Novel preparation method, catalytic performance and reaction mechanisms of PrxMn1−xOδ/3DOM ZSM-5 catalysts for the simultaneous removal of soot and NOx

Abstract

Three dimensionally-ordered macroporous (3DOM) ZSM-5 zeolite catalysts with hierarchical pore structures have obvious advantages for the catalytic reaction systems containing reactants with different sizes. However, due to the stringent preparation conditions and confined crystallization space, the successful preparation of 3DOM ZSM-5 remains challenging. Herein, we report a novel method for the preparation of 3DOM ZSM-5 zeolite, termed the steam seed-assisted colloid crystal template (SSAC) method. The SSAC method avoids the growth of ZSM-5 crystals based on the confinement effect of the interstices of the polymethylmethacrylate (PMMA) template. The crystallization temperature of ZSM-5 is lower than the glass transition temperature of PMMA, which facilitates the formation of the 3DOM structure. Using 3DOM ZSM-5 as a support, a series of PrxMn1-xOδ/3DOM ZSM-5 catalysts were prepared via incipient wetness impregnation. These catalysts exhibited good catalytic performance for the simultaneous removal of soot and NOx, which can be attributed to the unique hierarchical pore structure, excellent redox properties, the sufficient active oxygen species and appropriate acid sites of overall catalysts. Among the synthesized catalysts, Pr0.2Mn0.8Oδ/3DOM ZSM-5 achieved the highest catalytic activity with a low soot combustion temperature of 417 °C and a wide temperature window of 128 °C-288 °C at 90% NO conversion. Finally, we proposed reaction mechanisms for the catalysts under different temperatures based on the in situ characterization results, kinetic measurements and DFT calculations.