Na-β-AlO stabilized FeO oxygen carriers for chemical looping water splitting: correlating structure with redox stability.

Chemical looping is an emerging technology to produce high purity hydrogen from fossil fuels or biomass with the simultaneous capture of the CO produced at the distributed scale. This process requires the availability of stable FeO-based oxygen carriers. FeO-AlO based oxygen carriers exhibit a decay in the H yield with cycle number, due to the formation of FeAlO that possesses a very low capacity for water splitting at typical operating conditions of conventional chemical looping schemes (700-1000 °C). In this study, the addition of sodium ( a sodium salt) in the synthesis of FeO-AlO oxygen carriers was assessed as a means to counteract the cyclic deactivation of the oxygen carrier. Detailed insight into the oxygen carrier's structure was gained by combined X-ray powder diffraction (XRD), X-ray absorption spectroscopy (XAS) at the Al, Na and Fe K-edges and scanning transmission electron microscopy/energy-dispersive X-ray spectroscopy (STEM/EDX) analyses. The addition of sodium prevented the formation of FeAlO and stabilized the oxygen carrier the formation of a layered structure, Na-β-AlO phase. The material, Na-β-AlO stabilized FeO, showed a stable H yield of 13.3 mmol g over 15 cycles.