The interaction between supported Rh- and Nd2O3-enriched surface layer on ZrO2 for Rh sintering suppression

To suppress sintering of Rh supported on an oxide, the interaction between Rh and the support oxide was investigated. To eliminate the structural instability effect of the support oxide on Rh sintering, ZrO2 doped with a rare earth element was used in this study. La doping was found to be most effective for maintaining a specific surface area and the tetragonal phase of ZrO2 after the aging test at 1273 K in air. On this stabilized La-ZrO2 surface, Nd2O3 was introduced, with the aim of investigating its interaction with the supported Rh. Transmission electron microscopy observation with energy dispersive X-ray analysis showed that Nd enrichment existed around the surface of the primary particle of La-ZrO2. Investigations with hydrogen-temperature programmed reduction and extended X-ray absorption fine structure revealed that the supported Rh interacted with Nd2O3 on the surface of the La-ZrO2 and Rh–O–Nd bond formation in oxidizing atmosphere was the origin of the interaction. After a redox aging test at 1273 K, it was found that Rh sintering behavior depended on the Nd2O3 surface enrichment amount and sintering suppression was obtained with a 1–2 wt% Nd2O3 surface enrichment amount. This improvement was caused by the anchoring effect of the Nd2O3-enriched surface layer against supported Rh sintering. This study sets out a way to suppress Rh sintering by an adequate control of the interaction between supported Rh and Nd2O3 on the surface of stabilized ZrO2.

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► Large ionic radius ion doping was effective to improve thermal stability of ZrO2.
► Nd2O3-enriched surface layer was introduced on stabilized ZrO2.
► Supported Rh interacted with Nd2O3-enriched surface layer on ZrO2.
► The interaction originates from Rh–O–Nd bond formation in oxidizing atmosphere.
► The anchoring effect of Rh–Nd2O3 interaction suppressed Rh sintering.