Catalytic ozonation of chlorinated carboxylic acids with Ru/CeO2–TiO2catalyst in the aqueous system

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Abstract
The catalytic mineralization of chloroacetic acid (CAA) and chlorosuccinic acid (CSA) by ozone with Ru/CeO2–TiO2 solid catalyst in aqueous systems was studied. The catalyst significantly improves the oxidation and degradation at acidic pH. More than 80 to 90% of the converted CAA and CSA are mineralized during the reaction. The chloride is nearly completely released along with the decomposition of CAA and CSA. The catalytic oxidation of CAA and CSA and conversion of total organic carbon can be simply simulated with a pseudo-first-order behavior with little dependence on the concentration of the dissolved ozone in the aqueous systems, which is maintained in sufficient quantity during the reaction. The catalytic ozonation displays a higher ozone use efficiency than ozonation alone. CSA is apparently easier to degrade than CAA. The chloride ion in the solution has little detrimental influence on the catalytic effects under our experimental conditions. The oxidation of 2 mM CAA is apparently stopped after about 50 min when the CAA concentration decreases to about 0.6 mM and the pH value of the system is lower than the pKa of CAA. The explanation is that in very dilute systems with pH values lower than the pKa, the low-concentration of CAA ions slows the adsorption and reaction rates. The near-total elimination of CAA at low concentrations can be achieved only if the pH value is increased above the pKa. The results demonstrate that catalytic ozonation is an effective and promising method for the oxidation and elimination of chlorocarboxylic acids.

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