Tailored Rh–Al ₂ O ₃ –ZrO ₂ Interfaces: Insights into Rh Aluminate Formation and Enhanced Stability

Rhodium (Rh) is an extremely precious metal, well-known for its catalytic properties that make it indispensable in emission control systems. During their lifetime, Rh catalysts are exposed to high-temperature oxidizing environments. When supported on alumina, this leads to significant deactivation via the formation of rhodium aluminates (RhAl x O y ). However, the mechanism underlying the formation of such species remains a matter of debate. One leading hypothesis posits that Rh mobility on the support allows it to find defective alumina sites where it is converted into RhAl x O y, while others attribute this process to more generic Rh–alumina interfacial sites. In this work, we combine colloidally synthesized Rh nanocrystals with atomic layer deposition (ALD) of Al 2 O 3 and ZrO 2 to precisely engineer Rh/oxide interfaces and study their involvement in catalyst deactivation via RhAl x O y formation. We find that reducing the mobility of Rh nanoparticles via metal oxide encapsulation (ALD of Al 2 O 3 or ZrO 2 atop supported Rh catalysts) does not improve the catalyst stability. By modifying a ZrO 2 support with increasing amounts of Al 2 O 3 layers by ALD and subsequently depositing Rh nanocrystals, we find a correlation between the formation of RhAl x O y and the amount of deposited alumina. This observation suggests that a dissolution-based mechanism is responsible for catalyst deactivation and that the process is not interface-limited. Finally, by depositing Rh nanoparticles onto an alumina support coated with <0.3 wt % ZrO 2, we reduce the Rh–Al 2 O 3 interface and therefore catalyst deactivation, achieving a catalyst that remains 4 times more active after aging when compared to Rh/Al 2 O 3 .