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.
International audienceAdsorption behavior of a hydrocarbon mixture (propene, toluene, decane) mimicking Diesel cold-start was investigated under dry and wet conditions for commercial HY zeolites with a Si/Al ratio ranging from 2.5 to 100. Textural and structural characterizations were carried out using N-2 adsorption at 77 K and X-ray diffraction. In situ FTIR spectroscopy of adsorbed pyridine was exploited to probe acidic sites. The methodology used in this study consisted of adsorption phase at 35 degrees C with several kinds of mixtures followed by a Temperature-Programmed Desorption (TPD) at 10 degrees C/min. At high Si/Al ratio, a competitive thermodynamic adsorption between toluene and decane was demonstrated. To the opposite, propene is substantially not adsorbed whatever the Si/Al ratio of the zeolite. By decreasing the Si/Al ratio, the presence of large amounts of acidic sites enhances adsorption of unsaturated hydrocarbons. Water adsorption was found to be detrimental for HC storage due to hydrophilic nature
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