No abstract

No abstract

Amorphous V2O5 powders with zirconia (ZrO2) dopant are prepared by one-pot spray pyrolysis at temperatures above the melting temperature of V2O5. The powders with 7 wt % ZrO2 are completely spherical and dense with a clean surface, on which crystals of pure V2O5 powders are scarcely observed. The V2O5 powders with 7 wt % ZrO2 have uniformly distributed V and Zr components. The uniformly distributed Zr component disturbs the crystallization of V2O5 during the quenching of the melted powders. These powders also give smooth initial discharge curves with a single slope, which is typical to amorphous materials. The discharge capacities of the V2O5 powders with 7 wt % ZrO2 are 309, 269, and 222 mA h g(-1) after the first, second, and 50th cycles, respectively, even at a high current density of 294 mA g(-1). The capacity retention measured after the first cycle is 83% after 50 cycles.

The mesoporous undoped and Si-doped alumina were prepared with an ultrasonic spray process, and found to have well-developed mesopore structures and large surface areas. The mesoporous Si-doped alumina has a high thermal stability up to 1473 K. Its surface area and pore volume were found to slowly decrease with increasing temperature. Mesoporous undoped alumina is transformed to gamma-alumina at 1073 K, whereas the amorphous nature of the pore walls of the Si-doped alumina is maintained up to 1073 K. When heat treatment was carried out at 1473 K for 2 h, the mesopore-networks of the undoped alumina collapsed, and then all the pore walls were converted into the alpha-alumina phase. In contrast, the mesoporosity of the Si-doped alumina persisted during heat treatment, and its pore walls were transformed to gamma-alumina. The decreases in the pore volume of the undoped alumina at 1073 K and 1473 K were found to be 36% and 99% respectively, but for the Si-doped alumina were only 24% and 36% respectively. The surface area of the undoped alumina at 1473 K was found to be 11 m2/g but that of the Si-doped samples at the same temperature is higher than 100 m2/g. Thus this mesoporous Si-doped alumina can be used as a catalytic support in reactions at high temperatures.

No abstract