Thermal stability of Pd-containing LaAlO₃ perovskite as a modern TWC

TWC activity and thermal stability of LaAlO₃-based Pd catalysts were investigated under simulated gasoline engine exhaust conditions. The LaAlO₃-based catalysts revealed a stronger thermal stability than the conventional Al₂O₃-based ones. Pd-substituted for Al in the LaAlO₃ perovskite structure exhibits a stronger thermal stability than that impregnated on the LaAlO₃ surface. The increased electron density around Pd induced by the electron donation from the more electronegative La may enhance the thermal stability of PdO by suppressing the decomposition of PdO. The strong interaction between Pd and La appears also contributing to the improvement of the TOFs for the TWC reactions over the Pd-substituted LaAlO₃ (i.e., LaAlPdO₃) catalyst, as evidenced by CO-chemisorption, TGA, XPS, XANES, H₂-TPR, DRIFT and TPD studies. CO and C₃H₆ oxidation reactions over the LaAlO₃-based Pd catalysts are strongly structure-sensitive, while those over the Al₂O₃-based Pd catalysts are weakly structure-sensitive. The NO reduction and H₂ oxidation reactions are strongly structure-sensitive over all the Pd-containing catalysts examined.