Abstract
The production of H2 and CO by catalytic partial oxidation of CH4 in air or O2 at atmospheric pressure has been examined over Rh-coated monoliths at residence times between 10−4 and 10−2 s and compared to previously reported results for Pt-coated monoliths. Using O2, selectivities for H2 (\(S_{H_2 }\)) as high as 90% and CO selectivities (S CO) of 96% can be obtained with Rh catalysts. With room temperature feeds using air, Rh catalysts give\(S_{H_2 }\) of about 70% compared to only about 40% for Pt catalysts. The optimal selectivities for either Pt or Rh can be improved by increasing the adiabatic reaction temperature by preheating the reactant gases or using O2 instead of air. The superiority of Rh over Pt for H2 generation can be explained by a methane pyrolysis surface reaction mechanism of oxidation at high temperatures on these noble metals. Because of the higher activation energy for OH formation on Rh (20 kcal/mol) than on Pt (2.5 kcal/mol), H adatoms are more likely to combine and desorb as H2 than on Pt, on which the O+ H→ OH reaction is much faster.
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This research was partially supported by DOE under Grant No. DE-FG02-88ER13878-AO2.
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Hickman, D.A., Haupfear, E.A. & Schmidt, L.D. Synthesis gas formation by direct oxidation of methane over Rh monoliths. Catal Lett 17, 223–237 (1993). https://doi.org/10.1007/BF00766145
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DOI: https://doi.org/10.1007/BF00766145