Mesoporous Ceria and Ceria-Praseodymia as High Surface Area Supports for Pd-based Catalysts with Enhanced Methane Oxidation Activity

In recent years, Pd/CeO2 materials have proven to be effective catalysts for the total oxidation of methane. In this work, three different synthesis routes were used to prepare high specific surface area supports, consisting of pure CeO2 and 10 at% Pr-doped ceria (Ce90Pr10). Nano-structured spheres were obtained with a microwave-assisted synthesis, dumbbell-like particles were produced through a urea-based hydrothermal method, and ordered mesoporous oxides were prepared by using SBA-15 as hard-template. The six materials were then impregnated with 2 wt% Pd, calcined at 500 degrees C, and comprehensively characterized. All the samples retained their high surface area after impregnation (75-110 m2 g-1), allowing a good dispersion of palladium. No significant structural or morphological differences were observed upon Pr doping, but a higher Pd oxidation state was induced by Pr-doped supports. However, all Pd/CeO2 and Pd/Ce90Pr10 catalysts exhibited similar activity for dry methane oxidation below 500 degrees C, regardless of the synthesis technique and of the Pr presence: they all achieved almost complete CH4 oxidation at 400 degrees C, showing a really remarkable improvement with respect to analogous low surface area supports. A promoting role of Pr was instead noticed in wet conditions, thanks to its ability to counteract water-induced deactivation phenomena. High-surface-area materials consisting of pure and Pr-doped ceria were synthesized with different procedures and employed as supports for Pd-based catalysts. Thanks to their peculiar textural properties and better Pd dispersion, these mixed oxides exhibited remarkably higher activity towards methane oxidation with respect to analogous samples with low surface area. Pr-doping resulted particularly beneficial in wet conditions, reducing water-induced deactivation effects.image