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CBE Fall Seminar Series: Johannes Schwank

Johann Schwank
Professor
Department of Chemical Engineering
University of Michigan
Ann Arbor, MI

October 18 @ 4:00 PM 5:00 PM

Nanoscale Restructuring of Palladium Catalysts

Catalyst restructuring is an unavoidable phenomenon in many high-temperature applications. Typically, such restructuring causes the sintering of active metal and supporting domains, adversely affecting the catalytic activity and the utilization of precious metals. While several methodologies have been proposed for mitigating the processes that cause sintering, stabilizing high dispersions of active metal under frequent exposure to high temperatures during operation or maintenance remains challenging. Here we investigate how encapsulating catalyst architectures, where functional metal domains are explicitly separated through encapsulation by porous support, can be exploited to improve activity and durability in high-temperature applications.

We demonstrate that encapsulating a single palladium core in a porous ceria shell can facilitate beneficial high-temperature (800°C) restructuring outcomes with improved activity and durability. The encapsulating shell inhibits local agglomeration of Pd through its porous, tortuous structure. As a result, active metal becomes trapped on the support in a highly dispersed fashion. The coordination between palladium and ceria that arises during the favorable restructuring improves the recruitment of lattice oxygen and, consequently, catalytic performance. This coordination stabilizes metal and support species from agglomeration during repeated exposure to 800°C aging conditions. As such, core@shell morphologies appear to be a promising platform for promoting favorable high-temperature restructuring that improves catalytic performance, stability, and material utilization. The encapsulated architecture makes it possible to partially reverse the sintering of Pd during exposure to severe temperatures as high as 1000 °C, thereby enabling self-regenerating catalysts to maintain high activity.

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