Na-β-Al 2 O 3 stabilized Fe 2 O 3 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 2 produced at the distributed scale. This process requires the availability of stable Fe 2 O 3 -based oxygen carriers. Fe 2 O 3 -Al 2 O 3 based oxygen carriers exhibit a decay in the H 2 yield with cycle number, due to the formation of FeAl 2 O 4 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 ( via a sodium salt) in the synthesis of Fe 2 O 3 -Al 2 O 3 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 FeAl 2 O 4 and stabilized the oxygen carrier via the formation of a layered structure, Na-β-Al 2 O 3 phase. The material, i.e. Na-β-Al 2 O 3 stabilized Fe 2 O 3 , showed a stable H 2 yield of ca. 13.3 mmol g -1 over 15 cycles.