"Oxynitride trap" over N/S co-doped graphene-supported catalysts promoting low temperature NH3-SCR performance: Insight into the structure and mechanisms.

A series of nitrogen and sulfur (N/S) co-doped graphene supported catalysts (Mn-Ce-SnOx/NSG) were synthesized using an in situ method for enhancing selective catalytic reduction of NOx with NH3 (NH3-SCR) performance. The changes in catalysts' structure, morphology, and active sites were systematically researched to explore the promoting effect of N/S co-doped on catalytic performance. The prepared Mn-Ce-SnOx/NSG-0.3 catalyst achieves an excellent SCR activity at a low temperature, which is comparable to previous graphene-based catalysts. The Ce3+/(Ce3+ + Ce4+), Mn4+/Mn3+, and Oα/(Oα + Oβ) ratios in the catalyst are improved by N/S co-doping, which closely related to excellent SCR activity. Meanwhile, the unpaired electrons on N/S functional groups are effective in promoting the adsorption and further oxidation of gaseous NO. The ability to adsorb NH3 has also been promoted result of numerous Lewis acid sites over Mn-Ce-SnOx/NSG-0.3. In-situ DRIFTS and reaction kinetic results suggest that the Eley-Rideal mechanism should be the most significant pathway in the temperature range of ≥ 200 °C, where coordinated NH3 has higher activity than ionic NH4+. The Langmuir-Hinshelwood (L-H) mechanism is the main route of the low-temperature (L-T) (< 200 °C) SCR reaction. Particularly, the L-T SCR activity improves because the N/S functional groups act as an additional "oxynitride trap" (based on the L-H mechanism).