(53e) Tailored Rh-Al2O3-ZrO2 Interfaces: Insights into Rh Deactivation and Enhanced Stability

Rhodium (Rh) is an extremely precious metal, well known for its catalytic properties which make it indispensable in emission control systems. During their lifetime Rh catalysts will be exposed to high temperature oxidizing environments, which when supported on alumina carriers have been shown to lead to significant deactivation via the formation of Rh aluminates (RhAl_xO_y). However, the mechanism underlying the formation of such species remains under debate. One leading hypothesis posits that Rh mobility on the support allows it to find defective alumina sites where it is converted into RhAl_xO_y, while others attribute this to more generic Rh-alumina interfacial sites. In this work we combine colloidally synthesized Rh nanocrystals with atomic layer deposition (ALD) of Al₂O₃ and ZrO₂ to precisely engineer Rh catalysts and study their deactivation via RhAl_xO_y formation. We find that reducing the mobility of Rh nanoparticles via encapsulation does not improve their stability. By carefully modifying a ZrO₂ support coating it with increasing amounts of Al₂O₃ ALD and subsequently depositing Rh nanocrystals we are able to correlate the formation of RhAl_xO_y to the amount of alumina deposited, indicating a dissolution based mechanism that is not interface limited. Finally, by coating an alumina support with <1 weight% ZrO₂ and subsequently depositing Rh nanoparticles on this modified support, we mitigate Rh-Al₂O₃ interactions and Rh deactivation, achieving a catalyst that remains 4 times more active after aging when compared to Rh/Al₂O₃.