Surface Decomposition of Doped PrBaMn₂O_5+δ Induced by In Situ Nanoparticle Exsolution: Quantitative Characterization and Catalytic Effect in Methane Dry Reforming Reaction

The exsolution of metallic nanoparticles (NPs) from perovskite oxides is a promising strategy for synthesizing supported catalysts. The associated segregation of A-site cations on the surface is challenging to investigate experimentally and is often detrimental to the catalytic performance. In this work, we found that during the in situ exsolution of Ni-Co bimetallic nanoparticles from Pr0.45Ba0.45Mn1–x(Co1/3 Ni2/3)xO3±δ, A-site cation enrichment occurred on the surface when x is 0.1; yet, the perovskite surface decomposed when x reached 0.2, forming a thin layer comprising various nanocrystalline oxides, which partially blocked the active sites of the exsolved Ni-Co particles. A hydration and carbonation reaction facilitated the conversion of nanocrystalline BaO species into large and highly crystallized BaCO3 particles. This enabled the exposure of more Ni-Co active sites and offered a chance to quantify that the decomposed surface layer accounts for ∼7.2 wt % of the total perovskite. Because of this unique feature, the surface-decomposed catalyst showed higher activity in the dry methane reforming reaction with better stability. Importantly, the regeneration feature was not hampered as the complete exsolution-dissolution recyclability of the catalyst remained.