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

Lu Yao; Qingcai Liu; Susanne Mossin; David Nielsen; Ming Kong; Lijun Jiang; Jie Yang; Shan Ren; Juan Wen

doi:10.1016/j.jhazmat.2019.121704

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

J Hazard Mater. 2020 Apr 5:387:121704. doi: 10.1016/j.jhazmat.2019.121704. Epub 2019 Nov 17.

Authors

Lu Yao¹, Qingcai Liu², Susanne Mossin³, David Nielsen⁴, Ming Kong¹, Lijun Jiang⁵, Jie Yang⁵, Shan Ren⁶, Juan Wen⁷

Affiliations

¹ College of Materials Science and Engineering, Chongqing University, Chongqing, 400044, China; Department of Chemistry, Technical University of Denmark, Lyngby, 2800, Denmark.
² College of Materials Science and Engineering, Chongqing University, Chongqing, 400044, China. Electronic address: liu_qingcai@163.com.
³ Department of Chemistry, Technical University of Denmark, Lyngby, 2800, Denmark. Electronic address: slmo@kemi.dtu.dk.
⁴ Department of Chemistry, Technical University of Denmark, Lyngby, 2800, Denmark.
⁵ College of Materials Science and Engineering, Chongqing University, Chongqing, 400044, China.
⁶ College of Materials Science and Engineering, Chongqing University, Chongqing, 400044, China. Electronic address: shan.ren@cqu.edu.cn.
⁷ College of Materials Science and Engineering, Chongqing University, Chongqing, 400044, China; Chongqing Cheng Tou Road and Bridge Administration Co. Ltd, Chongqing, 400060, China.

PMID: 31780294
DOI: 10.1016/j.jhazmat.2019.121704

Abstract

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.

Keywords: Low-temperature SCR; MnOx/semi-coke catalyst; Nitrogen doping; Promotional mechanism; Surface chemistry.

Publication types

Research Support, Non-U.S. Gov't