Kenzo Oshihara

Catalytic performance for propane selective oxidation and surface properties of 12-molybdophosphoric acid treated with pyridine

Abstract When molybdophosphoric acid, H 3 PMo 12 O 40 , was treated with pyridine and heated in N 2 flow at 420°C as an optimized temperature, a black solid catalyst was formed with a structure of orthorhombic phase and in a reduced state. This reduced H 3 PMo 12 O 40 (Py) catalyst showed a high potentiality in the propane and isobutane oxidation with molecular oxygen to acrylic acid and methacrylic acid above 300°C. It was proved that the higher the reduction degree of the catalyst is, the higher the oxidation activity and selectivity to partial oxidation products are. The FT-IR study revealed that, in the lattice of the heat-treated H 3 PMo 12 O 40 (Py) catalyst, pyridinium ion remained to assume the highly resistant orthorhombic secondary structure against reoxidation, and on the surface, Lewis acid sites were generated with the formation of the primary oxygen-deficient Keggin structure. A possible reaction mechanism was proposed for alkane oxidation, where protons and electrons in the reduced H 3 PMo 12 O 40 (Py) catalyst cooperate to activate molecular oxygen.

Catalytic oxidative activation of light alkanes over Mo–V-based oxides having controlled surface

An arrangement of catalytically active elements of Mo, V, and Te in an oxide solid with a single crystallographic phase was successfully done by the hydrothermal synthetic method. A black solid powder with a rod-shape (by SEM) was obtained. This catalyst material was first air-treated at 280 °C for 2 h, by which Te was stabilized in the structure. The air-treated sample was then heat-treated at 600 °C in a nitrogen stream. It was revealed by XRD analysis that this treatment made the solid in a well-crystallized state. Finally, in order to break the rods into fine powders, the well-crystallized rod-shaped material was ground, by which a face of the cross-section of the rods seems to be preferentially appeared. Thus obtained catalyst, Mo6V3Te1Ox, showed a high activity for the selective oxidation of propane to acrylic acid at 360 °C. Since the grinding was found to be the most effectual determinant in the propane conversion and the acrylic acid formation, the surface on the cross-section part of the rod-shaped crystals is active for the selective oxidation. It was assumed that all the elements of Mo, V, and Te arrange in this surface and effectively promote the consecutive oxidation from propane to acrylic acid via propene and acrolein.

Hydrothermal Synthesis of Mo-Based Oxide Catalysts and Selective Oxidation of Alkanes

Mo-V-M(=Al, Ga, Bi, Sb and Te)–O mixed oxide catalysts were synthesized hydrothermally for the first time, characterized structurally, and tested for ethane and propane oxidation after activation by various ways. These catalysts were black solids of rod-shaped (fiber like) crystals, which had a layer structure in the direction of fiber axis and a high dimensional arrangement of metal octahedra in the cross-section plane. These fresh crystalline materials became active for catalytic oxidation of alkanes after heat-treatment at 600 °C and subsequent grinding in order to increase exposed plane of the cross-section. The resulting catalysts were very active for an oxidative dehydrogenation of ethane with 80% of the ethylene selectivity in the reaction temperature range of 300 to 400 °C and also showed about 50% selectivity to acrylic acid in the propane oxidation. Multi-functional character which derived from the high dimensional structure of the catalysts and mechanism of the selective alkane oxidation were discussed.

Hydrothermal synthesis of Mo–V–M–O complex metal oxide catalysts active for partial oxidation of ethane

Mo–V–M–O (M=Al, Fe, Cr and Ti) complex metal oxide catalysts have been prepared by hydrothermal synthesis for the first time and showed activity for the partial oxidation of ethane to ethene and acetic acid.

Selective Oxidation of Light Alkanes Over Mo-Based Oxide Catalysts

A highly reduced Keggin-type heteropolymolybdophosphate, H3PMo12O40(Py), which was formed by the heat-treatment of pyridinium salt of H3PMo12O40, can catalyze the propane oxidation to acrylic acid and acetic acid selectively. We propose a possible reaction mechanism for alkane oxidation, where protons and electrons on the reduced H3PMo12O40 catalyst cooperate for activating molecular oxygen to form electrophilic oxygen species for alkane oxidation. It is also reported that Anderson-type heteropolycompounds linked with vanadyl cations VO2+ were able to be synthesized by hydrothermal reaction and showed good catalytic activity for the ethene oxidation to acetic acid.