A simple method for blocking defects in zeolite membranes

•A layer of amorphous silica was deposited on MFI membranes to block defects•HR-SEM data showed the layer was ultrathin (~15 nm), even and continuous.•Permporometry indicated the amount of defects could be reduced by as much as 70%.•The membranes were evaluated for CO2/H2 separation before and after modification.•CO2/H2 separation factor increased from 8 to 36 after modification of the membrane.

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 μm) MFI zeolite membranes has been developed. The method is based on deposition of an ultra-thin (~15 nm) layer of amorphous silica on the top surface of the membrane. Permporometry data indicated that the amount of defects, especially defects larger than 4 nm, in the membranes was significantly reduced after the modification. In mixture separation experiments, the CO2/H2 separation factor increased dramatically after blocking the defects in a defective membrane that was selected for the experiments. For instance, at 263 K and 9 bar feed pressure, the CO2/H2 separation factor increased from 8.5 to 36 after modification of the membrane, whereas the CO2 flux only decreased by ca. 40%.