Studies of the activation process on Pd-perovskite-type oxides used for the catalytic oxidation of toluene

affiche exposée au "4th International Conference on Environment Catalysis"Pd dispersed on conventional supports such as alumina, zirconia (1) is active for the catalytic oxidation of VOCs into harmless products such as H2O and CO2. Improvement of the activity of Pd can be achieved in associating Pd in a metallic state which is well known to activate hydrocarbons with an oxide network support having a great oxygen mobility. For purpose, we have investigated the catalytic destruction of toluene (0.1%, F/w : 1000 NmL/min.g) on 0.5wt%Pd/LaBO3, (B = Co,Mn,Fe, Ni) catalysts derived from sol-gel preparations. The samples have been calcined (2h,400°C,2L/h) and reduced before catalytic testing (2h,200°C,2L/h). Physical characterization as TPR-H2, in situ XPS studies of the overall transformation (calcination, reduction, catalytic test) performed on Pd/LaCoO3 and Pd/LaFeO3 have demonstrated that after reduction treatment (1) : Pd(IV) is totally reduced into Pd(0), (2) the cation Fe3+ is not reduced on Pd/LaFeO3, whereas for others samples onset of reduction of the B cation has already occurred. Further, XRD measurements show that the integrity of the perovskite network is preserved in all cases after catalytic testing. The activity for toluene combustion has been determined from light-off curves (1°C/min) based on T50 (temperature at which 50% of toluene is converted).The catalytic activity of Pd-based samples decreases according to : Pd/LaFeO3(T50/°C :185)>Pd/LaMnO3(217)>Pd/LaCoO3(223)>Pd/LaNiO3(234). All catalysts are selective in CO2, traces of benzene being detected for all species, Pd/LaFeO3 excepted. The very good activity and selectivity of Pd/LaFeO3 compared to other samples should be attributed to the efficiency of the reductive treatment allowing to reduce Pd(IV) into Pd(0) without affecting the perovskite network