CO2-selective membranes containing both amine carriers and fumed silica (FS) in crosslinked poly(vinyl alcohol)-poly(siloxane) (PVA-POS) (FS loading < 22 wt%) and crosslinked PVA (FS loading > 22 wt%) were synthesized for CO2/H-2 separation. The effects of temperature, feed pressure, gas relative humidities (or water contents) on the feed and sweep sides, crosslinking degree of PVA, and FS loading on transport properties including CO2 permeability, CO2/H-2 selectivity, and H-2 permeability, were investigated using a mixed gas containing 20% CO2 and 80% H-2. The optimal temperature identified was 107 degrees C. The CO2 permeability and CO2/H-2 selectivity typically increased with the relative humidities on the feed and sweep sides. Increasing the crosslinking degree of PVA slightly decreased the CO2 permeability. The CO2 permeability and CO2/H-2 selectivity decreased with increasing feed pressure due to the carrier saturation phenomenon. The CO2/H-2 selectivity increased by 33.8% from 65 to 87 as FS loading increased from 12 wt% to 22.3 wt% while CO2 permeability remained nearly constant at about 1130 Barrers. Further increase of FS loading decreased both CO2/H-2 selectivity and CO2 permeability. At 107 degrees C and 220 psia, the membrane with 22.3 wt% FS loading showed the best performance with a CO2 permeability of 1296 Barrers (1 Barrer = 3.35 x 10(-16) mol m/(m(2) s Pa)) and a CO2/H-2 selectivity of 87. (C) 2010 Elsevier B.V. All rights reserved.