Toward Optimizing the Performance of Self-Regenerating Pt-Based Perovskite Catalysts

Self-regenerating automotive catalysts owe their remarkable performance to the repeated motion of the precious metal atoms in and out of the perovskite lattice under fluctuating oxidizing and reducing conditions, preventing coalescence of the metal nanoparticles. Here we use resonant inelastic X-ray scattering to characterize the occupied and unoccupied Pt 5d states in two self-regenerating Pt-perovskite catalysts, CaTi0.95Pt0.05O3 and CaZr0.95Pt0.05O3. Upon reduction, the element and symmetry-specific charge excitation spectra reveal a sizable hybridization between the Pt 5d and the Ti 3d or Zr 4d states at the interface between the nanoparticles and the perovskite, which involves the occupied states and is thus invisible in X-ray absorption spectra. A correlation is found between the strength of this d-band hybridization and the proportion of Pt nanoparticles that remain buried below the surface during reduction, indicating that the motion of the Pt atoms toward the surface is hindered by this hybridization specifically, rather than by the Pt–O bonding. These results provide direct evidence that the strength of the metal–metal d-band hybridization plays a pivotal role in determining the efficiency of self-regeneration in perovskite catalysts.