Jung Hun Kwak

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.