The role of Mn-doping for catalytic ozonation of phenol using Mn/γ-Al₂O₃ nanocatalyst: Performance and mechanism

Comparative ozonation experiments were carried out to investigate the catalytic ability and mechanism of γ-Al₂O₃ supported manganese oxide (Mn/γ-Al₂O₃) for the degradation of phenol in aqueous solution. The results showed that 4% Mn/γ-Al₂O₃ possessed highest catalytic efficiency for the ozonation of phenol than that of other catalysts. The influences of manganese content and catalyst dosage verified that surface hydroxyl groups affected by the solution pH and the point of zero charge (pH_PZC) of catalysts. The Mn/γ-Al₂O₃ exerted the strongest catalytic activity at initial solution pH of 3.45. The strong interaction between ozone and Mn/γ-Al₂O₃ was observed and confirmed as a critical step for the catalysis reaction. The surface hydroxyl groups and chemisorbed water acted as the active sites in promoting hydroxyl radicals, while Brönsted acid sites were confirmed as reactive centres for catalytic ozonation in the aqueous phase. The influence of tert-butanol showed that hydroxyl radicals and active oxygen species were involved in the catalytic ozonation of phenol. According to the X-ray photoelectron spectroscopy (XPS) results, the enhancement of electron transfer on the surface manganese oxides were responsible for the catalysis and promoting the formation of active oxygen species. A possible catalytic ozonation mechanism of phenol over Mn/γ-Al₂O₃ was proposed.