Electrochemical promotion of the complete catalytic oxidation of toluene at 310°C is reported, using a Ag/YSZ/Ag two electrode system where Ag films were deposited on YSZ from AgNO3 aqueous solution followed by reduction in H2. After on-stream activation, a non-negligible conversion (about 30%) at OCV is reached and then the rate of the catalytic toluene conversion into CO2 and H2O can be multiplied by a factor higher than 1.5, by application of a small negative current (about—4μAcm−2). The associated Faradaic efficiency is very high and may exceed −13,000.

Evident electrochemical promotion of the complete catalytic oxidation of toluene in the temperature range 300–330°C was observed, for the first time, on a silver film catalyst prepared by direct impregnation onto a Y2O3 stabilized ZrO2 (YSZ) solid electrolyte. It was found that the toluene conversion into CO2 and H2O on such a catalyst can be significantly promoted upon cathodic polarization, i.e. oxygen removal from the catalyst surface. The promotion effect increases with the temperature within the investigated range. Furthermore, it was found that the promotion effect was also strongly influenced by toluene and oxygen concentrations. With increasing the toluene concentration, the rate enhancement decreased while the Faradaic efficiency shows a volcano type behaviour. The relationships between the rate enhancement and Faradaic efficiency with the oxygen concentration are on the contrary, i.e. there is an optimum for rate enhancement when oxygen concentration is about 2%, the Faradaic efficiency monotonically decreasing with oxygen concentration. Finally, the promotion effect also increased with the thickness of Ag film, which may be interpreted by more available active sites.

A differential desorption technique, named intermittent temperature-programmed desorption (ITPD), has been used to get new insights into the properties of La1-xSrxCo0.8Fe0.2O3-delta perovskites. The apparent activation energy of desorption (E-app) and the frequency factor (v) were calculated from ITPD data, for the two distinct oxygen species desorbing from perovskite at temperatures lower than 400 degrees C. The low values (about 10(7)-10(8) s(-1)) obtained for V-app indicated that re-adsorption occurred during the TPD process and therefore that E-app is equal to the Heat of adsorption (E=-Delta H). The first oxygen species, related to lower desorption temperatures, exhibits a distribution of E from 105 to 125 kJ mol(-1). The second one, related to higher desorption temperatures, corresponds to E=146 +/- 4 kJ mol(-1) and 139 +/- 5 kJ mol(-1), for x=0.2 and x=0.3, respectively. The relative amounts of these species contributing to the desorption peak are dependent upon Sr content in the perovskite. (C) 2008 Elsevier B.V. All rights reserved.

A series of La1−xSrxCo1−yFeyO3 (LSCF) perovskite catalysts was synthesized by a combined citrate–EDTA complexing method. The powders obtained were characterized by XRD, N2 adsorption and O2-TPD. After comparing the activities of the LSCF catalysts for the catalytic combustion of toluene, it was found that the substitution by little amounts of Sr and Fe improved the activity of LaCoO3. Such improvement can be explained by the increased amount of weakly adsorbed oxygen, evidenced by O2-TPD profiles.

This paper is the first report on the possibility to electrochemically promote the catalytic complete oxidation of toluene on Ag films deposited on Y2O3 stabilized ZrO2 (YSZ) at relatively low temperature (300°C). It was found that the toluene conversion into CO2 and H2O on an Ag catalyst can be significantly promoted upon cathodic polarization, i.e. oxygen removal from the catalyst surface. Such an enhancement is strongly non-Faradaic. Conversely, anodic polarization, i.e. O2− supplying from the YSZ support toward the catalyst, has no significant influence on the activity of Ag film. The promotion effect is therefore typically an electrophilic one. Further investigation indicates that there are some optimum values for the negative potential or current. Beyond these values, the activity of catalyst remains the same, but the Faradaic efficiency decreases.

A series of noble metal (Pt, Pd, Ru) loaded zirconia catalysts were evaluated in the catalytic wet air oxidation (CWAO) of mono-chlorophenols (2-CP, 3-CP, 4-CP) under relatively mild reaction conditions. Among the investigated noble metals, Ru appeared to be the best to promote the CWAO of CPs as far as incipient-wetness impregnation was used to prepare all the catalysts. The position of the chlorine substitution on the aromatic ring was also shown to have a significant effect on the CP reactivity in the CWAO over 3wt.% Ru/ZrO(2). 2-CP was relatively easier to degradate compared to 3-CP and 4-CP. One reason could be the higher adsorption of 2-CP on the catalyst surface. Further investigations suggested that 3wt.% Ru/ZrO(2) is a very efficient catalyst in the CWAO of 2-CP as far as high 2-CP conversion and TOC abatement could still be reached at even lower temperature (393K) and lower total pressure (3MPa). Additionally, the conversion of 2-CP was demonstrated to increase with the initial pH of the 2-CP solution. The dechlorination reaction is promoted at higher pH. In all cases, the adsorption of the reactants and the reaction intermediates was shown to play a major role. All parameters that would control the molecule speciation in solution or the catalyst surface properties would have a key effect.