Catalytic wet air oxidation of phenol and acrylic acid over Ru/C and Ru-CeO2/C catalysts

Ru/C catalysts promoted, or not, by cerium were prepared by impregnation of an active carbon (961 m(2) g(-1)) with chlorine-free precursors of Ru and Ce, They were characterized by chemisorption of H-2 and of CO and by electron microscopy. TEM and H-2 chemisorption gives coherent results while CO chemisorption overestimates Ru dispersion. Tn Ru-Ce/C, Ce is in close contact with Ru and decreases Ru accessibility. Catalytic wet air oxidation (CWAO) of phenol and of acrylic acid (160 degrees C and 20 bar of O-2) was investigated over these catalysts and their performance (activity, selectivity to intermediate compounds) compared with that of a reference Ru/CeO2 catalyst. Carbon-supported catalysts were very active for the CWAO of phenol but not for acrylic acid. Although high conversions were obtained, phenol was not totally mineralized after 3 h. It was shown that acrylic acid was more strongly adsorbed than phenol. Moreover, the number of contact points between Ru particles and CeO2 crystallites constitutes a key parameter in these reactions. A high surface area of ceria is required to insure O-2 activation when the organic molecule is strongly adsorbed. (C) 2000 Elsevier Science B.V. All rights reserved.