Anti-coke BaFe1-xSnxO3-delta Oxygen Carriers for Enhanced Syngas Production via Chemical Looping Partial Oxidation of Methane

Iron-based oxides are promising oxygen carriers for chemical looping syngas production from methane; however, facile coke formation over reduced metallic Fe-0 largely limits the syngas productivity. This work demonstrates that the introduction of Sn promoters into BaFe1-xSnxO3-delta perovskite oxides significantly restrains coke formation and improves the syngas yield to above 19.2 mmol/g with a H-2/CO ratio of 2, which is 2.9-fold in comparison to BaFeO3-delta. Characterization results suggest that Sn cations are well-confined in the perovskite matrix by substitution of Fe. The Fe cations serve as main active sites for C-H bond activation with Sn cations as an oxygen reservoir, which donate the neighboring lattice oxygen to active Fe for selective methane oxidation. Besides, an intimate Fe-Sn interaction induces the formation of the FeSn alloy rather than metallic Fe-0 under a reducing atmosphere, which restrains methane pyrolysis and notably improves the coke resistance. When Sn loading (x) increases to above 0.6, all Fe cations can be deeply reduced to the metallic state without coke accumulation and oxygen storage capacity reaches as high as ca. 6.5 mmol/g with nearly 100% syngas selectivity, which breaks the "seesaw" effect between oxygen supply and syngas selectivity for traditional iron-based materials. These results provide meaningful guidance for fabricating prospective oxygen carriers or catalysts with better anti-coke property for the chemical looping process or specific catalytic reactions.