Rhodium Nanoparticle Anchoring on AlPO₄ for Efficient Catalyst Sintering Suppression

Rhodium catalysts exhibited higher dispersion with tridymite-type AlPO₄ supports than with Al₂O₃ during thermal aging at 900 °C under an oxidizing atmosphere. The local structural analysis via X-ray photoelectron spectroscopy, transmission electron microscopy, X-ray absorption fine structure, and infrared spectroscopy suggested that the sintering of AlPO₄-supported Rh nanoparticles was significantly suppressed because of anchoring via a Rh–O–P linkage at the interface between the metal and support. Most of the AlPO₄ surface was terminated by phosphate P–OH groups, which were converted into a Rh–O–P linkage when Rh oxide (RhO_<i>x</i>) was loaded. This interaction enables the thin planar RhO_<i>x</i> nanoparticles to establish close and stable contact with the AlPO₄ surface. It differs from Rh–O–Al bonding in the oxide-supported catalyst Rh/Al₂O₃, which causes undesired solid reactions that yield deactivated phases. The Rh–O–P interfacial linkage was preserved under oxidizing and reducing atmospheres, which contrasts with conventional metal oxide supports that only present the anchoring effect under an oxidizing atmosphere. These experimental results agree with a density functional theory optimized coherent interface RhO_<i>x</i>/AlPO₄ model