Oxidative and Reductive Pathways in Manganese-Catalyzed Fenton’s Reactions

Abstract

Soluble manganese (II) and amorphous and crystalline manganese (IV) oxides were investigated as catalysts for the Fenton-like decomposition of hydrogen peroxide into oxidants and reductants. 1-Hexanol was used as a hydroxyl radical probe and carbon tetrachloride (CT) was used as a reductant probe. Soluble manganese (II)-catalyzed reactions at acidic pH resulted in >99% degradation of 1-hexanol and no measurable transformation of CT, indicating that hydroxyl radicals were generated but reductants were not. However, when these reactions were conducted at near-neutral pH, an amorphous manganese oxide precipitate formed and 89% of the CT degraded in 60 min , while 1-hexanol degradation was negligible. Using an amorphous manganese oxide synthesized in a separate reactor, CT was rapidly degraded while 1-hexanol oxidation was undetectable. Reactions catalyzed by the crystalline manganese oxide pyrolusite (β-Mn O2 ) at near-neutral pH also resulted in significant CT degradation, indicating that reductants are gen...