The possibility of applying a catalytic membrane reactor (CMR) to SO 3 decomposition in a low-temperature range was theoreticallyevaluated with the purpose of producing CO 2-free hydrogen inan Iodine-Sulfur thermochemical cycle.Aone-dimensional, isothermal and plug-flowmodelwas developed for a cocurrentmembrane reactor with selective permeation from the reactant stream to the permeate stream. Simulation results have revealedthat CMRs can greatly reduce the reaction temperature for SO 3 decomposition from the conventional 1,200-1,400 K to about 900 K.We predicted that porous inorganic membranes with a high O 2 permeabilityand with selectivitiesof more than 50 for O 2 /SO 3 and less than 10 for O 2 /SO 2 had the potential to effectively improve SO 3 conversion.CMRs were simulated to carry out SO 3 decomposition at different catalyst weights, reaction temperatures, and SO 3 feed flow rates as well as pressures in feed and permeate streams.SO 3 conversion at 900 Kwas increased to 0.93beyond the equilibrium conversion of 0.28due to a shift in thermodynamicequilibrium.