Ambient-temperature CO oxidation activity of Pd/CeO2 was found to increase by more than 20 times after thermal aging at 900 °C in air. Although the aging resulted in a significant sintering accompanied by a 92% loss of surface area from 92 to 7 m2·g−1, Pd metal dispersion was preserved at a high value (0.57). The analysis using transmission electron microscopy (TEM), high-angle annular dark-field (HAADF)-scanning transmission electron microscopy (STEM), extended X-ray absorption fine structure (EXAFS), and X-ray photoelectron spectroscopy (XPS) demonstrated that the activation is driven by metal−support interactions followed by phase transformation. Owing to the formation of Pd−O−Ce bonding at the PdO/CeO2 interface, Pd oxide species are highly dispersed into the surface structure of CeO2. The Pd oxide becomes unstable when the temperature reaches ≥800 °C, where thermodynamic PdO/Pd phase equilibrium is reached. Finally, the Pd−O−Ce surface moiety is fragmented into metallic Pd particles with a size of 1 to 2 nm, which provide active sites for CO oxidation.

The influence of the redox behavior of Rh/AlPO4 on automotive three-way catalysis (TWC) was studied to correlate catalytic activity with thermal stability and metal–support interactions. Compared with a reference Rh/Al2O3 catalyst, Rh/AlPO4 exhibited a much higher stability against thermal aging under an oxidizing atmosphere; further deactivation was induced by a high-temperature reduction treatment. In situ X-ray absorption fine structure experiments revealed a higher reducibility of Rh oxide (RhO x ) to Rh, and the metal showed a higher tolerance to reoxidation when supported on AlPO4 compared with Al2O3. This unusual redox behavior is associated with an Rh–O–P interfacial linkage, which is preserved under oxidizing and reducing atmospheres. Another effect of the Rh–O–P interfacial linkage was observed for the metallic Rh with an electron-deficient character. This leads to the decreasing back-donation from Rh d-orbitals to the antibonding π* orbital of chemisorbed CO or NO, which is a possible reason for the deactivation by high-temperature reduction treatments. On the other hand, surface acid sites on AlPO4 promoted oxidative adsorption of C3H6 as aldehyde, which showed a higher reactivity toward O2, as well as NO, compared with carboxylate adsorbed on Al2O3. A precise control of the acid–base character of the metal phosphate supports is therefore a key to enhance the catalytic performance of supported Rh catalysts for TWC applications.

Ternary NiMoCo hybrid nanowire arrays with modulated electronic states and intermediate adsorption energies as efficient water splitting catalysts.

Rhodium catalysts exhibited higher dispersion with tridymite-type AlPO 4 supports than with Al 2 O 3 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 AlPO 4supported 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 AlPO 4 surface was terminated by phosphate P−OH groups, which were converted into a Rh−O−P linkage when Rh oxide (RhO x ) was loaded. This interaction enables the thin planar RhO x nanoparticles to establish close and stable contact with the AlPO 4 surface. It differs from Rh−O−Al bonding in the oxide-supported catalyst Rh/Al 2 O 3 , 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 x / AlPO 4 model.

Aluminum phosphate (AlPO4) was found to be an efficient and robust support material to produce optimum metal−support interactions that can reduce significantly Rh loading of automobile catalysts, owing to thermally stable and highly dispersed Rh nanoparticles anchored strongly onto the phosphate surface.

High catalytic activities for CO–O2 and CO–NO reactions that were superior to or comparable with those of platinum-group metal catalysts were achieved by synchronous dual-mode arc plasma deposition of a very small amount of Cr and Cu (0.07 wt % each) onto CeO2, followed by subsequent thermal aging at 900 °C for 25 h. The turnover frequency for CO oxidation over Cr–Cu/CeO2 was 3-fold higher than that over Cu/CeO2 and exceeded values for the Rh, Pd, and Pt catalysts loaded on CeO2, despite a significant decrease in the surface area from 169 to 5 m2 g–1 caused by thermal aging. Experimental structure characterization and density functional theory calculations based on CeO2 (111) surface slab models revealed that Cu+ substitution for surface Ce atoms leads to the formation of asymmetric 3-fold oxygen coordination sites capable of efficient CO chemisorption and catalytic activity. In addition, Cr3+ was incorporated into the surface structure of CeO2; it plays an important role in enhancing the surface concentration of Cu+. A CO oxidation rate with nearly zero partial orders with respect to O2 and isotopic C16O–18O2 reactions yielding C16O2 as the primary product demonstrated that the reaction proceeds via the Mars–van Krevelen mechanism.

Cubic La0.7Sr0.3Mn1−xNiyO3−δ undergoes the hydration reaction with the charge disproportionation between Mn and O atoms, and thus, can reduce the interfacial polarization of protonic solid oxide cells due to the H+/O2−/e− triple conductivity.

High CO oxidation activity of Pd/CeO2 as prepared by using an arc-plasma process was lost by thermal ageing at 600 °C in air, whereas further ageing at 900 °C enhanced significantly the activity, exceeding that of the as-prepared catalyst.