A polymer membrane having an asymmetric physical structure, dense at the surfaces with a fibrous interior, is developed to host the Ag, Au, Pd, Rh and Ru nanocatalysts that are formed by in situ reductions of the precursor ions with functional groups covalently attached to the membrane matrix. This membrane mimics an egg-shell membrane in terms of the reduction and stabilization of the nanocatalysts without involving external reagents. The nano catalysts in this membrane exhibit high catalytic activity in both inorganic and organic reductions.