(598b) Morphology-Directed Restructuring of Core@Shell Nanoparticles: A Catalyst Design Strategy to Improve Material Utilization

Catalyst restructuring is an unavoidable phenomenon in many high-temperature applications. This restructuring typically leads to the agglomeration or sintering of active metal and supporting domains, which adversely affects activity and the utilization of precious metal content. This work investigates how the initial catalyst architecture can be designed to facilitate beneficial restructuring and strongly inhibit sintering under high-temperature operating conditions.

Specifically, we examine the high-temperature (800 °C) restructuring of core@shell catalysts, where active metal domains are separated from one another through encapsulation by a porous supporting metal oxide shell. Using Pd as the core metal, we find that 800 °C aging redisperses Pd into the surrounding metal oxide shell, thereby enhancing low-temperature activity and increasing the number of available active sites by over two-fold. While both nonreducible SiO₂ and reducible CeO₂ supports are capable of anchoring Pd in high dispersions, Pd@CeO₂ retains its highly active structure after repeated 800 °C aging cycles, while Pd@SiO₂ reverses its restructuring trajectory and begins to exhibit active metal sintering. The Pd dispersion in the restructured Pd@CeO₂ is accompanied by a stabilization of the support structure and porosity, which helps maintain favorable activity. This observation contrasts with Pd@SiO₂, which exhibits an appreciable compromise in the porosity of the encapsulating SiO₂ environment after repeated aging. Our investigation identifies the nanoscale structure of the shell’s transport pathways and the chemistry that exists between the support and mobile metal as fundamental for directing active metal transport and trapping. These support considerations are complemented by an examination of catalysts with Au and composite Au–Pd cores, which demonstrates the importance of core metal chemistry for mediating favorable restructuring.

Ultimately, we demonstrate how the initial catalyst morphology can be used to leverage high-temperature restructuring as a design strategy to improve catalytic performance and material utilization.