1 research outputs found
Tuning the Electron Density of Rh Supported on Metal Phosphates for Three-Way Catalysis
The
automotive three-way catalysis (TWC) performance of Rh supported
on alkaline-earth and rare-earth phosphates was studied in comparison
to that of Rh on aluminum phosphate (AlPO<sub>4</sub>). The anchoring
of Rh via interfacial Rh–O–P bonding in Rh/AlPO<sub>4</sub> leads to efficient Rh sintering suppression. However, the
electron-withdrawing nature of the phosphate affords electron-deficient
Rh, which has a negative impact on its catalytic activity under a
reducing atmosphere due to a decrease in back-donation from the Rh <i>d</i>-orbitals to the antibonding π* orbitals of adsorbed
CO and NO molecules. Notably, the extent of this electron deficiency
could successfully be reduced by replacing AlPO<sub>4</sub> with alkaline-earth
or rare-earth phosphates, and the Rh oxide formed on these phosphate
supports was readily reduced to metallic Rh. This behavior is in complete
contrast to that of corresponding metal oxide supports, because the
higher basicity of these supports yields Rh oxides that are more difficult
to reduce. Among the phosphate-supported catalysts investigated in
the present study, Rh/LaPO<sub>4</sub> demonstrated the highest TWC
performance after thermal aging under both oxidizing and reducing
atmospheres. The effect of the higher basicity of LaPO<sub>4</sub> compared to that of AlPO<sub>4</sub> is most obvious in its improved
catalytic activity for elementary CO–O<sub>2</sub>, CO–H<sub>2</sub>O, and CO–NO reactions. Importantly, this improvement
is achieved while maintaining the activity toward C<sub>3</sub>H<sub>6</sub> as an advanced feature of phosphate supports