Inhibition and Catalysis of the Reaction of Steam on the Basal Plane of Graphite by Potassium Carbonate and Potassium Hydroxide

The etch decoration/transmission electron microscopy technique has been used to study the kinetics of the C-H20 reaction on the basal plane of single crystal graphite. The turnover frequency of the edge carbon surrounding monolayer pits on the basal plane varies with pit density. At 1 pit/μm², 23 torr of H₂O and 600 °C, the values are 0.037 s^-1 for uncoated graphite and 0.011 and 0.040 s^-1 for K₂CO₃ and KOH coated samples, respectively. A carbanion mechanism is proposed to explain the phenomenon of inhibition by K₂CO₃. At 550 °C, the K₂CO₃ forms hexagonal particles with a fixed orientation on the basal plane of graphite, probably due to particle growth in a preferred crystallographic direction of the substrate. These results are discussed in conjunction with the strong catalysis of the overall rates (on all edges and planes of carbon) by both K₂CO₃ and KOH, as reported by previous workers.