| Popis: |
The gasification of graphite by H2O vapor, wet H2, and wet O2, catalyzed by a NiK mixture is studied using controlled atmosphere electron microscopy (CAEM). In H2O vapor the carbon consumption, between 550 and 1100 °C, is catalyzed by an edge recession mode of attack in the [1120] direction, with no sign of deactivation. An activation energy of 30.8 ± 0.9 kcal/mol is obtained in this case. This value is similar to those obtained in kinetic studies of the steam gasification of both graphite and char, using this catalyst. In wet H2 both channeling and edge recession occur simultaneously. The activation energy obtained is equal to 30 ± 2 kcal/mol. The catalyst deactivates above 1000 °C, but can be regenerated by treating the sample in H2O vapor at 600 °C. In wet O2, graphite is also gasified by edge recession, but no preferred direction is observed. The catalyst maintains its activity up to 1000 °C, and an activation energy of 25 ± 2 kcal/mol is obtained. These results show that the catalytic properties of the NiK mixture are superior to those of Ni and K alone due to a cooperative effect between the components. |
