Tungsten oxides supported on nano-size zirconia for cyclic production of syngas and hydrogen by redox operations

For cyclic production of syngas and H₂ by redox (methane reforming-water splitting) operations, samples of tungsten oxides supported on nano-size zirconia (WO₃/n-ZrO₂) were investigated at 1,223 and 1,273 K and compared with those on micron-size zirconia (WO₃/µ-ZrO₂). The reduction characteristics of WO₃/n-ZrO₂ observed in this study were consistent with those of WO₃/µ-ZrO₂ reported in the literature. Specifically, the reduction process comprised three stages, the syngas production rate decreased as WO₃ content increased, and the overall degree of reduction gradually decreased with repeated cycles. However, there were differences due to the smaller particle size, namely, WO₃/n-ZrO₂ yielded a higher syngas production rate and a lower H₂/(CO+CO₂) ratio. In addition, the hydrogen yield by water splitting was significantly lower than the amount expected based on the overall degree of WO₃ reduction. The H₂/(CO+CO₂) ratio also gradually decreased with repeated cycles. These results were mainly attributed to rapid sintering of WO₃/n-ZrO₂, which gradually began to resemble WO₃/µ-ZrO₂