Pd and Pt/SiO2-Al2O3 tubular membranes were prepared with the aim of obtaining uniform pore size and precious metal distribution throughout the cross-section. Membrane permeability was controlled by depositing silica inside the pores of alpha-Al2O3 supports. This was achieved by immersing the support inside colloidal silica solution followed by freeze-drying and calcination. Various techniques were evaluated in order to avoid the formation of a thin SiO2 layer on the external support surface. Pt and Pd were introduced by impregnation of the SiO2-Al2O3 membrane with hexachloroplatinic acid and palladium nitrate solution, respectively. Freeze-drying provided more uniform metal distribution than conventional drying. (C) 2004 Elsevier B.V. All rights reserved.