Strong inhibitive effects of CO on hydrogen permeation through thin. Pd-based membranes have been found to exist. In this work, it is shown experimentally that the inhibition by CO was significantly reduced after heat treatment in air. A similar to 3 mu m thick Pd-Ag (23 wt.%) membrane was mounted in a microchannel configuration that allowed sweep gas and other transport effects to be eliminated. The CO inhibition was investigated at 300 and 350 degrees C before and after exposure to air at 300 degrees C for nearly five days, by determining the change in flux upon increasing CO concentration under constant hydrogen partial pressure. While the flux was decreased by 60% by going from 0 to 1 mol% CO at 350 degrees C before heat treatment in air, the reduction was only similar to 15% after the treatment. This relative improvement under CO comes in addition to the intrinsic improvement in hydrogen permeance upon heat treatment in air. An approach combining a Sieverts-Langmuir model equation and microkinetic modelling (through transition state and unity bond index-quadratic exponential potential theories), indicates that the effect can be explained by changes in CO and H(2) heats of adsorption upon the treatment. (C) 2010 Elsevier B.V. All rights reserved.