Metal modified hexaaluminates for syngas generation and CO2 utilization via chemical looping

Chemical looping CH4-CO2 reforming (CLDR) is an emerging technology for the generation of Fischer-Tropsch ready syngas and CO2 utilization, which is strongly dependent upon the improvement in the design of efficient oxygen carriers (OCs). In this present work, different metal additives (Si, Zr and Ce ions) were introduced into Fe-based hexaaluminates and used OCs for CLDR. The microstructure and reactivity of BaFe2.8M0.2Al9O19 (M = Fe, Si, Zr, and Ce) OCs were found greatly influenced by the metal additives and CH4/CO2 redox treatment. Pure Fe and Ce doped OCs showed the co-existence of both beta-Al2O3 and MP hexaaluminate phases, while the introduction of Si and Zr in the hexaaluminate structure led to the phase transformation from beta-Al2O3 into MP. During the CH4/CO2 redox process, large amounts of Fe species in both BaFe2.8Si0.2Al9O19 and BaFe2.8Zr0.2Al9O19 OCs were gradually stabilized in sintering FeAl2O4 with low oxygen-storage capacity, which resulted in low CH4 reactivity and weak cyclic stability. However, Ce-doped BaFe2.8Ce0.2Al9O19 OC showed good reactivity and stability during the 10 redox cycles with CH4 conversion of 93%, H-2/CO ratio of similar to 2, high syngas yield of 2.2 mmol/g, and high CO2 activation ability of 0.95 mmol/g, which was associated with the preservation of hexaaluminate main phase, the formation of CeFexAl1-xO3 and the abundant oxygen vacancies. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.