Redox reactivity of titania-doped YSZ-promoted iron-based oxygen carrier over multiple redox cycles for chemical looping reforming of methane and hydrogen production

Chemical looping using methane offers the potential for producing syngas or hydrogen with intrinsic separation of CO₂. An ilmenite (FeTiO₃)-based oxygen carrier is a suitable oxygen carrier for methane oxidation because of good reactivity and low cost. However, it underwent a phase separation during repeated redox cycles, thereby resulting in the decrease in the reactivity. Therefore, it is necessary to develop a TiO₂-supported iron oxide composite with high redox stability and reactivity. In this study, we synthesize a titania-doped YSZ (Y_0.20Ti_0.15Zr_0.65O_1.90)-promoted iron-based oxygen carrier. Inert material (ZrO₂), pure ionic material (YSZ), and electronic conductive material (TiO₂) are used as support materials for comparison. It is found that the Y_0.20Ti_0.15Zr_0.65O_1.90 promotes iron-based oxygen carrier showed the best performance (27%/min to achieve 66% conversion) in methane oxidation in TGA experiment, high syngas selectivity in fixed bed reactor, and the redox stability over 100 redox cycles. Meanwhile, the other oxygen carriers show low reactivity and the morphological changes (iron oxide layer) and/or the phase decomposition (ie, YSZ → Y₂O₃ and ZrO₂ and Fe₂TiO₅ → Fe₂O₃ and TiO₂). The enhanced reactivity and stability are mainly ascribed to the mixed ionic-electronic conductivity and the redox stability of titania-doped YSZ in the single-phase fluorite region.