Facile preparation, catalytic performance and reaction mechanism of MnxCo1−xOδ/3DOM-m Ti0.7Si0.2W0.1Oy catalysts for the simultaneous removal of soot and NOx

Abstract

In this work, three-dimensionally ordered macroporous–mesoporous Ti_0.7Si_0.2W_0.1O_y (3DOM-m TiSiWO) supported Mn_xCo_1−xO_δ catalysts with different x values were prepared using the colloidal crystal templating method and incipient wetness impregnation method. The characterization results reveal that the as-prepared catalysts have highly ordered macroporous and mesoporous structures. Among the developed catalysts, the Mn_0.5Co_0.5O_δ/3DOM-m TiSiWO catalyst exhibits the best catalytic performance for the simultaneous removal of diesel soot and NO_x under simulated real conditions owing to its best redox performance, largest number of active oxygen species and acid sites of medium strength, and highest O_latt/O_ad and TOF values compared to the other Mn_xCo_1−xO_δ/3DOM-m TiSiWO catalysts. Furthermore, the reaction mechanism of the Mn_0.5Co_0.5O_δ/3DOM-m TiSiWO catalyst was deduced using in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and the adsorption behaviors of NO, NO₂ and NH₃ on the Mn_0.5Co_0.5O_δ/3DOM-m TiSiWO catalyst surface were also analyzed using density functional theory (DFT) calculations. The proposed reaction mechanisms indicate that the catalyst follows both the Eley–Rideal (E–R) and Langmuir–Hinshelwood (L–H) schemes for selective catalytic reduction (SCR) at low temperatures. Meanwhile, the combustion of soot at high temperatures is mainly based on the NO₂-assisted mechanism. More importantly, the role of H₂O in simultaneous removal of soot and NO_x was also studied.