Catalytic ozonation of atrazine and linuron on MnOx/Al2O3 and MnOx/SBA-15 in a fixed bed reactor

The catalytic ozonation of the herbicides atrazine and linuron was studied in a fixed-bed reactor using alumina-supported manganese oxide catalysts. Two manganese oxides were supported, one on activated alumina, MnOx/Al2O3, the other, MnOx/SBA-15, after impregnating mesoporous silica by the minimum volume method. The adsorption of both compounds was not significant and the kinetic data indicated that the reaction with molecular ozone was a non-catalytic process which took place in homogeneous phase. The results of catalytic runs also showed no evidence that any of the catalysts increased the rate of the hydroxyl-mediated ozonation. Both catalysts, however, considerably increased the ozone decomposition rate constant, particularly MnOx/SBA-15 for which a MnOx bed load of 1.0 wt.% as MnO2 resulted in a 30 fold increase with respect to the homogeneous rate. The catalysts also improved the efficiency in the production of hydroxyl radicals from ozone with an average hydroxyl radical-to-ozone ratio as high as 10−6 for MnOx/Al2O3 and 3.0 × 10−6 for MnOx/SBA-15. The catalysts also led to lower ozone consumption per mole of converted organic compound, whether or not bicarbonate was present in the solution. Best results were obtained in all cases for MnOx/SBA-15, most probably due to a better distribution of the active phase on a larger surface.