High-dimensionally structured (HDS) mixed oxides of vanadium with metals (M) (e. g., Nb, Mo, and W; denoted as HDS-MVO) were constructed by {M 6 O 21 } 12À pentagonal units and {MO 6 } (M=Nb, Mo, W, or V) octahedra as linkers. The materials were synthesized using a hydrothermal method and rod-shaped solids. The random assembly of the pentagonal units and octahedra in the cross-sectional plane of the rods facilitated the formation of micropore channels along the long axis of the rods. Micropore formation was directly observed in the crosssection by HAADF-STEM. These structural features are common to HDS-NbVO, HDS-MoVO, and HDS-WVO. The catalytic activity of these three HDS-MVOs with V/Mo ratios in the range 0.35-0.39 was tested for the oxidative dehydrogenation of ethane and propane. The reaction rates per surface area for ethane oxidation and propane oxidation over the HDS-MoVO and HDS-WVO catalysts were comparable, whereas the HDS-NbVO catalyst showed an appreciable difference between the two reaction rates. Both HDS-MoVO and HDS-WVO exhibited higher selectivity for olefin formation during ethane oxidation than propane oxidation. Interestingly, the olefin selectivity over the HDS-NbVO catalyst was found to be almost independent of the alkane substrate. These catalytic features were discussed on the basis of VÀ OÀ V or VÀ OÀ Mo redox coupling and pore structure effects in HDS-MoVO and HDS-WVO and also of isolated and valence stable surface V in HDS-NbVO.

Molybdenum oxides are widely used in various fields due to their electronic and structural characteristics. These materials can generate lattice oxygen defects by reduction treatments, which sometimes play central roles in various applications. However, little has been understood about their properties since it is difficult to increase the amount of lattice oxygen defects due to the crystal structure changes in most cases. Here, we report a new class of high-dimensionally structured Mo oxide (HDS-MoO x ) constructed by the random assembly of {Mo 6 O 21 } 6− pentagonal units (PUs). Since the PU is a stable structural unit, the structural network based on the PU hardly caused structural changes to make the lattice oxygen defects vanish. Consequently, HDS-MoO x could generate a substantial amount of lattice oxygen defects, and their amount was controllable, at least in the range of MoO 2.64 −MoO 3.00 . HDS-MoO x was more redox active than typical Mo oxide (α-MoO 3 ) and demonstrated an oxidation ability for gas-phase isopropanol oxidation under the reaction conditions, whereas α-MoO 3 affords no oxidation products.