Methanation over transition metal catalysts: II. carbon deactivation of [formula omitted] in sulfur-free studies

Abstract

Hydrogenation of CO catalyzed by Co Al 2O 3 was studied in an all-quartz internal-recycle reactor between 200 and 400 °C and from 0.1 to 20% CO in H 2 at atmospheric pressure. The surface and subsurface regions of the aged Co Al 2O 3 catalysts were investigated using Auger electron spectroscopy (AES). Two pseudo steady states were observed. The upper pseudo steady state corresponds to a cobalt surface mainly containing active reaction intermediates; the lower pseudo steady state corresponds to deactivated cobalt which has large deposits of graphitic carbon on its surface, and for which the bulk CO is carburized to great depths as shown by AES. Methane is the primary reaction product; other hydrocarbons constitute less than 10% of the total products formed. The activation energy for methanation over Co Al 2O 3 in the upper pseudo steady state is 28 ± 2 kcal/mole, whereas that in the lower pseudo steady state is 16 ± 2 kcal/mole. The change in the activation energy appears to be caused by changes in the electronic structure of CO due to bulk carburization.