Reactivity of ceria–zirconia catalysts for the catalytic wet peroxidative oxidation of azo dyes: reactivity and quantification of surface Ce(<scp>IV</scp>)‐peroxo species

Abstract

Abstract BACKGROUND Doping nanoceria with zirconia often leads to improved catalytic properties due to enhanced concentration of structural defects in the resulting materials. This study aims to identify the parameters and mechanisms governing the reactivity of well‐characterized commercial ceria–zirconia ( Ce x Zr 1 ‐ x O 2 ) nanocatalysts with various Ce contents (x = 1, 0.80, 0.50, 0.21, 0) or surface area towards the degradation of Orange II dye in the presence of H 2 O 2 . RESULTS Discoloration and mineralization kinetics were found to be strongly related both to the composition and surface area of the single or mixed oxides. Under standard conditions (23 °C, dark, stoichiometric concentration in H 2 O 2 ), the best discoloration and mineralization performances were achieved for pure ceria (100% of color removal in 2 h and 65% mineralization in 8 h), but this arises mainly from its higher specific area by comparison with Zr‐doped materials. For the first time, the amount of Ce IV ( O 2 ) 2− surface species, intermediates in the production of hydroxyl radicals and generated from the reaction of H 2 O 2 with Ce( III ) sites, was quantitated using TPD‐MS in order to provide a rational basis to explain the catalytic performance. CONCLUSION Doping ceria with Zr increases the surface density of defective Ce( III ) sites that can be converted to Ce IV ( O 2 ) 2− species in the presence of H 2 O 2 , but other parameters, such as the specific surface area and surface Ce content of the catalysts, are also important. An in‐depth mechanism for the reaction of H 2 O 2 on the ceria–zirconia surface is discussed based on the experimental results. © 2015 Society of Chemical Industry