A Comparison of Oxygen-vacancy Effect on Activity Behaviors of Carbon Dioxide and Steam Reforming of Methane over Suppor
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Catalysis Letters Vol. 105, Nos. 3–4, December 2005 ( 2005) DOI: 10.1007/s10562-005-8697-2
A comparison of oxygen-vacancy effect on activity behaviors of carbon dioxide and steam reforming of methane over supported nickel catalysts Ta-Jen Huang*, Han-Jun Lin, and Tien-Chun Yu Department of Chemical Engineering, National Tsing Hua University, Hsinchu, Taiwan 300, ROC
Received 27 June 2005; accepted 12 September 2005
A comparison of the activity behaviors of the mechanistically similar reactions of carbon dioxide reforming and steam reforming of methane was carried out at 400550 C over nickel catalysts with samaria- and gadolinia-doped ceria and a-alumina as the supports. Results show that the activity behaviors of carbon dioxide reforming and steam reforming of methane are similar and very sensitive to the oxygen-vacancy properties of the support, with a drastic increase of the activities as the temperature increases from 450 to 500 C. Nevertheless, a difference in the activity behaviors between carbon dioxide and steam reforming has been observed and is due to a difference in the reaction mechanisms of CO2 and H2O dissociations. Possible carbon deposition (coking) is lessened due to the reaction of the surface carbon species with the lattice oxygen or the surface O species as produced from CO2 or H2O. It was found that the samaria-doped ceria supported nickel catalyst has better de-coking ability than that of the gadolinia-doped ceria supported one. An oxygen-transport reaction mechanism for doped-ceria supported Ni catalyst has been proposed and shown to explain the activity behaviors successfully. KEY WORDS: oxygen vacancy; carbon dioxide reforming; steam reforming; activity behavior; methane; doped ceria; nickel catalyst.
1. Introduction Steam reforming of methane has been employed for large scale production of hydrogen. Nickel catalyst has been found to exhibit promising catalytic performance for steam reforming of methane [1,2]. On the other hand, the reforming of methane with carbon dioxide to synthesis gas has gained growing interest partially due to environmental implications, since both methane and carbon dioxide are greenhouse gases, and partially due to the produced synthesis gas having a low H2:CO ratio, which is of particular interest to the synthesis of valuable oxygenated chemicals. Nickel catalyst has also been found to exhibit promising catalytic performance for carbon dioxide reforming of methane [3–5]. It is interesting to note that these reacions of steam reforming and carbon dioxide reforming of methane have been found to be mechanistically similar [6]. Thus, their activity behaviors are conceivably to be similar. The effect of the support on steam reforming of methane over nickel catalysts has been studied [2,7]. Strong metal–support interaction (SMSI) has been shown to play a very important role in the catalytic activity of these nickel catalysts. On the other hand, the effect of the support on carbon dioxide reforming of methane over nickel catalysts has also been studied [8– 10]. Thes
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