Thermally stable Pd/CeO₂@SiO₂ with a core-shell structure for catalytic lean methane combustion

Noble metal catalysts exhibit high catalytic activity in lean CH₄ combustion at low temperatures. However, the high surface energy of noble metal nanoparticles makes them susceptible to deactivation due to migratory-aggregation during the catalytic process. Herein, a core-shell structure with a Pd/CeO₂ core and a SiO₂ shell (denoted as Pd/CeO₂@SiO₂) was designed and prepared to enhance the thermal stability for catalytic lean CH₄ combustion. A series of characterization methods demonstrated the successful encapsulation of SiO₂ and the modified thermal stability. The results of activity tests indicated that Pd/CeO₂@SiO₂ exhibited the optimal catalytic performance. After seven runs, Pd/CeO₂@SiO₂ achieved 90% conversion of CH₄ at 385 °C compared to Pd/CeO₂ at 440 °C. The remarkable catalytic performance was attributed to the synergistic effect of strengthened metal-support interactions and the core-shell structure. On the one hand, the migration and aggregation of Pd nanoparticles were limited due to the protection of the SiO₂ shell layer. On the other hand, the SiO₂ shell layer further enhanced the interactions between the Pd nanoparticles and CeO₂, thus promoting the formation of PdCe_1-O_2- solid solutions and active oxygen species, which were beneficial for the improvement of the stability and redox capacity of the catalyst.