Mixed matrix membranes (MMMs) were prepared combining two different polymers (polysulfone Udel (R) and polyimide Matrimid (R)) and hollow silicalite-1 spheres (HZSs) with about 4 mu m in diameter. These HZSs were obtained by hydrothermal synthesis from solid mesoporous silica spheres (seeded with silicalite-1 nanocrystals). With filler loadings varying between 0 and 16 wt.%, the MMMs were applied to the separation of H-2/CH4, CO2/N-2, and O-2/N-2 mixtures. For all the gas pairs tested, it was found that with a loading of 8 wt.% the MMMs performed better than those prepared with pure polymer, other different loadings and conventional silicalite-1 crystals of similar size to that of the HZS diameter. The highest selectivities obtained here for H-2/CH4, CO2/N-2, and O-2/N-2 mixtures were 180 (H-2 permeability = 38.4 Barrer), 41.7 (CO2 permeability = 7.2 Barter), and 8.5 (O-2 permeability = 2.8 Barter), respectively. (C) 2011 Elsevier B.V. All rights reserved.