Search for a Self-Regenerating Perovskite Catalyst Using First-principles Thermodynamics Calculations

Development of catalysts for emission control in automotive with minimum amount of catalytic precious metals, or with commonly-used non-precious metals is strongly desired.  In conventional catalytic converters, precious metal nanoparticles are supported on metal oxides.  However, growth of the particle size due to sintering severely reduces the catalytic activity after continuous use under high-temperature reduction-oxidization (redox) fluctuations of the exhaust gas. Nishihata et al. [1,2] reported that Pd-containing perovskite oxide LaFe1-xPdxO3 excels in durability, by suppressing the metal particle growth during the redox cycle. It was proposed that precious metal nanoparticles self-regenerate during the redox  cycle, by reversibly forming solid-solution with the host perovskite and segregating as a metal nanoparticle depending on the redox conditions. As for mechanisms of the metal particle self-regeneration, rapid diffusion of the metal responding to the control frequency (~4 Hz) of an actual engine was proposed [1,3]. In addition, a role of the nanoscale spinodal decomposition of precious metals in the host perovskite was proposed [4,5]. By employing ab initio atomistic thermodynamics calculations, we investigated self-regeneration properties of a variety of ABO3-type perovskite oxides doped with Pd, Rh, Pt, Cu, and Fe [6-8].  Furthermore, it is desirable to develop a catalyst without precious metal elements.  Investigations have been done on performances of Cu or Fe nanoparticle for the catalytic conversion in automotive exhaust gas.

References

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