Unit Synthesis Approach for Creating High Dimensionally Structured Complex Metal Oxides as Catalysts for Selective Oxidations

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.

Design and synthesis of highly active MoVTeNb-oxides for ethane oxidative dehydrogenation

Ethane oxidative dehydrogenation (ODH) is an alternative route for ethene production. Crystalline M1 phase of Mo-V mixed metal oxide is an excellent catalyst for this reaction. Here we show a hydrothermal synthesis method that generates M1 phases with high surface areas starting from poorly soluble metal oxides. Use of organic additives allows control of the concentration of metals in aqueous suspension. Reactions leading to crystalline M1 take place at 190 °C, i.e., approximately 400 °C lower than under current synthesis conditions. The evolution of solvated polyoxometalate ions and crystalline phases in the solid is monitored by spectroscopies. Catalysts prepared by this route show higher ODH activity compared to conventionally prepared catalysts. The higher activity is due not only to the high specific surface area but also to the corrugated lateral termination of the M1 crystals, as seen by atomic resolution electron microscopy, exposing a high concentration of catalytically active sites.

Crystalline M1 phase of Mo-V-Te-Nb mixed oxide is an excellent catalyst for ethane oxidative dehydrogenation to ethene. Here, the authors show a method that synthesizes highly active materials by generating M1 crystals with corrugated terminations, thus exposing a large concentration of active sites.

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.

Needs and Gaps for Catalysis in Addressing Transitions in Chemistry and Energy from a Sustainability Perspective

Catalysis is undergoing a major transition resulting from significant changes in chemical and energy production. To honor the 50th anniversary of establishing the Jerzy Haber Institute of Catalysis and Surface Chemistry, this Essay discusses, from a forward-looking, personal and somewhat provocative perspective, the needs and gaps of catalysis to address the ongoing transition in chemistry and energy from a sustainability perspective. The focus is on a few selected aspects identified as crucial: i) The precise synthesis of catalytic materials, particularly focusing on mesoporous molecular sieves, metal-organic frameworks, and zeolites (particularly two-dimensional type); ii) advanced catalyst characterization methods; iii) new concepts and approaches needed in catalysis to meet the demands of a field of energy and chemistry in transition.

Experimental and theoretical study of multinuclear indium–oxo clusters in CHA zeolite for CH4 activation at room temperature

The local structure of CHA-zeolite supported indium–oxo clusters and CH₄ activation at room temperature were experimentally and theoretically studied.

Our Contributions in Synthesis of Diverse Heterocyclic Scaffolds by Using Mixed Oxides as Heterogeneous Catalysts

This personal account mainly introduces and reviews our recent contributions in developing different catalyst materials involving mixed oxides and their scope as renewable catalysts in multicomponent reactions to synthesize various novel heterocyclic scaffolds under green conditions. The application of various mixed oxides and their composites in the organic synthesis is emphasized through this review, in order to reveal the versatility, scope and importance of mixed oxides and their interactions during the reaction. We have also briefed the limitations of mixed oxides as catalysts, to put forward the broader prospective in the field.