The wet oxidation of organic compounds composed only of C, H, and O, dyes, amides, and water-soluble polymers is discussed to clarify the basic nature of this process. The reactivity of the organic compounds composed of C, H, and O, dyes, and some amides was correlated well with their carbon content in the molecule (C/MW) or carbon content in their skeletal structure (C/MW‘). This C/MW index can be applied to roughly estimate the behavior of wastewaters containing various organic compounds. Polymers are easily decomposed by the wet oxidation because they can undergo intramolecular hydrogen abstraction in the chain-propagation step. The biodegradability of polymers and amides was improved by wet oxidation treatment, indicating an asset of this process. The function of homogeneous copper salts and the effect of hydrogen peroxide are discussed. The action of Co/Bi composite oxide designed for the treatment of refractory carboxylic acids, Mn/Ce composite oxide for ammonia and other organic compounds, and Ru/CeO2 catalyst for the decomposition of PEG, formaldehyde, etc., is explained. The high potential of Ru and CeO2 as active catalyst components is emphasized.

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Wet oxidation of ammonia was carried out in the presence of Ce-based composite oxide catalysts. Reaction proceeded rapidly in the high pH region, indicating that ammonia was more reactive than ammonium ion. The Co/Ce and /Ce composite oxides were remarkably active. The maximum percentage decrease in ammonia was attained at a Ce content around 20 mol % for Co/Ce and 20-50 mol % for /Ce, respectively. They exhibited high activity in the decomposition of hydrogen peroxide, which suggested that the high activity of these composite oxides in the oxidation of ammonia was due partly to their high redox property. It was found that their strong affinity toward ammonia also contributed to their high activity in the oxidation of ammonia. The ESR spectral analysis indicated that interactions between Co and Ce, and Mn and Ce, were present in these composite oxides. The activity of the /Ce catalysts was higher than that of water-soluble copper compounds which are known as the most active catalyst in the wet oxidation.

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The catalytic activity of /Ce composite oxide in the wet oxidation of polyethylene glycol) and other organic compounds was investigated. The /Ce composite oxide had higher activity than either Co/Bi composite oxide or homogeneous copper catalyst. The catalyst had high redox property, and participation of a radical mechanism was suggested. The ESR and ESCA analyses indicated that the effect of Ce was to produce manganese species with lower valence states (Mn3+, Mn2+), and the combination of Mn4+ with Mn3+ or Mn2+ was assumed to be the cause of the high activity of the catalyst.

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