High-efficient hollow porous Mn_xCo_3-xO₄ nanoreactors for enhancing catalytic soot oxidation

Herein, we have elaborately designed and successfully fabricated the high-efficient hollow porous Mn_xCo_3-xO₄ nanoreactors (MnCo-HPs) by optimizing the heating decomposition conditions of metal-organic frameworks Mn₃[Co(CN)₆]₂·nH₂O precursors with a nanocube-like structures. The diameter of the nanopores on the shells of MnCo-HPs is around 10.0 nm, which is beneficial for improving the diffusion of NO and O₂ into the hollow porous cage and enhancing the activation of NO to NO₂. The feature of hollow porous structures can provide a larger surface area and more active sites, which can activate reaction gases and develop the contact efficiency between the nanoreactors and soot particles. The uniform distribution of Mn and Co species is conducive to the formation of coordination unsaturated defect sites and surface oxygen vacancies, resulting in the high catalytic activity for soot oxidation. As compared with conventional Mn_xCo_3-xO₄ nanoparticles (MnCo-NPs) and hollow porous Co₃O₄ nanoreactors (Co-HPs), MnCo-HPs possess the highest catalytic activity (T₅₀ = 341 °C), the lowest apparent activation energy (85.1 kJ·mol^-1) and excellent catalytic stability during soot oxidation. The catalytic activity of MnCo-HPs results from a perfect combination of the hollow porous structures, the strong interaction of manganese and cobalt oxide species, as well as the uniform distribution/accessibility of active sites. The related characterizations and density functional theory (DFT) calculations reveal that the active sites can decrease activation energy of O₂ and desorption energy of NO₂, which is the crucial steps of NO₂-assisted catalytic mechanism for soot oxidation. MnCo-HPs are promising candidates for the commercial soot oxidation. It highlights a promising way for the rationally design of high-performance non-noble metal catalysts for the removal of soot particles.