Reversible and rapid calcium intercalation into molybdenum vanadium oxides

Looming concerns regarding scarcity, high prices, and safety threaten the long-term use of lithium in energy storage devices. Calcium has been explored in batteries because of its abundance and low cost, but the larger size and higher charge density of calcium ions relative to lithium impairs diffusion kinetics and cyclic stability. In this work, an aqueous calcium-ion battery is demonstrated using orthorhombic, trigonal, and tetragonal polymorphs of molybdenum vanadium oxide (MoVO) as a host for calcium ions. Orthorhombic and trigonal MoVOs outperform the tetragonal structure because large hexagonal and heptagonal tunnels are ubiquitous in such crystals, providing facile pathways for calcium-ion diffusion. For trigonal MoVO, a specific capacity of ∼203 mAh g^-1 was obtained at 0.2C and at a 100 times faster rate of 20C, an ∼60 mAh g^-1 capacity was achieved. The open-tunnel trigonal and orthorhombic polymorphs also promoted cyclic stability and reversibility. A review of the literature indicates that MoVO provides one of the best performances reported to date for the storage of calcium ions.

Synthesis of Fluoride-Containing High Dimensionally Structured Nb Oxide and Its Catalytic Performance for Acid Reactions

High dimensionally structured niobium oxide (HDS-NbO) containing fluoride (F^-) was prepared by a hydrothermal synthesis. F^- could be introduced into HDS-NbO by replacing lattice oxygen up to a solid F^-/Nb ratio of 0.55. The introduction of an appropriate amount of F^- promoted the crystal growth of HDS-NbO, while niobium oxyfluoride having the hexagonal tungsten bronze structure (HTB-Nb(F,O)_x) was concomitantly formed by excess F^- addition. HAADF-STEM analysis suggested that the number of micropores (hexagonal and heptagonal channels) in HDS-NbO was increased by the introduction of an appropriate amount of F^-. The catalytic activity for Brønsted acid reactions was evaluated by Friedel-Crafts alkylation. The catalytic activity was significantly increased by the introduction of F^-, while excess introduction of F^- significantly decreased the activity. Catalytic activity for the Lewis acid reaction in the presence of water was evaluated by the transformation of pyruvaldehyde into lactic acid. The catalytic activity was changed by the introduction of F^- in a manner similar to that observed in the Friedel-Crafts alkylation. On the basis of the results obtained, we propose that the local catalyst structure around the micropores of HDS-NbO is crucial for the acid reactions.

Synthesis of High Dimensionally Structured Mo-Fe Mixed Metal Oxide and Its Catalytic Activity for Selective Oxidation of Methanol

High-dimensionally structured Mo-Fe oxide (HDS-MoFeO) was synthesized through an assembly of structural units supplied from Keplerate-type polyoxometalate, {Mo₇₂Fe₃₀}, under an appropriate hydrothermal condition. HDS-MoFeO showed excellent catalytic activity for the selective oxidation of methanol with slightly lower selectivity for formaldehyde than that of a conventional Mo-Fe oxide catalyst.

Advances in catalytic production processes of biomass-derived vinyl monomers

This review provides a summary and perspective for three bio-derived vinyl monomers – acrylic acid, methacrylic acid and styrene.

Thermal Behavior, Crystal Structure, and Solid-State Transformation of Orthorhombic Mo-V Oxide under Nitrogen Flow or in Air

Orthorhombic Mo-V oxide is one of the most active solid-state catalysts for selective oxidation of alkane, and revealing its detailed structure is important for understanding reaction mechanisms and for the design of better catalysts. We report the single-crystal X-ray structure analysis of orthorhombic Mo-V oxide heated under a N₂ flow; V is present in 6-membered rings with partial occupancy, similar to the structure reported by Trunschke's group for orthorhombic Mo-V oxide heated under an Ar flow (Trunschke, ACS Catal.2017, 7, 3061). Our previous paper (Ishikawa, J. Phys. Chem. C, 2015, 119, 7195) reported that V is not present in the 6-membered rings when orthorhombic Mo-V oxide is calcined in the presence of oxygen. Furthermore, Trunschke's paper reported that V in the 6-membered rings moves to the surface of the crystals under oxidation reaction conditions in the presence of H₂O. Our present results provide additional evidence for V migration in the 6-membered rings during heat treatment. We also report the differences in the thermal behaviors, ultraviolet-visible absorptions, N₂ isotherms, and elemental analysis results of Mo-V oxide heated in air and under a N₂ flow. Furthermore, we report the solid-state transformation of orthorhombic Mo-V oxide to tetragonal Mo-V oxide by controlled heat treatment.

Reactivity trends of the MoVOx mixed metal oxide catalyst from density functional modeling

We studied how polarons affect the oxidative dehydrogenation of hydrocarbons in a MoVO_x surface model and the related surface hydrolysis.

Pathways, mechanisms, and kinetics: a strategy to examine byproduct selectivity in partial oxidation catalytic transformations on reducible oxides

We review experimental practices, common reaction pathways, and kinetic modeling strategies effective in understanding partial oxidation catalysis over reducible oxides.

DFT Variants for Mixed-Metal Oxides. Benchmarks Using Multi-Center Cluster Models

Mixed-metal oxides, e.g., V-Mo and Bi-Mo, are promising selective oxidation catalysts. Yet, their intricate chemical composition and electronic structure often confound DFT methods. This study addresses problems arising from the simultaneous presence of two kinds of transition metals, by probing eight functionals-five hybrid functionals (MN15, M06, PBE0-D3, B3LYP-D3, and TPSSh-D3), the meta-GGA functional M06-L-D3, the range-separated functional ωB97XD, and the GGA functional PBE-D3. We examine the ability of these functionals to localize reducing electrons, and to reproduce reaction energies from CCSD(T) calculations. Accordingly, hybrid functionals containing 20% or more exact exchange perform considerably better in both tests. The B3LYP-D3 approach exhibits the lowest overall mean absolute deviation of reaction energies (OMAD), 21 kJ mol^-1, and gave electron distributions as expected from the local lattice structure according to the pseudo-Jahn-Teller effect. MN15 and PBE0-D3 reproduced the electron distributions, but bore slightly higher OMAD values, at 31 and 32 kJ mol^-1. Despite acceptable OMAD values, M06 (28 kJ mol^-1) and TPSSh (23 kJ mol^-1) in some cases did not yield the expected electron distributions. The range-separated functional ωB97XD experienced the opposite problem, yielding correct electron distributions but a poor OMAD of 41 kJ mol^-1. M06-L-D3 and PBE-D3 performed relatively poorly, regarding the electron distribution and the OMAD values, 39 and 65 kJ mol^-1, respectively.

Heterogeneously Catalyzed Aerobic Oxidation of Sulfides with a BaRuO3 Nanoperovskite

A rhombohedral BaRuO₃ nanoperovskite, which was synthesized by the sol-gel method using malic acid, could act as an efficient heterogeneous catalyst for the selective oxidation of various aromatic and aliphatic sulfides with molecular oxygen as the sole oxidant. BaRuO₃ showed much higher catalytic activities than other catalysts, including ruthenium-based perovskite oxides, under mild reaction conditions. The catalyst could be recovered by simple filtration and reused several times without obvious loss of its high catalytic performance. The catalyst effect, ¹⁸O-labeling experiments, and kinetic and mechanistic studies showed that substrate oxidation proceeds with oxygen species caused by the solid. The crystal structure of ruthenium-based oxides is crucial to control the nature of the oxygen atoms and significantly affects their oxygen transfer reactivity. Density functional theory calculations revealed that the face-sharing octahedra in BaRuO₃ likely are possible active sites in the present oxidation in sharp contrast to the corner-sharing octahedra in SrRuO₃, CaRuO₃, and RuO₂. The superior oxygen transfer ability of BaRuO₃ is also applicable to the quantitative conversion of dibenzothiophene into the corresponding sulfone and gram-scale oxidation of 4-methoxy thioanisole, in which 1.20 g (71% yield) of the analytically pure sulfoxide could be isolated.

Liquid-phase oxidation of alkanes with molecular oxygen catalyzed by high valent iron-based perovskite

Hexagonal BaFeO3-δ containing high valent iron species acted as an efficient heterogeneous catalyst for the aerobic oxidation of alkanes without the need for additives. The activity of BaFeO3-δ was much higher than that of typical Fe3+/Fe2+-containing iron oxide-based catalysts, and the recovered catalyst could be reused without significant loss of catalytic performance.

How the distribution of reduced vanadium centers affects structure and stability of the MoVOx material

The energy ordering of configurations, with 6 among the 10 V centers reduced, is predicted using 3 easily accessible variables.

Oxidation of p-toluic acid to terephthalic acid via a bromine-free process using nano manganese and manganese–copper mixed oxides

Challenges and technological opportunities for nano-mixed oxide (Cu–Mn) allowing a green route to valued terephthalic acid production from p-xylene.

Surfactant-assisted synthesis of Mo–V mixed oxide catalysts for upgraded one-step conversion of glycerol to acrylic acid

The catalytic properties of Mo–V mixed oxides hydrothermally synthetized in the presence of ionic surfactants (SDS and CTAB) were investigated in the gas-phase oxidative dehydration of glycerol. The presence of surfactants promoted a change in morphology of MoV₂O₈ phase, directing to formation of rod-shaped crystals, and, consequently, an increase in macroporosity of materials, generated by intercrystallite spaces, when compared to a reference sample. Rod-like morphology stabilized the MoV₂O₈ mixed oxide phase during glycerol conversion, avoiding migration of vanadium from crystalline to amorphous phase, like observed in the reference sample, favoring the dynamic of reduction/reoxidation of vanadium and, consequently contributing to an increase in efficiency and stability of the catalyst. Both SDS and CTAB catalysts presented higher productivity of acrylic acid and good catalytic stability, with no coke formation and considerable decrease in CO_X evolution during 6 h of reaction. SDS presented the best catalytic results with 100% of conversion, 57% of acrylic acid selectivity and 36% of CO_X selectivity.

Rod-like crystals of Mo–V mixed oxides obtained by surfactant-assisted synthesis are very stable and highly efficient to one-step conversion of glycerol into acrylic acid.