Promotional effects of nitrogen doping on catalytic performance over manganese-containing semi-coke catalysts for the NH₃-SCR at low temperatures

A series of nitrogen-doped MnO_x/semi-coke catalysts were studied for low-temperature (LT) de-NO_x performance in the NH₃-SCR reaction. Changes in morphology, structure, and surface chemistry of the semi-coke catalysts were systematically investigated to analyze the promotional effects of nitrogen doping on catalytic performance. The catalytic activity of ASC-10U10 Mn was found to be enhanced significantly in a broad temperature range of 100–300 °C, improving 44.2 % at 150 °C—the largest jump in this temperature range—and reaching 94.5 % at 275 °C. Nitrogen doping results in aromatic pyridinic-N, pyrrolic-N, and quaternary-N; the unpaired electrons on these groups play a critical role in enhancing the adsorption and oxidation of NO. NH₃ adsorption is enhanced due to numerous diverse Lewis acid sites on ASC-10U10 Mn. The electron distribution of MnO_x/semi-coke catalysts and the electron mobility between manganese and oxygen species are improved by nitrogen doping. The resulting nitrate intermediates, especially bridging nitrates, can be reduced by NH₃ species at low temperatures. The increase in the number of oxygen vacancies improves oxidation of coordinated NH₃. In addition, DRIFTS results suggest that coordinated NH₃ and intermediate -NH₂ are much more active and make a considerable positive contribution to the LT SCR reaction.