Thermally Induced Restructuring of Pd@CeO₂ and Pd@SiO₂ Nanoparticles as a Strategy for Enhancing Low-Temperature Catalytic Activity

Abstract

Retaining high catalytic activity after exposure to elevated temperatures remains a crucial challenge for applications such as automotive emissions control. While catalysts generally sinter and lose activity after aging at high temperature, here we illustrate that palladium in a core@shell morphology responds very differently. After 800 °C aging in oxygen, palladium redisperses into the encapsulating shell. The redispersion is more pronounced, and nearly complete, when palladium is encapsulated by reducible ceria, as opposed to nonreducible silica. This difference is likely due to the availability of lattice oxygen. Through comparisons with polycrystalline ceria nanoparticles, surface decorated with Pd, we show that for favorable restructuring to occur under our simple aging conditions, the process must start from a particular initial configuration, the core@shell. Furthermore, the redispersion of palladium in ceria is accompanied by a change in oxidation state and coordination that inhibits the growth of ceria crystallites in the shell, thereby producing sites that better access the reducibility of the ceria shell support. Together, these effects result in a decrease in the temperature required for 90% conversion (T90) of carbon monoxide. Our findings demonstrate that thermally induced restructuring of core@shell morphologies under controlled conditions provides a strategy for enhancing low-temperature catalytic activity.