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

Abstract

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 Pd_xCe_1−xO_2−δ solid solutions and active oxygen species, which were beneficial for the improvement of the stability and redox capacity of the catalyst.