This manuscript presents a new strategy for enhancing permselective films via the addition of a porous, catalytically active layer in a composite catalytic-permselective membrane design. A general mathematical analysis of reaction and diffusion within the catalytic layer is presented in order to establish design criteria. Numerical simulations are presented for the case of the water-gas-shift reaction supporting hydrogen purification, to demonstrate the advantages of the composite catalytic-permselective design concept. For the case of a water-gas-shift catalytic coating placed atop a hydrogen-permselective dense palladium film, an 84% reduction in carbon monoxide (CO) exposure is predicted, along with a mild (8%) increase in the overall hydrogen permeation rate; this reduction in carbon monoxide contamination of the palladium surface represents a significant improvement in palladium film utilization. For the case of the same catalytic coating placed atop a carbon dioxide (CO2)-permselective polymer film, CO2-CO permselectivities are increased by two orders of magnitude.