Highly efficient Pd membranes supported on porous ceramic tubes were synthesized by a modified electroless plating method and utilized in H-2 enrichment from the gas mixture that came from an NH3 cracker. Two Pd membranes whose permeation properties varied widely had been evaluated at temperatures ranging from 623 to 773 K and under pressures up to 5.06625 x 105 Pa (5.0 atm). Experimental results revealed that the concentration polarization phenomenon played a determining role in the case of gas separation by the highly permeable and selective membranes. It caused a significant loss in both H-2 yield and purity; and therefore, the separation efficiency of H-2 generation system decreased greatly. A mathematical model was built to describe the concentration polarization phenomena in H-2 enrichment by highly permeable and selective Pd membranes under the conditions utilized. In line with the experimental observations, this model accurately predicated the dependency of permeation performance on the operation parameters such as pressure, temperature, feed gas flow rate and permeability. (c) 2005 Elsevier B.V. All rights reserved.