Topological Aspect of the Distribution of Co Species and N2O Decomposition Performance for Co/Zeolite Catalysts

In this study, series of Co/zeolites with diverse microporous structures were prepared and applied for N2O catalytic decomposition. The corresponding activities followed the order Co/Beta > Co/Mordenite > Co/ZSM-5 > Co/MCM-49 > Co/ZSM-23 > Co/ZSM-35 > Co/SSZ-13, while the yield of NO2 byproduct followed the order Co/ZSM-23 > Co/ZSM-35 > Co/MCM-49 > Co/Mordenite > Co/ZSM-5 > Co/Beta > Co/SSZ-13. Under conditions of 30 vol % N2O and GHSV = 30 000 h–1, the best performing sample (Co/beta) achieved a remarkable N2O conversion of 99.6% at 450 °C. In addition, the formation of NO2 byproduct was significantly inhibited with the corresponding concentration varying from 1063 ppm for Co/ZSM-23 to 82 ppm for Co/Beta. Physicochemical characterization of these as-prepared catalysts was performed including XRD, BET, H2-TPR, NH3-TPD, XPS, UV-vis-DRS, and it was found that zeolites with higher dimensionally porous apertures (3D) and larger pore sizes (12-membered ring, 12-MR) were conducive to introducing Co ions onto the zeolite framework through the pore channels and further locating them on ion-exchange sites to form active centers (Co2+). Furthermore, molecular dynamics simulation demonstrated that the higher pore dimensions and larger pore sizes are more beneficial for the N2O diffusion inside the pores and channels of zeolites and promote N2O decomposition.