Investigation of hydrogen reactivity and its use as a surface probe on high surface area copper-chromium-silver impregnated charcoal

ASC whetlerite is a copper/chromium/silver impregnated, activated charcoal which is used effectively to remove and hydrolyze vapor contaminants from gas streams. Its catalytic activity is known to decrease as the chromium oxidation state is reduced from +6 to +3. A thermal treatment process was used to systematically reduce the Cr(+6) species to Cr(+3)-containing species and a pulse technique was developed to nondestructively quantify this reduction using hydrogen. The data illustrated that hydrogen uptake can be correlated with the oxidation state(s) of the chromium metal impregnant. In addition, total uptake of hydrogen was determined in a static adsorption system. These data showed that total hydrogen uptake was independent of the oxidation state of chromium on the charcoal surface and was much greater than a one-to-one relationship between metal atoms and hydrogen atoms. These results suggested that hydrogen molecules are adsorbed and dissociated by the Cr(+3)-containing species and then diffuse away from the "Cr(+3) centers" to the activated charcoal support. Finally, the hydrogen pulse results together with ESCA data indicated that the deactivation of whetlerite involves not only the reduction of chromium, but most likely also the separation of the chromium/copper impregnants.