V induced oxygen vacancies boost NO-Hg0 dual removal: Mechanistic evidence and DFT verification on Mn-Co-V catalysts.

Simultaneous low temperature removal of NO and elemental mercury (Hg0) during NH3-SCR is challenged by active site competition and NH3 poisoning. Here, we develop oxygen vacancy regulated ternary Mn-Co-V oxides and provide combined experimental and DFT evidence that oxygen vacancy enriched surfaces are associated with enhanced NO-Hg0 synergistic removal, thereby supporting the observed trends, but not definitively proving the underlying mechanism. The optimal Mn0.1Co0.08V0.03+V_O catalyst achieves >90% NO conversion and >96% Hg0 removal between 150 and 350 °C. Multimodal characterizations (XPS, TPR, TPD, DRIFTS) show that moderate V doping stabilizes abundant oxygen vacancy, enriches surface adsorbed oxygen (Oα, 40.48%), increases high valence metal centers, and optimizes Lewis acidity. These features promote ∗NH3 activation and the formation/coexistence of ∗NH2NO and monodentate/bidentate nitrates. In situ DRIFTS with reciprocal pre-adsorption sequences provides direct pathway criteria: on an NH3-precovered surface, the rapid emergence of ∗NH2NO (1380 cm-1) together with the consumption of adsorbed NH3/NH4+ bands (1620/1420/1240/1070 cm-1) after NO + O2 admission indicates an Eley-Rideal contribution, whereas on a NOx-precovered surface, preformed nitrate bands (1550/1015 cm-1) coexist/react with subsequently adsorbed NH3/NH4+ to generate ∗NH2NO, evidencing a Langmuir-Hinshelwood contribution. These parallel pathways are sustained by rapid O2→Oα replenishment under oxygen vacancy rich conditions. Density functional theory (DFT) indicates a V-oxygen vacancy synergy: DFT calculations show that V-oxygen vacancy synergy reduces the energy barrier for NH3 dehydrogenation (ΔG: +0.74 → +0.61 eV) and facilitates ∗NH2NO formation (ΔG: +0.64 → +0.15 eV). Hg0 adsorption is also enhanced (Eads: -0.57 → -0.72 eV), and Bader charge transfer increases, indicating stronger interaction with Hg0. Oxygen vacancy stabilizes the electronic structure, improving redox reactivity and mitigating NH3-Hg0 competition. These findings suggest practical formulation guidance for Mn-Co-V oxides (e.g., moderate V loading) toward low to mid-temperature NO-Hg0 co-control under simulated conditions.