State-of-the-Art Review of Oxidative Dehydrogenation of Ethane to Ethylene over MoVNbTeOx Catalysts

Ethylene is mainly produced by steam cracking of naphtha or light alkanes in the current petrochemical industry. However, the high-temperature operation results in high energy demands, high cost of gas separation, and huge CO2 emissions. With the growth of the verified shale gas reserves, oxidative dehydrogenation of ethane (ODHE) becomes a promising process to convert ethane from underutilized shale gas reserves to ethylene at a moderate reaction temperature. Among the catalysts for ODHE, MoVNbTeOx mixed oxide has exhibited superior catalytic performance in terms of ethane conversion, ethylene selectivity, and/or yield. Accordingly, the process design is compact, and the economic evaluation is more favorable in comparison to the mature steam cracking processes. This paper aims to provide a state-of-the-art review on the application of MoVNbTeOx catalysts in the ODHE process, involving the origin of MoVNbTeOx, (post-) treatment of the catalyst, material characterization, reaction mechanism, and evaluation as well as the reactor design, providing a comprehensive overview of M1 MoVNbTeOx catalysts for the oxidative dehydrogenation of ethane, thus contributing to the understanding and development of the ODHE process based on MoVNbTeOx catalysts.

Redox induced controlling microporosity of zeolitic transition metal oxides based on ε‑Keggin ironmolybdate in an ultra-fine level

Tuning microporosity of crystalline microporous materials is critical for achieving good application performance. Zeolitic ironmolybdate shows both redox property and microporosity, and a redox-triggered microporosity change is investigated. The micropore...

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.

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.

A critical review of cathodes for rechargeable Mg batteries

Benefiting from a higher volumetric capacity (3833 mA h cm-3 for Mg vs. 2046 mA h cm-3 for Li) and dendrite-free Mg metal anode, reversible Mg batteries (RMBs) are a promising chemistry for applications beyond Li ion batteries. However, RMBs are still severely restricted by the absence of high performance cathodes for any practical application. In this review, we provide a critical and rigorous review of Mg battery cathode materials, mainly reported since 2013, focusing on the impact of structure and composition on magnesiation kinetics. We discuss cathode materials, including intercalation compounds, conversion materials (O2, S, organic compounds), water co-intercalation cathodes (V2O5, MnO2etc.), as well as hybrid systems using Mg metal anode. Among them, intercalation cathodes are further categorized by 3D (Chevrel phase, spinel structure etc.), 2D (layered structure), and 1D materials (polyanion: phosphate and silicate), according to the diffusion pathway of Mg2+ in the framework. Instead of discussing every published work in detail, this review selects the most representative works and highlights the merits and challenges of each class of cathodes. Advances in theoretical analysis are also reviewed and compared with experimental results. This critical review will provide comprehensive knowledge of Mg cathodes and guidelines for exploring new cathodes for rechargeable magnesium batteries.

A zeolitic vanadotungstate family with structural diversity and ultrahigh porosity for catalysis

Design of the structure and composition of crystalline microporous inorganic oxides is of great importance in catalysis. Developing new zeolites is one approach towards this design because of the tunable pore system and high thermal stability. Zeolites are limited to main group elements, which limits their applications in redox catalysis. Another promising choice is zeolitic transition metal oxides providing both porosity and redox activity, thereby further expanding the diversity of porous materials. However, the examples of zeolitic transition metal oxides are rare. Here, we report a new class of zeolitic vanadotungstates with tunable frameworks exhibiting a large porosity and redox activity. The assembly of [W₄O₁₆]⁸⁻ units with VO²⁺ forms two isomeric porous frameworks. Owing to the complex redox properties and open porosity, the vanadotungstates efficiently catalyse the selective reduction of NO by NH₃. This finding provides an opportunity for design and synthesis of inorganic multifunctional materials for future catalytic applications.

Zeolitic transition metal oxides provide both porosity and redox activity, thereby further expanding the diversity of porous materials, but their design and development remain rare. Here, the authors report a new class of zeolitic vanadotungstates with tunable frameworks exhibiting a large porosity and redox activity.

Microporous crystalline Mo–V mixed oxides for selective oxidations

Recent developments of crystalline Mo₃VO_x catalysts (MoVO), a new type of oxidation catalysts for selective oxidations of ethane to ethene and of acrolein to acrylic acid, are reviewed.

Structure and electronic properties of MoVO type mixed-metal oxides – a combined view by experiment and theory

The current state of experimental and theoretical work on structure and reactivity of MoVO type mixed-metal oxides is critically reviewed.