Catalytic combustion of lean methane over different Co₃O₄ nanoparticle catalysts

Three types of Co₃O₄ catalyst, namely Co₃O₄ nanoparticles (denoted as Co₃O₄-NPs, ∼12 nm in diameter), Co₃O₄ nanoparticles encapsulated in mesoporou s SiO₂ (denoted as Co₃O₄@SiO₂), and Co₃O₄ nanoparticles inside microporous SiO₂ hollow sub-microspheres (denoted as Co₃O₄-in-SiO₂), were explored to catalyze the combustion of lean methane. It was found that the methane conversion over the three catalysts has the order of Co₃O₄-NPs ≈ Co₃O₄@SiO₂ > Co₃O₄-in-SiO₂ due to the different catalyst structure. The comparison experiments at high temperatures indicate the Co₃O₄@SiO₂ has a significantly improved anti-sintering performance. Combined with the TEM and BET measurements, the results prove that the presence of the mesoporous SiO₂ layer can maintain the catalytical activity and significantly improve the anti-sintering performance of Co₃O₄@SiO₂. In contrast, the microporous SiO₂ layer reduces the catalytical activity of Co₃O₄-in-SiO₂ possibly due to its less effective diffusion path of combustion product. Thus, the paper demonstrates the pore size of SiO₂ layer and catalyst structure are both crucial for the catalytical activity and stability.