The effect of CO and O2 on hydrogen permeation through a palladium membrane

Hydrogen permeation through a 25-mu m thick palladium membrane during continuous exposures of hydrogen together with different combinations of oxygen and carbon monoxide has been studied at membrane temperatures of 100 degrees C-250 degrees C (total pressures of 40-150 Torr). Both CO and O-2, individually, inhibit hydrogen permeation through the membrane. The cause of the inhibition is, however, somewhat different. CO blocks available hydrogen dissociation sites, while oxygen both blocks dissociation sites and also consumes adsorbed hydrogen through the production of water. When a combination of CO and O-2 is supplied together with hydrogen, new reaction pathways will emerge. The carbon dioxide formation will dominate the watts forming reaction, and consequently, the blocking effect caused by the formation of water will be suppressed. Tn a mixture of CO + O-2 + H-2, the hydrogen permeation can become either larger or smaller than that due to only O-2 + H-2 or CO + H-2 depending on the CO/O-2 ratio. It is thus possible to find a situation where carbon monoxide and oxygen react to form CO2 leaving adsorbed hydrogen free to permeate the membrane. (C) 2000 Elsevier Science B.V. All rights reserved.