Effects of Pd on enhancement of oxidation activity of LaBO3 (B = Mn, Fe, Co and Ni) pervoskite catalysts for pollution abatement from natural gas fueled vehicles

摘要

The effect of Pd on activity enhancement of perovskite catalysts for oxidation of CH4 and CO emitted from natural-gas fueled vehicles is investigated using a synthetic stoichiometric exhaust gas mixture. Various LaBO3 and LaBPd_(0.05)O3 (B = Mn, Fe, Co and Ni) perovskite-type nanocatalysts were prepared via a solution combustion synthesis, calcined at 700 °C for 5h, and characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), BET specific surface area measurement, H2 temperature programmed reduction (TPR) and O2 temperature programmed desorption (TPD). XRD results, confirms the presence of PdO in Pd-containing samples, which is highly active for CO and CH4 oxidation. TPR and TPD results show that Pd significantly facilitates the reducibility of B in LaBPd_(0.05)O3 pervoskites and enhances the mobility of lattice oxygen in the prepared samples, which results in activity enhancement for Pd-containing catalysts. Oxidation activity results reveal that Pd effect is more pronounced for CO oxidation as compared to that for CH4, probably due to the Pd transition from PdO to metallic Pd and/or its incorporation into the pervoskite structure occurred at elevated temperatures, which both seem to reduce its activity. Among the prepared samples, LaFePd_(0.05)O3 catalyst shows the highest activity for CO and CH4 oxidation, T_(90) of which occur at 165 and 558°C, 191 and 40°C lower than that for LaFeO3 respectively.