The preparation of composite catalytic membranes as a type of heterogeneous catalysts is considered. The necessity of the use of a catalyst material (bulk or supported) for the formation of the functional layers (selective or catalytic) of a catalytic membrane is substantiated. The procedure for the preparation of a catalytic membrane includes two stages: the initial formation of functional layers from a catalyst precursor followed by its activation. Changes in pore structure characteristics at different stages of preparation are exemplified by membranes with catalysts based on molybdenum compounds. The composite membrane structure has been formed from a precursor by chemical vapor deposition. Composite membranes based on a molybdenum carbide catalyst have been prepared using porous base layers with different porous structures. The effect of the stage of activation on the pore structure characteristics of a catalytic composite membrane has been experimentally demonstrated.