Involvement of free radicals in the aqueous-phase catalytic oxidation of phenol over copper oxide

OXIDATION OF PHENOL IN AQUEOUS SOLUTION WITH COPPER OXIDE CATALYSTS SUPPORTED ON γ-Al2O3, PILLARED CLAY AND TiO2: COMPARISON OF THE PERFORMANCE AND COSTS ASSOCIATED WITH EACH CATALYST

“…The CuO catalyst showed a higher activity, likely due to the formation of free radicals, as explained by Sadana and Katzer (1974). The operating conditions of the process potentially favored the formation of cuprous oxide or phenolic radicals on the catalyst surface.…”

“…Copper oxide-based catalysts have been widely researched in the last 35 years due to their high activity. However, the dissolution of copper catalysts in acidic environments is well known (Sadana and Katzer, 1974). In studies conducted by Pintar (1997), phenol was oxidized over a supported Zn-Cu-Co oxide catalyst, resulting in the dissolution of metals, including 20% Cu, 10% Zn and 15% Co.…”

Carbon materials and catalytic wet air oxidation of organic pollutants in wastewater

“…The following reactivity order was observed: m-xylene (99.8%) > o-cresol (83%) > o-chlorophenol (74%) > phenol (70%) > aniline (15%) > p-nitrophenol (9%) > sulfolane (5%) > nitrobenzene (<1%). The mechanism of oxidative phenol destruction is complex, but it is generally accepted that the liquid phase oxidation of phenols and substituted phenols by molecular oxygen is an electrophilic reaction that follows a heterogeneous-homogeneous free radical chain mechanism [65,[192][193][194]. According to the postulated mechanism, the easiness of the organic to form free radicals is a key parameter that can be inferred from critical oxidation [92] or halve-wave potentials [192].…”

Total catalytic wet oxidation of phenol and its chlorinated derivates with MnO2/CeO2 catalyst in a slurry

“…2 and Fig. 3 show short induction periods at the beginning of the reactions, indicating a probable free radical mechanism as observed by Sadana and Katzer (1974) and Pintar and Levec (1992).…”

“…In several applications, these processes have a slow conversion rate in the initial 'step' (induction period), followed by a faster stage, and finally increasing to total degradation of organic compounds contained in the liquid phase. The initial degradation step has often been cited in the scientific literature as 'the induction period', due to the time necessary to reach a critical concentration of organic radicals (Sadana and Katzer, 1974). Li, Chen and Gloyna (1991) have proposed that molecular oxygen reacts directly with phenol to produce organic radicals and hydroperoxyl radical (…”