Carbon-supported cobalt-iron catalysts for ammonia synthesis

The cobalt, iron and Co-Fe catalysts deposited on carbon were prepared, characterised (XRD, H-2 TPD) and studied in ammonia synthesis at 90 bar (H-2:N-2 = 3: 1). Partly graphitised carbon material obtained via high temperature treatment (1900 degrees C) of commercial activated carbon was used as a support for the active metals (10 wt.%) and barium or potassium were used as promoters. XRD studies of unpromoted materials have shown that cobalt (5-20% in Co + Fe) dissolves in the iron phase (alloy formation); the average sizes of crystallites (20-30 nm) are roughly independent of the metal kind (Co, Fe, Co-Fe). The effect of Ba and that of K on the catalyst performance proved to be strongly dependent on the choice of an active phase (Co or Fe or Co-Fe). In the case of Co/C, the promotional effect of barium was extremely large. Furthermore, the Ba-Co/C system was found to be less inhibited by the ammonia product than Ba-Fe/C. At low temperature (400 degrees C) and at high conversion (8% NH3 in the gas), the surface-based reaction rate (TOF) for Ba-Co/C is about six times higher than that for Ba-Fe/C. (c) 2005 Elsevier B.V. All rights reserved.