Aluminum was carefully anodized, then palladium salts were supported on its Al₂O₃ surface layer by ion-exchange. CO 3.76 vol% contained in the air can be eliminated at around 200℃. Both anodization conditions and the nature of the precursor solutions affect catalyst nature, particularly the pH value of the precursor solutions. The pH value of the solution suitable for supporting active components is 5-6. Palladium, which is present as Pd₂₊ and Pd₄₊ after calcination, distributes uniformly on the support surface which had a honeycomb structure.