Catalytic wet oxidation of 2-chlorophenol, 2,4-dichlorophenol and 2,4,6-trichlorophenol in water with Mn(II)-MCM41

Chlorinated phenols are persistent and toxic organic compounds, harmful to organisms and humans even at low concentrations. Biological oxidation used for removing organics from industrial effluents is not suitable for these compounds and catalytic wet oxidation is one of the major alternatives for their destruction. In the present work, Mn(II)-incorporated MCM41 is used as catalyst for oxidation of 2-chlorophenol (2-CP), 2,4-dichlorophenol (2,4-DCP) and 2,4,6-trichlorophenol (2,4,6-TCP) in water with or without an oxidant (H2O2). Mn(II)-MCM41 is prepared by both direct hydrothermal synthesis and impregnation into MCM41 molecular sieve. The catalysts are characterized by XRD and FT-IR measurements for the structural features and by atomic adsorption spectrophotometry for the amount of Mn(II) entering into MCM41. The materials are calcined at 773 K for 5 h before use. The oxidation is carried out in a high-pressure stirred reactor at 353 K under various reaction conditions. The conversion achieved with directly synthesized Mn(II)-MCM41 for 2-CP, 2,4-DCP and 2,4,6-TCP is respectively 90.3, 55.1 and 50.8 % in 5 h for the reactant: H2O2 mole ratio 1:1, and 85.5, 60.6 and 60.2 % in absence of H2O2. The conversion with impregnated Mn(II)-MCM41 for 2-CP, 2,4-DCP and 2,4,6-TCP is respectively 90.3, 78.0 and 75.0% in 5 h with H2O2 and 91.1, 85.0 and 79.7% without H2O2. The oxidation follows first order kinetics. Effects of various reaction conditions and the probable mechanisms of oxidation have been discussed.