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

Abstract

A series of nitrogen-doped MnOx/semi-coke catalysts were studied for low-temperature (LT) de-NOx 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 MnOx/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.