Heat-treated Dolomite-palygorskite clay supported MnO_x catalysts prepared by various methods for low temperature selective catalytic reduction (SCR) with NH_3

摘要

A series of manganese oxide catalysts loaded on thermally modified Dolomite-palygorskite clay (MnOx/M-DPC) were synthesized by adopting impregnation, precipitation and citric acid methods and investigated for the selective catalytic reduction of NOx by NH3 (NH3-SCR) at low temperature. The results showed that the precipitated sample was more active (with 83% NOx conversion at 120 degrees C) by comparing it with the other MnOx/MDPC samples prepared by impregnation and citric acid methods. Almost all NOx were completely removed by using this sample in the studied temperature range between 180 degrees C and 300 degrees C. In addition, all samples offered high N-2 selectivity ( 94%) in the whole temperature range, and their SCR performance were affected by H2O introduction and NOx oxidation to NO2 in the absence of NH3, but dependent on reaction temperature. The studied samples were characterized by specific surface area, pore size distribution, X-ray diffraction (XRD), Scanning electron microscope (SEM), electron diffraction spectra (EDS) and X-ray photoelectron spectroscopy (XPS). The results of specific surface area and pore size distribution suggested that the surface area and pore structure of catalysts obtained from various preparation methods were different, resulting in great difference in the catalytic performance. The irregular multi-modal mesoporous structure played a crucial role in the high catalytic activity over the precipitated MnOx/M-DPC sample. In addition, the results from XRD, SEM, EDS and XPS analyses indicated that Mn3O4 phase, good dispersion of manganese oxide, higher concentration of Mn as well as higher surface Mn4+ species, high lattice oxygen content on the surface were also beneficial to the superior catalytic efficiency of the precipitated sample.