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Iron phosphates (FePO(4)) are among the most promising candidate materials for advanced Li-ion battery cathodes. This work reports upon a combined nuclear magnetic resonance (NMR) experimental and periodic density functional theory (DFT) computational study of the environments and electronic structures occurring in a range of paramagnetic Fe(III) phosphates comprising FePO(4) (heterosite), monoclinic Li(3)Fe(2)(PO(4))(3) (anti-NASICON A type), rhombohedral Li(3)Fe(2)(PO(4))(3) (NASICON B type), LiFeP(2)O(7), orthorhombic FePO(4)·2H(2)O (strengite), monoclinic FePO(4)·2H(2)O (phosphosiderite), and the dehydrated forms of the latter two phases. Many of these materials serve as model compounds relevant to battery chemistry. The (31)P spin-echo mapping and (7)Li magic angle spinning NMR techniques yield the hyperfine shifts of the species of interest, complemented by periodic hybrid functional DFT calculations of the respective hyperfine and quadrupolar tensors. A Curie-Weiss-based magnetic model scaling the DFT-calculated hyperfine parameters from the ferromagnetic into the experimentally relevant paramagnetic state is derived and applied, providing quantitative finite temperature values for each phase. The sensitivity of the hyperfine parameters to the composition of the DFT exchange functional is characterized by the application of hybrid Hamiltonians containing admixtures 0%, 20%, and 35% of Fock exchange. Good agreement between experimental and calculated values is obtained, provided that the residual magnetic couplings persisting in the paramagnetic state are included. The potential applications of a similar combined experimental and theoretical NMR approach to a wider range of cathode materials are discussed.

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.

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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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