The oxidation of 1,3-dimethyladamantane and cyclooctane with potassium peroxosulfate catalyzed by manganese and iron complexes of alkylated tetrapyridylporphyrin which was either dissolved in a reaction medium or adsorbed on a layered aluminosilicate was studied. The Mn3+ porphyrin complex immobilized in the interlamellar space of montmorillonite modified with titanium hydroxide clusters was found to enhance the catalytic activity and stability against oxidative degradation.