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

Abstract

Ru/C catalysts promoted, or not, by cerium were prepared by impregnation of an active carbon (961m2g−1) with chlorine-free precursors of Ru and Ce. They were characterized by chemisorption of H2 and of CO and by electron microscopy. TEM and H2 chemisorption gives coherent results while CO chemisorption overestimates Ru dispersion. In 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°C and 20 bar of O2) 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 3h. 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 O2 activation when the organic molecule is strongly adsorbed.