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V2O5 fuses with transition metals to create dozens of different metal vanadates, whose acidic/redox traits can be diverse yet optimized for selective catalytic NOX reduction (SCR) by changing the metals used or their metal:vanadium stoichiometry. However, no metal vanadate has been compared with its metal oxide composite analogue as an active phase for SCR, albeit a vanadate occasionally outperforms an oxide composite simulating a commercial catalyst (V2O5–WO3). Herein, Cu3V2O8 and CuO–VO2/V2O5 were rationally selected as model phases of metal vanadates and oxide composites and isolated using pH regulation of their synthetic mixture to ≤∼5 (pH1/pH5) and ∼11 (pH11), respectively. The pH1/pH5/pH11 samples were comparable with regard to morphological, textural, and compositional traits but not for crystallographic features. This thus provided the impetus to simulate the pH1/pH5/pH11 surfaces under a SO2-containing feed-gas stream, by which SOA 2–/HSOA – functionalities (A = 3–4) were anchored on their (defective) Lewis acidic metals and/or labile oxygens (Oα). This could result in the formation of pH1-S/pH5-S/pH11-S, whose major surface species were Brönsted acidic bonds (SOA 2–/HSOA –) and redox sites (Oα; mobile oxygen (OM); oxygen vacancy (OV)). pH1-S/pH5-S/pH11-S were similar in terms of NH3 binding energies and energy barriers in SCR yet escalated collision frequencies among the surface species involved in the sequence of pH11-S < pH5-S < pH1-S (via kinetic assessments), as was the case with the numbers of SOA 2–/HSOA – functionalities of the catalysts (via temperature-resolved Raman spectroscopy). These were coupled to elevate the efficiency of acidic cycling on the order of pH11-S < pH5-S < pH1-S. Meanwhile, the amounts of Oα and OV (or OM) innate to pH1-S/pH5-S were smaller than and comparable to those of pH11-S, respectively. Nonetheless, pH1-S/pH5-S provided greater OM mobility than pH11-S, thereby proceeding better with redox cycling than pH11-S (via 18O-labeling O2-on/off runs). Furthermore, pH1-S/pH5-S outperformed pH11-S in SCR under diffusion-limited domains, while enhancing the resistance to H2O, ammonium (bi)­sulfate poisons, or hydro-thermal aging over pH11-S by diversifying the selective N2 production pathway other than SCR.

SO A 2– (A = 3–4; B–) functionalities are anchored on metal oxides used to catalyze NH3-assisted selective NO X reduction (SCR) for a SO2-bearing feed gas stream. SO A 2– species act as conjugate bases of Brönsted acidic bonds (B––H+) and modifiers of redox sites (M(n–1)+–O–), both of which are combined to dictate the activities of SCR (−r NOX ) and ammonium (bi) sulfate (AS/ABS) poison degradation (−r AS/ABS) at low temperatures. Nonetheless, their pathways have been barely clarified and underexplored, while questioning catalytic significance of mono-dentate or bi-dentate SO A 2– species in dominating −r NOX and −r AS/ABS. While using Sb-promoted MnV2O6 as a reservoir of SO A 2– functionalities with distinct binding arrays, elementary stages for the SCR and AS/ABS degradation were proposed, thermodynamically assessed, and analyzed using kinetic control runs in tandem with density functional theory calculations. These allowed for the conclusions that the reaction stage between B––H+•••NH3•••O––M(n–1)+ and gaseous NO and the liberation stage of H2O/SO2 from B–•••H2O•••SO2•••H2O via dissociative desorption are endothermic and dominate −r NOX and −r AS/ABS as the rate-determining steps of the SCR and AS/ABS degradation, respectively. In addition, mono-dentate and bi-dentate SO A 2– species are verified central in directing −r NOX and −r AS/ABS by elevating collision frequency between B––H+•••NH3•••O––M(n–1)+ and NO and declining the energy barrier required for dissociative H2O/SO2 desorption for the SCR and AS/ABS degradation, respectively. In particular, mono-dentate SO A 2– functionalities can improve the overall redox trait of the surface, thereby substantially promoting its low-temperature SCR performance under a SO2-excluding feed gas stream. Meanwhile, bi-dentate SO A 2– functionalities can slightly improve the overall redox trait of the surface, yet, can readily degrade AS/ABS by accelerating the endothermic fragmentation of S2O7 2– innate to ammonium pyrosulfate, while compensating for the moderate efficiency in fragmenting NH4 + of ammonium pyrosulfate via Eley–Rideal-type SCR. This can significantly elevate the SCR performance of the bi-dentate SO A 2–-containing surface under a SO2-including feed gas stream alongside with the promotion of its long-term stability at low temperatures. These can be adaptable and exploited in discovering/amending a host of metal oxides (or vanadates) imperatively functionalized with SO A 2– or poisoned with AS/ABS under low thermal energies.

Rare-earth metal vanadates (RMVO4) typically possess an iso-structural tetragonal architecture but vary in terms of their Lewis acidic (LA) properties, which depend on the nature of the RM element. This...

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