Resistance to ionic Pt insertion in oxygen excess LaMnO3 perovskite lattices and its effect in water gas shift reaction

• Resistance to B site Pt doping in oxygen excess perovskite LaMnO3.
• Pt species interaction with amorphous phase stabilizes it as PtOx upto 600 °C.
• The WGS activities compared with those of the Pt impregnated samples.
• WGS activity due to the Pt nanoparticles and PtOx is not active.

Pt doped and impregnated LaMnO3 perovskites are synthesized at different temperatures and Pt and Mn states are compared in an attempt to get insight into extent of lattice incorporation of Pt in perovskite. Various characterization studies indicate that oxygen excess system like LaMnO3 presents substantial resistance to B site doping with Pt. This behavior is different from other oxygen deficient perovskites like LaCoO3 and LaFeO3 in which lattice incorporation stabilizes the active species against sintering. Water gas shift reaction was used as a probe reaction to understand the effect of this difference in the activity. In case of LaMnO3, failure in lattice substitution leads to sintering and deactivation at high synthesis temperatures (≥700 °C) in both impregnated and doped samples. In doped samples, however, a strong interaction of Pt species with a persistent amorphous phase prevents sintering at lower synthesis temperature thereby enhancing the activity when compared to impregnated sample. The study reveals a possible mechanism in which only Pt(0) species is active with perovskite playing a minimal role in this system due to the resistance to lattice incorporation.

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