Relationship between the structure of Ru/CeO2 catalysts and their activityin the catalytic ozonation of succinic acid aqueous solutions

Two Ru/CeO2 catalysts were used for the study of the catalytic ozonation of aqueous solutions of succinic acid (SA). These catalysts were prepared eit her by impregnation (I) or by acid exchange (AE). The objectives were (I) t o determine the efficiency towards the oxidation of the organic molecule in relation to the catalysts characterization, and (2) to examine the modific ations of the structure induced by ozonation. For each catalyst, two experi mental conditions of catalyst and succinic acid concentrations were studied . The diluted conditions ([SA](0) = 1 mM, weight(cata) = 0.8 g/l) were appl ied for the study of the behavior of the catalysts during successive uses. The efficiency was also studied for higher initial concentrations ([SA](0) = 5 mM, weight(cata) = 3.2 g/l). Under both conditions the best efficiency was obtained with the impregnated catalyst. Transmission electronic microscopy analyses indicated that before ozonation of SA, ruthenium was distributed within the whole volume of the grain of C eO2 fur the AE catalyst, and included only in an external layer for the I c atalyst. The size of the particles determined by X-ray diffraction (XRD) wa s around 3.5 nm for Ru and in the range 10-75 nm for CeO2. In most cases, t he catalytic ozonation induced Ru sintering with the formation of clusters. After four successive ozonation experiments the AE catalyst efficiency was significantly decreased and the structure totally disorganized. (C) 2001 E lsevier Science B.V. All rights reserved.