Inhibition of Rh sintering and improved reducibility of Rh on ZrO2 nanocomposite with an Al2O3 diffusion barrier

• Al2O3, a diffusion barrier, suppressed sintering of La2O3-stabilized ZrO2 in Nd-A80ZL.
• Nd2O3 mainly enriched on La2O3-stabilized ZrO2 in Nd-A80ZL despite Al2O3 barrier.
• Nd2O3 on ZrO2 in Rh/Nd-A80ZL provided the anchoring sites for Rh.
• Nd2O3 and Al2O3 layers maintained the balance between Rh dispersion and reducibility.
• The balance could be maintained by adjusting the basicity of the Nd-A80ZL support.

To enhance the durability of Rh catalysts for vehicle emissions control, a novel support, Nd-A80ZL, was designed. This support was composed of La2O3-stabilized ZrO2 particles that contained a Nd2O3-enriched surface layer and nanosized Al2O3 particles, which acted as a diffusion barrier. Nd2O3 was mainly loaded on ZrO2 after high-temperature aging, as anticipated. Then, Rh was also mainly loaded on the ZrO2 with the Nd2O3 surface enrichment; the inhibition of Rh sintering during the aging test suggests that the surface Nd2O3 functioned as anchoring sites for Rh. The results of the hydrogen temperature-programmed reduction showed that Rh on the Nd-A80ZL support was more easily reduced than that on a La2O3-stabilized ZrO2 support with Nd2O3 surface enrichment (Nd-ZL). Rh/Nd-A80ZL also had a more appropriate solid basicity than Rh/Nd-ZL. These results showed that the introduced Al2O3 diffusion barrier in Nd-A80ZL controlled the basicity derived from the addition of Nd2O3 and balanced the inhibition of Rh sintering and Rh reducibility.

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