. Eng. Chem. Res. 2000, 39, 285. (12) Claridge, J. B.; York, A. P.; Brungs, A. J.; Alvarez, C. M.; Sloan, J.; Tsang, S. C.; Green, M. L. New Catalysts for the Conversion of Methane to Synthesis Gas. J. Catal. 1998, 180, 85.
Received for review July 27, 2001 Revised manuscript received November 26, 2001 Accepted December 7, 2001 IE010636E
