Deactivation of a Co FTS catalyst by carbon: insights from theory and experiment, from real catalysts to single crystal surfaces

摘要

Laydown of detrimental carbon was identified as a deactivation mechanism on Co FTS catalysts [1]. Extensive characterization of catalysts exposed to industrial scale FTS revealed that polymeric carbon builds up with time on line. This carbon is located both on the Co and on the support. Intentional carbon laydown followed by FTS activity tests confirmed the detrimental effect of carbon. nUsing a combination of experiment and theory the surface chemistry of carbon on cobalt was studied on the close-packed Co surface [1]. These studies revealed that (i) atomic carbon can reconstruct the cobalt surface, (ii) it is a weak poison, and can be easily removed, (iii) atomic C can generate active step sites (B5) by transformation of inactive step sites (iv), C2Hx intermediates readily form graphene, via surface-catalyzed polymerization reactions. (v) Graphene acts as a strong poison by covering the Co surface, thereby preventing adsorption of CO and H2.