Zeolite LTA membranes supported on macroporous carbon discs have been modified by means of ion exchange and tested for their H-2 purification performance using a simulated reformer mixture as feed stream. As-prepared membranes (i.e. sodium form, Na-LTA/carbon) have been ion-exchanged with CsNO3 (Cs-LTA/carbon) to tailor the membrane pore size and tested in a Wicke-Kallenbach (WK) cell in order to study their permeation properties. Both membranes have been tested using a simulated reformer mixture in dry conditions (50% H-2, 1.25% CO and n% CO2 in He), where the CO2 concentration has been modified (n% = 0, 2, 5, 10, 15 and 20%), and their permeation properties studied. In addition, these membranes (Na- and Cs-forms) have been also tested using a simulated reformer mixture on humid conditions (50% H-2, 1.25% CO, 20% CO2 and 5% H2O in He). All the experiments using different stream compositions have been carried out at three different temperatures (303, 398 and 423 K). Furthermore, in order to analyze and understand the permeation characteristics of the composite materials, commercial zeolite A in powder form has been used to study the interaction between CO2 and the zeolite. Therefore, thermogravimetric analysis (TGA), in situ diffuse reflectance infrared Fourier transform spectroscopic (DRIFTS) experiments and CO2 adsorption isotherms at different temperatures (303 K. 398 K and 423 K) have been used in order to analyze this interaction. The final composite, Cs-LTA/carbon can separate H-2 from CO under all the experimental conditions studied and possesses high permeance and an excellent H-2/CO separation factor. (C) 2011 Elsevier B.V. All rights reserved.