Effect of the nature of the B cation on the catalytic performances of La-based perovskites for the combustion of toluene and chlorobenzene

Catalytic combustion at low concentrations of VOCs has the advantages owing to its low temperature regime to be a more selective and lower cost process compared to thermal incineration. As perovskites are good catalytic combustion catalysts (1) we focused our studies on the effect of the nature of the B cation (Co,Mn,Fe,Ni) on the catalytic performances of LaBO3 synthesized by sol-gel based methods both for the total oxidation of toluene and chlorobenzene. IR, BET surface area, XRD, TPR-H2 and TPD-O2 have been used to characterize and understand the catalytic behaviour of the solids. The activity for toluene combustion (0.1%, F/w : 450-850 NmL/min.g) has been determined from light-off curves (1°C/min) based on T50 (temperature at which 50% of toluene is converted). The activity decreases in the following sequence : LaCoO3>LaMnO3+d>LaNiO3»LaFeO3. All catalysts are selective in CO2, traces of benzene being nevertheless detected on Co and Mn based catalysts. Oxidation of chlorobenzene (0.1%, F/w : 220NmL/min.g) gives the sequence : LaMnO3+d> LaCoO3 > LaNiO3 > LaFeO3. By opposition with Co and Ni, along CO2 detection, CO production to a less extent is observed on Mn and Fe based catalysts. In our experimental conditions Cl is preferentially converted into HCl. If LaMnO3+d and LaFeO3 structure keep unchanged by XRD, LaCoO3 and LaNiO3 decompose to give LaOCl and the resultant oxides NiO and Co3O4. Results based on T50 values show that toluene molecule is more reactive than chlorobenzene for total oxidation on LaBO3. Considering both activity, selectivity and stability LaMnO3+d appears to be the best catalyst due its ability to accommodate O overstoechiometry.