Catalytic wet oxidation of phenol with Mn-Ce-based oxide catalysts: Impact of reactive adsorption on TOC removal

Catalytic wet oxidation of phenol solutions at low temperatures of 80-130 °C and space velocities of 1-100 h^-1 using Mn-Ce catalysts was studied with an emphasis on the reactive adsorption mechanism and total organic carbon (TOC) removal. Eight catalysts (Mn/Ce = 6:4) were activated under different conditions and promoted with alkali metals (K, Cs) or noble metals (Pt, Ru). The compositions and physical properties of all catalysts were measured. Preliminary runs were conducted in a batch reactor, but most experiments were carried out in a continuous-flow trickle-bed reactor. Catalysts containing mixed Mn₃O₄-CeO₂ phases pure and promoted with alkali metals displayed a higher activity and a higher adsorption of organic deposits on their surface. Noble metals had little effect on process performance. The adsorption capacity of the catalysts was found to be considerably higher than that reported for activated carbon. Furthermore, complete regeneration of a catalyst in three consecutive tests was demonstrated under relatively low temperature and with no loss of activity. The selectivity toward reactive adsorption was highest on Mn-Ce-Cs catalysts. Low space velocity yielded essentially complete adsorption of phenol, resulting in deposits on the catalyst surface. The conversion of phenol to water-soluble oxygenates was found to increase water toxicity. The catalytic reactive adsorption-regeneration process should become an attractive treatment method for phenol solutions and other complex waste streams.