Methane reforming and water splitting by zirconia-supported cerium-tungsten composite oxides for cyclic production of syngas and hydrogen

Redox cycles of methane reforming (MR) and water splitting (WS) of cerium-tungsten composite oxides were investigated at 1223 K for the cyclic production of syngas and hydrogen. Among various composite oxides tested having different Ce/W ratios, the sample with the Ce/W molar ratio of 1, CeW1/Zr, showed the best performance. When the sample was stabilized after several cycles, most of the Ce was present as Ce3+ and thus only W participated in the redox process. Production of CO2 during MR by the cerium-tungsten composite sample was much less than that by the WO3-only sample, yielding a H2/(CO + CO2) ratio much closer to the desired value of 2. The extent of reduction of W by MR remained nearly constant during repeated cycles, but re-oxidation by WS was not complete during the first several cycles. However, the re-oxidation extent increased to full re-oxidation during repeated cycles; the redox system became very stable after the sixth cycle. These are both beneficial effects owing to the presence of Ce.