The abatement of defects in zeolite membranes is essential for achieving high selectivity. In the present work, a simple and effective method for blocking defects in ultra-thin (ca. 0.5 mu m) MCI zeolite membranes has been developed. The method is based on deposition of an ultra-thin (similar to 15 nm) layer of amorphous silica on the top surface of the membrane. Permporometry data indicated that the amount of detects, especially detects larger than 4 nm, in the membranes was significantly reduced after the modification. In mixture separation experiments, the CO2/G(2) separation factor increased dramatically after blocking the detects in a defective membrane that was selected for the experiments. For instance, at 263 K and 9 bar feed pressure, the CO2/H-2 separation factor increased from 8.5 to 36 after modification of the membrane, whereas the CO2 flux only decreased by ca. 40%. (C) 2015 Elsevier B.V. All rights reserved.