A TiO2/Al2O3 catalyst to improve the ozonation of oxalic acid in water

Removal of oxalic acid from water has been accomplished through TiO2/Al2O3 catalytic ozonation. The combined use of ozone and the titanium catalyst leads to a conspicuous 80% of oxalic acid conversion in 3 h which compares favorably to the hardly 2% reached in the absence of the catalyst at pH 2.5. At the experimental conditions applied, the catalytic process develops under complete carbon mineralization and does not proceed through hydroxyl radical oxidation. The process rate can be described by considering an Eley-Rideal mechanism. Thus, it is proposed that adsorbed oxalic acid reacts directly with ozone in solution, the oxalic acid adsorption stage being the rate-limiting step. This mechanism justifies the experimental kinetic orders found in the range 1 and 0-1 for oxalic acid and ozone, respectively. The apparent activation energy of the catalytic ozonation was also found to be 14 kcal mol(-1). (C) 2003 Elsevier B.V. All rights reserved.