The influence of typical syngas CO concentrations (20-33%) on the stability of 3 mu m thick Pd membranes was investigated between 593 and 773 K in the limit of maximum H-2 extraction. Two kinds of CO inhibition effects were observed: CO adsorption and carbon deposition resulting from catalytic decomposition of CO on the Pd surface. CO adsorption reduced the H-2 permeation rate in particular below 623 K due to reversible blocking of Pd surface sites. Carbon deposition became more severe at higher temperatures and feed gas velocities and accumulated with time. In particular, the formation of a Pd1-xCx phase was observed above 723 K with x = 0.1. The propensity to PdC formation increased with temperature and the CO concentration in the retentate. Although the carbon incorporated into the Pd membrane could be effectively removed by H-2 and O-2 at 723 K, an irreversible increase of the N-2 flux after the removal of the carbon was observed in particular after treatment with O-2. (c) 2007 Elsevier BX All rights reserved.