The effect of CO and O-2 on hydrogen permeation through a palladium membrane

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