%A Qiuzhun Chen, Xiang Zhang, Bing Li, Shengli Niu, Gaiju Zhao, Dong Wang, Yue Peng, Junhua Li, Chunmei Lu, John Crittenden %T Insight into the promotion mechanism of activated carbon on the monolithic honeycomb red mud catalyst for selective catalytic reduction of NOx %0 Journal Article %D 2021 %J Front. Environ. Sci. Eng. %J Frontiers of Environmental Science & Engineering %@ 2095-2201 %R 10.1007/s11783-020-1337-7 %P 92- %V 15 %N 5 %U {https://journal.hep.com.cn/fese/EN/10.1007/s11783-020-1337-7 %8 2021-10-15 %X

• Activated carbon was proposed to be an efficient accelerant for molded red mud catalyst.

• The surface acidity and reducibility were highly improved, as well as the pore structure.

• The enrichment of the surface Fe2+ and the adsorbed oxygen account for the improvement.

Our previous study proved that the acid-pretreatment process could efficiently activate red mud (RM) for the selective catalytic reduction (SCR) of NOx. However, in terms of the molding process, which is the key step determining whether it can be applied in large-scale industrial, the surface acidity and reducibility of catalyst always decreased dramatically, and part of surface area and pore structure were lost. In this study, we prepared monolithic honeycomb red mud (MHRM) catalysts with activated carbon (AC) as an accelerant and investigated the effect of AC on the MHRM. The results showed that the MHRM with 3 wt.% of AC (MHRM-AC3) exhibited the best SCR performance, and kept more than 80% NOx conversion in the range of 325°C–400°C. Compared with the MHRM, MHRM-AC1, and HMRM-AC5, the MHRM-AC3 has more mesoporous and macroporous structures, which can provide more adsorption active sites. The AC significantly improved NH3 adsorption and surface reducibility, which was mainly due to the increase of the surface acid sites (especially the Brönsted acid sites), the concentration of Fe(II), and the surface adsorbed oxygen. The presence of more Fe(II) enriched the surface oxygen vacancies, as well as the surface adsorbed oxygen, due to the charge imbalance and unsaturated chemical bond. And surface adsorbed oxygen exhibited more active than lattice oxygen owing to its higher mobility, which was conducive to NOx reduction in the SCR reaction.